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teddillard
01 January 2012, 0600
Suddenly, this whole question seems to make sense to me. Obviously, I'm tragically mistaken about something... but bear with me.

The implications of adding a second, or bigger motor rather than a transmission started falling into place when I starting thinking about adding a two-motor configuration to the R5e. Here's the basic jist of it.

When you add a second motor, in parallel, then you're doubling the torque (and load) at any given RPM. You're also doubling the current handling capacity- a 300amp system becomes a 600amp system.

It's all about the overall system. The ideal system has current delivery and motor load that's balanced. If you have high current delivery but your motor is not big enough, you need to add motor (either by adding a motor, or by substituting a bigger motor). If your motor is not running close to it's capacity, you need to add current delivery, or, if you have maxed out your current delivery you can add load to the motor- through gearing- either just adding taller gearing if the motor has the torque, or adding a transmission to spread the torque out on the curve. Or the motor is simply too big for your system.

Even as I type this (as per Jack Rickard "typing yourself smart") the transmission starts sounding like a bandaid for a system that's poorly balanced... :O

Anyway, more here: http://evmc2.wordpress.com/2012/01/01/transmissions-vs-dual-motors/

Richard230
01 January 2012, 0757
The nice thing about transmissions in an electric vehicle is that now you can start an oil thread! :eek:

cycleguy
01 January 2012, 0955
Happy New Year Ted! Your take on this ongoing transmission issue is right on! Additionally, your charactarization of thinking in terms of the "overall system" can also be thought of in terms of horsepower. A dual motor system not only only produces twice the torque, twice the current handling and thermal mass capacity, but most importantly, produces twice the HP. HP, the measure of work, is the only thing that matter ultimately.

teddillard
01 January 2012, 1027
Thanks, and Happy New Year back atcha!

Right, as much as HP is watts, (which is current x voltage), and what the motor is rated as maximum, yeah. You have two 10kw motors in parallel, you've got the same voltage and twice the amperage, so you now have 20kw capability. You "get" 20kw assuming that your system (batteries and controller) can supply that kind of power.

Brutus
01 January 2012, 1055
Being the only die hard transmission supporter here I am going to say you summed it all up pretty well with the last sentence in your article "It all depends on what you’re designing the system to do." You touched back on the Weight issue and as I stated before a 5 speed trans only weighs 35lbs wet. Also you are not factoring in extra battery cost and the extra electronics to power and control a dual motor system. I am pretty sure between the electronics and higher battery requirements plus an additional motor the 600 bucks a trans costs to broaden the useable power band is the more economical route for a reliable long lasting powertrain. At any rate in the next few weeks you will see what a transmission can really do when set up on lipo and using what I feel is some of the best electronics in the EV industry.
Happy New Years Ted!

podolefsky
01 January 2012, 1152
Let me see if I can say what Ted said using the AC-20 as an example. Let's assume that if I can fit an AC-20 + transmition, then I could fit an AC-31. They use the same controller, have the same voltage and current ratings.

Spec says:

Motor Weight Torque
AC-20 53 lb 72 ft-lb
AC-31 85 lb 112 ft-lb

So, roughly, the AC-31 gives me similar final torque to an AC-20 + 30 lb transmission with a 1.5:1 low gear.

That does start to make sense...but to really make the comparison in performance you'd have to plot torque and HP curves vs speed for both setups.

What the AC-31 won't give you is the equivalent of a 2:1 or 5:1 drive ratio. I think this is what Brutus is getting at - you can only make the motor so big before you have to mount your batteries in the passenger seat. If you want that kind of torque at the rear wheel, a transmission will get you there.

I think it comes down to "want" vs "need".

teddillard
01 January 2012, 1218
Well, holy crap. We're starting out the New Year basically in agreement about transmissions? Just what the hell is going on here? :D

Brutus, can't wait to see your results, for sure. As far as batteries and electronics, I'm just basing this on the same battery pack (about 20ah of 20C lipo) and running it in parallel off a single controller. So there's nothing extra, just the bracket assembly for the motor, which is lighter than your transmission - at least in my case.

At any rate, the R5e- it's just by way of a very simple illustration. But yeah. It's all about what you want out of it. As long as you understand the notion that the entire system needs to be a balance of the individual component characteristics, then you can design a system, transmission or no, that takes the most advantage of all the parts.

mechanic
01 January 2012, 1224
Wait... What are you telling me that two motors (or one twice the size) are twice as good as one? And that balance system is better than an unbalanced system? And that a transmission does not make HP?

There goes my plan for 2012. I was going to outdo the geniuses at Brammo by building a 12 speed transmission and go twice as fast as them- Damn... foiled again!

As stated before- look to the torque curves, they hold all the answers! (everything else is a waste of time)

teddillard
01 January 2012, 1301
I keep thinking about this from the basis of my experience- building gas motors, and I keep coming back to it all being about finding the bottleneck, as RC says. On a gas motor, the first thing you do is get the thing breathing- reduce the intake and exhaust restrictions, which gives you more mixture with more potential energy, and more efficiency through the cycle.

As I've said before, the motor is almost like the piston- it's function is to transform the energy from one form (either the explosion of the gas/air mix, in the ICE model or the current in the electric model) to mechanical energy- watts, HP, whatever you want to call it. Putting in a bigger motor, or dual motors, is almost like boring, porting and polishing. You're putting in more energy handling capacity... trying to take advantage of the increased breathing- again, removing bottlenecks.

For us math-challenged guys, the curves only tell me so much... I need to hold it in my hand, or feel it kick me in the ass at some point. Then it becomes obvious... :p

Nuts & Volts
01 January 2012, 1410
Wait... What are you telling me that two motors (or one twice the size) are twice as good as one? And that balance system is better than an unbalanced system? And that a transmission does not make HP?

There goes my plan for 2012. I was going to outdo the geniuses at Brammo by building a 12 speed transmission and go twice as fast as them- Damn... foiled again!

As stated before- look to the torque curves, they hold all the answers!

Really unnecessary man. What may seem obvious to you is a whole can of worms for someone else. A little respect is greatly appreciated on this site.


...(everything else is a waste of time)

Wrong, so much can be learned by thinking an idea through. Going down the wrong path and making a mistake teaches you so much more than just getting it right the first time. Not everyone on El Moto was born building electric motorcycle, but we sure as hell love everything about them. Many of us spend our hard earned money farting around with these things for that single moment when the wheel spins up for the first time. Maybe we can't understand half the things that are going on under our seat, but we come on ElMoto trying to find answers to our questions and share our experiences. No one wants to stick their necks out with any ideas if some member just kicks them under the bus for no good reason.

I really wish you would use all that knowledge you apparently have and help someone on this site instead of speaking out your ass all the time.

podolefsky
01 January 2012, 1545
Wait... What are you telling me that two motors (or one twice the size) are twice as good as one? And that balance system is better than an unbalanced system? And that a transmission does not make HP?

There goes my plan for 2012. I was going to outdo the geniuses at Brammo by building a 12 speed transmission and go twice as fast as them- Damn... foiled again!

As stated before- look to the torque curves, they hold all the answers! (everything else is a waste of time)

Putting aside the inflammatory nature of your post, it's not that obvious.

Here's a chart of HP vs speed for various motors, gear ratios, all compared to Ninja 250. This might help folks get their head around what HP actually looks like for an electric motor.

* Note that it has a *peak* just like an ICE...but the curve is generally broader.

* Changing gearing doesn't affect the peak HP, but it does change where that peak is. Look at the two D&D lines (red & orange). If you gear lower, bike will feel great around 35 mph, but be a slug at 60...and you'll never get over ~65 mph (even though you have the power to go over 100). If you want to go 80 mph, you need to gear higher. So in a way, a transmission does make more *useful* HP at different speeds.

* The D&D is pretty much limited to 72V, 450A. The AC-20 is the same size, but can handle 96V, 550A (actually more). That alone gives you more power without going to a larger motor. It also envelopes the curves for the D&D with different gears. So if you have a choice of transmission + D&D or more batteries + AC, the batteries + AC will give you better performance.

A lot more can be understood from these graphs, but I'll stop now so folks can digest what I said so far.



http://www.colorado.edu/physics/EducationIssues/podolefsky/EV_project/ICE_HP.png

mechanic
01 January 2012, 1646
Putting aside the inflammatory nature of your post, it's not that obvious.

Looks pretty obvious to me (nice chart!)...Happy with a 35mph avg. (67 top speed) use the 14/65 4.64:1 reduction. Want an target. speed closer to 55mph (top around 83mph, thermal aside) then you must choose the 16/52 3.25:1 reduction. Want both? build a two speed box 1st gear; 4.64:1, 2nd gear; 3.25:1. Want the best option (assuming you can deliver 96V) use the AC20 motor. All the "holding in my hand or kicking me in the ass" will never generate a clearer bases for decision making than data like this. (FYI- it would be even more useful if HP was replaced with torque, as peak HP is a constant)

As far as helping. Most of my posts have information in them, even may last one; my ass spoke and said "look to the curves", if you choose to use it or not is your decision.

teddillard
01 January 2012, 1704
All the "holding in my hand or kicking me in the ass" will never generate a clearer bases for decision making than data like this.

Sorry pal. My brain doesn't work like that. It may be a shock to you, but people process information differently, and not everybody is as gifted as you apparently are. I have, however, somehow been able to muddle through and build a bike with some fairly respectable performance numbers.

Thanks, Noah, Kyle.

Skeezmour
01 January 2012, 1727
Moral of the story is that there is no single always 100% correct way to do it. Thanks for posting it Ted.

jazclrint
01 January 2012, 1749
Suddenly, this whole question seems to make sense to me. Obviously, I'm tragically mistaken about something... but bear with me.

The implications of adding a second, or bigger motor rather than a transmission started falling into place when I starting thinking about adding a two-motor configuration to the R5e. Here's the basic jist of it.

When you add a second motor, in parallel, then you're doubling the torque (and load) at any given RPM. You're also doubling the current handling capacity- a 300amp system becomes a 600amp system.

It's all about the overall system. The ideal system has current delivery and motor load that's balanced. If you have high current delivery but your motor is not big enough, you need to add motor (either by adding a motor, or by substituting a bigger motor). If your motor is not running close to it's capacity, you need to add current delivery, or, if you have maxed out your current delivery you can add load to the motor- through gearing- either just adding taller gearing if the motor has the torque, or adding a transmission to spread the torque out on the curve. Or the motor is simply too big for your system.

Even as I type this (as per Jack Rickard "typing yourself smart") the transmission starts sounding like a bandaid for a system that's poorly balanced... :O

Anyway, more here: http://evmc2.wordpress.com/2012/01/01/transmissions-vs-dual-motors/

Hey Ted,

I appreciate the insight. Just yet another way to look or explain things so more people can get the concept.

I was wondering what your, well everyone's, thought was on rearranging the pack so it is double the voltage and half the amperage. Then wiring the motors in series. Could this potentially put less of a strain on each individual cell, and possibly the controller (or able to use a lighter controller? i.e. balance system) while still supplying the same volts and amps to each motor?

teddillard
01 January 2012, 1750
Moral of the story is that there is no single always 100% correct way to do it.

No, there's mechanic's way, it's obvious. :cool:

(Sorry, you know I can't resist a set like that Gene. BAM! :D)

EVcycle
01 January 2012, 1810
Here we are again.....

It really has never been an issue about having one. It is finding one that
matches the Electric Motorcycle world. Not an ICE reject, but getting one that
is designed to highlight the output of the electric motor in a particular application.


Ready?

Wait for it....



GO!

SplinterOz
01 January 2012, 1822
What is also "obvious" from the chart is that the AC20 bets them all. So do you gear or upgrade the motor, controller and battery system? The question is if you are designing the WHOLE system do you want or need to add a transmission.


Sent from my GT-P7500 using Tapatalk

Brutus
01 January 2012, 1848
This old gear head thinks he knows a thing or two but now he just plays dumb so I banished him to the patio to hold up plants:)2224
I thought the thread was very thoughtful and would turn out better than it did. Amazing how 8 hours later a thread dies into this.... again.

Happy New Year EVERYBODY!

Let the love-fest continue

Richard230
01 January 2012, 1848
My question is why are the major EV auto manufacturers not using transmissions (to my knowledge)? Tesla gave it a try early on and apparently ran into reliabilty issues and hasn't been down that path again, as far as I know. I think the Leaf is a single speed and if any other manufacturer of electric vehicles uses a transmission, I haven't heard of it. So I wonder why? In theory, a transmission would seem to offer better performance that a single speed system, but no manufacturer seems to be doing it.

I would think that the size and weight of a simple transmission in an automobile would not be a major detriment as far as size and weight is concerned. Brammo is giving it a try and it will be interesting to see how it works. But if I was them, I would use a singe-speed system first and then retrofit a transmission later - just in case it doesn't work out due to reliability or other issues in the field. You would think that it would be tough enough to design and build a high-performance motorcycle using mostly untested (by the consumer) technology, without also adding the complication of an untested transmission to the mix. I hope it works and it will be interesting to see how it compares with direct-drive, which can be approximated by just sticking the transmission in a single gear and leaving it there (although that won't account for the extra weight and mechanical losses of the transmission).

Could the substantial torque of an electric motor, compared with an IC engine, make life tough on a transmission and clutch setup?

Brutus
01 January 2012, 1854
Could the substantial torque of an electric motor, compared with an IC engine, make life tough on a transmission and clutch setup?

More so on the clutch than the trans, truth is you do not need the clutch in electric because letting off the throttle "unloads" the trans making it shift like butter.

Richard230
01 January 2012, 1902
I was wondering about how the clutch would work in the Brammo system. When I spoke to the Brammo staff earlier this year, I was told that the transmission system would employ a clutch and one of their design issues was getting the clutch to work like one on an IC motorcycle when shifting between gears. Up until that point, I didn't think a clutch would be necessary.

Brutus
01 January 2012, 1914
That is interesting because I had the same "feel" issues on Brutus. An electric motor doesn't want to continue spinning when the throttle is off and it wreaks havoc with the clutch and shifting feel. I decided to eliminate the clutch all together and it hasn't had a single issue yet. The hardest part to get used to is remembering that it is a brake lever now and not the clutch :)

There are a few ways to correct the clutch issue I just felt it wasn't worth the cost or time to continue with the clutch just to have it.

mechanic
01 January 2012, 1929
truth is you do not need the clutch in electric because letting off the throttle "unloads" the trans making it shift like butter.

Not exactly- upshifting yes (reduction in ratio) only requires an "unload" however downshifting requires an "unload" via raised or lowered RPM's depending on the current torque command (i.e. rider is off throttle because they are braking for a corner requires an RPM increase to "unload" as the gears are loaded by the rear wheel and not the motor) followed immediately (.040 sec's max.) by a raise in the motors RPM (blip) to match the increased ratio change and current wheel speed then followed by an RPM reduction to employe desired engine braking effect, easy in theory, very hard (and risky) in practice.

There are other, very advanced theories but too difficult (and unnecessary) to explain here, at this time. The clutch (unless executed perfectly) is a VERY costly addition...

DaveAK
01 January 2012, 1931
101 ways to skin this cat, but if I'm going to be putting in two motors then I'd be looking at serial/parallel switching. If I were going with a transmission I'd go with two or three gears depending on what I needed. As it so happens the bike that I have works for my needs with just a single motor and a single gear. I've considered all three options and will continue to consider them for any future projects, as they all have their merits. All the torque curves in the world won't get you anywhere unless you can apply them to any given design situation. As someone mentioned above it all depends on your design needs, and whatever you end up with will always be a compromise based on any number of factors. That's just the nature of the beast.


As far as helping. Most of my posts have information in them, even may last one; my ass spoke and said "look to the curves", if you choose to use it or not is your decision.
That's not helping though. Giving someone a set of torque curves is meaningless without some explanation. It's the explanation that's the helping part. Noah could give me any number of textbooks and tell me go read them, but that wouldn't teach me physics. Likewise Ted could give me a camera and a bag full of lenses and filters and I wouldn't be able to just go out and take a picture of a beautiful landscape. If you really want to help then you need to expand a little on the point you're trying to make.

Brutus
01 January 2012, 1940
The whole downshift "theory" is a little flawed because of the whole compression thingy going on with an ICE motor. I can shift from 5th to 2nd and not experience anything you are describing.

mechanic
01 January 2012, 1959
You are not running any significant regen and an induction motor?

Brutus
01 January 2012, 2008
You are not running any significant regen and an induction motor?

No regen and I am quite fond of the series dc that I started with.

mechanic
01 January 2012, 2020
No regen and I am quite fond of the series dc that I started with.I suspect this is not a sport bike? With regen, downshifting will become more challenging.

Brutus
01 January 2012, 2030
I suspect this is not a sport bike? With regen, downshifting will become more challenging.
I am not interested in regen and don't think it would work well in the system I built. I did stumble onto something that eliminates all the issues with shifting you talk about. Since you are a transmission guy you will smack your head when you see what it is.

podolefsky
01 January 2012, 2031
All the "holding in my hand or kicking me in the ass" will never generate a clearer bases for decision making than data like this. (FYI- it would be even more useful if HP was replaced with torque, as peak HP is a constant)

All due respect, have you built and/or ridden an electric bike? I didn't start messing with all these charts and data until I had ridden with different ratios and felt the difference. The butt dyno is a perfectly valid way of decision making - at the end of the day, that what tells you if the bike is more fun to ride. Both ways of thinking about it are important.

I'm not sure what you mean by "peak HP is a constant". I'll grant you it's a single number, but HP isn't constant throughout RPM - which is why statements like "a transmission won't get you more HP" are only part of the story.

Here are the torque curves (have to keep in mind this isn't exactly apples to apples - but it can give you an idea of effects of gearing vs more voltage).

http://www.colorado.edu/physics/EducationIssues/podolefsky/EV_project/ICE_gears.png

SplinterOz
01 January 2012, 2037
I suspect this is not a sport bike? With regen, downshifting will become more challenging.

If you have a look through the forum a bit you will see his completed, fully functional bike with transmission. Brutus is one of the few to have done what we are discussing. As for the regen making downshift more problematic it kind of depends how you impliment it. If enabled on throttle off, maybe. If implimented via seperate switch or pot then no.

A simple microswitch disabling regen when the shift lever is pressed that cuts regen and one that cuts throttle when lifted would most likely replace a clutch completely.

I am not one for making our electric bikes "feel" like ICE bikes. I think our bikes should behave like electric bikes!

mechanic
01 January 2012, 2040
I am not interested in regen and don't think it would work well in the system I built. I did stumble onto something that eliminates all the issues with shifting you talk about. Since you are a transmission guy you will smack your head when you see what it is.
With no regen, sprag bearings et al, can work but a real motorcycle has some amount of engine braking and so should an electric... besides being more efficient.

Brutus
01 January 2012, 2043
One thing that is not measured is timed acceleration and that is an important factor. How fast does each set-up achieve those speeds?

Brutus
01 January 2012, 2048
With no regen, sprag bearings et al, can work but a real motorcycle has some amount of engine braking and so should an electric... besides being more efficient.
Why does it have to be "engine" or motor braking?

mechanic
01 January 2012, 2059
One thing that is not measured is timed acceleration and that is an important factor. How fast does each set-up achieve those speeds?

No need; Drive torque = acceleration (once adjusted for cg. and rolling resistance)

Good luck to all the designers that want to build an eMoto that does not at least resemble an ICE bike in basic function. THE biggest advancements in motos over the last decade have been improvements in TC and engine braking... Managing engine braking NOT eliminating it.

Anyway...

SplinterOz
01 January 2012, 2107
With no regen, sprag bearings et al, can work but a real motorcycle has some amount of engine braking and so should an electric... besides being more efficient.

