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Comments 5
  1. — Jesse    Feb 20, 2007 17:14 PM    #

    Hello Again,
    I am still planning out my EV and I appreciate your help. I was thinking about an El Camino as the donor vehicle but I know this car is pretty heavy. To save weight, I was thinking I could remove the engine and transmission together and beef up the differential. Upon crunching some numbers, I discovered that even with somewhat small tires the axle would only have to spin about 1500 times per minute to achieve 90 mph. It seems like a motor could be linked to it with a 1:1 ratio and be just fine. Why use a transmission or differential at all?

    Thanks again,


  2. Seth    Mar 06, 2007 11:35 AM    #

    There’s an El Camino in the
    EV Album – you could ask the owner www.evalbum.com

  3. — peter gabrielsson    Mar 06, 2007 14:38 PM    #

    You’d want to use some transmission to allow the motor to spin at higher RPM. Power is torque times RPM, so if your motor is rated at say 50hp at 5000 RPM, then running it at 1500 RPM gives you only 15 hp, not nearly enough to propel you at 90 mph.

    You could ofcourse get a motor designed to run at 1500 RPM but it would have to be very large to give enough torque to propel your vehicle, this translates to either very heavy or very expensive.

    Using the differential you’d get something like a 4.11 gear ratio, meaning the motor will spin at ~6000 rpm at 90 mph. This setup can be direct driven by a 11”-14” forklift style traction motor, which are both cheap and plentyful.

    You wouldn’t exactly get up to 90mph though since this size motor tends to top out at 4500 rpm. If you truly need 90mph direct drive then two 8” motors in series direct driving the diff is your best bet.


  4. jerry Halstead    Mar 09, 2007 08:18 AM    #

    DC motors generate peak torque more or less at a standstill, as RPM goes up the available torque begins to go down. A torque chart like this (pdf) for the FB-4001A helps to demonstrate this. Here’s a similar chart for a Siemens AC motor, which I can’t say that I fully understand but appears to show a wider torque/rpm range.

    Someone had written a while back that they thought using a stock, or slightly modified, differential would probably work. I’ve seen a Solectria pickup with the motors (2) mounted directly to the differential. The differential was flipped so the “input” was pointing backwards, allowing more clearance for the motors. If I remember correctly Solectria used AC motor/drives in their EVs.

  5. — Charles    Mar 09, 2007 12:58 PM    #

    heres some pics of a solectria pickup
    The motors do appear to be AC