What is servo motor, working principle?

A servo is a type of electric motor that only moves part of a rotation. There is usually an arm on the motor shaft to change circular motion into linear mtion.

A servomechanism, or servo, is a device used to provide control of a desired operation through the use of feedback

A servomechanism, or servo, is a device used to provide control of a desired operation through the use of feedback. (copied from Wikipedia) I can use Wikipedia too but I thought this person was asking for an explanation. I appreciated his rating of me as helpful but only fair. I did not think this was a test, I thought someone needed help. That's what we do here.

For industrial application, servo motor are used in distribution power transformer to drive the tap changer to its desired setting. To increase and lower its voltage.

Servo motor is type of motor that can give us positional control by rotating a part and taking a feedback from the encoder.

Hey... think this article could do away with yourdoubts...
Servo Motor Basics
By Mike Charmaine

“A servomotor (servo) is an electromechanical device in which an electrical input determines the position of the armature of a motor,” according to the Engineering Department of Duke University. The purpose of servomotor is to supplement a primary control operated by a comparatively feeble force. In ships, the steam engine regulator/governor was considered to be the first type of a servomotor. It was developed to move the rudder. The history of this mechanism is also cited in the 19th century. During the World War II, servo motors found application in fire controllers, in adjusting the firing angle and the air-fuel ratio. Servomotors were also used in the field of computers in the early stages of development.

Motor Parts
1. A servo could be considered as a small device that has a shaft for the purpose of output. The shaft's angular moment could be regulated by the sending of a signal (coded) to the servo. The angular position of the output device, which is the shaft, would be maintained until the servo keeps receiving signals. By changing the signal sent, the position of the shaft could also be regulated. There are various uses for servomotors in applications ranging from robots to airplanes.
Applications
2. The best use of servomotors can be seen in the field of robotics. Though the servos are small, they are extremely powerful for their size, and they controlled by a built-in circuit. Futaba S-48 is considered the standard servo in robotics. It is said to derive power that is proportional to the load, which is also referred to as the mechanical load. These servos are highly known for their energy conservation. The parts in this motor are basically a circuit, a set of gears and a case that covers them.
Mechanism
3. The working mechanism of a servo is not very complicated. The control circuits that are present inside the servo and a potentiometer are linked with the shaft, which is the output device. The angle of this shaft is regulated by the potentiometer with the help of the coded signals that are received from the control circuit. The shaft can be easily angled between 0 to 180 degrees. The shaft is, however, claimed to have a range of beyond 180 degrees, depending on the manufacturer. The shaft has such limitation in its angular moment due to the presence of a stopper in the gear case.
Technology Used
4. The servomotor contains a control wire that controls the angle of the output device. This wire is given a pulse application for a specified duration, which in turn controls the angle of the shaft in a particular position for a certain point of time. This modulation is famously referred to as the PCM (Pulse Coded Modulation). The servomotor expects a coded signal every few seconds. The duration of the pulse determines the angular degree of the shaft.
Efficiency
5. In order to achieve high levels of error reduction, it is considered appropriate for any mechanism to have a servomotor that helps in the optimum efficiency of the mechanism. For example, a fuel engine servo loading device includes a permanent magnet machine that has a couple of rotors--the first rotor and the second rotor. The rotational axle of the fuel engine is mounted with the first rotor, while the driving shaft is connected to the second rotor. Power is supplied between the rotors through electromagnetic coupling, where a servo regulates the electromagnetic torque between the rotors, thereby controlling of the torque load of the fuel engine. As a result, the fuel engine operates at optimum efficiency, providing maximum mechanical energy, as well as exhibiting optimum fuel efficiency.

Servomotor is actually a dubakoor motor .

It's a step by step motor,but not common usage

What the puki

Servo motor rotates into a half circle.
We can manage its rotation by giving it input in the form of angle(degree).
e.g. assume if we give input 45 so it will rotate by 45 degree angle.

A servo motor is a motor which helps in smoothly rotation
It is used to making robotic hands,legs and other rotary part to provide smooth rotation.
It is also a electromechanical motor.

By Sharvan Rai
Instrumentation and Control Engineering