Note most of the top line sports bikes try to minimize unpredictable engine braking motorcycle-usa.com/1451/Motorcycle-Photo-Gallery/2009-Aprilia-RSV4-Factory-First-Ride.aspx uing a slipper clutch.

However even if your "real bike" has engine braking that does not mean that an electric bike should have it. Note jet planes don't have torque roll like propeller planes but no-one thinks we should artificially add it. Last year during the TTXGP down here none off the teams implimented roll off regen to simulate engine braking. One did impliment a second lever to activate regen.

Another thing to note with motor cycles is that 90% of the braking is on he front and the harder you ride the more it is like that. That is why on racing bikes they try to eliminate engine braking as locking up the rear during a down shift is worse than the tiny amount of additional braking the engine can provide.

SplinterOz
01 January 2012, 2112
No need; Drive torque = acceleration (once adjusted for cg. and rolling resistance)

Good luck to all the designers that want to build an eMoto that does not at least resemble an ICE bike in basic function. THE biggest advancements in motos over the last decade have been improvements in TC and engine braking... Managing engine braking NOT eliminating it.

Anyway...

Ok so now I understand where you are coming from... you think we are building bikes for general use. Most of us here build for our own use and do not have to cripple our bike to conform to "way an ice bike behaves". I am sure if the engineers could eliminate engine braking then they would. Tell me what good is engine braking on a bike that already has a rear disk brake?

podolefsky
01 January 2012, 2129
Wow - how did we get on engine braking?

Back to Ted's original point...I noted that the graphs I posted weren't exactly apples-to-apples. But, it does highlight the point about having a "balanced system". The D&D system is balanced with a 72V pack capable of 450A. With that system, you're stuck with the different curves if you only have one speed. You could add a transmission (which is what Brutus did with the same motor in v 1.0, I believe).

The same pack would under power the AC-20. That system wouldn't be "balanced", so one might be tempted to add a transmission...but you might be better off adding cells since the motor can handle it.

That about right Ted?

Remotecontact
01 January 2012, 2129
I keep thinking about this from the basis of my experience- building gas motors, and I keep coming back to it all being about finding the bottleneck, as RC says. On a gas motor, the first thing you do is get the thing breathing- reduce the intake and exhaust restrictions, which gives you more mixture with more potential energy, and more efficiency through the cycle.


Bottleneck™

I agree with Noah about the butt dyno. The whole point of all of this is fun.

- RC

mechanic
01 January 2012, 2141
I am sure if the engineers could eliminate engine braking then they would.

Of course they can... but managed, predictable engine braking is desirable, even more so on an elmoto.

This thread went from high level/tech. to very low level/basics. Sorry- but really not interested in having motorcycling 101 discussions- good luck.

Remotecontact
01 January 2012, 2144
I for one love the coasting an Elmoto is capable of.

Brutus
01 January 2012, 2221
This thread went from high level/tech. to very low level/basics. Sorry- but really not interested in having motorcycling 101 discussions- good luck.

Henry Ford had a very unique way of making his cars get down the road and I am thankful his concept of controls didn't take off. Trying to continually make an electric motorcycle perform exactly like an ICE bike is like re-inventing the wheel. And I too love the coasting feel of an Elmoto so why duplicate old hat it is time to think different and solve issues rather than copy existing thoughts.

podolefsky
01 January 2012, 2221
So anyway...transmissions...

SplinterOz
01 January 2012, 2231
agreed , transmissions. I think we should look at the brammo argument that the transmission can keep the motor in its most efficient zone. Efficiency graphs may show if this is true :-)

podolefsky
01 January 2012, 2246
agreed , transmissions. I think we should look at the brammo argument that the transmission can keep the motor in its most efficient zone. Efficiency graphs may show if this is true :-)

This was discussed somewhat in another thread (which I can't find now). What you need are efficiency maps, and very few manufacturers provide them (I know UQM does). I think we figure out that you could gain a bit by getting into a higher efficiency zone, but it wasn't clear whether the gains were worth the effort (or greater than losses).

__Tango
02 January 2012, 0109
One thing that is not measured is timed acceleration and that is an important factor. How fast does each set-up achieve those speeds?

Let me first admit that I'm completely out of my league here, since I ended up skipping this whole issue by putting a hub motor in my bike.

However, from looking at the torque and wheel ft-lbs charts that noah posted:

http://www.colorado.edu/physics/EducationIssues/podolefsky/EV_project/ICE_gears.png

it seems that if a motor can produce more torque/ft-lbs at a given speed, it should be able to "get to the next point in the chart" (speed wise) faster. So, if from looking at this chart, would it be possible to infer that the D&D with 14:65 gearing would accelerate faster than a stock Ninja250 to about 35mph, but then get out accelerated past that?

I agree though, timed accelerations would help me put this into a bit more context.

__Tango
02 January 2012, 0113
Also a total newbie question, when talking about running a AC-20 at 96V and 550A, does that mean 550A from the battery? You'd have to get a battery setup that is not something like a bunch of thundersky's right?

SplinterOz
02 January 2012, 0125
Also a total newbie question, when talking about running a AC-20 at 96V and 550A, does that mean 550A from the battery? You'd have to get a battery setup that is not something like a bunch of thundersky's right?
No you don't have to get 550amps out of you battry. I think of it like this... the controller is supplying an average voltage to the motor appropriate for the current speed. Now as it can,t create power as it shifts the volts down it multiplies the amps. I have seen a 50 times multiplication of amps at low rpm.

teddillard
02 January 2012, 0413
The D&D system is balanced with a 72V pack capable of 450A. With that system, you're stuck with the different curves if you only have one speed. You could add a transmission (which is what Brutus did with the same motor in v 1.0, I believe).

The same pack would under power the AC-20. That system wouldn't be "balanced", so one might be tempted to add a transmission...but you might be better off adding cells since the motor can handle it.

That about right Ted?

I think so. I was trying to work out (understand) and describe a system where a transmission would be part of a balanced system and didn't get that far, but I think you just did.

‎jazclrint- Sorry for the delay getting back to that, but I'm confused by the question. Can you draw out a wiring diagram, you think? My voltage is limited by the controller and the motor, so I'm running it at max. My current is running more than my motor can handle at anything more than a few minutes... so there's not much room to do what you're asking. Maybe you're just asking theoretically? And maybe someone running an AC (with higher voltage) can help you out more.

This discussion has brought out another important conclusion I've made in the past year or so... the importance of actually building and trying out theories and principles.

I find it fascinating that Brutus ran a clutch and then eliminated it, due, basically, to ride feel. Ed's right on target- if I had access to a good two-speed transmission I'd be able to try it out. My first "build" was a BMX bike (remember "Sparky"?) and getting hands-on with even a basic drivetrain (on/off switch, overvolted brushed hub motor that I had to "rebuild" about 3 times after melting it) and a gaggle of scooter batteries taught me the difference between reading something on the internet and holding something in my hand (and having it kick me in the ass).

As I've posted on other threads, I've now moved from building the R5e to trying out motor options on that build. I think this is one of the really cool things about electric bikes, basically the ability to swap components out in very little time. ...and part of a good design, in my opinion, is thinking forward to anticipate what you might want to try out in the future- batteries, motors, final drives, controllers...

I don't know many people on here who've built bikes that consider them "done". It seems like we're all building works in progress... test beds for learning how the systems work. I'll tell you something- from my experience with gas motors, it's a whole hell of a lot easier (and more fun) doing this on an electric system than a gas system, ain't it? (Anybody up for rejetting a Mikuni? lol)

I don't by any stretch intend to say that if you haven't built something your theory isn't valid- but if you're trying to learn (or teach) about this stuff, you should try building something - anything. Stuff gets "obvious" real fast, especially (for me, anyway) if you have a specific goal in mind.


This thread went from high level/tech. to very low level/basics. Sorry- but really not interested in having motorcycling 101 discussions- good luck.

Oh, what a shame. Now I'll have to go to the local Yankees bar to get my required abuse.

teddillard
02 January 2012, 0452
Not exactly- upshifting yes (reduction in ratio) only requires an "unload" however downshifting requires an "unload" via raised or lowered RPM's depending on the current torque command (i.e. rider is off throttle because they are braking for a corner requires an RPM increase to "unload" as the gears are loaded by the rear wheel and not the motor) followed immediately (.040 sec's max.) by a raise in the motors RPM (blip) to match the increased ratio change and current wheel speed then followed by an RPM reduction to employe desired engine braking effect, easy in theory, very hard (and risky) in practice.

There are other, very advanced theories but too difficult (and unnecessary) to explain here, at this time. The clutch (unless executed perfectly) is a VERY costly addition...

This is a good example of what I'm saying in my previous post. Here's a guy explaining transmission and clutch theory to tell a guy who's built a bike with a transmission and clutch to prove that he needs a clutch, except he's never built (or at least shown us) a build trying out any of the theory and the other guy has built one with a transmission and clutch and decided to discard the clutch based on some real-world decisions and as the discussion moves on (pointedly avoiding the use of the term "forward") it becomes clear that the first guy doesn't even understand the specific realities and goals of the builder's build.

deep breath.

There's a lesson here somewhere. :O

jazclrint
02 January 2012, 0512
I have an interview lined up with BrammoBrian next week. I'll add this to my list of questions.

markcycle
02 January 2012, 0620
Also a total newbie question, when talking about running a AC-20 at 96V and 550A, does that mean 550A from the battery? You'd have to get a battery setup that is not something like a bunch of thundersky's right?

Isn't it possible to look at phase amps with the CAN bus of the Kelly Controller. Generally I see peaks 2.5 times battery current. Kelly Controllers are rated by there phase current, so to think in terms of the AC motor you have, it would be about twice the phase amps, so yea if you push an AC-20 to its max Thundersky 60 AH cell are going to sag big and die early.

teddillard
02 January 2012, 0706
I did some reading this morning on setting up dual parallel PMDC motors, and it ain't easy. I'm going to, at some point, put a post together on what I've found, but this train of thought led me to consider simply a bigger motor rather than the two ETEKs. Sorry, can't seem to migrate the little comparison spreadsheet I did, but it's posted here:
http://evmc2.wordpress.com/2012/01/02/motor-comparisons-including-dual-etek/

Conclusion. i can haz ME1003?

(But Ed already knew that... :D)

DaveAK
02 January 2012, 0939
I for one love the coasting an Elmoto is capable of.
Ever thought of pulling in the clutch? :D Anything's capable of coasting. My bike is setup to regen or coast. I of course love the ability of my Elmoto to regen.

__Tango
02 January 2012, 0949
... Sorry, can't seem to migrate the little comparison spreadsheet I did, but it's posted here:
http://evmc2.wordpress.com/2012/01/02/motor-comparisons-including-dual-etek/

Conclusion. i can haz ME1003?

So ted, are you basically assuming that motors with the same voltage and current specs will roughly the same torque and horsepower? Is this a valid assumption to make? Is it more or less correct for motors of the same type (all PMDC vs. all AC)?

Also, how would the AC-20 fit in to this list?

I know, i know. So many questions... :)

podolefsky
02 January 2012, 1006
No you don't have to get 550amps out of you battry. I think of it like this... the controller is supplying an average voltage to the motor appropriate for the current speed. Now as it can,t create power as it shifts the volts down it multiplies the amps. I have seen a 50 times multiplication of amps at low rpm.

Right. Here's *another* chart that I've used to try and explain battery vs motor amps.

(Apologies to folks who are getting tired of my charts and graphs...I think once you understand them, it really helps get your head around what's going on.)

Basically power in = power out (x efficiency). So P = I_batt * V_batt = I_motor * V_motor.

The controller limits motor current by limiting motor *voltage*, which is equivalent to the black line. So at low RPM, the motor voltage could be just a few volts. That means battery current can be just a few amps, even though motor amps is near 500. The controller is basically a power converter.

The only time motor amps = battery amps is at the peak (and after). This is the same point as the "knee" in a torque vs RPM curve.

A couple notes: battery voltage changes due to sag at high battery current. The controller sets the voltage at the motor through PWM. It has a feedback circuit that watches the output current and limits it by reducing the duty cycle (50% duty cycle = 50% of pack voltage).

[Aside - I'm running a 650A controller that is capable of pulling 700A from the batteries. My pack is rated for 600A peak. The reason I can get away with this is that the only time the controller will actually pull 700A battery side is at the peak, so I can tune the controller to avoid this. I can still get 650A to the motor without damaging the batteries everywhere before the peak.]

http://www.colorado.edu/physics/EducationIssues/podolefsky/EV_project/batt_motor_amps.png

teddillard
02 January 2012, 1009
So ted, are you basically assuming that motors with the same voltage and current specs will roughly the same torque and horsepower? Is this a valid assumption to make? Is it more or less correct for motors of the same type (all PMDC vs. all AC)?

Also, how would the AC-20 fit in to this list?

I know, i know. So many questions... :)
HHHAHAHAhahahahaAHaha!

The First Law of Product Comparisons is, as soon as you post one, someone's going to ask you why you didn't include some additional product or specs. You WIN!

No, I wasn't at all careful about the power or the torque specs, I probably should add and verify them. And yeah, since the AC20 is at the top of a lot of people's lists, maybe that should go on there too, but I was being selfish. I'm not considering that motor right at the moment, just trying to decide which direction to go on the PMDC front right now.

Thanks for the feedback, though, seriously. Oh crap. You sent me an email a while back. Answering it now. :O

SplinterOz
02 January 2012, 1520
I have an interview lined up with BrammoBrian next week. I'll add this to my list of questions.

Can you ask about regen? (last regen comment on this thread)

Ken Will
02 January 2012, 1809
I believe that a heavy bike/rider can benefit from a lower gear for acceleration.
I believe a aerodynamic bike can benefit from a higher gear for top speed.
So, a heavy aerodynamic bike/rider would benefit the most from a transmission.

A light bike/rider doesn't need a low gear for acceleration and a bike with poor aerodynamics can't push a high gear.
So, an added transmission would not add as much benefit.

Ted and his bike are very light, and he doesn't have any aerodynamic fairings, so a bigger motor is probably a better choice.

IMHO!

jazclrint
02 January 2012, 2159
Can you ask about regen? (last regen comment on this thread)

Yes I can. Could you please PM me your question, as things are getting a little scattered in here? :D

Oh, and I promise I will get to you Aussie guys. I am just trying to get my skills a little more polished (like a rusty bumper, they are) before I go too international.

harlan
22 April 2012, 1645
I'm surprised this thread hasn't been revived given the recent news.

liveforphysics
22 April 2012, 1736
I believe that a heavy bike/rider can benefit from a lower gear for acceleration.
I believe a aerodynamic bike can benefit from a higher gear for top speed.
So, a heavy aerodynamic bike/rider would benefit the most from a transmission.

A light bike/rider doesn't need a low gear for acceleration and a bike with poor aerodynamics can't push a high gear.
So, an added transmission would not add as much benefit.

Ted and his bike are very light, and he doesn't have any aerodynamic fairings, so a bigger motor is probably a better choice.

IMHO!


What if you took the same space, weight, complexity, and cost, of adding a tranny, but instead applied it to the motor? ;-) You end up with a higher power, higher continuous power, higher efficiency (gears all make drag and friction), quieter, shift-delay-free machine. :-)

magicsmoke
22 April 2012, 1809
What if you took the same space, weight, complexity, and cost, of adding a tranny, but instead applied it to the motor? ;-) You end up with a higher power, higher continuous power, higher efficiency (gears all make drag and friction), quieter, shift-delay-free machine. :-)

Higher power, yes, but of course has to be supplied by a more capable battery and controller.
Higher continuous power, yes, but with a higher capacity battery.
Higher efficiency. Absolutely not.
Quieter. Marginal.
Shift delay. Bothered?

It's all very well having a powerful motor, but the torque it develops may not be sufficient to creep up a steep incline. This is the crux of a gearbox... a torque multiplier.

DRZ400
22 April 2012, 1850
no, a gearbox is for wheelies....everybody who ever had a schwinn stingray knows that!

DaveAK
22 April 2012, 1923
I see I haven't missed much from my time away. Still arguing about transmissions, and still haven't agreed on the color. :rolleyes:

podolefsky
22 April 2012, 2324
Higher power, yes, but of course has to be supplied by a more capable battery and controller.
Higher continuous power, yes, but with a higher capacity battery.
Higher efficiency. Absolutely not.
Quieter. Marginal.
Shift delay. Bothered?

It's all very well having a powerful motor, but the torque it develops may not be sufficient to creep up a steep incline. This is the crux of a gearbox... a torque multiplier.


OK then, replace the tranny with a larger motor, controller, and batteries. :D

Chip Yates had no need for a transmission - at some point, some company will finally make a motor about half the size of his (which is probably about right), liquid cooled, 144V lipo pack, and the whole transmission discussion will be moot.

Actually, who am I kidding...

liveforphysics
23 April 2012, 0019
Higher power, yes, but of course has to be supplied by a more capable battery and controller.
Higher continuous power, yes, but with a higher capacity battery.
Higher efficiency. Absolutely not.
Quieter. Marginal.
Shift delay. Bothered?

It's all very well having a powerful motor, but the torque it develops may not be sufficient to creep up a steep incline. This is the crux of a gearbox... a torque multiplier.


Please do explain how you gain efficiency by adding more friction and components to drag. Particularly if this is in the assumption of using a lower torque higher RPM motor that will have high comutation freq core loss, and less copper. You're going to have to do better than saying some BS like, "the motor stays in the efficient zone for more of the time", because that's simply not how it works.

teddillard
23 April 2012, 0219
I'm surprised this thread hasn't been revived given the recent news.

troublemaker. :p

sparky_mark
23 April 2012, 0521
OK then, replace the tranny with a larger motor, controller, and batteries
You mean replace a $200-$300 part with several thousand dollars worth of kit? :)


Please do explain how you gain efficiency by adding more friction and components to drag
A gearbox on an electric bike allows you to select a gear to suit the riding conditions, and therefore give your batteries an easier life, doesn't it?. For example, if you have an electric bike with a gearbox that has a max. top speed of around 80mph but you were riding around town at no more than 30mph in stop/start traffic then you'd use the lower gears. This would give you very good acceleration from standstill, you'd still have reasonable top speed, and the load on your battery pack would be lower. If you then take the bike on the motorway/freeway you'd work your way up through the gears until you achieve top speed.

I don't know if this is true, but it certainly sounds plausible doesn't it? That a gearbox would, in certain conditions, give your batteries an easier life and could extend range? Wether its true or not, I think this is one reason that the idea of a gearbox/transmission refuses to die.

Nuts & Volts
23 April 2012, 0544
You mean replace a $200-$300 part with several thousand dollars worth of kit? :)


A gearbox on an electric bike allows you to select a gear to suit the riding conditions, and therefore give your batteries an easier life, doesn't it?. For example, if you have an electric bike with a gearbox that has a max. top speed of around 80mph but you were riding around town at no more than 30mph in stop/start traffic then you'd use the lower gears. This would give you very good acceleration from standstill, you'd still have reasonable top speed, and the load on your battery pack would be lower. If you then take the bike on the motorway/freeway you'd work your way up through the gears until you achieve top speed.

I don't know if this is true, but it certainly sounds plausible doesn't it? That a gearbox would, in certain conditions, give your batteries an easier life and could extend range? Wether its true or not, I think this is one reason that the idea of a gearbox/transmission refuses to die.

A gearbox only gives your motor and maybe your controller a better life. A given speed (on a given motorcycle) will still require the same amount of energy (minus improved efficiency gains/losses). This energy will come from your battery in the same magnitude of voltage and current with or without a gearbox.

lugnut
23 April 2012, 0554
That a gearbox would, in certain conditions, give your batteries an easier life and could extend range? Wether its true or not, I think this is one reason that the idea of a gearbox/transmission refuses to die.

