Print some accessories to to attach to a mousetrap and turn it into a spring-loaded car! Note that although the car assembled and the mechanism works, the spring mechanism provies way too much torque. The wheels spin too fast and end up slipping in place. Eventually, it slows down enough to move a foot or two. Much more detailed information is available on this blog post: http://netninja.com/2013/11/04/son-of-ratracer-mouse-car/ Download mousecar-src.zip for the OpenSCAD source for all three components.Pull back the U-bar and, while carefully holding it down and not releasing it onto your fingers, thread the string through the hole in the axle. Wind it around the axle. Put the car on the floor. Quickly release the snappy part. In theory, the string is pulled, spinning the axle and wheels, making the car go.