A normal servo is used to control an angular motion of 0 to 180 degrees. Usually, it is somewhere in the 210-degree range, however, it varies depending on the manufacturer. The output shaft of the servo is capable of traveling somewhere around 180 degrees. If the circuit finds that the angle is not correct, it will turn the motor until it is at a desired angle. If the shaft is at the correct angle, then the motor shuts off. This pot allows the control circuitry to monitor the current angle of the servo motor. In the picture above, the pot can be seen on the right side of the circuit board. The servo motor has some control circuits and a potentiometer (a variable resistor, aka pot) connected to the output shaft. One is for power (+5volts), ground, and the white wire is the control wire.
You can also see the 3 wires that connect to the outside world. You can see the control circuitry, the motor, a set of gears, and the case. The guts of a servo motor is shown in the following picture. A lightly loaded servo, therefore, does not consume much energy. It also draws power proportional to the mechanical load. A standard servo such as the Futaba S-148 has 42 oz/inches of torque, which is strong for its size.
The motors are small, have built-in control circuitry, and are extremely powerful for their size. They are also used in radio-controlled cars, puppets, and of course, robots. In practice, servos are used in radio-controlled airplanes to position control surfaces like the elevators and rudders.
If the coded signal changes, the angular position of the shaft changes. As long as the coded signal exists on the input line, the servo will maintain the angular position of the shaft. This shaft can be positioned to specific angular positions by sending the servo a coded signal. A Servo Motor is a small device that has an output shaft.