It is not true. It requires the same energy from the battery to accelerate the bike regardless of the drive ratio. A lower ratio (higher numerical) which increases motor speed and lowers motor torque will simply work the motor controller at a higher PWM but not significantly affect the battery current. Therefore the life and range on the battery is about the same. There may be reasons to use a multispeed gearbox in an electric, but increased battery life or range is not one of them.

Hugues
23 April 2012, 0621
...I don't know if this is true, but it certainly sounds plausible doesn't it? That a gearbox would, in certain conditions, give your batteries an easier life and could extend range? Wether its true or not, I think this is one reason that the idea of a gearbox/transmission refuses to die.

I'll add my 2 cents to the fun,

what do you mean by "easier life". We need to put figures on that. Batteries are not there to have an easy life. As long as you don't pull amps above rated specs and don't bring volts below rated specs too, in between, it's just business as usual. A battery will wear less rapidly i think than a transmission , if the 2 can be compared.

If a battery is sized correctly, i see not much weight to your argument above about "easy life", please explain

thanks

Brutus
23 April 2012, 0655
I see I haven't missed much from my time away. Still arguing about transmissions, and still haven't agreed on the color. :rolleyes:

Mine is black because she was cheaper than the pretty ones! :)

Frank
23 April 2012, 0700
Another factor is heat buildup. I suspect a motor/gearbox would allow one to tradeoff amps for rpm to generate same at-road driving force with less I^2R losses and heating.

larryrose11
23 April 2012, 0709
To jump off futher in the unavalble products, what about a e-transmission - a dual winding motor?
Have a paralell / series switch for the motor windings, like Markcycles protptype motor? This would effectily have a switchable motor KV.

Brutus
23 April 2012, 0716
Just to add to the discussion on a serious note, I have found it extremely hard to get anything hot on the bike. I have also ran my little D&D up to 105v 700a now(its only rated for 72v 450a) and still cant get things to heat up or go wrong.

Maybe the key is in continuous throttle vs. off throttle for gear changes? I did a 40 minute hard ride with speeds in the 90mph range and hard "drag race" starts, when I got off the bike there wasn't a single part of the drivetrain that couldn't be touched with bare hands. Is this common for everyone else' Elmoto's to run so cool? I do take temps and my highest temp ever reached through testing was 158f on the com and brushes and that was taken when I had the Zilla set at 88v and 400a.

Honestly even if a trans is useless for electrics it sure is fun to ride and that is what's most important to me.

Frank
23 April 2012, 0825
My D&D Sepex motor is warm to the touch when you first stop but I've had it go as high as 150*F when soaking. D&D says this is barely warm. :)

podolefsky
23 April 2012, 0831
My D&D Sepex motor is warm to the touch when you first stop but I've had it go as high as 150*F when soaking. D&D says this is barely warm. :)

Most motors use Class H insulation, rated to 350 F. If you can touch it without getting burned, it's fine.

podolefsky
23 April 2012, 0832
Honestly even if a trans is useless for electrics it sure is fun to ride and that is what's most important to me.

That's the best reasoning I've heard so far...

Athlon
23 April 2012, 0841
I'm not a big fan of transmission for EV , but sometimes they can save the day , on light well powered vehicles like bike there is almost no need to have a gearbox , but on commercial truck with some overload and very step hill to climb a transmission is the only way to climb on top with a chap motor , motor prices grow up faster than transmission prices when you go up with power , so for a 10Kw bike can be cheaper adding a second motor , but for a 50Kw truck can be cheaper adding a 2-3 speed gearbox

harlan
23 April 2012, 0859
troublemaker. :p

Ha! Just thought we finally had some data points to analyze, maybe plug into the elmoto spreadsheet. :p

As someone has said before, (Noah?), the only fair comparison would be identical bikes with/without transmissions. At a glance, it doesn't look like transmissions cause the dramatic efficiency/range boost that was eluded to.

Maybe Brutus can chime in on the subject since he's the only one with any experience with trannys on an elmoto. Have you had the chance to measure your power consumption at different speeds? You have said in the past you were expecting to get about 100 miles on a ~4kWh pack which would certainly make a strong case for transmissions. Any data you can share? Does it give an efficiency advantage or is it just a fun factor?

Biff
23 April 2012, 0938
A gearbox gives you the ability to use your full power at more speeds, so it allows you to use your battery faster if that is what you want.

For example if you have a bike with a single speed, and it puts its peak power, say 30hp, down at 60mph. Now say you put a 2 speed gearbox with a 1:1 and a 1:2 ratio. now you have the ability to put that 30hp down at 30mph and 60mph if you want to.

Another way to look at it is: if you get harder acceleration, that power accelerating you needs to come from somewhere, and on an electric motorbike, that is from the battery.

lugnut
23 April 2012, 1015
For example if you have a bike with a single speed, and it puts its peak power, say 30hp, down at 60mph. Now say you put a 2 speed gearbox with a 1:1 and a 1:2 ratio. now you have the ability to put that 30hp down at 30mph and 60mph if you want to.

Or you could use an AC system (like the AC15, 80V) and get constant torque up to 30mph and the same power (about 30hp) at both 30 and 60mph with a fixed ratio. You'd have less gear loss and more space for battery.

DaveAK
23 April 2012, 1016
Honestly even if a trans is useless for electrics it sure is fun to ride and that is what's most important to me.
Bingo! We have a winner!

But black? Really? That's so 2010.

liveforphysics
23 April 2012, 1058
You mean replace a $200-$300 part with several thousand dollars worth of kit? :)


A gearbox on an electric bike allows you to select a gear to suit the riding conditions, and therefore give your batteries an easier life, doesn't it?. For example, if you have an electric bike with a gearbox that has a max. top speed of around 80mph but you were riding around town at no more than 30mph in stop/start traffic then you'd use the lower gears. This would give you very good acceleration from standstill, you'd still have reasonable top speed, and the load on your battery pack would be lower. If you then take the bike on the motorway/freeway you'd work your way up through the gears until you achieve top speed.

I don't know if this is true, but it certainly sounds plausible doesn't it? That a gearbox would, in certain conditions, give your batteries an easier life and could extend range? Wether its true or not, I think this is one reason that the idea of a gearbox/transmission refuses to die.


No. If your motor is able to turn faster, the BEMF is higher, and you have the ability to draw more power from the battery for any given phase current limit your controller does. When you have a tranny and you're in 1st gear and it's accelerating harder than if it was in 2nd gear, it's because you're able to draw more power in first gear because the motor is spinning faster.

Likewise, though no amount of changing KV in a motor through changing the number of turns, changing how turns are grouped in series or parallel, changing from Delta to Wye etc, NONE of these things can give your motor the ability to have higher torque, higher continuous torque, etc (assuming the amount of copper in the slot is identical still).

What it can do, is enable you to pull more power out of your battery because it's BEMF is higher. When you change from a higher KV wind to a lower KV wind, you now have the ability to hit the batteries harder for a given amount of phase current your controller is capable of, and it's this additional power you draw that makes higher torque for a given controller phase current limit. HOWEVER! The motor is not capable of any additional torque at all, it's capable of exactly the same torque as before, it would have just required higher phase amps from the controller to be feeding it the same amount of power that the lower KV motor can draw with less phase amps, because it's getting it's phase current is multiplied by a higher phase voltage (because BEMF climbs faster with a low KV motor, and phase resistance grows at the square of turns).


Also, there are some massive misconceptions about motor windings and I^2*R loss. The misconceptions are written a few times in this very thread, and are seen in pretty much every thread related to motors anywhere that confused people talk about motors.

If the copper fill is the same in the slots of the motor, you make the exact same amount of heat if you're a 1-turn winding or a 100-turn winding.

The resistive loss grows at the square of current, and the coppers resistance grows at the square of turns, so if you have a 2-turn motor with 10mOhm resistance, when you make that a 4-turn motor, the wire has to get twice as long to make double the turns, and it also has to get half the thickness to enable it to fit in the slot, so the 4-turn version of the same motor is 40mOhm of resistance. If we put 100amps through the 2-turn motor, we only need to put 50amps through the 4-turn motor to make the same torque, the 10mOhm winding with 100amps I^2*R = 100watts of resistive copper loss (heating). The 50amps through the 40mOhm I^2*R = 100watts of resistive copper loss (heating). How about the power they both draw to make that torque? The 2-turn motor needs 1v of drop to draw it's 100amps, making 100watts of power needed to make x amount of torque, and the 4 turn motor needs 2v of drop at 50amps to make it's x amount of torque, also 100watts.


Long story short, apply that expense and weight and bulk of the tranny towards putting a motor properly suited for the job rather than trying to band-aid an incorrectly sized motor, and you end up winning everywhere if your pursuit is performance and durability.


If you're building something to be a utility tractor, and you want to crawl around at 1mph and pull stumps out of the ground with it, and then also be able to cruise along the highway at 80mph, then a tranny makes more sense than making a giant motor to do it. For situations like 0-200mph on a motorcycle, you're simply going to be most happy and have the best performance by filling that area with more motor rather than tranny. If you don't have the physics skills to see why, you can see excellent evidence of this in examples like Chip Yates bike getting to 190mph in the standing mile... Any addition of a tranny would have just slowed him down from shifting delays, and taken away space and added weight that could be going towards a higher power motor.

http://www.youtube.com/watch?v=b-SYq8H4xnI

sparky_mark
23 April 2012, 1543
No. If your motor is able to turn faster, the BEMF is higher, and you have the ability to draw more power from the battery for any given phase current limit your controller does. When you have a tranny and you're in 1st gear and it's accelerating harder than if it was in 2nd gear, it's because you're able to draw more power in first gear because the motor is spinning faster.
But what if you are in 1st gear and you aren't accelerating hard? You don't ride everywhere flat out do you? Surely if you were in 1st gear and the bike was only accelerating moderately, say at the same rate as if you were in 2nd or 3rd gear, then aren't you achieving the same rate of acceleration using less power?

sparky_mark
23 April 2012, 1555
Or you could use an AC system (like the AC15, 80V) and get constant torque up to 30mph and the same power (about 30hp) at both 30 and 60mph with a fixed ratio. You'd have less gear loss and more space for battery.
30bhp to do 60mph? Is this a real world example? Do you really need 30bhp to do 60mph? My old 12bhp Honda 125cc could go faster with less....

Nuts & Volts
23 April 2012, 1606
But what if you are in 1st gear and you aren't accelerating hard? You don't ride everywhere flat out do you? Surely if you were in 1st gear and the bike was only accelerating moderately, say at the same rate as if you were in 2nd or 3rd gear, then aren't you achieving the same rate of acceleration using less power?

Nope, to move a given mass, m, at a certain acceleration, a, you need the same force regardless of gearing.
F=m*a

This force equals the torque divided by the wheel radius. So for the same 'a' you will need to generate the same amount of torque with the same amount of battery voltage and current (ie power).

liveforphysics
23 April 2012, 1657
But what if you are in 1st gear and you aren't accelerating hard? You don't ride everywhere flat out do you? Surely if you were in 1st gear and the bike was only accelerating moderately, say at the same rate as if you were in 2nd or 3rd gear, then aren't you achieving the same rate of acceleration using less power?

Not at all. There is no free lunch. To cruise at a given rate, you need x amount of power. You can achieve that power by spinning your motor at a certain speed (say 1000rpm) and 20ft-lbs of torque (say this requires 200amps), or you can have twice as short of gearing, and achieve the same X power needed to cruise at your intended speed, now your motor is at 2,000rpm and you only need 10ft-lbs of torque (requires only 100amps), but requires DOUBLE the voltage, so you end up drawing exactly the same power of the battery as before. (Keep in mind, motor amps are NOT battery amps)

Every transmission will always add some amount of friction and drag and weight, and require space to package on the bike, and not give any higher power levels or continuous power levels etc. It can just enable your motor to draw more power sooner while in shorter gears. If you just have a motor that can handle more power, you win everywhere.

At least that's my $0.02

Frank
23 April 2012, 1905
But don't the 100 motor-amps imply less losses/heating than 200 motor-amps?

Nuts & Volts
23 April 2012, 1918
But don't the 100 motor-amps imply less losses/heating than 200 motor-amps?

Slighty. The higher speed of the motor will have increased eddy current, windage drag, and frictional losses. Depending on where you are in the motor speed range the 100A may or may not be more efficient than the 200A motor.

And this increase, if any, still needs to offset the additionally power needed from the added tranny weight and the additional frictional losses of the tranny to be benefical (in efficiency regards). I still like a tranny from a performance/cost advantage

liveforphysics
23 April 2012, 1950
But don't the 100 motor-amps imply less losses/heating than 200 motor-amps?


Every motor peaks efficiency at the point which copper loss is equal to all other losses. When you're at a lower power output, core losses are greater than copper losses, when you're at a higher power output, copper losses exceed core losses, all the way to the point at which you continue to feed the motor power until efficiency drops to 50%, this is every motors peak maximum power output point.


If your motorcycle is remotely sporty, you have much more power on tap than is needed to maintain cruising pace. This means when cruising you're operating in the reduced efficiency area where core losses are exceeding copper loss. When you keep RPM the same (and hence core loss stays the same), but add more current (increasing torque to make your power increase), you improve efficiency of the motor right up to the point at which they are balanced losses. For cruising situations, you're very likely to increase efficiency of your drivetrain with additional current, almost guaranteed to unless you picked a tiny motor that is maxed up just trying to cruise.

For an extreme example, Chip's bike or Mission's bike cruising at 60mph is using perhaps 3-5% of it's available power. If they were geared taller so more current was going to the motor at lower speeds, they would definitely increase efficiency through the reduction in core loss and increase in copper loss getting them closer to matching. However, they are all ready geared for as high of speed as they have power to achieve, so while it would improve the economy of the bike, it would decrease the acceleration performance, and they are designed to be racing bikes not commuters, so they are geared just fine for the job they have.

liveforphysics
23 April 2012, 1954
But don't the 100 motor-amps imply less losses/heating than 200 motor-amps?


Also, if the motors are outputting identical torque and power, meaning the 100amp motor has twice the turns of the 200amp motor, then the heating is exactly the same between the two motors.

podolefsky
23 April 2012, 1958
No. If your motor is able to turn faster, the BEMF is higher, and you have the ability to draw more power from the battery for any given phase current limit your controller does. When you have a tranny and you're in 1st gear and it's accelerating harder than if it was in 2nd gear, it's because you're able to draw more power in first gear because the motor is spinning faster.

Yup. Another way to look at it is conservation of energy. If you go from 0-60 mph, you have put the same amount of energy into the bike whether you did it in 5 seconds or 5 minutes, and whether you did it in 1st gear or 3rd. The power (which is energy / time) is different if you accelerate faster, but not whether you're in a different gear (unless the efficiency varies with current and RPM, which is does, but not very much throughout most of the range).



Likewise, though no amount of changing KV in a motor through changing the number of turns, changing how turns are grouped in series or parallel, changing from Delta to Wye etc, NONE of these things can give your motor the ability to have higher torque, higher continuous torque, etc (assuming the amount of copper in the slot is identical still).

What it can do, is enable you to pull more power out of your battery because it's BEMF is higher. When you change from a higher KV wind to a lower KV wind, you now have the ability to hit the batteries harder for a given amount of phase current your controller is capable of, and it's this additional power you draw that makes higher torque for a given controller phase current limit. HOWEVER! The motor is not capable of any additional torque at all, it's capable of exactly the same torque as before, it would have just required higher phase amps from the controller to be feeding it the same amount of power that the lower KV motor can draw with less phase amps, because it's getting it's phase current is multiplied by a higher phase voltage (because BEMF climbs faster with a low KV motor, and phase resistance grows at the square of turns).


What about at peak when you're controller is current limiting? In that case you can't trade current for voltage.

If you have one motor rated 0.15 ft-lb/amp and another rated 0.3 ft-lb/amp, and you have a 500 amp controller, then one motor will give you 75 ft-lb and the other will give you 150 (peak). Now, if you have a 1000A controller for the 0.15 ft-lb/amp motor, then you can get the same torque...but that means having a bigger controller. All else being equal, the lower kV motor will give you more torque (but lower RPM, so the same power).


Also, why do you keep calling it phase current? For DC motors, I thought it was just current.

liveforphysics
23 April 2012, 2013
What about at peak when you're controller is current limiting? In that case you can't trade current for voltage.

If you have one motor rated 0.15 ft-lb/amp and another rated 0.3 ft-lb/amp, and you have a 500 amp controller, then one motor will give you 75 ft-lb and the other will give you 150 (peak). Now, if you have a 1000A controller for the 0.15 ft-lb/amp motor, then you can get the same torque...but that means having a bigger controller. All else being equal, the lower kV motor will give you more torque (but lower RPM, so the same power).


Good question.
What I wrote:

"Likewise, though no amount of changing KV in a motor through changing the number of turns, changing how turns are grouped in series or parallel, changing from Delta to Wye etc, NONE of these things can give your motor the ability to have higher torque, higher continuous torque, etc (assuming the amount of copper in the slot is identical still). "

This is with respect to the motors ability. Obviously if you pick something that your controller can't work with, you choose poorly and it will perform poorly. If you have a 2,000amp 10v controller you pick the 1-turn motor and get identical performance to the 100v 200amp controller with 10x more turns, or the 1000v 20amp controller with 100x more turns. All of the setups make identical heat and power and perform identically, except they require the phase wires to grow in cross section inversely proportional to the number of turns of course to balance system loss, so your wires from controller to motor will be much bigger and heavier in the 2,000amp 10v setup than they need to be in the 1000v 20amp setup, but both will have identical performance and heating and losses etc.





Also, why do you keep calling it phase current? For DC motors, I thought it was just current.

I personally work exclusively with BLDC motors these days, so I'm pretty used to viewing it all as phase leads, on a brushed motor they just commutate later down the path. :-)

podolefsky
23 April 2012, 2112
Good question.
What I wrote:

"Likewise, though no amount of changing KV in a motor through changing the number of turns, changing how turns are grouped in series or parallel, changing from Delta to Wye etc, NONE of these things can give your motor the ability to have higher torque, higher continuous torque, etc (assuming the amount of copper in the slot is identical still). "

This is with respect to the motors ability. Obviously if you pick something that your controller can't work with, you choose poorly and it will perform poorly. If you have a 2,000amp 10v controller you pick the 1-turn motor and get identical performance to the 100v 200amp controller with 10x more turns, or the 1000v 20amp controller with 100x more turns. All of the setups make identical heat and power and perform identically, except they require the phase wires to grow in cross section inversely proportional to the number of turns of course to balance system loss, so your wires from controller to motor will be much bigger and heavier in the 2,000amp 10v setup than they need to be in the 1000v 20amp setup, but both will have identical performance and heating and losses etc.


I see your point. Just clarifying that motors have both speed and torque constants...you're right about the *ability* of the motor, given that the rest of the system is matched.



I personally work exclusively with BLDC motors these days, so I'm pretty used to viewing it all as phase leads, on a brushed motor they just commutate later down the path. :-)

That's what I figured...just didn't want to confuse people anymore with extra terminology.

sparky_mark
24 April 2012, 0041
To cruise at a given rate, you need x amount of power. You can achieve that power by spinning your motor at a certain speed (say 1000rpm) and 20ft-lbs of torque (say this requires 200amps), or you can have twice as short of gearing, and achieve the same X power needed to cruise at your intended speed, now your motor is at 2,000rpm and you only need 10ft-lbs of torque (requires only 100amps), but requires DOUBLE the voltage, so you end up drawing exactly the same power of the battery as before. (Keep in mind, motor amps are NOT battery amps)
So in the second scenario where you need more rpm and volts but less torque and fewer amps, isn't the discharge rate on the batteries lower (say 5C instead of 10C)? If that's the case, then that's what I meant when I put forward the idea that a gearbox would give the batteries an easier life.

teddillard
24 April 2012, 0225
oh the pain.

