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Momentum Powered Uphill Roller? Help

  1. May 13, 2011 #1
    Momentum Powered Uphill Roller!? Help!!

    Basically, I need to make a rubber-band powered device that will roll up a hill. The hill is very very shallow, and 3 meters long. I CANNOT simply use something that utilizes a center of gravity (i.e. the double cone roller).

    Right now I have 2 liter bottle, with a hook in one end. The hook is mounted to the bottle in a way that it DOES NOT spin. A rubber band goes from this hook inside the bottle to a weight in the center of the bottle. The weight has a rod attached to it, that goes straight through the center of the cap. This rod and weight CAN spin and it does. But, when I test it on just a flat surface, the bottle just jumps a little and settles, not rolling at all.

    Another way of showing my design is like this:


    The parenthesis being the cap and bottom of the bottle. The zero is the weight. The dotted line on the left is a rubber band, mounted to the bottle on a non-rotating hook. The dotted line on the right is a rod that goes all the way through the bottle, and has a small handle at the end for twisting up the rubber band.

    The question is, how can I fix this to make it move, and eventually to roll up a hill??
  2. jcsd
  3. May 13, 2011 #2


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    Re: Momentum Powered Uphill Roller!? Help!!

    It looks like the old thread spool cars we used to make as little kids.
    But the "small handle" needs to be long on one end so it pushes against the floor and provides torque to make the bottle rotate.

    Perhaps that doesn't meet your description of "momentum powered". What exactly does that mean?
  4. May 13, 2011 #3
    Re: Momentum Powered Uphill Roller!? Help!!

    Can you post a picture or video of the device?
  5. May 14, 2011 #4
    Re: Momentum Powered Uphill Roller!? Help!!

    Basically the idea is that somehow the rubber band needs to be wound up, and then when you let go the weight inside, thats attached to the rubber band spins. I was thinking that the weight should be a lot heavier than the rest of the project as a whole, so that its less "work" for the rubber band to spin the whole project than just the weight.

    In the pics, the weight is the big thing covered in duct tape. (It was a bolt, which I later duct taped two metal rods to just to increase the mass) Its held in place by the white plastic you see, which has a whole in it, and is oiled up. Very little friction here. The rod goes through that and throught the bottle, out the other side. Thats the handle you use to spin the weight. The rubber band goes between the stationary hook on the cap, and the hook on the tip of the weight you see in the pictures.

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  6. May 14, 2011 #5


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    Re: Momentum Powered Uphill Roller!? Help!!

    So you are trying to get the bottle to rotate one way while the weight rotates the other way, conserving angular momentum, right? Is this what you mean by "momentum powered"? It seems more like "elastic powered" to me.

    The small handle must not slip on the bottle - do you have a slot or something to hold it?
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