Controlling the motion of a robot by electrical connection is essential for the motion of a robot. Make a car chassis which moves in a straight line and then change its connection to move it on its own axis?
It is a simple bot structure that moves linearly on supplying power. The battery supplies power to the motor and then the motor converts the electrical energy into mechanical energy and thus rotates the wheels which are connected to it. This causes linear motion of the bot. But on changing the motor connections, the motor will rotate the wheels in the opposite direction and henceforth bot will move backwards linearly.