Here's what I've found. My bike, with lower gearing, goes 0-60 in 4 sec or so, but has a top speed of 75mph. I don't know what the top speed is with higher gearing. I'm pretty certain it's higher. :rolleyes: But I'm also pretty certain it won't accelerate as fast. I'm also pretty certain that if I strapped on a 30lb weight that it wouldn't change either the acceleration or the top speed much.

It's easy enough to test, and I'll be doing so as soon as a 30lb two-speed transmission becomes available, or, I decide to do the "break the ton" run attempt. Anybody with some time, a chain, a 30lb weight and some extra front sprockets could test it too.

Anyone running a bike with a transmission could test it as well, easier. Run some speed tests with your transmission, with a 30lb weight in your backpack. Then run the same tests in one gear without the 30lb weight.

I think it was my very first post on transmissions... asking if it wasn't a very simple thing to model, for you engineer guys, and test, for us non-engineer guys. It is.

(Mr. T, in my head, saying "STOP yo JIBBAH-JABBA")

And yes, Chris, on the fun part, but for me, not to beat the horse, but the fun is in not shifting - and pretending I'm in the launch tube of Battlestar Galactica. :D

<iframe width="640" height="360" src="http://www.youtube.com/embed/9XcBsmVgC3s" frameborder="0" allowfullscreen></iframe>

Nuts & Volts
24 April 2012, 0328
So in the second scenario where you need more rpm and volts but less torque and fewer amps, isn't the discharge rate on the batteries lower (say 5C instead of 10C)? If that's the case, then that's what I meant when I put forward the idea that a gearbox would give the batteries an easier life.

No because the difference in volts is relative to the output of the controller and into the motor. The battery side will always deliver the same voltage and thus for the same power as was stated the current from the batteries must be the same. Volts*Current= Power (Watts)

Frank
24 April 2012, 0354
Pragmatically speaking, can't you get more turns of a smaller wire into a given slot size than larger wire? Does this mean that for a given motor size that a higher voltage rating might indicate higher efficiency or performance?

BTW, thanks for the discussion. I'm a mechanical guy and am still learning about these electric doo-dads.

Nuts & Volts
24 April 2012, 0413
Pragmatically speaking, can't you get more turns of a smaller wire into a given slot size than larger wire? Does this mean that for a given motor size that a higher voltage rating might indicate higher efficiency or performance?

BTW, thanks for the discussion. I'm a mechanical guy and am still learning about these electric doo-dads.

I believe you are correct. A higher copper fill will make a motor more power dense, and I would think that efficiency may improve, but doesnt necessarily have too...

lugnut
24 April 2012, 0415
Pragmatically speaking, can't you get more turns of a smaller wire into a given slot size than larger wire? Does this mean that for a given motor size that a higher voltage rating might indicate higher efficiency or performance?

You can use parallel strands of finer wire opposed to thicker if it allows for better slot fill, so, no it is not necessarily true. But that means you have more insulation on the wires and insulation consumes slot space and is non productive.

lugnut
24 April 2012, 0527
30bhp to do 60mph? Is this a real world example? Do you really need 30bhp to do 60mph? My old 12bhp Honda 125cc could go faster with less....

I was responding to Biff's example.
now you have the ability to put that 30hp down at 30mph and 60mph if you want to. And I did use a published motor curve so it can be considered a real world example. While you may not need 30hp for 60mph, you certainly can use 30hp at 60mph for various reasons like a strong headwind, uphill or acceleration.

Brutus
24 April 2012, 0723
I did the tests Ted spoke of and what was found with a 45 pound weight was depending on the gear I started in made more difference than the extra weight. Starting in 1st or 2nd with and without extra weight was Identical but as you start in 3rd-5th the heavy tests got way slower times than without the extra weight. Voltage sag showed out in the same way too but the weight had no difference in those tests, just more sag in the higher gear starts along with more heat.

In the end I could of built a bike that had no trans and followed years of conventional wisdom, or just converted an existing platform but that would have been easy and pushes no limits for me, I wanted something different that gave me a challenge. Looking back I wouldn't do it any different at all.

liveforphysics
24 April 2012, 1019
Your ideal method to fit the most copper in the slot is to simply slide a solid bus wrapped in a thin film of kapton down the slot. (see, solid-slot motors, and the difficultly of controlling these low inductance beasts, it's a case of extremely high motor performance and efficiency capability, but controller tech isn't up to the point of controlling them effectively)

Your second best option is what Remy does, custom forming flat strips of copper and welding the ends down close so end-turn loss is minimized. (see Remy HVH)

Your third best option (though extremely difficult labor to do) is to wind square enameled wire into the slot stacking blocks of copper cross section to fill the slot.

Your 4th best option is a single strand of the fattest wire that fits the slot to make the number of turns you need. This is because the ratio of copper cross section to wasted insulation space is minimized if there are no additional parallel strands.


Your 5th best option (and what is most commonly done because the winding process is easy to do with human hands) is bundles of fine wire. This can not achieve the copper fill theoretical limits that a single large wire can achieve because of the additional wasted volume of the insulation, however they easily straighten and lay flat in the slot where the bigger thicker wires tend to bow when wound by humans.


If you had big wires and small wires with no insulation, it would make no difference on your limits of copper fill. Small wires with insulation will always be theoretically worse than big wires with insulation. However, in practice when wound by human hands rather than a machine with plastic die it forces through the slot to make each pass lay flat in the correct place, small wires generally result in the best fill.


Here is a decent page going over the geometry and copper fill associated with large wires vs small wires, and should clear up many of these misconceptions.

http://www.flyelectric.ukgateway.net/winding.htm

podolefsky
24 April 2012, 1259
And yes, Chris, on the fun part, but for me, not to beat the horse, but the fun is in not shifting - and pretending I'm in the launch tube of Battlestar Galactica.

Agreed...and I'll just add, in my opinion, the elegant simplicity of direct drive.

liveforphysics
24 April 2012, 1336
Agreed...and I'll just add, in my opinion, the elegant simplicity of direct drive.

Canyon carving is so much better without your rear wheel getting jerked around on downshifts under braking. You can run that much closer to the limit safely. You never have that problem of exiting in the wrong gear either, you're always in the right gear. I do quite a bit of riding Electrics with gas bikes, the shifting delays and interruptions seem so dinosaur. My GSXR1000 has crazy power, but in a technical set of twisties, I run faster on a zero because you don't have to leave margin in the tires for the back torque jerks upsetting the chassis on downshifts. I know some super bikes made in the last few years have special back torque limiting clutches to help reduce that problem, they likely feel better.

Square Wave
24 April 2012, 1344
Your ideal method to fit the most copper in the slot is to simply slide a solid bus wrapped in a thin film of kapton down the slot. (see, solid-slot motors, and the difficultly of controlling these low inductance beasts, it's a case of extremely high motor performance and efficiency capability, but controller tech isn't up to the point of controlling them effectively)

Your second best option is what Remy does, custom forming flat strips of copper and welding the ends down close so end-turn loss is minimized. (see Remy HVH)

Your third best option (though extremely difficult labor to do) is to wind square enameled wire into the slot stacking blocks of copper cross section to fill the slot.

Your 4th best option is a single strand of the fattest wire that fits the slot to make the number of turns you need. This is because the ratio of copper cross section to wasted insulation space is minimized if there are no additional parallel strands.


Your 5th best option (and what is most commonly done because the winding process is easy to do with human hands) is bundles of fine wire. This can not achieve the copper fill theoretical limits that a single large wire can achieve because of the additional wasted volume of the insulation, however they easily straighten and lay flat in the slot where the bigger thicker wires tend to bow when wound by humans.


If you had big wires and small wires with no insulation, it would make no difference on your limits of copper fill. Small wires with insulation will always be theoretically worse than big wires with insulation. However, in practice when wound by human hands rather than a machine with plastic die it forces through the slot to make each pass lay flat in the correct place, small wires generally result in the best fill.


Here is a decent page going over the geometry and copper fill associated with large wires vs small wires, and should clear up many of these misconceptions.

http://www.flyelectric.ukgateway.net/winding.htm

Doesn’t a bunch of fine wire also reduce heat from eddy currents? Rather like the laminations in a stator core?

liveforphysics
24 April 2012, 1353
Doesn’t a bunch of fine wire also reduce heat from eddy currents? Rather like the laminations in a stator core?

It does in an ironless motor (which is why they use litz wire). In a motor with iron, the copper never has flux lines cutting through it, this is the job of the iron to attract and guide the flux lines from the head of the tooth down the shank of the tooth. The copper doesn't attract or guide the flux, the iron does very effectively, and keeps it all away from the copper in the slot.

This is true even with motors where they fill the slot very wide so it's bulging with copper out exposed between the edges of the tooth heads. I had thought it would be a massive eddy current failure, but it turns out, the iron guides 100% of that flux down it's heads and into the shaft of the tooth and the copper doesn't see a thing (other than the net change in flux of the iron core it's wrapped around, which is what creates the BEMF). Take the iron out of that picture, and you've got yourself an eddy brake. Put the iron in, and you've got a pretty free spinning motor (just normal core-losses).

DaveAK
24 April 2012, 1357
Agreed...and I'll just add, in my opinion, the elegant simplicity of direct drive.
So easy the brainless can use it. :p

podolefsky
24 April 2012, 1407
Here's a question:

Suppose I have an AC-20, 650A controller (which I do). Even at 72V, I can gear this to go 90+ mph and have acceleration that makes me smile. At 96V, I'd be rockin even harder.

Now, suppose I'm totally happy with the power available...I don't need to go over 90. But I want more starting torque. Here are my options:

1) get a transmission.
2) get a bigger motor/controller.

Let's say option 1 adds 30 lb and takes up about the volume of a 2nd AC-20. If it had a 2:1 reduction, I'd get 2X the wheel torque with the same drive system. (Actually, if it were just 2-speed, the transmission could probably be about 1/2 the size and more like 15-20lb).

So to me, that's the crux of the issue. Transmissions give you a mechanical advantage with less added size and weight compared to a larger drive system. There's no motor/controller/battery combination available, that I know of, that will double the starting torque of a typical large drive system (like my AC-20) and only adds 15-30 lb.

Even supposing there was - suppose someone made a 1200A, liquid cooled beast of a system about the same size and weight as my AC-20. You'd have to ask the same question. Is there another drive system that will double your starting torque and only adds 15-30 lb? Probably not - you'd be back asking same question - how can I get more wheel torque?

I still stick to my personal opinion that direct drive is a joy. I love that it's possible. Chip Yates has (had?) a bike with an over abundance of torque, should make anyone happy, but it weighed over 600 lb and he had to hang his pack off the back of the bike.

I submit that if you want neck snapping, wheelie popping acceleration off the line, a transmission is going to be the cheapest and lightest way to get there. Don't give me this crap about a transmission being a bandaid for an under-powered motor. My motor is plenty powerful - with the right gearing, I could do 100+ mph. It's just that I can't have that AND neck snapping acceleration without adding significantly more weight and cost than a transmission.

Prove me wrong. Actually describe a system (real or theoretical) that only adds 15-30 lb and will double the wheel torque available from 0-30 mph.

Nuts & Volts
24 April 2012, 1424
Noah,

Using an AC-20 system I will agree with you that for the cost part of it you can't beat a tranny. This may not be turn with all motor setups thou. I will disagree with you on the weight. There are a couple motors out there lighter than the AC-20 that can beat its performance for 0 to 20% more weight. However then you're cost goes through the roof.

I'll add a little bit more fuel to the fire, why not add liquid cooling to get more power out of the same system. Maybe be cheaper than a tranny and will weigh less...might not actually work in the motors in practice, but who knows?

podolefsky
24 April 2012, 1441
Noah,

Using an AC-20 system I will agree with you that for the cost part of it you can't beat a tranny. This may not be turn with all motor setups thou. I will disagree with you on the weight. There are a couple motors out there lighter than the AC-20 that can beat its performance for 0 to 20% more weight. However then you're cost goes through the roof.

I'll add a little bit more fuel to the fire, why not add liquid cooling to get more power out of the same system. Maybe be cheaper than a tranny and will weigh less...might not actually work in the motors in practice, but who knows?


True, the AC-20 isn't the lightest or most efficient motor. But that's what I was saying, that no matter what you start with, you're always going to be able to ask the question "could I double the 0-30mph torque for only 15-30 more lb? ...and a few hundred $$?"

Yeah, liquid cooling is a good place to start. Then you have the same size motor that can handle more current, thus increasing the torque and power capability. Same goes or adding brushes (i.e., ME1003 vs 0709). But I keep coming back to the same question...what if you want even more?

I guess there's a break even point - probably around the place where you can do 100 mph, pop wheelies, and keep the bike under 500 lb (and hopefully under $20k). Until that bike is available, a transmission makes sense...assuming that's what you're into.

teddillard
24 April 2012, 1446
...why not add liquid cooling to get more power out of the same system. Maybe be cheaper than a tranny and will weigh less...

Every liquid cooling system I've looked at weighs in at a minimum of 15lbs, FWIW.

liveforphysics
24 April 2012, 1538
Prove me wrong. Actually describe a system (real or theoretical) that only adds 15-30 lb and will double the wheel torque available from 0-30 mph.


No problem.

AC20 = 53lbs. 50hp, though in my experience dyno'ing them at 50hp output they start having smoke rising up off the windings in about 10seconds, even with a good fan blowing through them. Fortunately it's rare to use 50hp continuously in a motorcycle application.

Switch to mission's PM motor.
http://ridemission.com/wp-content/uploads/2012/01/Traction-Motor-Spec-Sheet.pdf

You can have 1 speed, the same top speed, 3x the starting torque (because you can gear it about 3x shorter than the AC20), and if you like, put the same battery current limit you've currently got so you're not pulling a single extra watt, just getting >10% more power from the efficiency improvement, achieving the same top-speed, and getting 3x the starting torque.

You save 2.5lbs off the motor weight, but will need to add a 2lbs pump, a 2lbs oil cooler, 2lbs of hoses, 3lbs of oil, and then likely require a jack-shaft unless you're willing to run a massive rear sprocket and deal with the chordal motion noise of a tiny front sprocket. The jack-shaft won't blow the weight budget though. :-)

Is this the sort of thing you were looking for? Or are you looking for something to add to your existing AC-20? Because 4x the cooling and 2x the motor current would do the trick.

liveforphysics
24 April 2012, 1558
I guess there's a break even point - probably around the place where you can do 100 mph, pop wheelies, and keep the bike under 500 lb (and hopefully under $20k). Until that bike is available, a transmission makes sense...assuming that's what you're into.

My bicycle found that point. Continuous power wheelie capable from 0mph to 60mph. Top speed capable of higher than I like to go on a bicycle (triple digits).
I can not use all of it's torque until 50-60mph, and I do not run it's top speed out to maximum. It's a very odd feeling, it's like the first vehicle I've ever piloted that can always provide you more torque and power than you can dare ask it for at almost any point.

Naturally, this is why we're adding a twin giant sevcon and bigger motor to double it's power. :-) My personal goal is to have over 100rwhp and over 800ft-lbs at the tire of my 100lbs bicycle. It's all possible, just need the time to finish.

DaveAK
24 April 2012, 1559
Switch to mission's PM motor.
http://ridemission.com/wp-content/uploads/2012/01/Traction-Motor-Spec-Sheet.pdf
And do Mission sell this motor to anyone at an affordable price? I know Noah said real or theoretical, but I prefer real, and if I can't afford it then it's just theory. Cost is a major variable in this discussion, or at least it should be.

podolefsky
24 April 2012, 1612
But according to the spec, you need 450V to hit 16000 rpm...and 550A for that torque. So basically a pack with 6x the power of mine. Even with lipo, that's going to be more than 30lb (I think).

Sent from my PC36100 using Tapatalk 2

liveforphysics
24 April 2012, 1641
But according to the spec, you need 450V to hit 16000 rpm...and 550A for that torque. So basically a pack with 6x the power of mine. Even with lipo, that's going to be more than 30lb (I think).

Sent from my PC36100 using Tapatalk 2

It can also be 45v to achieve the same performance, it would just be a 1 turn rather than 10 turn and the controller would need to be designed around higher currents of course.

But, no reason your battery would need to be any bigger or heavier, likely you could save a little weight and space with smaller battery to controller cables.
For example, the 25Ah 30S (114v) pack on my bicycle can simply have the bullet connectors re-arranged to become a 5Ah (150s) 570v nominal pack. It doesn't make it a bit larger, doesn't make a bit higher power or higher energy or lower energy, just makes it 570v nominal rather than 114v.

liveforphysics
24 April 2012, 1643
And do Mission sell this motor to anyone at an affordable price? I know Noah said real or theoretical, but I prefer real, and if I can't afford it then it's just theory. Cost is a major variable in this discussion, or at least it should be.

I think they are looking for OEM deals rather than the hobby market.
What's amazing though, is at the OEM production scale, I bet this motor costs under $1000.

podolefsky
24 April 2012, 1727
So basically, if I could run my AC20 at 144V instead of 72, and it could spin at 12000 RPM without flying apart, and I had 30Ah cells that could do 20C...I could gear down by 2x, double the wheel torque and keep the same top speed.

Interesting...


Sent from my PC36100 using Tapatalk 2

DaveAK
24 April 2012, 1758
I think they are looking for OEM deals rather than the hobby market.
What's amazing though, is at the OEM production scale, I bet this motor costs under $1000.
So I just need to commit to 10,000 units? Sweet!

podolefsky
24 April 2012, 1808
No problem...the controller, on the other hand, is $15,000... :rolleyes:

Sent from my PC36100 using Tapatalk 2

liveforphysics
24 April 2012, 1811
So basically, if I could run my AC20 at 144V instead of 72, and it could spin at 12000 RPM without flying apart, and I had 30Ah cells that could do 20C...I could gear down by 2x, double the wheel torque and keep the same top speed.

Interesting...


Sent from my PC36100 using Tapatalk 2


Yep. Some core losses grow at the square of RPM, one grows at the cube of RPM, so you might find yourself with rapidly diminishing efficiency trying to spin a motor to 12k that was designed for 6k (aside from the rotor flying apart), BUT! Yes, if you could do it, you would have exactly what you're looking for with no tranny. This is part of why some motors are more clever than others. (Mission's motor is a pretty clever one)


if you could do something to improve efficiency of your motor from 70% under high loads to 85% under high loads, you could also more than double your torque and continuous torque etc (with the addition of a controller that doubles phase current, battery current will still be low because you're looking to do it at low speeds).


But... the most realistic option for your existing setup, is to simply add in another 10s to your pack (or whatever your controller voltage limit is), and then run 30-40% more shorter gearing. You will have the same top speed, 30-40% more torque, more range from the additional cells. BUT! You will have lower efficiency from increased core loss from averaging higher RPMs as you're riding. This will enable you to pull more power from your batteries sooner (the way it gets more power), but you've added the same amount of additional batteries in series, so it's going to be a wash.

That gives you a real-world nice performance increase that is affordable and simple to do, but it's not a torque doubler, and it does hit your cruise efficiency a bit, likely about the same hit as friction from gear drag in a tranny could cause.

podolefsky
24 April 2012, 2058
...and we come full circle, yet again...

I had actually worked this out a while ago (when I was still contemplating the AC conversion). The Curtis maxes out at 130V, which means I could run 36s (115.2V nominal, 131.4 off the charger, but <130V resting). That's a factor of 1.6, so not 2x but still pretty good.

BTW, the factor of 2 isn't arbitrary - it comes from comparing the rear wheel torque of a GSX-R 600 in 1st, which is about 740 ft-lb...meaning I'd need about 2x the torque with a 5:1 reduction to match it...or the same torque with 10:1. Of course, I'd have that torque from 0 RPM and no shifting delay, which would pretty much rock.

