A commutator is an electrical switch that periodically reverses the current in an electric motor or electrical generator. Commutators enable motors to run on, and a generator to produce usable energy. Pending the configuration of commutators, direct current (or continuous current) can be transformed from an alternating current source.
In relation to electric-powered radio control, the commutator of an electric model's drive motor consists of a set of copper contacts fixed around the circumference of the rotating part of motor, or armature. A set of spring-loaded carbon brushes fixed to the stationary part of the motor completes the electrical circuit from the rotor's windings to the outside of the motor. Friction between the copper contacts and the brushes eventually causes wear to both surfaces. The carbon brushes, being made of a softer material, wear faster and are designed to be replaced easily without dismantling the motor. The copper contacts are usually inaccessible and, on small motors or on IFMAR-regulated "stock" car and truck motors, are not designed to be repaired, though the commutator may be cleaned with the aid of a special abrasive stick inserted through the brush hoods. On so-called "modified" motors with their removable endbell and adjustable timing, the entire armature may be removed from the motor can and the commutator resurfaced with a special lathe designed specifically for R/C motors. This sort of treatment is generally reserved for motors used in a serious racing environment as opposed to a non-competitive one. Each segment of the commutator is insulated from the adjacent segments; while a small R/C motor usually contains three segments, a large industrial or traction motor may contain hundreds of segments.