Servo motor

A servo motor is not one type of motor but any motor wrapped in a feedback loop that makes it hit a commanded position, speed, or torque exactly and hold it against disturbance. The defining ingredient is the sensor — an encoder or resolver — that constantly reports where the shaft actually is; a controller compares that to where you asked it to be and corrects the error continuously, like a driver nudging the wheel to stay in lane. Push back on a good servo's arm and it pushes right back to its set point.

Servos are how robots, CNC machines, factory automation, and even the steering on a model plane achieve fast, accurate, repeatable motion under varying load. A hobby RC servo bundles a small motor, gears, a potentiometer, and a tiny control circuit into one package that obeys a position command; an industrial servo pairs a high-performance PMSM with a precise encoder and a powerful drive. The word 'servo' (from Latin servus, slave) captures the idea: the motor is enslaved to faithfully follow the command.