Scooter Motor Project

Discussion in 'The Projects Forum' started by bgm94, Nov 22, 2011.

  1. bgm94

    Thread Starter New Member

    Nov 21, 2011
    3
    0
    I took apart a scooter to make a small electric car for something i'm building in woodshop. I have a 36V Motor that is 17.8 amps and 500 watts, and i need to find a way to make a throttle device. i was thinking about using a potentiometer of some sort. how would i complete this for cheap.

    My setup currently is a push button switch wired in series to 3, 12v batteries, and that is connected to the motor.

    [​IMG]
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    You might go to the junkyard and scrounge a Throttle Position Sensor from the throttle body of one of the cars. TPS'es are variable resistors that have a travel of just about 90°, and they are far more reliable than a standard potentiometer that you would buy at an electronics store. A standard pot has about 270° of travel, so it would be difficult to use for a throttle.

    When you get the TPS, you might just as well grab the accelerator pedal, the cable assembly, and the linkage between the cable end and the TPS - you're going to need stuff like that anyway.

    Your front wheels are not adequate for your intended use. They are the cheapest lawnmower replacement wheels that one can buy. You will be subjecting them to far more weight than they were designed for, at greater speeds than they were designed for, and far more side loading than they were designed for. If you hit a bump or chuckhole, you'll probably break the hubs of the wheels. The steering will likely be quite poor.
     
  3. strantor

    AAC Fanatic!

    Oct 3, 2010
    4,302
    1,988
    If you just use a pot to vary current to the motor, then at high throttle or wide open throttle, you are going to have LOTS (relative to what pots are generally capable of)of current flowing through the pot. 36V @ 17.8A works out to 640W, not 500, and you can expect it to draw a lot more amps when stalled, or with a high load on it. expect that more than 1KW will be going through the pot @ WOT, and thats way too much. I'm not sure about a throttle position sensor, but I assume the same is true there, since it is a sensor, and not a power component. In order to do this simply with a pot, it would have to be a very robust (large, expensive) pot.

    I would recommend a small PWM controller.

    BTW cool little cart there.
     
  4. shortbus

    AAC Fanatic!

    Sep 30, 2009
    4,013
    1,531
    @SgtWookie - a throttle position sensor would need to be used with some kind of speed control. They are only made to supply a input to a computer, and will not have enough current carrying capacity to control a motor on there own.
     
  5. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Yes, I meant to say that. It's just a means of providing an input to a motor controller. A standard pot just would not work very well, which is the reason for digging around for a TPS.
     
  6. MrResistor

    New Member

    Nov 28, 2011
    1
    0
    I think what you want here is a pulse width modulation circuit. A TPS could be used to vary its output, but I think you could use a pot as well. Current consumption is a consideration as well. A rheostat made from nichrome wire might work as well, but you would waste a lot of current as heat.
     
  7. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,172
    397
    Past exp on electric tractor, pre association with AAC: Add 360 mΩ in series with motor. Use wire from batt.- to motor - for current monitoring[ do not over filter signal- cost me 4 FETs]. Use DPDT, center off switch for reverse. Use multiple FETs with total rating well over 100A. Look into Sgt Wookie's voltage controlled PWM ckt.
     
  8. bgm94

    Thread Starter New Member

    Nov 21, 2011
    3
    0
    Thanks for all the answers! thinking about probably getting a PWM controller, anyone have a link for one rated for 36v and 17 amps?
     
  9. bgm94

    Thread Starter New Member

    Nov 21, 2011
    3
    0
    actually, what if i just purchase a scooter controller and throttle from ebay for about $40 total?
     
  10. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    I don't see why a scooter controller wouldn't work - as long as the voltage and current ranges are compatible.
     
Loading...