It's hard to say how this would affect 50-60 mph cruising efficiency. If it's geared to max out at 90-100mph, then 50-60 is right in the middle of the RPM range (where I believe efficiency tends to be highest, but there's no way to be sure without a power vs speed efficiency map, which of course doesn't exist for that motor).

There's no way to fit 12s more GBS cells - I probably couldn't even fit 8 more. But a 36s5p Headway pack would fit just fine...or lipo. Always options...just not cheap options. Maybe once I get the KZE done, loans paid off...I can get myself into debt again and make this next winter's project :D

[edit] Incidentally, I checked and a 36s5p Headway pack (38120s) would be almost dead on same weight as my 72V, 60Ah GBS pack. Hmmm....

Biff
24 April 2012, 2119
Canyon carving is so much better without your rear wheel getting jerked around on downshifts under braking. You can run that much closer to the limit safely. You never have that problem of exiting in the wrong gear either, you're always in the right gear. I do quite a bit of riding Electrics with gas bikes, the shifting delays and interruptions seem so dinosaur. My GSXR1000 has crazy power, but in a technical set of twisties, I run faster on a zero because you don't have to leave margin in the tires for the back torque jerks upsetting the chassis on downshifts. I know some super bikes made in the last few years have special back torque limiting clutches to help reduce that problem, they likely feel better.

Say you had a six speed gearbox on an electric motorcycle, there is probably one gear that would get you to the top speed for the road you are riding, if you didn't want to shift gears, you could just leave it in that one gear and not have to worry about shifting if you didn't want the faster acceleration from down shifting when appropriate, and then have to up-shift if you max out your RPM. The only disadvantage would be the approx 3% power loss in the gearbox. You would also have the advantage of being able to pull in the clutch to avoid regen if your bike had regen braking and no easy way to control the regen through the throttle.

podolefsky
25 April 2012, 0501
I had actually worked this out a while ago (when I was still contemplating the AC conversion). The Curtis maxes out at 130V, which means I could run 36s (115.2V nominal, 131.4 off the charger, but <130V resting). That's a factor of 1.6, so not 2x but still pretty good.

A little research - turns out, the Curtis max RPM setting is 8000. I'm guessing that's about the physical limit of the motor as well.

If I want my same top speed of around 90 mph, with 8000 RPM I need a gear ratio of about 6.5:1. Right now I'm at 5:1, so I'm not going to get my 1.6x increase that I thought I could. More like 1.3x. If I went to a 36s pack and geared 8:1, I'd be RPM limited to 74 mph, so it would basically be a wash. (I'd have a pretty broad torque band, but it wouldn't get me to my other goals).

Square Wave
25 April 2012, 0555
Noah,
You are calculating the lessons that Moto Electra learned through experience over the past seasons of TTXGP racing.
We started with the AC20 and just cooked it. Then we used the AC35 because HPEVs said it would stay cooler, which it did. The battery on the bike could put out more amperage than the motor or controller could use, but with 130 volts we couldn’t get the motor speed high enough to gear low enough to make the bike as fast around the track as the faster teams. The AC20 and AC35 are excellent motors for making sport bikes, but they are not competitive with the much more expensive options that are available if you look hard enough.

DaveAK
25 April 2012, 0821
Noah,
You are calculating the lessons that Moto Electra learned through experience over the past seasons of TTXGP racing.
We started with the AC20 and just cooked it. Then we used the AC35 because HPEVs said it would stay cooler, which it did. The battery on the bike could put out more amperage than the motor or controller could use, but with 130 volts we couldn’t get the motor speed high enough to gear low enough to make the bike as fast around the track as the faster teams. The AC20 and AC35 are excellent motors for making sport bikes, but they are not competitive with the much more expensive options that are available if you look hard enough.
So in this specific instance, assuming that you're limited to and by this specific motor/controller/voltage combo, would a transmission help? Maybe not to the extent of being competitive, but at least in regards of improving what you have? That's the answer I'm looking for.

podolefsky
25 April 2012, 0852
So in this specific instance, assuming that you're limited to and by this specific motor/controller/voltage combo, would a transmission help? Maybe not to the extent of being competitive, but at least in regards of improving what you have? That's the answer I'm looking for.

Yeah, that's kinda what I'm after...although I'd extend it a bit to ask about any motor/controller/battery combo that we can actually buy and is within a reasonable budget.

The goal: a bike with a top speed of 100mph, 50 mi range (at average of 45 mph), and acceleration on par with a 750cc sportbike. Seem about right?

How about, for the sake of structuring the discussion, we set three reality categories:

-real and available
-real but unavailable (for your average consumer)
-theoretical (but based on sound principles)

Then three cost categories for motor/controller/battery:

- under $10k (since an AC-20 (or similar performing) with 96V pack and a transmission would be a little less than that.)
- under $20k (steep, but not outside the real of possibility)
- over $20k (you basically need to be loaded or sponsored to go this route)

Brutus
25 April 2012, 0926
Noah,
The parameters you set down are less than I am already achieving with reliability, and it will only get better with a few more refinements and the cost of the drive train is well within your low end range.

podolefsky
25 April 2012, 0927
Noah, are those prices for just the drive train and batteries or the entire motorcycle?

Just the drive train and batteries.


The parameters you set down are less than I am already achieving with reliability, and it will only get better with a few more refinements and the cost of the drive train is well within your low end range.

yeah...I'm aware ;)

DaveAK
25 April 2012, 1024
Yeah, that's kinda what I'm after...although I'd extend it a bit to ask about any motor/controller/battery combo that we can actually buy and is within a reasonable budget.

The goal: a bike with a top speed of 100mph, 50 mi range (at average of 45 mph), and acceleration on par with a 750cc sportbike. Seem about right?

How about, for the sake of structuring the discussion, we set three reality categories:

-real and available
-real but unavailable (for your average consumer)
-theoretical (but based on sound principles)

Then three cost categories for motor/controller/battery:

- under $10k (since an AC-20 (or similar performing) with 96V pack and a transmission would be a little less than that.)
- under $20k (steep, but not outside the real of possibility)
- over $20k (you basically need to be loaded or sponsored to go this route)
Kind of. But I disagree with the notion of setting performance goals, as the goal in my mind is simply what kind of performance gains can you make with a transmission. If you can already get 100mph/50miles just with the appropriate off-the-shelf components, then how much better can you get with a tranny? I don't want Luke telling me he can already do that with his bicycle because that's not the point to me. That's why the Moto Electra example is an excellent starting point. It's a nicely defined set up. It's reached the limits of motor/controller/batteries so what can you do next?

So the criteria for me is real and available, off-the-shelf, within a DIYers budget. While an AC20/Curtis is outside my budget it's not an unrealistic target for someone with more money than me, but no one on here is going to get a UQM or Remy motor for a home built daily rider project. Once you've got that defined then you can start throwing the what ifs at it. And your what ifs do make sense to me.

podolefsky
25 April 2012, 1030
Kind of. But I disagree with the notion of setting performance goals, as the goal in my mind is simply what kind of performance gains can you make with a transmission. If you can already get 100mph/50miles just with the appropriate off-the-shelf components, then how much better can you get with a tranny? I don't want Luke telling me he can already do that with his bicycle because that's not the point to me. That's why the Moto Electra example is an excellent starting point. It's a nicely defined set up. It's reached the limits of motor/controller/batteries so what can you do next?

So the criteria for me is real and available, off-the-shelf, within a DIYers budget. While an AC20/Curtis is outside my budget it's not an unrealistic target for someone with more money than me, but no one on here is going to get a UQM or Remy motor for a home built daily rider project. Once you've got that defined then you can start throwing the what ifs at it. And your what ifs do make sense to me.


Good point. That's sort of what I was getting at before, unless you have a UQM/Remy (or used a bicycle as the chassis), you're probably going to hit a performance wall at some point.

So more criteria - needs to be street legal, ride like a motorcycle.

And yeah, more to Dave's point, are there any DIY systems that are already such high performance that a transmission would buy you nothing.

liveforphysics
25 April 2012, 1139
The more I think about Biff's post (basically, pick a gear for the road and leave it alone), I do think it could be worth the ~3% friction hit in some situations (the extra weight etc is kinda up to the rider to decide what they value most in the riding experience). You could view it not so much like how you use a transmission on a normal bike (constantly rowing up and down through the gears), but more like a select-able final drive change.

Got a section of tight twisties ahead? Drop into low gear and enjoy. Don't need to be shifting, just leave it alone and ride it. Got some high speed stuff ahead, drop into a taller gear and ride it like a single speed. I definitely could see it being an improvement to an existing motor/controller combo that doesn't have the ability to accomplish your goals as a single speed. If you get to design a system from the ground up though, it's tough to see where you're going to find more performance for that given amount of volume/weight the tranny uses just going towards the motor itself. If you're DIY's bike powertrains from stuff you've got, I could see it being the best bang for the buck, and that's what most folks here are looking for in their builds.

DaveAK
25 April 2012, 1155
Got a section of tight twisties ahead? Drop into low gear and enjoy. Don't need to be shifting, just leave it alone and ride it. Got some high speed stuff ahead, drop into a taller gear and ride it like a single speed. I definitely could see it being an improvement to an existing motor/controller combo that doesn't have the ability to accomplish your goals as a single speed. If you get to design a system from the ground up though, it's tough to see where you're going to find more performance for that given amount of volume/weight the tranny uses just going towards the motor itself. If you're DIY's bike powertrains from stuff you've got, I could see it being the best bang for the buck, and that's what most folks here are looking for in their builds.
This is what I'm thinking when I'm thinking about gears. What I would need might be different than someone else, but I'm thinking along the lines of a two speed box. Top gear would be as high as you could make it within the performance limits of your motor/controller combo. This would give you your top speed, but might make it a little too sluggish from the lights in town, so this is where you'd go for a lower gear. Around town you'd never change from the lower gear, and on the open road you'd never change from the higher one. You might need a third gear for the twisties or not, that's where the tinkering would come in to it. I doubt your lower gear would be so low as to need a third one though.

DaveAK
25 April 2012, 1208
I think what I would probably do is find the top gearing that I could for a given setup and find what speed that tops out at. A gearbox isn't going to improve on that. Now what I would do is make my lower gear such that I'd maybe get 80% of that top speed flat out. Just complete guesswork on my part, but I think that's where I'd start.

podolefsky
25 April 2012, 1220
Holy crap...this sounds like CONSENSUS.

I thought this day would never come...it is bittersweet.

Square Wave
25 April 2012, 1223
I think what I would probably do is find the top gearing that I could for a given setup and find what speed that tops out at. A gearbox isn't going to improve on that. Now what I would do is make my lower gear such that I'd maybe get 80% of that top speed flat out. Just complete guesswork on my part, but I think that's where I'd start.
If I could get the funding this is what I would try. I think one could make a 2 speed box that was less than 10lbs and had losses equivalent to a jack shaft. 80% of top gear is where I would start, too. I imagine that would give me a quick launch at the start and maybe help me run up a hill out of a slow corner. Maybe going to 85% or 90% would give you a ratio that could be used more often. It’s all just dreaming at this point.

Hey! I found an interesting link today.
http://iedrives.com/performance

Square Wave
25 April 2012, 1225
Holy crap...this sounds like CONSENSUS.

I thought this day would never come...it is bittersweet.

I think we have finally agreed on terms. Maybe before we all had different ideas of what we were talking about.

skyclark
25 April 2012, 1333
I think we have finally agreed on terms. Maybe before we all had different ideas of what we were talking about.

The terms do help define the conversation.
I agree with Luke that if designing from scratch a single speed machine is a good route but when working with some of the existing motors a two speed box would be nice.

The problem that I see is that there is not an appropriate two or three speed transmission that fits our power, weight, and packaging requirements.

Is it more useful to spend time and effort developing the right transmission for an existing motor or developing a motor/ battery/ controller package that is right for an electric motorcycle?
I imagine that the answer will be different for people of different expertise.

liveforphysics
25 April 2012, 1346
On ES, about 3 folks made trannys from scratch for ebikes.

Here is my favorite one, very clever garage-built engineering, and it worked great, I rode the bike later putting around at the death-race in AZ (he ended up burning up a motor, then running on a single motor, and then blowing up the controller, I ended up cooking my motor about 80% of the way through the final... which was exactly what happened at my last race as well... LOL, guys like me that like to push the limits never learn :p ). However, he found that just leaving it in high-gear only yielded him the best results on the track and street, so he ended up converting back to a 1-speed in the next version of the build.

http://endless-sphere.com/forums/viewtopic.php?f=28&t=13731&hilit=thud%2C+transmission


3086

skyclark
25 April 2012, 1428
That is a very cool home-build.

Its also interesting that he moved back to a single speed after testing.

liveforphysics
25 April 2012, 1525
If some of you guys are interested in learning about motors, there is a section on ES called "motor technology" and it's pretty killer.

The posts by members "Biff", "Bigmoose", "Miles", "Jeremy Harris" are all pure gold to folks looking to pickup a bit of motor understanding.

Reading old posts by myself "liveforphysics" would unfortunately just reinforce the common misconceptions that you commonly see on the intarwibs. Like, run higher voltage to keep the motor cooler, etc etc. It's funny how I was SO convinced I had it all figured out while writing that stuff at the time, and it's just 100% incorrect BS. I need to go back through and make edits to fix that stuff, or at least add-in an "edit" comment and write that I didn't understand crap and it's all bull-sh*t. lol

After a few years of testing various motors and lots dyno time and so much help from those above listed folks contributing some wisdom, I think I have a crude semi-decent working grasp on motors now, fully realizing that it's severely lacking in many areas, and completely lacking in many areas that I don't even know enough to know I'm lacking in.

Fortunately, the folks like Biff and Bigmoose were so patent and understanding in helping me to learn. The info shared in these threads can help interested folks in learning about motors start the voyage.

http://endless-sphere.com/forums/viewtopic.php?f=30&t=16056

podolefsky
25 April 2012, 1639
Hey! I found an interesting link today.
http://iedrives.com/performance

Yes! I love those efficiency maps. I wish every manufacturer made them.

It's also helpful to look at power vs rpm maps, that can be found here (http://www.iliofos.gr/ILIOFOS%20C.O.%20Us/Pdf's/PP150%20Spec%20Sheet%207.14.10.pdf).

Look on page 5 and imagine your cruising along using 15 kW. If you're at 4000RPM, you're at about 65% efficiency. If you could drop to 2000RPM, you would jump up to about 80%...and at 1000RPM you'd be up to 85%. A 20% gain in efficiency (and thus range) by having a higher gear available.

That said, it's a lot easier to justify the size and weight of a transmission on a delivery truck or bus, since it's not that big a fraction of the whole vehicle. Things get tight on a motorcycle.

protomech
26 April 2012, 0742
The more I think about Biff's post (basically, pick a gear for the road and leave it alone), I do think it could be worth the ~3% friction hit in some situations (the extra weight etc is kinda up to the rider to decide what they value most in the riding experience). You could view it not so much like how you use a transmission on a normal bike (constantly rowing up and down through the gears), but more like a select-able final drive change.

Got a section of tight twisties ahead? Drop into low gear and enjoy. Don't need to be shifting, just leave it alone and ride it. Got some high speed stuff ahead, drop into a taller gear and ride it like a single speed. I definitely could see it being an improvement to an existing motor/controller combo that doesn't have the ability to accomplish your goals as a single speed.

If you get to design a system from the ground up though, it's tough to see where you're going to find more performance for that given amount of volume/weight the tranny uses just going towards the motor itself. If you're DIY's bike powertrains from stuff you've got, I could see it being the best bang for the buck, and that's what most folks here are looking for in their builds.

What about taking an existing e-bike and modifying it for more speed? Let's say my 2012 Zero, I'd love to see a efficiency map for the motor.. curious whether a lower RPM would help at interstate speeds (180 Wh/mile @ 70 mph is thirsty, 4600 rpm), or even state highway speeds (55 mph, 3600 rpm). Similarly, a shorter gear ratio would be great for days when I'll do most of my riding on back roads at 45-55 mph and have more energy to burn : ) Empulse R claims 166 Wh/mile (56 miles @ 70 mph), wondering how much of that is possible aero improvements vs driving the motor in a more efficient RPM.

If we want more power, what are some alternative larger motors to a transmission? I know the ZF9 battery pack can support a larger motor, but maybe the existing controller is tapped out? (66V @ 420A = 27 kW? bike does about 22 kW peak at the rear wheel)

Maybe just thought experiments while the bike is under warranty ..

Warren
26 April 2012, 0921
You could check with these guys, about the two speed tranny they built.

http://www.wroum.dk/silvergiant/

Biff
27 April 2012, 0859
What about taking an existing e-bike and modifying it for more speed? Let's say my 2012 Zero, I'd love to see a efficiency map for the motor.. curious whether a lower RPM would help at interstate speeds (180 Wh/mile @ 70 mph is thirsty, 4600 rpm), or even state highway speeds (55 mph, 3600 rpm). Similarly, a shorter gear ratio would be great for days when I'll do most of my riding on back roads at 45-55 mph and have more energy to burn : ) Empulse R claims 166 Wh/mile (56 miles @ 70 mph), wondering how much of that is possible aero improvements vs driving the motor in a more efficient RPM.

If we want more power, what are some alternative larger motors to a transmission? I know the ZF9 battery pack can support a larger motor, but maybe the existing controller is tapped out? (66V @ 420A = 27 kW? bike does about 22 kW peak at the rear wheel)

Maybe just thought experiments while the bike is under warranty ..

If you look at the dyno plot you can get a good guess at peak efficiency Typically it occurs around peak power. So on the DS, according to motorcycle.com http://www.motorcycle.com/gallery/gallery.php?g2_view=largephotos.Largephotos&g2_itemId=325658 that would be around 45-50mph. If you geared the DS to have its peak power and probably therefore efficiency at 65mph, it would have 70% of the off the line torque, which is probably about as much off the line feel as the "eco" mode provides.

Has anyone thought about the other issues that a transmission might induce? like the difficulty of controlling a motor with no-load? if you were to pull in the clutch and go wide open throttle, the motor would spin up so fast (maybe 4x faster than it would if had to spin a tire) that it might cause issues with the motor controller. And what about if someone downshifts while the motor is already at maximum RPM? that would put the motor faster than max RPM for a bit of time, and with a Wide ratio 2 speed gearbox that could cause significant problems for both physical destruction of the motor and the controller through higher back emf.

-ryan

Brutus
27 April 2012, 0936
Has anyone thought about the other issues that a transmission might induce? like the difficulty of controlling a motor with no-load? if you were to pull in the clutch and go wide open throttle, the motor would spin up so fast (maybe 4x faster than it would if had to spin a tire) that it might cause issues with the motor controller. And what about if someone downshifts while the motor is already at maximum RPM? that would put the motor faster than max RPM for a bit of time, and with a Wide ratio 2 speed gearbox that could cause significant problems for both physical destruction of the motor and the controller through higher back emf.

-ryan

Controlling the motor with no load has not been an issue at all because it is hooked up to a trans/primary and even when it is in neutral or clutch in at a stop there is drag on the primary drive and trans internally, more so than when rolling in a selected gear. Downshifting the trans at max rpm has not induced "lock-up" or "over rev" conditions(part of the reason to have 4-6 speeds instead of 2). Also I still say the clutch is useless for an electric other than another part to wear out or break.

liveforphysics
27 April 2012, 1106
Controlling the motor with no load has not been an issue at all because it is hooked up to a trans/primary and even when it is in neutral or clutch in at a stop there is drag on the primary drive and trans internally, more so than when rolling in a selected gear. Downshifting the trans at max rpm has not induced "lock-up" or "over rev" conditions(part of the reason to have 4-6 speeds instead of 2). Also I still say the clutch is useless for an electric other than another part to wear out or break.

