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Hugues
19 June 2012, 0420
Hi guys,

In the next few weeks we're gonna mount the motor on the frame and I now have to decide which gear ratio we're going to use. But I'm not 100% sure what to take into account in order to decide this. We're going to use a chain and sprocket at first.

My setup:
Motor AC-20, max RPM 7'500
Controller Curtis 1238-7601, running at 96 V nominal
Battery pack 32s GBS cells, 100ah, 5 to 10 C pulse.
Rear tire diameter 67.42 cm

I've used the EV_Super_Estimator spreadsheet to estimate acceleration based on different gear ratios, and i made a simple spreadsheet to check my top speed based on the same gear ratio.

I want to give priority to nice and firm acceleration over top speed. Then I want to maximize my range. I'm planning to ride the bike on secondary roads, not highways, not racing, so a good part will be done between 60 and 80 km/h. If the top speed ends-up to be 100 or max 120 km/h, i will be more than ok. I'll often ride in the hills, cannot avoid that here. Bike weight incl driver should be around 380 kgs

From what I see, it seems that a 8:1 ratio will give me a top speed of ~120 km/h and a 0-100km/h (or ~60 mi/h) around 6 seconds, all this on flat roads. So it seems to fit what I want, but...

- is it ok to use the max RPM of the motor to target my max speed of 120 km/h ? Shouldn't I build in some margin ?
- What about efficiency and the impact on range ? If i'm gonna ride often between 60-80 km/h, shouldn't i try to set my gear ratio so that I end up using the motor at it's best efficiency RPM ? Or that does not weigh much in the equation ? And what is the RPM range with the best efficiency for my motor ? I have not seen any specs like this. Can I make a reasonable assumption here ?
- other factors to consider ?

Of course we can go for 8:1, then test it, and if it is not so good, then move to 7:1 or 6:1. But all this takes time and might cost a little money. So if i can figure out a good ratio on paper, the better.

thanks for your input,

EVcycle
19 June 2012, 0437
Most of the ratios have been in the 4.5:1 range.
If you run 8:1 with that motor you will be doing Ted Wheelies!
Plus the rear sprocket would be HUGE!

With that Motor rpm Range a 5:1 would be real close.

IMHO I would not use the MAX RPM unless you are racing.

I am sure several with a similar motor combo can throw in some of their
ratios.

Please keep us posted on your results!

liveforphysics
19 June 2012, 1003
Getting 8:1 is nearly impossible with large sized chain in a single stage (no jack-shaft).

Your front needs to be at least 12T to minimize chordal motion (or it will be super loud and annoying to ride), and that means you would need a 96T rear, which in an appropriate chain size #520, your rear sprocket would be about the same size as the rear wheel.

You may just want to start off with the most reduction you can achieve with cheap available parts and see how it feels. Then in a worst case where neither front or rear sprocket are suitable for your needs, you're still only out about $100, and you will have good insight on where to gear it for next time.


Ideally you would choose a top speed you would be happy with (eg, 80mph), look at an estimated motorcycle speed vs power required curve for your chassis, see that to do 80mph you need say 18kw at the rear wheel (just a wild guess), then look at a motor dyno plot for your motor at your battery voltage (batt voltage compensated for sag when drawing 18kw), and see what the highest RPM your motor can still output 18kw happens to be. Lets say it's 6200rpm (again just a random wild guess, don't use these numbers), then you would measure the OD of the rear tire you plan to use, say it's 24ft OD, then you know 80mph is 117feet/second, and you know your wheel moved you forward 6.28feet/revolution, so you need the rear wheel to turn 1117rpm (18.6revolutions/second) to move you at 80mph, and your motor is spinning 6200rpm at it's highest RPM that it can deliver the 18kw needed to do 80mph, so your ideal gearing for this imaginary example would be 5.55:1, or more realistically, something like a 12t front and a 65t rear, or a 13t front and a 71t rear (but a 71t sprocket in #520 is going to be HUGE!).

