How do carbon brushes transfer electric current from a rotating DC generator to stationary terminals?

In a direct-current (DC) generator, carbon brushes serve as the critical interface between the rotating components and the stationary output terminals.

The rotor of the generator is equipped with a mechanical rotating switch known as a commutator. This commutator consists of segments connected to the armature coils. As the rotor turns, the carbon brushes remain stationary while bearing down on the rotating commutator segments.1

This physical contact allows the brushes to collect the electrical current generated within the rotating coils and transfer it to the stationary external terminals. Because the commutator reverses the connections at specific points during each rotation, it ensures that the voltage delivered to the stationary terminals remains unidirectional, despite the inherently alternating nature of the voltage induced in the rotor coils.1