We can talk about servo motors as a combination of four things: a DC motor, a gearing set, a control circuit, & a position-sensor, usually a potentiometer. Servo motors are known in the industry as motors that can be controlled most accurately. Compared to servos with standard DC motors, servos typically have three wires power, ground, and control.
Power is continuously applied to the servo motors. The servo controller controls the current draw to drive the motor. This motor is designed for more specific tasks where the position needs to be defined. In addition, servo motors are used for precise tasks, for example, to move a robotic arm or robotic leg within a certain range, to move the camera to some object and etc.
Although we should mention that servo motors do not spin freely like a standard DC motor, unless it is modified for continuous rotation, there is no limit on the range of motion of these types of motors. And instead of being the input signal that determines which position the servo should be in to rotate, continuous rotation relates the speed of the output and direction to the servo input.
However, for most servo motors, the angle of rotation is limited to 180 degrees forward and backward. The servo motor receives a control signal that represents an output position and applies power to the DC motor until the shaft is turned to the precise position, determined by the position sensor. Unlike DC motors, a PWM signal is used to control the servo motor.
Durations of positive pulse determine the position rather than the speed of the servo shaft. A neutral pulse value usually around 1.5ms, dependent on the servo, keeps the servo shafts in the center position. Increasing that pulses values will make servos rotate clockwise, and a shorter pulse will rotate the shaft counterclockwise.
The servo control pulse is typically repeated every 20 milliseconds depending on the servo motor. We must always tell the servo where to go, even if it means staying in that position. When a servo receives a command to move, it will move into position and try to maintain that position even if an external force pushes against it.