That would be the way to calculate it. In practice though, pick some cheap sprocket combo to get it geared in the ball-park and see how you like it. You might find you almost never use the last 10mph of the top speed you picked, and would much rather trade it for 10% harder acceleration, or you might find it accelerates great but you wish it just did another 10mph, etc etc.

Allen_okc
19 June 2012, 1136
my motorcycle is set to 12 tooth gear and a 60 tooth rear sprocket - 5:1 ratio...

but i keep a 13, 14, and a 15 tooth motor gear at hand if i need to adjust for a higher top end, but my take offs would be pretty sluggish...

Hugues
19 June 2012, 1201
Thanks for the reality check guys, I did not know 12 was the minimum I could have on the motor side.

But 5:1 gives me 10 sec for 0-60 mph, not great really. 8:1 gives me 6sec, much better.

Any possibility to go below 12 on motor side by using a smaller chain ? Or 2 smaller chains if the strength is a problem ? Maybe I'm saying something stupid here...

ZoomSmith
19 June 2012, 1202
Hughes,

The first thing you need to figure out is how big of a sprocket will fit your rear wheel with adequate clearance for the swing arm.

Start cutting some cardboard circles.

--z

liveforphysics
19 June 2012, 1209
Figure out the real power/rpm capability of your motor controller battery combo first if you want to work meaningful numbers.

Hugues
19 June 2012, 1209
Hughes,

The first thing you need to figure out is how big of a sprocket will fit your rear wheel with adequate clearance for the swing arm.

Start cutting some cardboard circles.

--z
Tire is 310/35 R18
Any possibilit to calculate max diameter with this ?

ZoomSmith
19 June 2012, 1335
3276

Swing arm clearance is usually the limiting factor for rear-sprocket size. Tire size has very little to do with it.

In the image above there's about .25" between the sprocket and the swingarm at the indicated point. I wouldn't want to make it any tighter. For reference, my 68T sprocket has a diameter of 13.875".

liveforphysics
19 June 2012, 1353
Aproximately 26.54" diameter, but this will not be your distance per rev, which will be slightly less as the tire carcass makes a flat spot on the bottom as it rolls.

I would figure on 26.4", meaning 746revs per mile, so to go every 7.08rpm of the wheel gets you 1mph. So, if you want 60mph, 424rpm wheel speed, if you want 70mph 495rpm wheel speed, 80mph 566rpm wheel speed.

But these numbers don't help you much until you know what your motor/controller/battery combo power curve looks like. It may be that at 7500rpm you have plenty of power, it may be that your useful high speed power level drops off by 4500rpm.

EVcycle
19 June 2012, 1410
We run a 420 racing chain which reduces the size of the sprockets.

Our sprockets were cut at Sprocket Specialists.

DRZ400
19 June 2012, 1411
I have a #40 chain. Run 72t in rear and 12t in front 6:1 I tried a 10t up front for 7.2:1 Ran fine, just a little short on top end.

ZoomSmith
19 June 2012, 1701
Run 72t in rear

DRZ: Did you have make any modifications so it fits in Ninja 250 swing-arm?

Hugues
20 June 2012, 0415
Thanks for all the input, much appreciated.

In terms of clerance between swingarm and sprocket, that should not be a problem. I attach a picture showing the wheel mounted with a belt pulley, and there is still space.

I suppose the angle that makes the chain around the sprocket on the drive side is also important. Because my chain will be quite short as the motor will be mounted under the seat, so the angle will be wide.

We'll probably start with 12 and 72 then, and if not enough, try to see if we can go with 10 and 72, or push the rear to 84 if that fits.

But then i'm not all that clear about chain size. Some speak about 520, 420 and also #40. Can anyone give me some pointers on this topic. Or it's pretty obvious that I need a specific chain size: 420 allow for smaller sprocket ?.

