Gather a mousetrap or rat trap, a lightweight chassis, 4 wheels, 2 axles, 2 straw or tube axle guides, string, a wooden dowel, glue, tape, and basic tools
Build a lightweight rectangular chassis from balsa wood, cardboard, or thin plywood
Attach two straw or tube guides underneath the chassis, parallel to each other
Slide the front and rear axles through the guides
Attach the wheels securely to both ends of each axle
Mount the trap on top of the chassis with the spring bar facing the rear
Secure a wooden dowel to the drive axle
Tie one end of the string to the trap’s spring bar or lever arm
Wrap the other end of the string around the dowel on the drive axle
Pull the trap arm back carefully and wind the string onto the dowel
Set the car on the floor and release the trap arm to make it move
Adjust wheel alignment, axle friction, and string length if needed
Keep fingers clear of the trap when setting it