This DIY Gear Reciprocating Car consists of a wooden frame, reduction motor, battery box and gear sets. When powered on, the motor converts electric energy into mechanical energy to drive the wheels through gear meshing. As the car reaches the table edge, gravity pulls the movable gear down to change the gear combination and reverse wheel rotation. The car returns automatically and resets on flat surface, repeating the cycle. It demonstrates gear transmission, energy conversion, gravity and friction.