@LFP: the only graph that seems to be available for this motor/controller is for 48 V, and I'll be runing at 96v, and no efficiency data.

thanks all

3277

Allen_okc
20 June 2012, 0513
:cool: what they need to do is come up with a wider range of belt drive gears...

EVcycle
20 June 2012, 0747
520/530 is standard cruiser/sport chain, strong but big for most EV motorcycles.

420 is used on Dirt bikes. Zero and others use 420. Zero is where I got the front sprockets.
It is very strong (unless you buy the cheap stuff) smaller in size and less rotating weight.
I have been using 420 chain for years with no issues and am still on the original chain!

frodus
20 June 2012, 1009
Don't go below 12 tooth on the front. You'll have wear and potentially binding issues due to the tight bend radius. Go up on the back. I know this from experience and seeing others have issues.

For a bike like yours I'd use a 530 chain and sprocket due to the weight and torque. I think 72 is a bit large but if you can fit it, then great. I used a 60 and 12 on a less powerful motor and it worked well and gave good acceleration. Maybe do like 66 tooth? 72 and 530 chain sounds big.

Also 530 chain is equivalent to ANSI #50 so finding front sprockets will be much much easier and you wont have to machine one. And you can use cheap #50 chain to get it dialed in then switch to O-ring chain later once you get the final ratio.

podolefsky
20 June 2012, 1107
I'm running an 11 front. No issues so far - we'll see how it does long term.

This site (http://gizmology.net/sprockets.htm) and Wikipedia (http://en.wikipedia.org/wiki/Roller_chain) contain good information.

Torque from the motor is the same whether your bike weighs 300 lb or 800 lb. The important parameter is working load.

Working load = torque / sprocket radius (x some factors that are usually 1.0 for our application).

So for an AC-20, let's say 75 ft-lb max torque.

For 420, that's 75 / 0.08 = 937 lb. That's going to be too much for a 420 chain - it'll work, since this is within the tensile strength, but the chain won't last since it's over the working load.

For 530, the working load is 75 / 0.1 = 750 lb. Well within the limits.

Hugues
20 June 2012, 1108
.... And you can use cheap #50 chain to get it dialed in then switch to O-ring chain later once you get the final ratio.

Someone was telling me about these o-ring today. What are their purpose ? DOes it help to make less noise too ?

what does 530 mean ? 30 is the pitch, and what about the 5 ?

thanks

podolefsky
20 June 2012, 1116
O-ring chain actually has o-rings that seal the pivots, so it keeps dirt out of the chain pivots. They last longer and don't need to lubricated as much. Probably a little quieter. O-ring chain is pretty standard.

5 is the pitch (number of 1/8ths of an inch, so 5*0.125 = 0.625" pitch). 30 is the width, so 3.0*0.125 = 0.375" roller width.

Hugues
20 June 2012, 1126
Thanks for the links Noha, i now understand better.

we'll check what the bike shop has on hand for testing, probably starting with a 530 and 12 teeth at the front and at least 72 at the back,
And we'll work from there.

I'm really looking forward to the day when i can sit on the bike and twist that throttle, and not just play with numbers on an excel sheet !

We're getting there, although slowly, batteries are due to arrive tomorrow. So all the basic components are here, now it's time to mount that motor.

thanks all !

EVcycle
20 June 2012, 1526
I'm running an 11 front. No issues so far - we'll see how it does long term.

This site (http://gizmology.net/sprockets.htm) and Wikipedia (http://en.wikipedia.org/wiki/Roller_chain) contain good information.

Torque from the motor is the same whether your bike weighs 300 lb or 800 lb. The important parameter is working load.

Working load = torque / sprocket radius (x some factors that are usually 1.0 for our application).

So for an AC-20, let's say 75 ft-lb max torque.

For 420, that's 75 / 0.08 = 937 lb. That's going to be too much for a 420 chain - it'll work, since this is within the tensile strength, but the chain won't last since it's over the working load.

For 530, the working load is 75 / 0.1 = 750 lb. Well within the limits.

