An electrical/mechanical device that receives a signal and power from the receiver and moves an output shaft with an electric motor. The position of the shaft depends upon the signal from the receiver. As the shaft rotates, that changes the position of a lever on the output shaft of the servo, which, in turn, changes the position of whatever control surface to which it’s attached. Servos can be designed for more than one type of input signal and to employ more than one type of internal circuitry to achieve the mechanical movement. Servo selection plays a key role in the successful performance of the aircraft.