The servo adopts closed-loop control, and there is a position tracking error like closed-loop stepping. Servo needs debugging before it can be used. When the original torque of stepper and servo motors is not enough, it is often necessary to work with a reducer, and a reduction gear set or a planetary reducer can be used. The servo (servo) is a common name from the Chinese, it is a type of DC servo motor, which was first used for small model aircraft, and now is used for small robot joints. From the structural analysis, the steering gear includes a small DC motor, plus sensors, control chips, and reduction gear sets, which are installed in an integrated housing. The rotation angle can be controlled by an input signal (usually a PWM signal, but also a digital signal).