Point - counter point.... I am sorry, but I must disagree. (This will be a first for Noha and I...)


The Renthal R1 420 has a average tensile strength of 4,271 lbs. I did mention getting GOOD chain.

Running 530 is a waste of energy and too much rotation weight. Unless you are drag racing your bike (and I
did read how you are planning this project) IMHO 420 is more than sufficient.

:P

liveforphysics
20 June 2012, 1558
#530 is way excessive. I run it on my 190hp GSXR1000, and it lasts forever under massive wheelie abuse.

#520 would be as big as you would ever want to go, and it's nice because it has more available sprockets for it than any other chain size.

#420 would be iffy at these power levels. It's fine for ~25hp, but for 50hp it wears out pretty damn quick.

EVcycle
20 June 2012, 1605
#530 is way excessive. I run it on my 190hp GSXR1000, and it lasts forever under massive wheelie abuse.

#520 would be as big as you would ever want to go, and it's nice because it has more available sprockets for it than any other chain size.

#420 would be iffy at these power levels. It's fine for ~25hp, but for 50hp it wears out pretty damn quick.

Is has not on mine. :)

On a 500 pound (without rider) bike, maybe, but most of these bikes with lithium are under 350 Lbs.

and I have the ME1003 motor... :O

I also place a challenge the folks that say run a 530 chain to show me you have run both a (quality) 420 and 530.

Show the difference. :P

added Note: Brammo and Zero run 420 chain...

podolefsky
20 June 2012, 1614
#530 is way excessive. I run it on my 190hp GSXR1000, and it lasts forever under massive wheelie abuse.

#520 would be as big as you would ever want to go, and it's nice because it has more available sprockets for it than any other chain size.

#420 would be iffy at these power levels. It's fine for ~25hp, but for 50hp it wears out pretty damn quick.


520 has very few sprocket choices for the electric motors we use. Actually, as far as I know, there are no 7/8" keyed shaft 520 sprockets out there. You have to get a #50 and turn it down.




Point - counter point.... I am sorry, but I must disagree. (This will be a first for Noha and I...)


The Renthal R1 420 has a average tensile strength of 4,271 lbs. I did mention getting GOOD chain.

Running 530 is a waste of energy and too much rotation weight. Unless you are drag racing your bike (and I
did read how you are planning this project) IMHO 420 is more than sufficient.

:P


Working load can be significantly less than tensile strength. Tensile strength is just the point at which the chain will stretch and snap all at once. Working load is the level you can run the chain continuously. With a tensile strength of 4271 lb, the working load is probably around 1500 lb...so yeah, getting good chain is important.

Also, since we only hit peak torque for short durations on our bikes, you can probably get away with a chain that's slightly under spec.

My opinion - people worry about rotating weight way too much. An extra few lb of rotating weight really doesn't make that much difference compared to the 400-500 lb of non-rotating weight.

EVcycle
20 June 2012, 1619
520 has very few sprocket choices for the electric motors we use. Actually, as far as I know, there are no 7/8" keyed shaft 520 sprockets out there. You have to get a #50 and turn it down.



Working load can be significantly less than tensile strength. Tensile strength is just the point at which the chain will stretch and snap all at once. Working load is the level you can run the chain continuously. With a tensile strength of 4271 lb, the working load is probably around 1500 lb...so yeah, getting good chain is important.

Also, since we only hit peak torque for short durations on our bikes, you can probably get away with a chain that's slightly under spec.

My opinion - people worry about rotating weight way too much. An extra few lb of rotating weight really doesn't make that much difference compared to the 400-500 lb of non-rotating weight.

A few pounds to 400-500 pounds. Apple-oranges?

Every ounce counts.....

frodus
20 June 2012, 1651
Easy to find front stock sprockets + my motorcycle was already 530 were my reasons. No hunting for hard to get or custom parts. Is a few ounces of chain going to really rob you of that much power? I doubt it.