You're working with a brushed motor, I think it's series wound too right? So when you have rapid changes in RPM your controller doesn't know, care, or need to know or care. Your controller is equally happy running a hot water heater as it is a motor.

In a brushless motor (way more so with a PM motor than induction) your controller needs to precisely always know rotor position to know which banks of FET's to switch on an off, getting the sequence off by a bit, even by 10deg of rotor position (which could be 100deg electrical off-set in a 10 pole motor) can result in instantly exploding the controller into plasma (by trying to clamp BEMF). Having large dRPM/dt makes it very difficult to resolve accurate rotor position in a timely manor to control the commutation correctly. Brushes actually rock for this, they just float and skip a bit when things get hairy, end up back where they belong, and can't really get out of time unless the whole assembly melts into charred goo. This takes all the difficult burden of controlling away from the controller.

DaveAK
27 April 2012, 1147
In a brushless motor (way more so with a PM motor than induction) your controller needs to precisely always know rotor position to know which banks of FET's to switch on an off, getting the sequence off by a bit, even by 10deg of rotor position (which could be 100deg electrical off-set in a 10 pole motor) can result in instantly exploding the controller into plasma (by trying to clamp BEMF). Having large dRPM/dt makes it very difficult to resolve accurate rotor position in a timely manor to control the commutation correctly. Brushes actually rock for this, they just float and skip a bit when things get hairy, end up back where they belong, and can't really get out of time unless the whole assembly melts into charred goo. This takes all the difficult burden of controlling away from the controller.
Interesting. So how does the controller cope with just normal slowing down of the bike? I assume that the bikes momentum will cause the rear wheel to drive the motor to some extent. Is this handled normally, and you're just raising the issue of a more extreme case caused by down shifting?

Brutus
27 April 2012, 1228
You're working with a brushed motor, I think it's series wound too right? So when you have rapid changes in RPM your controller doesn't know, care, or need to know or care. Your controller is equally happy running a hot water heater as it is a motor.

Yup Series wound dc, because it is cheaper, rebuild-able, upgradeable, and doesn't have the issues you speak of in the rest of your post. I am happy to know I can pull stumps and re-purpose the bike into a water heater though. Can I classify it as a tri-purpose machine now? ;)

podolefsky
27 April 2012, 1241
In a brushless motor (way more so with a PM motor than induction) your controller needs to precisely always know rotor position

Induction doesn't need to know position at all, just RPM.

Allen_okc
27 April 2012, 1254
There's Tesla again - i wish i could have worked with him.

:p as everyone stands in line to slaps me upside the head...

Hugues
27 April 2012, 1446
Induction doesn't need to know position at all, just RPM.
ok,
but then what's the purpose of the motor encoder on the AC-20 ?

liveforphysics
27 April 2012, 1450
Interesting. So how does the controller cope with just normal slowing down of the bike? I assume that the bikes momentum will cause the rear wheel to drive the motor to some extent. Is this handled normally, and you're just raising the issue of a more extreme case caused by down shifting?


PMBLDC motors are equipped with systems to resolve rotor position. You can do it sensorlessly, by measuring the change in inductance of the phases, as its influenced by the magnets position in relation to the teeth. This involves taking precise measurements of inductance very quickly a thousand times a second. This is known as flux vector drive, or vector drive, or various other trade names. It's pretty awesome. Processor and ADC use heavy, $$$, can only work at low-ish rotor speeds.

You can do it like an RC controller, have a pre-determined algorithm sequence it plays into the motor to attempt to get any rotor motion. It is only possible to have 1/3rd of available torque on the motor, while the other 2 phases are purely canceling their torque in the form of heating the motor. It works fine for RC propellers and very high power motors in light vehicles because in the first second you get enough rotor motion. Once the motor has rotor motion, it has high speed compairators watching between all the phases, and they send a signal everytime they have a zero crossing point on the BEMF. This gives the controller processor the input it needs to know magnet position, and once it has motion it can continue to run effectively. It's limitations are only a maximum of 1/3rd of stall torque or very low RPM torque torque while making massive amounts of heat to do it. This makes its use model OK in a bicycle (pedaling to get a little speed before hitting the throttle helps it work perfectly), but you're not going to be starting on a hill in a motorcycle or car with it, or trying to roll slowly under high loads etc.

Hall sensors latch when the magnet passes them. When embedded at the right points in the stator, they pulse at the right times to provide the controller processor the info of where the poles are at in relation to the stator, so it knows which of the 6 fet banks to turn on. You can actually make processor-less analog controllers with hall sensors. This style has some weaknesses in getting any precision in rotor position, because it only can tell you a range of the magnet location. This makes them have a high torque ripple and be jerky at low RPMs (unless you do things like skew the stator lams, but this comes at a pretty big torque and efficiency penalty). This is the industry standard method for ebike hubmotors. They are kinda jerky and noisy and rough at low RPMs, you feel each pulse clearly almost like an engine chugging. They do handle high RPM's pretty well though, but they are never super accurate for any speed.


Optical encoders have a disk with tons of little slits that flash by in a pattern that indicates position. It works well, it's high-speed capable, but if you have the speed rate change very rapidly, it only knows it's location by measuring the time between pulses, so having very rapid changes in the rate it gets pulses can fault them. Most are pretty damn good though, and do well.

Sine-Cosine encoders read a spinning magnetic field very precisely, and output a sine wave and it's 180deg shifted buddy, the co-sine wave. The controller reads the potential between them and knows the exact rotor position at all times. It's high speed capable, and you're only limited by your ability to accurately sample and read this voltage. Good controllers sample it thousands of times a second, but it's still not fast enough to handle super rapid changes in rotor speed sometimes...

liveforphysics
27 April 2012, 1452
You can also combine any of these you like. Very often the top one gets combined with the second one, as the top one is great at very low RPMs, and the second one is great at high rpms.

Combo's of #3 to start and #2 to run at high speeds are also done quite a bit.

podolefsky
27 April 2012, 1812
ok,
but then what's the purpose of the motor encoder on the AC-20 ?

The encoder tells the controller the actual RPM of the rotor. Then the controller varies the field rotation frequency accordingly.

On an induction motor, the torque is proportional to the difference between field rotation speed and the rotor speed (also known as "slip").

http://www.engineeringtoolbox.com/electrical-motor-slip-d_652.html

T Rush
29 March 2018, 0437
I've been reading thru a bunch of these threads, and Ted's blog
....and when I read on Ted's blog the TRANSMISSIONS VS. DUAL MOTORS (https://evmc2.wordpress.com/2012/01/01/transmissions-vs-dual-motors/) he used to start this thread....it gave me an idea

see, I think the basic idea behind the EV transmission is to change the compromise from "acceleration OR speed" to "acceleration THEN speed"....ok, but don't we really want "acceleration AND speed" ?


and while some people enter this debate from the stand point of 'its fun to change gears and slip a clutch, gives my other hand and foot something to do' ...well, I guess you could leave those leftover controls from the ICE on the bike after the conversion, maybe hook them up to a noise maker, and those people would be happy just pretending without actually having a trans.....but thats not important
...and yeah yeah yeah, you still ultimately use the same amount of energy to go fast, slow, quick, long whatever no matter what gear you are in or if you got a big motor or little ones....or however that goes...to go just as quick or fast the same as another setup....but I think we are trying to use more power at slow speed, then change the drive ratio to be able to use more at fast speed...I guess like an ICE does, changing the drive ratios to allow the engine to run where it can suck the most air-fuel into power; thus use more energy and go quicker then faster


so this 'dual motor' thing...sure, I get Ted's point that if you are going to add weight with a trans, you could maybe get the same result and weight with adding a second motor(doubling torque at lower speed, like a lower gear; while still maintaining the same gearing for highest rpm)
...but it seemed everyone(even he did?) take the 'dual motor' thing as only theoretical, and just assumed that in practice it would be easier to upgrade to one single larger motor thats twice the size....however either way that kinda puts you right back where you started with the single fixed speed(tho sure, now its more powerful) so you didn't really fix the problem, just the symptom, and only moved the problem to a different place(where you will find it again once you want more acceleration OR speed, and go back to still thinking about that trans to be able do the one THEN the other thing since you still cant have both)

- and this is where I got my idea -

what about looking at this the other way? say instead you start with one big motor with a big nice hp hump, and you split that motor into two smaller motors(and say their power adds together to give you the same hp hump as the one big motor on that dyno graph)
... so while you got the complexity of chaining all this stuff together with dual drive sprockets to the final drive on the wheel, here is where you have some fun using the idea of what a transmission does! say you are after something like a two speed trans with a higher and lower gears....see where I'm going with this?
...you put a different drive sprocket on each motor, say one has a 13 tooth and the other has a 17 tooth...but both motors are still being driven at the same time together, just at different RPMs
....now you don't quite get as high of a peak in the middle of your hp hump as with your single large motor, but the two smaller motors are still adding together for the mid-range overlap and averaging out to a nice flat plateau of hp...but one motor is now more efficient for pulling wheelies, while the other motor isn't out of breath for top speed
...you are running two gears at the same time to get that 'and' in the "acceleration AND speed" thing....maybe even optimized further with dual controllers running different mapping?
...sure, the two motors working best at different ends of the RPM range aren't going to be as strong as the one big motor geared to run slow OR fast; but thats only at a peak, and now you don't have to change gear ratios....and your pretty much going to be doing most of your riding in the mid range anyway, right where you made that band wider(and maybe actually taller vs slopping off quickly on either side of that one peak)...you have just flattened out your power band, you compromise max power at a single peak RPM to spread that out more to the low and high speeds...maybe even did something weird to the thermal issues and soaking, so that each separate motor can work harder if they are taking turns at different RPM, each able to hit their peak output at different times, for a longer total time together; ultimately being able to use more power, and longer, than a single bigger motor? idk

here, look at this picture


http://www.colorado.edu/physics/EducationIssues/podolefsky/EV_project/ICE_HP.png blue line is one big motor; yellow and red lines are two small motors with different gear ratios but say we have these two motors on the same bike turning the same chain at the same time, working together(now in that graph, the ratios are likely set at a normal compromise so that the bike operates fairly with a single motor; but with dual motors you could spread the ratios farther apart)

...the red motor is showing more power than the yellow under 35mph
...say at 10mph the red motor is transferring 9hp + yellow motor just doing 6hp = 15hp total
...next at 25mph the red might be pulling hard at 22hp, but the yellow is still adding 15hp for 37hp total
...and at 38mph they both are capable of 25hp each, for a total of 50hp
...then at 50mph the red motor is running out at 16hp + the yellow motor now up to 28hp = 44hp total
...but by 80mph the red motor has nothing left, while the yellow motor is still going
now they might only combine to have 50hp max with the power peaks offset(vs closer to 60hp if they both focused on one speed, like the blue motor is doing only at 50mph) but together they average that power from 30mph to 45mph

ok, you can go back to the other forum threads not about transmissions now, sorry, hope I didn't break anything

dcb
29 March 2018, 0911
dual ratios doesn't seem to add up. I've compared/resized/overlayed enough torque graphs to convince myself anyway.

1. larger motors are typically more efficient (not even considering additional friction losses). Dual motors isn't really a consideration for green field applications (save for 4wd convenience or somesuch).

2. you are still left with a combined torque curve w/2 motors. in peak mode, I doubt there is any "win" there that a single motor ratio change couldn't cover.

3. using 2:1, your continuous power (i.e. for cruising) is cut basically in half. Compared to single motor, one motor is about to melt, while the other one is about to grenade from overspeed. Changing the ratio doesn't change the nature of the problem, the system isn't balanced anymore.

So I wouldn't consider different ratios at all.

trans or not, it depends what you want and what you got. A trans can be an affordable way to get decent off the line acceleration and a decent cruising speed from a lower power motor. And in a well-matched system, a larger motor means more battery and controller as well that you have to pack into the frame. But the reality is that not a lot of affordable transmission options have materialized, and most people aren't going to bother to figure one out. There's a few threads here about considering a 2 stroke trans.

I'm *considering* keeping the trans on my gs750, or at least parts of it, but if the system can get me near the traction limit for the first 15-20mph (say 1000 ft-lbs at the wheel on the high side) and give me a usable continuous top speed with out it, then I wouldn't bother either. but two speeds would help a lot there.

Ideally I'd stay at the traction limit till 60mph, but a transmission won't help there anyway, as you need to be on the flat part of the torque curve for that to be smooth. But also I'd have to sort out a 120hp bike, transmission or not. (edit, I'm more on the beer budget side of things, also the traction limit will go up as I add mass to the bike)

Stevo
29 March 2018, 0922
You kind of hit the nail on the head when you mentioned efficiency at speed. There's always going to be compromise whether its ICE or electric. If you want to squeeze the most miles out of your battery pack, then you want to design a system that delivers the speed you want to travel in "most" of the time using the least energy, not more. If MOST of your vehicle's use is at hwy speeds of 65 mph, then you would try to gear for that speed at the most efficient sweet spot on your motor/controller combo. If most of your use is at 45 mph city street commuting, then that's where you should set the final gear drive for. This is why I think a 2 or 3 speed gear box would come in handy at making the most efficiency at a few different speed selections for versitility sake. On a dirt bike, a 2 speed gear box would be awesome for down low technical terrain single track cow trails, and up high for dualsport hwy speeds. I just went with a bigger motor to make life simpler :p "Go Big or Go Home!" LOL!

Spaceweasel
29 March 2018, 1041
One of the problems we face with most electric conversion motors is a narrow RPM range. While a Tesla will spin up to 15k, my ES-15-6c maxes out at 5.5k before it threatens to melt. While torque is high (compared to ICE) over this whole range, the lack of ability to shift that range to a higher ratio means compromise. Even if MOST of my riding is at 45mph, I can't gear to that speed if SOME of my riding is at 85mph. And if I gear for 85mph max, then acceleration at 15mph will suffer.

One solution is accepting that compromise - which is mitigated by the broad torque range of electrics. Another solution is a transmission - few of which are optimized for electrics.

Or you could just get a used Tesla motor to stuff in your bike...

T Rush
29 March 2018, 1056
I've been reading thru a bunch of these threads, and Ted's blog
....and when I read on Ted's blog the TRANSMISSIONS VS. DUAL MOTORS (https://evmc2.wordpress.com/2012/01/01/transmissions-vs-dual-motors/) he used to start this thread....it gave me an idea

see, I think the basic idea behind the EV transmission is to change the compromise from "acceleration OR speed" to "acceleration THEN speed"....ok, but don't we really want "acceleration AND speed" ?


and while some people enter this debate from the stand point of 'its fun to change gears and slip a clutch, gives my other hand and foot something to do' ...well, I guess you could leave those leftover controls from the ICE on the bike after the conversion, maybe hook them up to a noise maker, and those people would be happy just pretending without actually having a trans.....but thats not important
...and yeah yeah yeah, you still ultimately use the same amount of energy to go fast, slow, quick, long whatever no matter what gear you are in or if you got a big motor or little ones....or however that goes...to go just as quick or fast the same as another setup....but I think we are trying to use more power at slow speed, then change the drive ratio to be able to use more at fast speed...I guess like an ICE does, changing the drive ratios to allow the engine to run where it can suck the most air-fuel into power; thus use more energy and go quicker then faster


so this 'dual motor' thing...sure, I get Ted's point that if you are going to add weight with a trans, you could maybe get the same result and weight with adding a second motor(doubling torque at lower speed, like a lower gear; while still maintaining the same gearing for highest rpm)
...but it seemed everyone(even he did?) take the 'dual motor' thing as only theoretical, and just assumed that in practice it would be easier to upgrade to one single larger motor thats twice the size....however either way that kinda puts you right back where you started with the single fixed speed(tho sure, now its more powerful) so you didn't really fix the problem, just the symptom, and only moved the problem to a different place(where you will find it again once you want more acceleration OR speed, and go back to still thinking about that trans to be able do the one THEN the other thing since you still cant have both)

- and this is where I got my idea -

what about looking at this the other way? say instead you start with one big motor with a big nice hp hump, and you split that motor into two smaller motors(and say their power adds together to give you the same hp hump as the one big motor on that dyno graph)
... so while you got the complexity of chaining all this stuff together with dual drive sprockets to the final drive on the wheel, here is where you have some fun using the idea of what a transmission does! say you are after something like a two speed trans with a higher and lower gears....see where I'm going with this?
...you put a different drive sprocket on each motor, say one has a 13 tooth and the other has a 17 tooth...but both motors are still being driven at the same time together, just at different RPMs
....now you don't quite get as high of a peak in the middle of your hp hump as with your single large motor, but the two smaller motors are still adding together for the mid-range overlap and averaging out to a nice flat plateau of hp...but one motor is now more efficient for pulling wheelies, while the other motor isn't out of breath for top speed
...you are running two gears at the same time to get that 'and' in the "acceleration AND speed" thing....maybe even optimized further with dual controllers running different mapping?
...sure, the two motors working best at different ends of the RPM range aren't going to be as strong as the one big motor geared to run slow OR fast; but thats only at a peak, and now you don't have to change gear ratios....and your pretty much going to be doing most of your riding in the mid range anyway, right where you made that band wider(and maybe actually taller vs slopping off quickly on either side of that one peak)...you have just flattened out your power band, you compromise max power at a single peak RPM to spread that out more to the low and high speeds...maybe even did something weird to the thermal issues and soaking, so that each separate motor can work harder if they are taking turns at different RPM, each able to hit their peak output at different times, for a longer total time together; ultimately being able to use more power, and longer, than a single bigger motor? idk

here, look at this picture
http://www.colorado.edu/physics/EducationIssues/podolefsky/EV_project/ICE_HP.png
blue line is one big motor; yellow and red lines are two small motors with different gear ratios but say we have these two motors on the same bike turning the same chain at the same time, working together(now in that graph, the ratios are likely set at a normal compromise so that the bike operates fairly with a single motor; but with dual motors you could spread the ratios farther apart)

...the red motor is showing more power than the yellow under 35mph
...say at 10mph the red motor is transferring 9hp + yellow motor just doing 6hp = 15hp total
...next at 25mph the red might be pulling hard at 22hp, but the yellow is still adding 15hp for 37hp total
...and at 38mph they both are capable of 25hp each, for a total of 50hp
...then at 50mph the red motor is running out at 16hp + the yellow motor now up to 28hp = 44hp total
...but by 80mph the red motor has nothing left, while the yellow motor is still going
now they might only combine to have 50hp max with the power peaks offset(vs closer to 60hp if they both focused on one speed, like the blue motor is doing only at 50mph) but together they average that power from 30mph to 45mph

ok, you can go back to the other forum threads not about transmissions now, sorry, hope I didn't break anything


dual ratios doesn't seem to add up. ..... Compared to single motor, one motor is about to melt, while the other one is about to grenade from overspeed. Changing the ratio doesn't change the nature of the problem, the system isn't balanced anymore....
see thats exactly what I was wondering about...but I don't think you could run 3phase motors like these in series or parallel...so wouldn't they each need their own controller? and then you wouldn't have to put a bunch of current thru both motors the same if they are geared that differently, as they aren't going to be able to 'handle' the same power at the same mph
(remember that while the motors both have the same peak power capabilities at the same RPM, they spin different RPM's per speed so rarely could handle the same load and have the same output hp, at the same time)
....of course one of the motors would be spinning slow at low speeds while the other is nearing a good RPM to really put some power out, but you wouldn't ask that slower motor to match that others hp(so wouldn't overload it to melting point) just help some for acceleration(which the other motor would presently be geared way better for)
...then at the other end nearing max bike speed where the formally too slow motor is coming into its own range and humming along, the first motor is out of its power range and spinning faster than it can keep up(sure you will have to watch max RPM so that it doesn't fly apart) but again you would have the controller backing off on the currant and it just has to be a helper(or at least not a parasitic drag)
....I mean maybe at mid range bike speeds you would supply both the motors with a somewhat balanced load...but then at slower speeds you would want to focus the majority of the amp draw to the motor geared to run the best(red line on graph) and change that to the other motor(yellow line on graph) for higher bike speeds....look at where the two different geared motors can handle the most hp on that graph and thus utilize the most current, I'm not trying to change that...I want the motors to perform differently at different mph speeds(as seen in that graph)
... or heck, you could even try two completely different performing motor types together at the same RPM(if having different ratio sprockets bothers you, or its easier to think of like that) one motor that performs best at low RPM, and another that performs better at high RPM(and thats not to say that they can't run at all at the RPM's the other one can, or do it so badly they melt or explode...thats just not each their same forté) but you still want them to add to each others performance, and not totally be responsible for doing their respective jobs alone

as far as 'changing the nature of the problem', I think first it depends on what you think the problem is....I think its simply that fixed single gearing compromises top speed OR acceleration, because no single motor is perfect at both; so the possible easy fix(if having a two speed trans is a hassle) is to use two motors, one thats good for top speed AND another one thats good for acceleration...and simply changing the gearing different per motor(with two of the same motors, for looks :cool:) does that


