Mousetrap car "Back-Wind" Propulsion System
By Doc Fizzix // Published March 24, 2010
Any mousetrap car can be made to go forward and then back depending how you wind the string around the drive axle. To make a mousetrap car go forward and then come back you need to "back-wind" the string. Back-winding it a technique by which you first wind the string around the axle in the direction need to bring the car home again (where you started); then, you wind string around the axle in the direction needed to make the car move forward. This system of winding the string so that the mouse trap car will go forward and then back is called "back-winding"
The string is attached to the mouse trap's lever arm and then hooked to the drive axle using a loop knot tied at the other end of the string that is designed to "catch" a hook attached to the drive axle.
The string is wound around the drive axle by turning the wheels in the direction opposite to the vehicles motion needed to move the car back to it's starting point. The string you are winding in this step will be the string that pulls the car home (the back-wind) after the mousetrap car has reached it's stopping point.
After winding the correct amount of string around the drive axle that is needed to pull the mouse trap car back, loop the string around the axle hook and begin winding the string in the opposite direction as before.
The photo above shows the string looped around the axle hook and being pulled tight. Make sure that you wind the "forward-wind" string on the opposite side of the axle hook so it does not become tangled with the "back-wind" sting.
The photo above shows the "forward-wind" string being wound around the drive axle. Notice that the string is being wound on the opposite side of the axle hook as the "back-wind".
Once the car is released, the string is pulled off the axle it cause the wheels to rotate propelling the vehicle forward. The only hard part of this technique is finding the "turn-around" point on the string; the "turn-around" point on the string is where you change from the back to the forward-wind. Through trial and error you can find the exact "turn-around" point on the string and then mark it, making winding easier.
See the following related articles to get started:
• basic mousetrap car propulsion
• how to make a mousetrap powered car
• how to make a good distance traveler
• how to make a good speed-trap racer