What is a carbon brush for?

Carbon brush is a device that transmits signals or energy between the fixed part and the rotating part of some motors or generators. The purpose of the carbon brush is to conduct the current between the moving parts of the motor, and are able to transfer the current from the fixed end to the rotating part of the generator or motor. In DC motors, it is also responsible for commutation (rectification) of the alternating electromotive force in the armature winding.
(1) In the commutator motor, the brush also plays a commutation role, which can change the direction of the current;
(2) Grounding carbon brush, which can output current and introduce the electrostatic charge on the large shaft into the ground through the carbon brush;
(3) The external current (excitation current) is added to the rotating rotor (input current) through the carbon brush, and the motor carbon brush is added;
(4) The large shaft (ground) is led to the protection device for the rotor grounding protection and measuring the positive and negative of the rotor, and the commutator of the ground voltage is composed of brushes and commutation rings, and the carbon brush is a kind of brush.
To put it simply, the carbon brush is used to rotate the motor, input the electrical energy to the coil through the commutator, and change the direction of the current.