1. larger motors are typically more efficient (not even considering additional friction losses).
yes, and in the graph you can see that the blue line motor also peaks much higher hp than the smaller ones individually....I'm not looking for peak power at one RPM, nor am I looking for efficiency and range(the way the blue motor is geared, wouldn't you want to ride at a boring constant 50mph for that)
I'm considering a different option to a transmission for 'performance', to have acceleration at low speed AND still have higher max speed; those will never be 'efficient' things to be after



2. you are still left with a combined torque curve w/2 motors. in peak mode, I doubt there is any "win" there that a single motor ratio change couldn't cover. exactly, and thats why I posted: "...sure, the two motors working best at different ends of the RPM range aren't going to be as strong as the one big motor geared to run slow OR fast; but thats only at a peak, and now you don't have to change gear ratios"
...as the ratio change answer IS a transmission(and I'm avoiding that)



3. using 2:1, your continuous power (i.e. for cruising) is cut basically in half. right, but its not flying out the window...its being divided in half, running thru two motors, and then coming back together at the rear tire
....for these part throttle situations, yes efficiency is lower because two motors might only be operating at like ¼ of what they are built to do where a single motor would be better running at ½ power

for performance full throttle; if the dual controllers are running in parallel, they will still have the same voltage supplied, but to each half the amps available from the battery(so you would have to design the battery to flow a bunch of current) however, with smaller dual motors, each can handle less current per motor anyway....it still would be the same as a single motor rated to handle twice as much...and if anything, I'd want the dual motors(and controllers) to be able to transfer more than what a single setup could....distribute that power, might be a benefit to thermal issues too



So I wouldn't consider different ratios at all. I think its a neat idea....a different solution to the odd "no transmission problem"(which isn't even a 'problem' to begin with) its strange crazy different, unheard of, maybe even delusional; but don't kill it with fire just because of that ... I have no clue if it would actually work tho, or what all other problems it would create....and it surely wouldn't work for everything

that and I'm still learning all this....so actually have no idea what I'm talking about...just flying it up the old flag pole to see who can knock it down....so go for it, I'll keep seeing if I can defend it

dcb
29 March 2018, 1716
so go for it, I'll keep seeing if I can defend it

You haven't defended it at all. if you take 2 1/2 sized motors, 1 at 1:1 and 1 at 2:1, you can do better with a single motor at ~1.5:1. You assumed I meant multi-speed transmission when I said ratio change. I didn't say multi-speed transmission.

This isn't a fun game. I have done your homework for you, please try to understand it and ask specific questions instead of continuing to speculate wildly in defense of wild speculation. attached graphic.

edit, image attachments are apparently brain dead at elmoto, here is a link https://imgur.com/a/OI1LC

Ted Dillard
29 March 2018, 1725
oh god no. make it stop.

Ted Dillard
30 March 2018, 0241
SERIOUSLY though. Nobody likes a theoretical discussion more than me, but this is SO 2010. :rolleyes:

In around 2014, several companies started fielding liquid-cooled, AC axial flux motors. https://evmc2.wordpress.com/2014/08/04/yasa-motor-axial-flux-2-0/

Here's YASA's current site: http://www.yasa.com/

Then there's EMRAX, which the Ohio State team used to whomp a little butt on Pikes Peak and the IOM TTZero. So yeah, you want to talk the difference between theory and practice, there you go. A little theory in practice.

Then there's Brammo, the company that ran an undersized motor and put a transmission on it, in case you want some market research. The claim, specious though it may have been, was that they wanted to replicate the "rider experience" of traditional motorcycles, while several insiders dished that it was the only way they could keep that motor from chowing itself. (My favorite quote of that period of time - "The only way they could keep the Empulse motor from overheating was to have Brian -Wismann, lead engineer- ride it.")

Then there's every electric car on the market, including Tesla, who, by the way, have a sideline of whomping the crap outta drag racing ICE wanna-be contenders. Transmish? ...nowhere to be seen. Think they may just have the resources to test and offer a good tranny? Ya think?

You want power and speed? Put in the most power-capable, lightest motor you can, end of discussion. That's axial flux, liquid cooled AC today. It's not a transmission.

As demonstrated by about 4 years of discussion on this forum, much of it by me, unfortunately, no amount of discussion will illustrate the physics if you can't quite wrap your head around it. I still think some basic modeling (which is beyond me) could illustrate this, but nobody has really produced that.

Sorry to rain on the thread, but some things should be left to die a natural, if not noble and dignified, death.

:cool:

T Rush
30 March 2018, 0334
You assumed I meant multi-speed transmission when I said ratio change. I didn't say multi-speed transmission.
huh? no I didn't....I read where you said "ratio change", and interpreted that to mean "ratio change"(I even set it in bold type when I quoted it) and agreed with you, and showed you that I had originally also said the same thing...here, I'll just post a direct quote, again


2. you are still left with a combined torque curve w/2 motors. in peak mode, I doubt there is any "win" there that a single motor ratio change couldn't cover.
exactly, and thats why I posted: "...sure, the two motors working best at different ends of the RPM range aren't going to be as strong as the one big motor geared to run slow OR fast; but thats only at a peak, and now you don't have to change gear ratios" but this added part might of confused you


...as the ratio change answer IS a transmission(and I'm avoiding that)
see, when you are saying "ratio change" I can only assume that you are talking about taking half the bike apart to "change" the final drive "ratio" with the motor and/or rear wheel sprockets...the "answer" to that "is" to use "a transmission" so you don't have to take the bike apart every time you want to alter the gearing




... I have done your homework for you, please try to understand it .... attached graphic.

..., here is a link https://imgur.com/a/OI1LC
ok, thank you for doing that, and showing interest in this topic
yes, it took me some time studying your graph layout to figure out what and how you are speculating data, and now I do understand most of it, besides the conclusion

first lets kinda forget about the 'larger single motor'[green hp and torque lines] as to form a direct comparison(of 1 motor vs two ½ motors) all things would have to be equal(price, weight, size, effort to install, etc. as well as the two smaller motors also being exactly ½ torque with the same performance profile) and while that could only be done theoretically; the only real world way to do that would simply be to have the same bike with dual motors geared the same vs dual motors each with differing drive ratios
...not looking at the green lines helps clean up your graphs to make them more readable

now its looking like what you did was to take the same graph[red hp and orange torque lines] and 'skew' the scale(using resize in MS Paint?) to produce a second graph to represent a different gear ratio for an overlay
....however I dont think you can simply do that and get accurate torque to hp calculations(notice that you stretched the graph longer to represent a 'longer gear' but shrunk the height to represent less physical torque multiplication output) eh, maybe....but ultimately, even tho the motors are geared differently, they still operate at the same 'drive shaft' torque output(not one shrunk like you have it)....at the 'rear wheel' with different drive ratios, yes the torque would be 'shrunk' with the 'longer gear' but also final RPM would be different, so the math calculations would be different(look back on page two of this thread (http://elmoto.net/showthread.php?t=1924&page=2) for the more professional graphs Podolefsky posted on Motor HP at MPH, notice how the hp output doesnt 'shrink' in height with the different drive ratios[red and yellow lines] of the D&D nor with the different gear changes of the Ninja 250, altho each mapped curve of HP does 'stretch' in length with speed from different drive ratios)
...so you get what I'm saying there? your graph representation is flawed

but still the conclusion[fascia line circled in red on the last combined graph] is the most confusing part I don't understand
... ask specific questions ... how in the hell did you come to the conclusion that the combined torque of two motors would be [B]less than one of those same motors ???
(shown as the fascia line dropping off sooner compared to one of the orange lines on the graph)

...wait, don't answer that...I don't want to know...






first says
oh god no. make it stop. then immediately continues in the next post 'not' to stop

...

... transmission

Transmish? ...

tranny?

transmission.


ah...you did get that I wasn't posting about a "transmission", right?
...I was only using this thread because a while ago I read your blog post about dual motors...so I did a forum search here to see if there were any threads already on it...and there was this one(one of the many you made with your obsession of posting about transmissions again :p )

but yeah, you had your "fun" with it for years I get that...but I'm doing something else here, and not just for 'fun'...you can read some of my progress and first ideas as they began to develop here (http://elmoto.net/showthread.php?t=4629)....I'm working on this dual motor concept to circumvent a trans(as I've posted a few times the drawbacks and lack of necessity) as NO I can't fit one single larger motor, and YES I do need lower speed response while also having to occasionally hit higher speeds

unless Ted, you would like to convince me that you have already thought, posted, and built everything to do with eMotorbikes, so I should just abandon my project ( hehe ;) )

Ted Dillard
30 March 2018, 0512
"ah...you did get that I wasn't posting about a "transmission", right?"

Then I'd respectfully suggest you start a new thread appropriate to your intended discussion, rather than trying to push an ancient discussion off-topic.

Also, not for nothin':
"first says
Quote Originally Posted by Ted Dillard View Post
oh god no. make it stop.
then immediately continues in the next post 'not' to stop"

I was talking about motors, and how these motors ca. 2014 pretty much checked anything you are talking about into the cheap seats. Sorry that wasn't crystal clear.

Besides that, it was a joke. We occasionally do that here.

T Rush
30 March 2018, 0542
.
Besides that, it was a joke. We occasionally do that here.yeah, I know those motors that I read about in your post...its just too bad they don't fit my budget, power requirements, or physically into my bike at all...but thanks, still trying to come up with something else tho

and yeah, I know jokes...I was doing that too

however, I actually look at this thread as if you guys missed half the subject(I did read the whole thing), and only talked about the trans and forgot to talk about the duals....so I'm bringing it back on topic :cool:


I think one of the big stumbling blocks people are having with the idea I'm working on for my bike...
(besides realizing that its not actually about adding a transmission, which is totally my fault for posting it in a thread titled "Transmissions. Yeah"...but it does directly deal with the core of why anyone would want a trans, and that whole "dual motor" thing in the OP)
...is that its too easy to over complicate the concept of having two motors geared differently on the same drive chain

first of all
...electric motors operate just fine in a very broad RPM range....
this is different than an ICE where you really would have a problem with miss matched engine speeds...like say you took the engine out of my GSX R750(peak power @ 11,000RPM), and put it in my big GL 350 mercedes connected it directly to its diesel engine(peak power @ 2,000RPM) doing this thinking now the mercedes would still be able to pull my 30' cabin cruiser boat out of the water, but then could also run at 153mph like the gixxer can.... whelp nope, thats obviously not going to work, as someone else already posted their concerns about(which would be valid in this case) the 750 engine would be burning up struggling to make power at low RPM, but then the 350 would just explode at high RPM
....but here is the catch; the high speed motor doesn't have to make a bunch of power at low RPM, it just has to sit their ticking over...but the low speed motor does still have to spin up, and sure thats impossible for the torquey diesel, but not horrible for an electric motor if the max RPM is kept within reason(and keep in mind, the low speed motor doesn't need to be in its performance speed band anymore when at those high RPMs)

next
...the idea of running two motors connected directly together, but running different RPM's will mess with your head if you let it...
seriously its no big deal, it just sounds "un-possible"...like you don't freak out because in a single motor bike the motor is directly connected by a chain to the back wheel, and they spin totally different RPMs....it will be fine....and really there won't be a huge difference in motor RPM where one is burning up while the other one explodes

last
...the idea of running an eMotorbike motor with different fixed final drive ratios, thats not hard to swallow, really....
I keep pointing people to look at the nice big graph on page 2 of this thread (http://elmoto.net/showthread.php?t=1924&page=2) (sorry Ted, while yes I found this thread because it was started with the blog post about dual motors, I used this thread because it had that wonderful graph posted in it...yes I realize this thread got sucked into the transmission rabbit hole vortex, but it can't hurt to also spend some time on the other side of the OP's subject ) anyway, if you just forget about running both those D&D motors represented in the graph connected together, you can see where they both can go the same MPH speeds, and no, nothing bad is happening
.....now yes, say your buddy has the red motor, and you have the yellow one; so you want to go riding together... he wants to spend the day riding around town(because his motor is geared for that) but you want to go flying down the highway(because your motor is geared for that) and here is where bad things will happen....if you ride in town all day your motor will strain from lack of RPMs, but if he runs highways speeds for too long his motor will explode...ok, ok, ok, are you ready for this? as this is the really cool part...to fix this problem, you get a tow rope and connect the bikes together(wow, just like having the two motors on the same chain now) so for in town where he has all the torque, he helps you out by pulling you along; but out on the highway, you pull him....and wait wait wait, I know what you are thinking: "but hey, wont you only go half as fast on the highway if you have to pull another bike?" to which I would reply "remember in my concept, there is no another bike, both motors are on the same single bike"

Ted Dillard
30 March 2018, 0552
Let me try to explain to you why it's fairly important to keep a thread on-topic, and start threads appropriate to the intended subject.

So you can find stuff later.

I've been a member here since about a year after this forum started, and we have had many incredibly productive discussions. Yes, dual and triple motors, how to control them and all that. It's useless in the future if you can't find it. If you want to link nice graphs, I can show you how to do that. There are a couple of ways... As far as me building everything, no, I've only built about 6 bikes, but a whole lot of people here have built a whole lot of things. Dice, for example, has run twin motors in various record-holding drag bikes you may want to look into.

Seems like you're into poking people, I'm not. Anyway, I'll leave it up to Mike or whoever's moderating these days about the off-topic issue, and go back to pretty much ignoring this thread, have a blast.

T Rush
30 March 2018, 0638
Let me try to explain to you why it's fairly important to keep a thread on-topic, and start threads appropriate to the intended subject.

So you can find stuff later.
. oops, sorry, maybe you missed this part of my post right before your last one

...
however, I actually look at this thread as if you guys missed half the subject(I did read the whole thing), and only talked about the trans and forgot to talk about the duals....so I'm bringing it back on topic :cool:

.....

I keep pointing people to look at the nice big graph on page 2 of this thread (http://elmoto.net/showthread.php?t=1924&page=2) (sorry Ted, while yes I found this thread because it was started with the blog post about dual motors, I used this thread because it had that wonderful graph posted in it...yes I realize this thread got sucked into the transmission rabbit hole vortex, but it can't hurt to also spend some time on the other side of the OP's subject

... and this is what I first said to 'bump' this thread
I've been reading thru a bunch of these threads, and Ted's blog
....and when I read on Ted's blog the TRANSMISSIONS VS. DUAL MOTORS (https://evmc2.wordpress.com/2012/01/01/transmissions-vs-dual-motors/) he used to start this thread....it gave me an idea
and of course in my first reply to you

...I was only using this thread because a while ago I read your blog post about dual motors...so I did a forum search here to see if there were any threads already on it...and there was this onebut I'll tell you what.....no one seems to be grasping my 'non transmission dual ratio motors' concept here anyway(tho I did get a 'like' on one of my posts here, for whatever thats worth) and because you asked, and you are the thread starter...I'll go elsewhere *sigh*
(gosh, wouldn't it suck if I started another thread with my idea, and someone posts: 'just get a transmission instead' and that thread joins this one in the rabbit hole trans vortex of hell...lol)

seriously tho, sorry if I miss-used your thread, that was not my intention at all




Seems like you're into poking people, I'm not. Anyway, I'll leave it up to Mike or whoever's moderating these days about the off-topic issue, and go back to pretty much ignoring this thread, have a blast.
ok, this is actually why I bothered to still post in this thread besides just leaving it as you have asked

yes Ted, you and cdc actually started the 'poking'...I can(and did) quote you on it

but peace man, I have big respect for you and your writing
...moving on now :(

Richard230
30 March 2018, 0723
I still like the concept of using a compact two-speed transmission on an electric motorcycle, but finding an off-the-shelf transmission like that that is of the correct size and has sufficient torque capacity, is likely to be a real challenge. I seem to recall that at one time the Japanese manufacturers had some off-road (and on-road, which really didn't make any sense at all) motorcycle models with a secondary two-speed transmission that would change the overall drive ratio to provide a "granny" gear for low speed, high torque, running. I wonder if any of those old bikes are still around?

dcb
30 March 2018, 0736
(half bakery 2 motor 2 ratio discussion continued here: http://elmoto.net/showthread.php?t=4629&page=5 )

I'm w/you Richard, nothing wrong with the cheap seats :) Especially if your goals are a simple commuter that can operate continuously at speed and not leave you stranded at the bottom of a hill. The jury is still out on raw performance, but no-trans seems to be in the lead, but that is subject to change as various kinds of unobtanium come to market.

edit: I wouldn't entirely rule out a transmission that reverses the order of ratio change on startup for that matter, if you look at it from a wheel torque control perspective and figure out how to get rid of the flat part of the torque graph. (%99.999 certain the idea is half baked, but maybe).

Ted Dillard
30 March 2018, 0743
They are still around, Richard, but the way they're designed they're almost impossible to implement effectively in an electric bike. Chris Bell actually built a custom reduction gearbox, complete with housing, and we chatted for a while about a simple switch-while-stopped dual range (2 speed) gearbox. Unless you're Chris Bell, however, it's a pretty tough machine to build.

And, I might add, pretty much unproven concept.

T Rush
30 March 2018, 0751
[sheepishly pokes head back in this thread]

ah, sure, I can talk 'on topic' about transmissions, I guess
I still like the concept of using a compact two-speed transmission on an electric motorcycle, but finding an off-the-shelf transmission like that that is of the correct size and has sufficient torque capacity, is likely to be a real challenge. I seem to recall that at one time the Japanese manufacturers had some off-road (and on-road, which really didn't make any sense at all) motorcycle models with a secondary two-speed transmission that would change the overall drive ratio to provide a "granny" gear for low speed, high torque, running. I wonder if any of those old bikes are still around?

yeah, sadly not only did I read all of this thread...but I read many others on this too...so I know where that information is posted
here:

...

Doing a little googling I discovered that there was at least one production motorcycle that used a similar scheme, the 1980-82 Honda CB900C (and maybe a goldwing of similar era?):
http://www.motorcyclespecs.co.za/model/Honda/honda_cb900c%2082.htm
...


I've thought(and many others have posted over the years) that there are actually a lot of motorcycle transmissions you could use if you wanted
...you just don't have to use all their gears


[/runs away and hides again]

Ted Dillard
30 March 2018, 0802
...which is how a lot of Brammo Empulse users report they actually ride with the thing.

That idea about "you could use if you wanted" is fine, until you have to actually design an interface or housing with your motor. When you start to do the actual work (which I've started, even to buying a bike just for the tranny), it becomes pretty clear pretty fast that it's easier just to design one from scratch. Especially since none of them are designed for an electric motor's torque delivery.

Am I still talking? Dammit.

