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I Mousetrap race car is not working

  1. Feb 28, 2017 #1
    Hello, so for school I'm building a mousetrap with my group for a project, but our car isn't moving. We filmed it snapping, and it doesn't seem like it is because of friction, since the axle spins pretty well. We thought that it was because the thing that holds the axle bends, but after fixing it, it still doesn't roll. We tested it without the mousetrap being set, but when pushing the dowel towards where the mousetrap would snap, it did not move the wheels or the axle. We noticed that when pushing it back, it did roll. I have a picture of it set, but we're not quite sure why it still doesn't work. Could anyone help? Thanks!
    upload_2017-2-28_18-51-10.png
     
  2. jcsd
  3. Feb 28, 2017 #2
    Oops did I post this in the wrong place? Sorry!
     
  4. Feb 28, 2017 #3

    fresh_42

    Staff: Mentor

    Since the axis spin, it's likely a problem with friction. Have you considered to test it on a different surface, or clue some rubber like tires on the wheels?
     
  5. Feb 28, 2017 #4
    We looked at it again, but the axle doesn't spin at all, the string just pulls it up, and then down. But, when we wound it the other way (the way the wheels would roll), the wheels spun, just in the wrong direction. Do you think we attached the mousetrap on the wrong way? Thanks so much!
     
  6. Feb 28, 2017 #5

    fresh_42

    Staff: Mentor

    Difficult to tell from the picture, but go ahead and test it. It's probably sufficient to change the direction of the winding rather than to turn the trap. The principle is simple: the energy stored in the spring has to be transported to the axis. so it's always a matter of traction and friction.
     
  7. Feb 28, 2017 #6
    Oh okay thank you so much!
     
  8. Feb 28, 2017 #7

    fresh_42

    Staff: Mentor

    The release of the stored energy is probably very sudden. So either you invent some delay mechanism to get an energy supply for a longer time period, an intermediate storage if you will, e.g. a ribbon that get spun first and releases its energy afterwards, or you must ensure there will be no wheel spins anywhere, neither on the cords you use, nor on the axis. It's the same effect as with spinning wheels in car races.

    And watch out your fingers! :wink:
     
  9. Feb 28, 2017 #8
    I see! Thank you so so much!!! :smile:
     
  10. Mar 1, 2017 #9

    haruspex

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    Science Advisor
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    I cannot see from your diagram where the string goes. It looks like it passes under a pulley of some sort mounted on the front axle, then proceeds to a bobbin at the rear, but not in a straight line.
    Please explain the structure there.
     
  11. Mar 2, 2017 #10
    Now it drives, but it didn't move far. We noticed that after the highest point the dowel goes to on the mousetrap, it stops pulling the string. Did we do something wrong? Thanks!
     
  12. Mar 2, 2017 #11
    It is attached to one side of the axle, the right side, and there aren't really any pulleys, or anything, it is just attached to the axle. Thanks!
     
  13. Mar 3, 2017 #12
    We aren't quite sure why it doesn't work, but we think it is because the axle is too thin, and the wheel spins too fast. The axle is made of one of those barbecue skewers, and the car is about 30 by 12 cm
     
  14. Mar 6, 2017 #13
    Sorry for bothering again, but we changed the thing attaching the axle to the chassis to cardboard, and now when we pull the string the wheels won't spin that much, maybe 3 rotations before they stop. Is this because there is too much friction or is it still the mousetrap? And if it is, how should we fix it? Thanks!
     
  15. Mar 7, 2017 #14

    gneill

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    Staff: Mentor

    I think you need to provide some drawings of the mechanism so that others can evaluate it. Just saying you changed something and it doesn't work doesn't provide enough information for any meaningful discussion.
     
  16. Mar 7, 2017 #15
    It looks like a very strange design. It looks like the spring-rod is pulling the string mostly in a direction that is perpendicular to the string, so it isn't really applying much tension to the string. A lot of movement is wasted in slack motion of the string.
     
  17. Mar 8, 2017 #16
    I'm sorry (I'm dumb), but I don't really understand what you mean? Thanks!
     
  18. Mar 8, 2017 #17
    It worked!!! Thank you everyone!!!!
     
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