Now back to ratios. Noah did some calcs before on the ac20. Cruise his thread on the gsxr build.

I did mine based on a few things:
I wanted a top speed of about 70 originally with a K91-4003 motor. I had the torque curve for it and knew what rpm the torque starts to drop. If its too low you wont have the HP to overcome air resistance no matter how many rpm the motor says it will do.
I also wantedgood starting torque and back calculated acceleration to get a fair estimate for what would be reasonable. From that I got torque at the rear Wheel and the calculated the ratio of motor stall torque verses the wheel torque I wanted and got something around 4.5 but I wanted options.

I ended up with 5:1 because I wanted to be able to go up or down depending on how it rode with a 5:1. I could go to 11 or up to 13,14,15 etc. 10 tooth wore down my 530 chain.

Surpluscenter.com had chain and front sprockets and master links and a chain break for under $50. That's not bad for experimentation.

I might go with a different ratio but higher than 60 is just too big for my setup.

Read an old post of mine:
HTTP://blog.evfr.net/?p=95

Brutus
20 June 2012, 1810
If you were ever curious what happens when you experience a chain failure while riding this should illustrate it perfectly.

<iframe width="420" height="315" src="http://www.youtube.com/embed/SHY72ZvA-mI" frameborder="0" allowfullscreen></iframe>

podolefsky
20 June 2012, 2006
A few pounds to 400-500 pounds. Apple-oranges?

Every ounce counts.....

True - every little bit helps...a little bit.

When you're going constant speed, shaving weight doesn't save you any energy (except for the tiny amount of difference in rolling resistance). It only really matters when you're accelerating.

The energy of a rolling hoop shaped object (like a chain wrapped around a sprocket) is twice what the energy would be if it weren't rotating. The difference in mass between a 530 chain and a 420 chain, both wrapped around a 65 tooth sprocket, is about 1.6 lb. So basically, when you're accelerating, switching from 530 to 420 is like taking about 3 lb of non-rotating weight off the bike. Not zero, but not much...if you and your bike together weigh 600 lb, it's about 0.5%.

Since energy is proportional to mass, you save about 0.5% on energy during acceleration. Another way to think about it is that if you accelerate from 0-60mph in 10 sec, you save about 100 watts. Again, not zero, but not much...and it's only when you're accelerating.

I suppose if you're drag racing this would be enough to worry about.

Interesting to note that if you replace all your lights with LEDs, you save about the same amount...except you save it the whole time you're riding (assuming you ride with your lights on).

podolefsky
20 June 2012, 2301
OK - sorry for the big fuss about weight. Coming from the cycling world, where people will shell out $200 to shave 10 grams, I'm overly sensitive to this weight weenie stuff. And don't get me started on the rotating weight thing...really, don't.

There are good arguments for 420 - you fit rear sprockets with more teeth, they're lighter (slightly), less friction. It's a bit difficult to find front sprockets because #40 is too wide, and #41 isn't quite the right roller size (but maybe close enough to work). But it's also hard to get 520 front sprockets (with 7/8" bore). 530 is the easiest size if you just want to use off-the-shelf sprockets.

I thought one place to look would be what's speced on other bikes. 420 chain is used almost exclusively on bikes under 100 cc. 125 cc and up mostly have 520s. A Ninja 250 has a 520.

The Zeros that have a 420 chain use an Agni, which only makes 36 ft-lb. That's about 1/2 the torque of the ME1003 or AC-20.

The Brammo Empulse uses a 520.

EVcycle
21 June 2012, 0538
If you were ever curious what happens when you experience a chain failure while riding this should illustrate it perfectly.



Nice Arse shot. :O Not a commuting electric bike I gather. He needs a 630 chain! :)

DRZ400
21 June 2012, 0656
DRZ: Did you have make any modifications so it fits in Ninja 250 swing-arm? No, only had to mod the bracket for the chain guard. The sprocket is for 420, had it been a 520 it would have looked size of pizza.

