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Homework Help: I'm building a cart, need help

  1. Dec 26, 2004 #1
    I'm building a cart which must be powered by TWO elastic bands only,

    it must ran at least 2 meters, which isn't hard, but my goal is at

    least 12 meters, which isn't very hard either(the longer the better).

    I have some ideas of how to power the cart and please help me to

    choose and give me some more ideas!

    (it must be in 3/4 wheels)


  2. jcsd
  3. Dec 26, 2004 #2
    The basic "rubber band car" is two axles with wheels on each end, and a rubber band wound around the axle to spin it. You anchor one end of the band to the car, wind up the wheels in reverse, and when you release the car the rubber band spins the axle and wheels and it rolls forward.
  4. Dec 27, 2004 #3


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    One option would be to have a gear driven axle. The rubber band would be attached to a fixed spot on the cart chassis, then over to the gear driving an axle. This would probably provide the most distance, as the rubber band can be twisted quite a bit wihtout changing it's overall legth very much. You should be able to find this stuff in a radio control / hobby store.

    If gears and pullyes are not allowed I'd recommend wrapping the rubber bands under the front axle and over the rear axle so that both axles are being pulled at the same time. I would not have the rubber bands attached to either axle, so they just drop off once they've done their job, and the cart can then coast.

    If letting the rubber bands fall off isn't allowed, then attached the rubber bands to the center of the car so they don't interfere with the cart as it coasts.

    You'd have to manually initiate the wrap of each axle since the rubber bands aren't attached.
  5. Dec 27, 2004 #4
    If it is only specifed that the car be powered by the bands, hook the two bands together, put a hook on the front of the car and pull the car back letting it fly like a sling shot! I wouldn't be surprised to see 15 or 20 meters.

    If you use the bands as a motor, make sure you have just enough weight to press on the drive wheels, and the wheels should have enough traction to transfer the energy stored without slipping too much early in the trip.
  6. Dec 27, 2004 #5
    Thank you for your suggestions! Can you guys please draw me some diagrams?
    You can upload your img at www.imageshack.us
  7. Dec 29, 2004 #6
    quick question...say there was only 1 elastic band (to make things simple) would the car travel furthere if the elastic spun the front axle or the rear axle? (not both)
  8. Dec 29, 2004 #7
    it won't matter but front axle is more stable.
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