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Review my mouse trap car design

Discussion in 'Other Off Topic Forum' started by nsxnick, Feb 24, 2010.

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  1. nsxnick

    nsxnick Formula 3

    Jul 24, 2001
    1,481
    Detroit
    Full Name:
    Nick
    #1 nsxnick, Feb 24, 2010
    Last edited: Feb 24, 2010
    I'm entering a mouse trap car competition at work. I'm going for longest distance.
    Please review my design.

    http://img72.imageshack.us/img72/9079/21421613.gif

    I have the parts and will begin construction soon. The lever is a 3 feet carbon fiber hollow rod. The axel is solid 3/16" aluminum on ball bearings. The frame will be balsa wood. I don't know about the wheels yet. They need to be larger and lighter than LP records or LD's. I may make wagon wheels out of balsa. They provided the mouse trap. It cannot be modified in any way and must be the only thing that drives the car.

    The counter weight dangling from the top is only to offset the weight of the lever and not to add torque to the wheels (you think the judges will buy that?). The weight is designed to drop off when the lever reaches vertical.

    The large half circle is there so that the string travels the true length of the arc. I have not seen this done on any other car I've seen online.

    The axel will have varying diameter discs that the string will wrap around to act as a transmission.

    Ideas welcome.
     
  2. smokeyrabbit

    smokeyrabbit Rookie

    Nov 2, 2009
    39
    OH
    Full Name:
    Dave
    #2 smokeyrabbit, Feb 25, 2010
    Do you have to have more than 2 wheels? In high school I made a mouse trap car out of 2 LP's, a rebuilt bicycle wheel axle, and a relatively short lever arm (smaller than an LP radius) and they couldn't find a hall long enough to test it due to it's momentum and low rolling resistance. It went all the way across the gym diagonal and it still ran into the wall at the other end. It depends on your rules, but everyone always focuses on the lever part of the design instead of on making it go. Also, use a cone rather than a stepped transmission. Get an axle that already is designed to go with little friction.
     
  3. Prova7

    Prova7 Formula Junior

    Nov 17, 2003
    257
    Dallas, TX
    Full Name:
    DamonB
    #3 Prova7, Feb 26, 2010
    How much string you can pull off the axle determines over what distance the vehicle remains "powered". However the long lever arm on the trap means there is relatively little force from the springs exerted at the tip of the lever. If limited to a single trap you may find there is not enough power available to get the vehicle rolling due to the long lever arm. Instead go with a shorter lever and the thinnest axle you can make do with. Put a pin or hook on the axle and a loop at the end of the string. The loop on the string engages the hook and ensures the string cannot slip. Carefully measure the length of the string so that when the trap is fully released the string is pulled completely free from the axle. Distance now is all about maintaining momentum. Add weight near the outside circumference of the wheels to turn them into flywheels and the car will coast for hundreds of feet.

    Larger wheels increase the distance traveled for each revolution of the axle but they also result in a decreased mechanical advantage and make it difficult or impossible to get the vehicle rolling. Smaller, weighted wheels however have greater mechanical advantage for greater acceleration and will maintain their momentum over a longer distance. The diameter of the wheel does play an important role but the key is accelerating the vehicle and then maintaining that momentum once the powered phase is over. Wheels which are too large will not allow momentum to build high enough as they sacrifice too much acceleration. Most overlook this and instead focus on staying powered over a long distance. Momentum wins.
     

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