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Thread: Brammo Shifts Gears (article)

              
   
   
  1. #21
    Empulse R #24 frodus's Avatar
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    but since efficiency is on a curve, you need to have a torque curve showing the eff at that RPM.

    Most reliable way is a Dyno, which none of us "currently" have.... lol... waiting for it Noah!
    Travis

  2. #22
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    My top speed is about 70 mph. It takes around 9 HP. My bike will actually produce over 30 HP, but not at 4000 RPM.
    Do you mean that it needs 9hp to get you to 70mph, or that it needs 9hp to keep you at 70mph?

  3. #23
    Seņor Member podolefsky's Avatar
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    Quote Originally Posted by sparky_mark View Post
    Do you mean that it needs 9hp to get you to 70mph, or that it needs 9hp to keep you at 70mph?
    Technically, both. 9 HP will keep you at 70 mph, and if you're willing to wait a while it will get you there too.

    I also have an electric scooter. It makes about 4 HP peak, it'll go 50 mph.
    - Noah Podolefsky -
    The GSX-E

  4. #24
    Seņor Member podolefsky's Avatar
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    Quote Originally Posted by frodus View Post
    but since efficiency is on a curve, you need to have a torque curve showing the eff at that RPM.

    Most reliable way is a Dyno, which none of us "currently" have.... lol... waiting for it Noah!
    True. I have that curve. Assuming the data is right, my D&D is 65% efficient at 480A and 1800 RPM, where it makes peak power of about 30 HP. This also depends on the fact that my battery pack sags to 68V at 500A. In D&D's data, their pack sags to 58V at 480A, so they only get 25 HP out of the motor.

    Anyway, bottom line is - it's complicated, but volts*current*efficiency is in the ballpark. It's also bhp (at the motor), not wheel HP...

    Speaking of that dyno...yeah...I'm working on it.
    - Noah Podolefsky -
    The GSX-E

  5. #25
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    Technically, both. 9 HP will keep you at 70 mph, and if you're willing to wait a while it will get you there too.
    I think I see what you mean.... Are you saying that your bike uses 9hp to overcome rolling and wind resistances at 70mph, and also makes 30hp peak but only at lower rpms?

  6. #26
    Seņor Member podolefsky's Avatar
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    Quote Originally Posted by sparky_mark View Post
    I think I see what you mean.... Are you saying that your bike uses 9hp to overcome rolling and wind resistances at 70mph, and also makes 30hp peak but only at lower rpms?
    Exactly. HP increases to a peak at mid RPM, about 2000 on my motor, then starts to fall off again. Top speed is where the power required to overcome air and rolling drag equals the HP that the motor can put out. If you gear lower, you get back down into a higher HP band and can go faster (but get slower acceleration from a stop).
    - Noah Podolefsky -
    The GSX-E

  7. #27
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    If you gear lower, you get back down into a higher HP band and can go faster (but get slower acceleration from a stop).
    And if you had a transmission, you would have both good acceleration and good top speed

    One of the things that has always annoyed me about the whole 'transmissions are good/bad' argument is that people would say things like "you pick your drive ratio to give good acceleration or good top speed. you can't have both". These same people would then go on to say that electric bikes don't need a transmission! The two statements clearly contradict each other to some degree. Obviously your top speed will always be governed by your peak hp.

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