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Building a small electric vehicle

  1. Nov 6, 2007 #1
    I have recently come across a few electric motors (donated to me for my school's Technology Club), two from a wheel chair with gear reduction and another power window motor from a car. The power window motor has a worm gear on it of course, which is directly attached to the axle, but can be cut off.

    I was wondering, would either of these motors have high enough torque to be useful in making some sort of small electric vehicle? If the power window motor is powerful enough, I would want to make a mini bike with it and a chain drive to a larger gear. Since all of the label has been worn off of this motor, I have no idea what kind it is nor what torque it has, but I'm looking for a general estimate. If it's not up to this heavy task, I would want to make a small RC vehicle with it. Because the wheelchair motors are bulky and require 24 volts, I am not as interested in them as much as the window motor.

    I have seen plans on a bar stool racing site for modifying an electric starter motor from a car to be run continuously and, it is claimed, power one of these contraptions up to ~30 MPH. Is modifying one a realistic solution, or are there others? Thanks!
  2. jcsd
  3. Nov 6, 2007 #2


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    I would imagine that the window motor would not be capable of handling the continous duty cycle required by an electric vehicle. However, the wheel chair motor may.

    I'm not sure on the torque output of the window motor, but obviously the wheel chair motor has enough torque to transport a frame and at least one person. Of course, it wouldn't be very fast!
  4. Nov 6, 2007 #3
    I wonder if you had four electric wheel chair motors installed into a soap box derby car if it would move any faster.

    The "controller" is the most important part right?

    Have you seen this video?

  5. Nov 6, 2007 #4
    kach, thats a cool video. I have seen another vehicle, the Killacycle, which is capable of very high speeds and able to charge in <5 minutes. The batteries on it are really high-end. I think I'll try to go the starter motor route, although it requires some extra work on the motor, as mentioned in these plans. Has anyone here made an electric vehicle themselves?
  6. Nov 8, 2007 #5
    I'm thinking of using a car starter motor to power an electric mini-bike project. Does anyone have an idea how many amps a starter motor could draw if it was to be on a bike moving ~300 lbs. (max), with a gear and chain drive to reduce the speed and increase the torque (ex. 1/2 speed, 2x torque)?

    I'm looking for an estimate because I want to get a speed controller for one, but don't know what the max amperage should be, and it makes a BIG difference in which speed controller I buy. Thanks!
  7. Nov 8, 2007 #6


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    That is one freaky video, Kach. As a gas-burning speed freak, I'm very impressed (if it's legit).
    TheRyan, I have 3 wheelchair motors that are quite impressive. They cost over $300 each originally, and I got them for $10 each from an elderly fellow who salvaged them from the chairs of friends who no longer needed them. They're 12 VDC, 1/2 hp with worm-drive to a chain sprocket. Each has 2 field coils, with 6 wires coming out of it, originally to be connected through a joystick to the battery. If the wires are hooked up one way, the coils are in series; the other way puts them in parallel. You can thus double the torque at the expense of rpm's, or the opposite for speed. I wish that I had a few hundred more lying around.
    As to how many amps a starter motor will draw, that depends upon the load. When I first rebuilt the motor in my Roadrunner, with the compression ratio kicked up to 12 1/2:1, it fused the windings in the starter. Had to get one custom wound, and it pulls 1,000 amps to start at -35 C (when plugged in; don't even think about it otherwise).
  8. Nov 8, 2007 #7
    Thanks for the info, Danger. Pulling 1,000 amps to start the motor is a lot, but then again you said it's got a 12.5:1 compression ratio, which is quite a bit higher than most vehicles. The wheelchair motors I had were originally connected to a joystick controller, with forwards, backwards, and 2 speeds. I still need to test them, but I'm guessing they can pull quite a bit, especially if they're meant to carry someone who is possibly overweight and would put a ton of stress on the machine. The best part is they aren't all that heavy either, but the problem is the batteries. So far I've found a 30A continuous 24V max rated DC speed controller which is small enough for what I want to do, but I think I'll need a higher rating than that.
  9. Nov 8, 2007 #8


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    I really have no clue about power supplies, but I think that you're correct in your assumption. The wheelchairs that these things came out of used regular lead/acid car batteries, which are rated for something like 350 amps cold-cranking amps. I don't know what the regular operating amperage would be, but I'm pretty sure that 30 wouldn't do it. Since electricity isn't one of my areas of knowledge, I don't even know how the fact of yours being 24 VDC units would affect that. Since most small aircraft run 24 volt systems, maybe a battery setup from your friendly neighbourhood Cessna dealer would be appropriate.
  10. Nov 10, 2007 #9
  11. Nov 12, 2007 #10
    talkin about the amperes a starter motor drinks, its 35 amps in a normal car starting during a room temperature startup
  12. Nov 12, 2007 #11
    Thanks ank_gl! Guess I'll need to look for a fairly hefty speed controller then...
  13. Nov 12, 2007 #12
    u also need such heavy batteries ryan. remember the size of batteries increases as the wattage increases. or else if you have got $$$ you can go for lighter battery packs like Li-ion cells etc
  14. Nov 12, 2007 #13
    I know I would need more batteries, and Li-ion are really not an option (although they are much better) due to the large price difference.
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