Allen_okc
21 June 2012, 0923
If you were ever curious what happens when you experience a chain failure while riding this should illustrate it perfectly.

<iframe width="420" height="315" src="http://www.youtube.com/embed/SHY72ZvA-mI" frameborder="0" allowfullscreen></iframe>

OK that looked like it hurt - ive been chain whip myself, by a factory chain on a class B dirt bike, it happens when it happens no matter what size chain...

Allen_okc
21 June 2012, 0929
my thought for Hugues who has a full size chopper, he will definitely exceed the 500lb weight of machine. a heavier chain might a good thing for you...

:p myself im running a 420 set up with a Harley Davidson/Honda Shadow "Harlonda" or "Honda Davidson" components...

Hugues
21 June 2012, 1039
my thought for Hugues who has a full size chopper, he will definitely exceed the 500lb weight of machine. a heavier chain might a good thing for you...

......
Definitely. 850 lbs incl driver actually.

podolefsky
21 June 2012, 1107
Definitely. 850 lbs incl driver actually.


Maximum motor torque is what matters, I believe. Doesn't matter how much your bike weighs - if the motor can only put out 75 ft-lb, that's what the chain is going to feel. If you put a tiny little 5 ft-lb motor on, you could use a bicycle chain.

The exception is that if the bike is really light, or geared really low, then the motor won't load up enough to actually produce maximum torque.

But...a 600 lb cruiser with a 420 chain would look, well, kinda weird (IMO).

Allen_okc
21 June 2012, 1335
:confused: i dont know the 420 chain looks pretty hefty for my motorcycle - by the way all my batteries are here, weh hew...

:rolleyes: sorry Hugues didnt mean to through that in on your thread, got a moment of excitement - :O as Noah slapppppps me upsides the head...

Hugues
24 June 2012, 0326
ok, i'm back on this topic.
Discussed with the bike shop about the chain, he would see a 520 fit nicely on this one.
He's not too keen to go on 420, he mostly used belts or sometimes 530 chain on the Harley and other bikes he's customizing.

So i made myself a little table showing gear ratios, sprocket diamters, speed vs rpm and ratio....
from what i could read, 9 tooth sprocket for a 520 chain is probably not possible, but 10 is.

If i stick to my 8:1 ratio, that gives 80 teeth at the back, that's about 16 inches rear sprocket diameter, my rim is 18 inches diameter, so it fits, although it might not look that great.

with 8:1 i can reach my max speed target of 120 km/h at 7500 rpm, so fine, although i could build a bit of margin here I guess.

QUestions:
- how can i check if my motor will run in it's most efficient sweet spot with that ratio ? When i will want to go for a long ride, i'll do most of my driving between 60 and 80 km/h. SO i guess i should adjust my gear ratio to have the most efficient speed of the motor fall between these speeds, right ? Or is it not realistic ? Motor data can be seen here, although i'll be running at 96 V:
http://www.electricmotorsport.com/store/pdf-downloads/AC_Drives/AC20.pdf
Anyone know at which RPM is this motor the most efficient ?
- then, how about peak power ? at 48 V, this motor peaks at around 2'000 rpm. Is it fair to assume that peak power will be around 4'000 rpm runnign at 96 V ? . If so, should I adjust my ratio to hit peak power around my cruising speed of 60-80 km/h ?

or is it just newbie's worries ? :)

Skeezmour
24 June 2012, 0804
Huges those charts very alot depending on RPM, load, temprature ect. 2000rpm may be the best at 200 amps but not at 300. those charts don't tell the whole story. (check out the UQM charts to get an idea).

podolefsky
24 June 2012, 0937
LIke Skeezmour said, you need a 2D efficiency map to really know for sure. But basically, efficiency tends to be highest around the peak power RPM, and only drops a few % withing a couple 1000 RPM of that. So you want to gear for cruising speed to be around peak power, just as a rule of thumb. That would be about 6:1 for your cruising speeds.

