Power in Flux
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Thread: Transmissions. yeah.

              
   
   
  1. #11
    Seņor Member podolefsky's Avatar
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    Quote Originally Posted by mechanic View Post

    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.



    - Noah Podolefsky -
    The GSX-E

  2. #12
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    Quote Originally Posted by podolefsky View Post
    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.
    Last edited by mechanic; 01 January 2012 at 1844. Reason: error

  3. #13
    teddillard
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    Quote Originally Posted by mechanic View Post
    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.
    Last edited by teddillard; 01 January 2012 at 1725.

  4. #14
    Senior Member Skeezmour's Avatar
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    Moral of the story is that there is no single always 100% correct way to do it. Thanks for posting it Ted.

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    Quote Originally Posted by teddillard View Post
    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...

    Anyway, more here: http://evmc2.wordpress.com/2012/01/0...s-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?

  6. #16
    teddillard
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    Quote Originally Posted by Skeezmour View Post
    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.

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

  7. #17
    Old EV Racer EVcycle's Avatar
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    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!
    EV Ed
    Never let being a responsible adult get in the way of passion and curiosity.
    Juiced Drag Racing
    Motenergy.com
    Ev album 2456, 2458, 2457, 2681, 3456, 3630

  8. #18
    Senior Member SplinterOz's Avatar
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    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
    SplinterOz
    From Australia'a Capital
    http://rgelectric.wordpress.com/

  9. #19
    Senior Member Brutus's Avatar
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    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 plantsDSC_0007.jpg
    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

  10. #20
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    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?

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