The servo is a special motor, or more specifically it is a closed-loop control system (servo system). When it is given a command signal, it converts the command signal to the output shaft angle and holds it, even if the load change is very Large, it can also automatically adjust its internal current, more accurate to maintain the command signal output.
In general, the command signal of the servo is a PWM wave, where the period is matched with the servo type, and the duty ratio indicates the angle at which the servo is to be output. The difference is that the analog servo needs to continuously send a PWM signal to keep it at a predetermined angle. The digital servo only needs to send a PWM signal to maintain the desired angle.