Max RPM doesn't necessarily tell you maximum speed. Max speed is limited by motor power at that speed...I'm not sure if the AC-20 will produce enough power for 120 km/h geared 8:1. The data I have says it will just do it, barely, but that's with a lighter bike, and only "in theory".

Another thing to consider is how the bike feels at those speeds. If you gear really low, then at your cruising speed you won't have much power left over if you need to accelerate quickly. The bike will feel great off the line, but then performance will be crappy at cruising speeds (like if you hit hills or try to pass people).

Yeah, peak power should RPM should be roughly proportional to voltage.

One more thing - a 10 front spinning up to 7500 RPM is asking for trouble. I'm running an 11 with a 72V system, which means lower RPM. Still, I'm pushing the limits. A 10 is likely to bind and wear out quickly at high RPMs.

Hugues
24 June 2012, 0953
ok, got it all clear, well almost.

so let's stay at 11 then in front, with a ratio of 7, i still can fit the corresponding sprocket at the back (85% of the rim diameter), that'll give:
- my max speed of 120 km/h at 6600 rpm, so some margin till 7500 rpm
- 0 to 60 mph in 7.1 sec, this at 72 V, so 96 V should be 6 something, that's all right
- assuming peak power is at 4000 rpm @96V, i get 72 km/h, my average cruising speed, that's all right too

so we'll start with this , and 520 chain

thanks a lot guys for your feed-back , and patience ! :cool:

podolefsky
24 June 2012, 2236
ok, got it all clear, well almost.

so let's stay at 11 then in front, with a ratio of 7, i still can fit the corresponding sprocket at the back (85% of the rim diameter), that'll give:
- my max speed of 120 km/h at 6600 rpm, so some margin till 7500 rpm
- 0 to 60 mph in 7.1 sec, this at 72 V, so 96 V should be 6 something, that's all right
- assuming peak power is at 4000 rpm @96V, i get 72 km/h, my average cruising speed, that's all right too

so we'll start with this , and 520 chain

thanks a lot guys for your feed-back , and patience ! :cool:


That seems like a good place to start.

Can't wait to see this project really start coming together.

EVcycle
01 November 2012, 1200
As a side note, the 420 ran without issue all weekend at the Savannah race. I am keeping an eye on it and if it shows
and sign of a problem, I will be upping it to 520.

So far so good... :)

Athlon
02 November 2012, 0931
high RPM have very low efficiency both for iron loss (high Hz) and for field weakening current , I think an AC-20 can run up to 5000 rpm but not more , at higher rpm power will decrease and are usable only for short time ( eve if continuous power is low you can still have a good peak power) , you best gear ratio is probably more in the 1:8 zone than 1:7 for a responsive bike , but you will loose some top speed.

You can have the best efficiency out of an induction electric motor when iron loss are equal to cooper loss , iron loss goes up with Hz ( Rpm) , copper loss goes up with current ( I2r) , so with longer gear you can keep RPM low but you will have higher current , a short gearing will keep the current down but will cause high RPM.

You should ask to the motor factory what kind of iron lamination they used for the motor , if is M400-50A or better then the best way is for sure to go up with rpm and keep current low

Btw I'm developing a lower Rpm 6 pole induction motor for bike , if the AC-20 is too small for your bike and Emrax are too expensive this may be an option.

podolefsky
02 November 2012, 1258
An AC-20 will run up to 8000 RPM, and it's only limited by the controller (the Curtis you can get now only goes to 130V max, and you can't set the synchronous speed above 8000 RPM).

I have mine at 5:1, with 76V nominal, and that feels about right. With 102V nominal 7:1 would be OK, but 8:1 would limit top speed and torque available in the 40-60 mph range. It's a matter of what you're going for, but at 8:1 I think you'd be at the limit for highway riding, which isn't very safe. Around town it would be a blast though, lots of torque at the rear wheel.