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Mouse Trap Cars: Adjusting the Pulling Force

January 20, 2012

Pulling force is a critical component that determines the gearing of a mousetrap vehicle. Learn various ways to adjust the pulling force of a mousetrap racer.

Changing the length of a mouse trap's snapper (or lever arm) is how you control a mousetrap vehicle's acceleration and/or travel distance. Different lengths of lever arms can be used to increase and/or decrease the pulling force and change the amount of string that can be pulled off the drive axle. Changing the length of the lever arm does not change the total energy and/or the torque produced by the mouse trap but it does change the pulling force applied to the drive axle. Longer lever arms will have less pulling force than shorter lever arm but longer lever arm will pull more string from the drive axle than shorter lever arm. Changing and/or attaching a lever arm to the mouse trap is the number one way to control a mousetrap vehicles performance.

bonus tip: the length of the lever arm determines the pulling force and the length of string that can be wrapped around the drive axle.

Lever Arm Basics

Changing the length of the mouse trap's lever arm controls the pulling force and the amount of string that can be wound around the drive axle. Making the length of the mouse trap's lever arm longer will decrease the pulling force but increase the amount of string that can be pulling from the drive axle. Shortening the length of the lever arm increases the pulling force but decrease the amount of string that can be pulled from the drive axle. Understanding this basic concept is the key to building a successful mousetrap powered vehicle. Before you build your first mousetrap powered car you will have to identify the objective of the challenge in order to correctly determine the size of pulling force and thus the length of the mouse trap's lever arm that will be needed. Speed-trap racers require more pulling force in order to accelerate as fast as possible. Long distance-traveling racers require more string length and less pulling force in order to travel as far as possible. Even with these concepts in mind you may still need to adjust the length of the mouse trap's lever arm even after your mousetrap vehicle is assembled.

distance racers: long-distance racers will have longer lever arms to decrease the pulling force in order to conserve energy.

speed-trap racers: speed-trap racers will be geared to use a shorter lever arm in order to increase the pulling force and increase the acceleration.

Increase the Pulling Force

If a mousetrap vehicle is struggling to move and/or needs more acceleration then the lever arms can be shortened in order to increase the pulling force. Keep in mind that you will also have to reposition the mouse trap closer to the drive axle or the system will not work as intended.

bonus tip: a lever arm is cut using a dremal tool and a cutting wheel.

Decrease the Pulling Force

If a mousetrap car is spinning its wheels at the start or you need a longer pulling string then increasing the length of the lever arms will decrease the pulling force and increase the length of the pulling string. Remember that when you change the length of a lever arm you will also need to reposition the mouse trap on the chassis (see how to attach the mouse trap).

bonus tip: a longer lever arm is added by using couplers to attach two pieces of tubing together. If the lever arm is a 1/8 inch tubing than a 5/32 inch coupler can be used to join two pieces of tubing.

Repositioning the Mouse Trap

For optimal performance the mouse trap should be positioned on the chassis so that the tip of the lever arm falls directly above the drive axle when the mousetrap vehicle is in it's fully wound position (as pictured bellow). If the mouse trap is not aligned properly with the drive axle energy will be wasted off the start. After testing your mousetrap vehicle you may discover that you need to adjust the pulling force by changing the length of the lever arm. When ever you change the length of the lever arm you will also need to reposition the mouse trap on the chassis; for this reason, the mouse trap should not be glued to the chassis but instead held in place by some type of adjustable anchor system.

bonus tip: the mouse trap is positioned on the chassis so that the tip of the lever arm lines up with the drive axle when the mouse trap car is fully wound-up.

bonus tip: to find the correct position for the mouse trap, hold down the lever arm and line-up the mouse trap on the chassis.

Final Notes

Depending on how your mousetrap vehicle performs you may have to consider adjusting the length of the lever arm. If you place your mousetrap vehicle on the ground and the vehicle does not move, or it does not accelerate as quickly as needed, then you can do one of two things, you can shorten the length of the lever arm and reposition the mouse trap closer to the drive axle or you can build up the drive axle with tape (see how to change the gearing). If instead the mousetrap vehicle is shins it's wheels when placed on the ground, or traveling two fast causing it to have to much friction, you may have to increase the length of the mouse trap's lever arm and reposition the mouse trap away from the drive axle in order to slow the vehicle down and decrease the pulling force.

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