Gather a mousetrap, a lightweight chassis, 4 wheels, 2 axles, 2 straw or tube axle guides, string, a wooden dowel or CD axle spool, glue, tape, and basic tools
Cut a rectangular chassis from wood, foam board, or sturdy cardboard
Attach two straw or tube guides underneath the chassis, parallel to each other
Slide the axles through the guides
Attach the wheels firmly to the ends of the axles
Secure the mousetrap to the top of the chassis near the rear
Attach a wooden dowel or spool to the drive axle
Tie one end of the string to the mousetrap arm
Wrap the string around the dowel or spool on the drive axle
Pull the mousetrap arm back and hold it in place while winding the string
Set the car on a flat surface and release the mousetrap arm
Adjust wheel alignment, axle straightness, and string length if needed
Reduce weight and friction for better performance