The batteries provide electrical power to the motor which spins the rotor at high speed. When the rotor spins, it makes the robot vibrate from side to side and up and down. The vibrations cause the brushes to jump on the surface and land again at high frequency. As the large brush lands after each vibration, its bristles bend, pushing the entire robot slightly, in the same way that the brush is positioned at an angle. When the brush jumps again, the bristles straighten. This process repeats continuously, making the brush robot move forward.