Warren
30 March 2018, 0826
The Eindhoven Storm ran a two speed to good effect. Whether this would be a value proposition in a bike you actually had to sell, and make money on, is anybody's guess.

https://www.storm-eindhoven.com/STORM_Wave

T Rush
30 March 2018, 0830
that looks novel

yeah, out of all the ways I've looked at it, and excuses for adding in a trans to an EV(that really doesn't need one in the way they are traditionally used with ICE)
...like I thought: 'hey, if I have to do a jackshaft anyway, I guess it might as well be a trans so the motor can spin the default direction'
it just didn't seem worth it to add an extra part that likely wouldn't get utilized in all occasions, and goes back to requiring oil changes

its like one of those problems you think you might have, but maybe never really is that bad.....I haven't seen a lot of people posting where they are so frustrated with their EVs, because they don't like the fixed final drive ratio they have

dcb
30 March 2018, 0933
fwiw, the cb900 only changes the ratio by ~%17, hardly worth the effort IMHO.

If you don't have specific performance goals, plenty of things are perfectly drive-able. I wan't my 750 sized motorcycle to leave the line... like a 750 motorcycle, and don't mind if it is just plain old driveable after 20mph or so (you are already out in front of traffic from the light, so it doesn't matter much as long as you don't get in the way), which is why I entertain this stuff.

the jackshaft tranny doesn't have to be soaked in oil fwiw, if you use toothed pullies/belts and a dog clutch. http://www.thepixelpump.com/widdershins/images/simple-gearbox-anim.gif and belts are a better fit for the high rpm side of things. But bla bla bla.

Speaking of cheap, I did make a retro-direct 2 speed scooter a long time ago, made a HUGE difference, could actually climb the hills and have ok top speed (for a cheapie scooter). You reverse the motor to change gears (with a switch).

http://ecomodder.com/wiki/images/3/3f/Twospeed.JPG

Stevo
30 March 2018, 0944
T-Rush, I had stumbled upon a video some time back that you may find some answers to your questions: http://elmoto.net/showthread.php?t=4536

Ted, sorry for keeping this thread alive! LOL

T Rush
30 March 2018, 1035
yeah, hehe...I saw that video awhile ago too...had totally forgotten about his buddies voice tho

...I didn't know I was asking any questions here :confused:

thought about this a bit, and I have to say: I still just think its sad Ted started this thread about something kinda neat and different...and everyone just turned it into another 'transmission thread' I found tons of other ones of those...and no way was I starting anything that could remotely resemble another one
(go back and read the OP, then look thru the thread and see if you can find much of anything that relates to that like I didn't)
..so now I am going to ask a question

did Ted or anyone(here) try this?

The implications of adding a second, or bigger motor rather than a transmission started falling into place when I starting thinking about adding a two-motor configuration to the R5e. Here's the basic jist of it.

When you add a second motor, in parallel, then you're doubling the torque (and load) at any given RPM. You're also doubling the current handling capacity- a 300amp system becomes a 600amp system. I know other bikes did it years ago
...think I saw some of the first Isle of Man TT Zero bikes doing it, maybe even before they did the first running in 2010, I thought I saw something when they were testing, but I'd already gotten out of my second involvement with EVs by then(this is going to be my third try with it now, but a motorcycle this time..so actually I'm not as noob as I might appear)

or heck, I'll just go back to the search again...screw it

Ted Dillard
30 March 2018, 1051
Thanks for making me go back and look at the start of the thread. "Brutus", on the first page by the way, is the aforementioned Chris Bell, who at the time thought transmissions were a good thing. After only one bike - not one model, one bike - he changed his mind. This is a guy who can build a reduction gearbox so beautiful it'd make you cry. So yeah.

Just so you understand, back then you simply couldn't buy a motor that was big enough, and light enough in any sort of axial, liquid cooled design. That's why Motoczysz ran 3 of the Agni motors on their first IOM bike (and blew them all up). THIS is why I mentioned the YASA, EMRAX etc.

What we learned was that running twin PMDC motors is damned near impossible. Even Cedric Lynch couldn't balance his motors for Czysz, and they're his motors. Running dual or more AC motors (loosely using that term) is not as much of a problem. Still touchy, but do-able. But no, to answer your question, I never did it, and I don't remember anyone on the group at the time doing it either, save Dice running the Predator with series-wound DC motors.

furyphoto
30 March 2018, 1154
Isn't the Enertac dual hub motor basically doing this? (running two motors). Although, while adding significant un-sprung weight.

Ted Dillard
30 March 2018, 1215
Yup, that's exactly right. Also you can stack most of the motors like the YASA etc.

Richard230
30 March 2018, 1414
I always wondered what happened to the blown Aprilia RS50 engine that I sent to chdfarl, in MA. He said that he planned to use the engine's 6-speed transmission on his build. Since he never posted about giving it a try, I guess it just didn't work out. :confused: But I did get rid of that broken lump without being arrested by the CA EPA for disposing of a container of toxic waste in a landfill. :O

Ted Dillard
30 March 2018, 1503
I feel like, well, I started this thread and it's run it's course. Any discussion of transmissions is pretty much academic, as well as a complete waste of time. I'm asking Mike to close the thread.

T Rush
03 April 2018, 0722
eh, I don't know about that.....and not that I'm trying to be rude or funny or anything; but don't you think it would be odd if I started a new thread on the exact same subject instead of using the forum search function to make use of the information thats already here?....isn't that what this site is here for.....and if you guys missed some information back in the day, that now could make this work, wouldn't you want to know about it?

I get that this thread is 6 years old, and now its great that you can afford and fit those bigger more expensive motors....but its still new to me, and I can't have those newer motors

personally I'd like to actually see performance data of electric motors running different gear ratios....because I remember stuff like this from back when I was into this whole DIY EV stuff before
http://23.21.184.60/evtv-word-press/wp-content/uploads/2011/04/spyder7601horsepower.jpg
http://evtv.me/2011/04/1955-porsche-550-spyder-on-the-dyno-comparing-curtis-1238-7501-and-7601-controllers-650-amp-upgrade/ sure you could drive an EV like that around all day in the same gear...but if you wanted to be in the powerband for acceleration at lower speeds shifting would be a good option .....seems like otherwise you guys are just building bikes with fixed ratios to only have peak power at one smaller mph range(wouldn't even the newer fancy motors still have a peak power point?)....so what does it hurt to consider my unbalanced system of dual fixed ratio motors to widen that peak into a plateau?

cause it seems that most of the hardware I have available to me is still about the same as what was around then...and I don't want to use a transmission


.... If MOST of your vehicle's use is at hwy speeds of 65 mph, then you would try to gear for that speed at the most efficient sweet spot on your motor/controller combo. If most of your use is at 45 mph city street commuting, then that's where you should set the final gear drive for. ....
the motorcycle I'm converting doesn't allow space for a large motor where I'd be able to have a wide enough power band(sweet spot) where a compromise would work well...I'd either end up where its geared for the lower speed acceleration for 25 and 35mph speed limits in town maybe just barely reaching 45mph max bike speed; and not even able to get up to the 50~60mph the bike could originally do with the 50cc and upgraded 80cc ICE...or....if I gear for the 55mph speed limit road my shop is on(which I have to drive daily) the eMotorbike will just have laughable performance in town where I would want to enjoy it more....but....I could fit two of the motors that are available to me(which will give me a nice power boost no matter how its geared) ..... so .....this is when I had the idea to look and see if there was any info about dual motors vs transmissions to also help with my gearing issue...which...led me to Ted's blog post and thus this thread....however....the new "Ted Dillard"(with only 49 posts) now very disappointingly wants to shut that discussion down? and I wish the old "teddillard"(who started this thread, and was very active here) would consider my idea (http://elmoto.net/showthread.php?t=1924&p=51794&viewfull=1#post51794) that continues on his own plus directly is inline and exactly on-topic with this thread :)
(maybe you guys just missed my first post because it was at the bottom of the page, and that dude with only 20posts and who hadn't posted here since 2016 started being weird?) ...or 'in my case' am I better reconsidering a trans? :(

Stevo
03 April 2018, 1004
Ultimately, your thread is not about transmissions, per se, its about your derby conversion.
You either design your conversion around the chassis you have, or decide what you want to design and get the chassis that will be best for your design. That sums it up nicely.

Spaceweasel
03 April 2018, 1058
I'm not a big fan of shutting any thread down that hasn't become abusive. New people come in and have questions or insights. It's not like the collective braintrust came to one final decision on a math problem that doesn't need further elaboration. As with any discussion, you can always walk away for a bit if you don't want to participate. I have gotten up from a table and taken a stroll to the bar to wait for the tone or topic to drift more than once.:)

Ted Dillard
03 April 2018, 1155
Yeah, like I said, it's about finding stuff later. Go on ES and look at threads that are 43 pages long, and cover 6 topics. I'm only saying this because I've spent a lot of time doing just that. My opinion, you want to talk about dual motors and thrash around ideas about that? Have a blast, on a Dual Motors vs Transmission Random Speculation thread. Then, old bastids like me can find them, if per chance someone actually comes to some conclusions that make sense.

Please do me a favor and stop trying to troll me out into this "discussion". Old Ted, new Ted, I left this forum for several very good reasons, and I'm starting to reconsider recently re-joining it.

...back to the peanut gallery. Done with this foolishness.

T Rush
03 April 2018, 1212
oh then, I tried :(

Ted Dillard
05 April 2018, 0601
27,000 views on this thread. wow.

I was waxing sentimental, and went back and started reading it again. This thread, mind you, was after months, if not years, of discussion, research, illustration, and actual attempts at proof of concept and use. Not to mention some very heated debate. Not at all an easy thing to manage, considering the nature of a forum and the internet.

In spite of all that, it was a great, respectful (for the most part) discussion, if not final conclusion, amongst people who were committed to building bikes. Funny story, that one guy, mechanic, was the one standout, typically pretty snarky and abrasive, and pretty opinionated. At one point the moderators tracked his IP, and it turned out it was coming from the office of one of the most talented and brilliant engineers/builders on the planet. Even with his snark, after that, the people who knew tended to at least try to understand his points.

Now we're in a much different time... and the transmission discussion has some real, actual testing and demonstration out there, as I've said before. Kinda cool.

What can I say? I'm a history nerd.

Michael Moore
08 July 2018, 1705
I still like the concept of using a compact two-speed transmission on an electric motorcycle, but finding an off-the-shelf transmission like that that is of the correct size and has sufficient torque capacity, is likely to be a real challenge.

Since I didn't see a mention of it keep in mind that the ICE transmission/clutch needs to be designed for the torque spikes, and not just for the average/nominal peak torque.

I talked with an engineer at Tilton (race car clutches) about clutches many years ago when I had a small-block Guzzi hopup project. He said they'd built a clutch for the 1000cc Wittner Guzzi endurance racer based on the torque shown on dyno runs. It didn't do the job. They had not done a clutch for a big twin like that and hadn't taken into account the torque spikes, and they ended up with a lot higher capacity clutch on the redesign.

So a transmission for a 100 hp 4-8 cylinder ICE is likely to be much less beefy than a 100 hp twin, because the multi is having a lot of small torque spikes from the multiple small cylinders (bangbangbangbang) vs the large and less frequent events (BANG . . . BANG . . . BANG) hammering of the twin.

So I'll speculate that a 50 hp e-motor with a smooth/constant flow of power might get away with a lighter transmission than a 50 hp 4T single would need. A 50 hp 2T single will use a lighter gearbox than the 4T because the power events are twice as frequent and the BMEP is significantly less.

Of course, all that is of only academic interest if you aren't going to put a transmission on your electric vehicle.

cheers,
Michael

Richard230
08 July 2018, 1730
Since I didn't see a mention of it keep in mind that the ICE transmission/clutch needs to be designed for the torque spikes, and not just for the average/nominal peak torque.

I talked with an engineer at Tilton (race car clutches) about clutches many years ago when I had a small-block Guzzi hopup project. He said they'd built a clutch for the 1000cc Wittner Guzzi endurance racer based on the torque shown on dyno runs. It didn't do the job. They had not done a clutch for a big twin like that and hadn't taken into account the torque spikes, and they ended up with a lot higher capacity clutch on the redesign.

So a transmission for a 100 hp 4-8 cylinder ICE is likely to be much less beefy than a 100 hp twin, because the multi is having a lot of small torque spikes from the multiple small cylinders (bangbangbangbang) vs the large and less frequent events (BANG . . . BANG . . . BANG) hammering of the twin.

So I'll speculate that a 50 hp e-motor with a smooth/constant flow of power might get away with a lighter transmission than a 50 hp 4T single would need. A 50 hp 2T single will use a lighter gearbox than the 4T because the power events are twice as frequent and the BMEP is significantly less.

Of course, all that is of only academic interest if you aren't going to put a transmission on your electric vehicle.

cheers,
Michael

Like Brammo. ;)

Ted Dillard
09 July 2018, 0904
7754

Stevo
09 July 2018, 0953
LOL... now that's funny shit, I don't care who you are!! (But Ted, look at your view count NOW!!)

I agree with Michael though, I was toying with the idea of using a tranny out of a YZ125 (2T) when I first started this adventure years ago... though with only 3 gears instead of 5.... I just settled on the idea that it was way more complexity than was needed.

Michael Moore
09 July 2018, 1423
A friend told me of some simulations he did for a clients e-scooter project some years ago.

This was a 45 mph top speed, 770 pound total weight with rider, lead acid battery, 10.2 kW continuous power simulation. He compared the direct drive version against a CVT with a 4:1 speed range. He pointed out that if the final drive is optimized for high steady-state cruising speed then it is a wash on either version when they are operating at that cruising speed. But the CVT version had much better acceleration to speed as well as enhanced range if operating in the "less than maximum" speed range (as with in-city use). At that time and for that project he felt trading L-A battery mass/space for the CVT would have been a good choice.

Direct drive time to top speed was 40 seconds and the CVT reached it in about 15 seconds. For a 40 second run the direct drive would have covered about 590 meters and the CVT version about 720 meters. Energy efficiency against distance traveled for 600 meters saw the direct drive at about 35% driving efficiency at 100 meters and 70% at 600 meters, while the CVT was about 78% at 100 meters and 91-92% at 600 meters. The CVT curve on that last rose steeply to 100 meters and then was pretty flat from 400 meters on while the direct drive curve was rising the entire distance and presumably would have needed more distance to reach top speed and equal efficiency with both running on an final equal gearing..

But that was then. He told me he saw the situation now as being like with personal computers -- if you want better performance you don't optimize the code, you just add more CPUs and RAM to the PC. With modern motors and controllers and batteries performing better for less money it is easy to add more battery and higher power motor/controllers and have direct drive work fine and there's not as much need for a transmission for efficiency. He did say that doesn't invalidate the benefits of some sort of transmission in variable speed use, but the payoff in the riding experience is smaller.

I'd guess that if you are handed a low power system to use for stop/start traffic and then told that's all you are going to get then you may want to give serious thought to some sort of variable speed transmission.

YMMV,
Michael

Stevo
10 July 2018, 0044
I still think a 2 or 3 speed tranny for use in a true dual sport would have advantages on an emc. A nicer, usable low end to power through technical single track and up/down slippery hills, then throw Hwy speeds and city commuting into the mix. But, is it necessary? Especially after next gen batteries lose some weight. Tranny=Added complexity, added weight, & power lost thru mechanical losses

Well, The Guys at Alta think so!

Michael Moore
10 July 2018, 0818
An acquaintance who is a very fast MXer had a test ride on an Alta and he gave it a very positive review and liked it a lot.

Yes, next-gen batteries+next-gen motors/controllers will probably put the transmission question off the table for very many applications. But I suspect it is a good idea to be open to using them IF it appears that will give the best results for a particular project. It is easy to let preconceptions blind one to potential solutions.

Ted Dillard
10 July 2018, 1016
So this thread is now into 20 pages, and has had over 30k views. I don't know how you could say anyone who's made it this far has preconceptions. Sorry. :rolleyes:

Funny, I was just reading a friend's ride review of a Zero, after owning an Empulse (and having it totally die on him). He said if he'd ridden it before buying the Brammo, he probably wouldn't have bought the Brammo. One of the things he cited as a better thing was "no transmission". I think the jury is in on this one. Game over, the results are in.

As far as potential solutions on a particular project? I still have yet to see any transmission product that's even available, so I don't really understand how that could be a potential solution.

Michael Moore
10 July 2018, 1035
Ted, I've got a Honda CTX700 with DCT. There is no clutch lever (though dual clutches) and no foot shift lever. I LIKE the automatic and I expect my e-project will be direct drive.

Are you really saying there is no possible case where an e-moto might benefit from a transmission? I'm fine with "with modern technology there may rarely be a benefit" but I'm generally pretty cautious about making absolute statements. For example, a telescopic fork is a horrible thing, it is a long lever that puts extra loads into the frames, it wants to bend and bind up instead of sliding, it requires sophisticated machinery to make one and it should never be used on a motorcycle. That's a perfectly sensible and defendable statement about teleforks, but it ignores the cases where they work fine. :)

The world is full of transmissions, all you have to do is look around you. If you want a CVT there's decades of them that have been installed on scooters and snomobiles. There's no shortage of transmissions around. But just as people have seemed to feel a need to build a electric bike because there wasn't one like they wanted, you may need to do a bit of work to come up with the transmission that you (may) want. They aren't rocket science.

BTW, I'm looking forward to the arrival of your book tomorrow.

cheers,
Michael

Ted Dillard
10 July 2018, 1156
good grief.

Ted Dillard
10 July 2018, 1202
I'll answer that, and then I swear on my mother's grave I'm not rising to any bait on this thread ever again as long as I live.

NO. WHAT I'M SAYING is what I SAID. If you've read this thread and understand it, you couldn't hold preconceptions. Unless you just didn't want to learn anything.

Transmissions have been tried, and every instance I've seen they've proven to be no better - no faster, no more efficient, no quicker, and ultimately not worth the trouble. Back when this thread started, this wasn't the case. CVTs have been tried, and none of them have held up to the stress of an electric drive on a motorcycle. Point me to one transmission that I could bolt into a bike with an electric drivetrain that makes sense. Just one. I've looked for one for a decade or more now. The world is full of transmissions? Great, get one, put it in your bike, and show me it's worth the overhead.

THAT is what I'm saying. If I'm coming off as testy, just go back a few pages and you'll see we had this exact same conversation with a new member who hadn't read the thread, and thought dismissing trannys was foolish. And mind you, that was opinion, based on no experience.

I hope you enjoy the book.

Ted Dillard
10 July 2018, 1211
MIKE FOR THE LOVE OF ALL THAT IS GOOD AND RIGHTEOUS COULD YOU PLEASE CLOSE THIS THREAD

EVcycle
10 July 2018, 1254
7756

:p

Michael Moore
10 July 2018, 1322
Ted, it seems like I hit a hot button. I did read through the thread, I always do before commenting.

If a transmission is needed (which may or may not be the case) the world has a pretty good supply of machinists, weldors, fabricators, mechanical engineers and and awful lot of gears and shafts. If there's no turnkey transmission product labeled "for electric motorcycle use" one could be put together if someone has a need for one and the energy/budget to start the project and follow through on it. I've got some familiarity with machine tools and building things and I've got friends who've designed and built ICE from scratch, so an e-motorcycle transmission looks like a pretty straight forward project to me. I could build one, but only if it is needed for my goals.

My project will be direct drive because with the components I'm going to use I don't see a transmission being needed for the type of use the vehicle will see. A different set of components and goals might convince me that a transmission of one type or another would be a good plan. I'll use one, or not, as seems most appropriate. Everyone else is free to make their own decisions about their own projects and I hope those decisions give them a vehicle that satisfies their goals for the project.

Ted Dillard
11 July 2018, 0328
Hot button? Yah think?

Please see this: http://elmoto.net/showthread.php?t=4742