Working OF A Servo Motor

Have you ever wondered how robots and machinery do precise rotations? If yes, then in today’s article, you will understand how it actually works in the backend. A Servo motor is the main reason behind the precise movement, it is basically a motor or actuator which is used for a precise linear position as well as angular position and velocity, etc. Servo motors are closed-loop servomechanisms. 

Closed-Loop Servomechanism is an intelligent mechanism that can cancel or null the disagreements between the input and is also able to modify the output to the desired value. A servo motor uses position feedback to control the position and motion which helps it in achieving the level of preciseness that is required. 

Servo motors are widely used in robotics, DVDs and remote control toy cars, and many more electrical components. Also, Servo motors can rotate up to 180 degrees making the movement more precise. There are a total of 3 wires present in the servo motors which are needed to be connected for proper functioning. 

If a servo motor is powered by DC current then it is called a DC servo motor and if it is powered by AC current then it is called an AC servo motor. In today’s article, we will be discussing DC servo motors. The Servo motor is a combination of four components which are a normal DC motor, a gear reduction unit, a position-sensing device, and a control circuit.

For feedback to a position sensor, we basically use a potentiometer that is connected to the DC motor. 

That is all in the introduction of the servo motor. Now, we will discuss the parts of the Servo motors. 

Parts OF The Servo Motors

The parts of the servo motor are listed below


The housing of a servo motor has a thickness of 1 inch and is coated in an aluminum casing which protects the inner workings of the servo motor from external contaminants. The housing of the servo motor is designed to be disassembled and reassembled quickly and easily.

Motor shaft

The motor shaft is connected with the gearbox and pulley system which can utilize energy in order to boost the motor’s torque while lowering its speed. Generally, the motor is made up of cold-rolled steel or hot-rolled steel.


The servo motor gets benefits from bearings as they help servo motors in achieving great precision with minimal vibration. This results in very smooth and cool functioning. The life of these bearings can be enhanced using new greases and also adapting new ways to reduce fret.


The rotor of the Servo motor is generally attached to the motor’s shaft and is held in position with the help of two bearings. This rotor is the moving portion of the servo motor. 

The rotor of the motor rotates in the appropriate direction with the specified amount of voltage until the error is zero.


As its name suggests this part of the servo motor is the stationary part. The job of the stator is to establish or create a rotating magnetic field that is capable of generating torque efficiently. 

The stator normally consists of 12 separately wrapped winding segments which are joined by a single copper wire.


The brakes of the Servo motor are built from merely a few parts and are used in holding various objects in place whenever the machine is shut off or the E-stop is triggered. 

We have to keep this in mind that whenever the voltage is provided, the spring will let go, so we have to be careful when releasing the brakes because it can cause motor failure

Snap ring

Whenever the servo motor gets a direct hit from an undesired force, a snap ring helps in preventing damage to the motor while keeping the shaft position. The shaft would simply slide back into the housing if it didn’t have it.

O ring

The servo motor has an O ring which is used to prevent fluid from entering. An O-ring is placed between the two pieces in order to form a seal. 

Servo motors are made up of multiple o-rings, which are made up of plastic polymers to prevent any damage due to fluids. 

Bearing keeper

As its name suggests a bearing keeper is a portable plate which is used to keep the bearing at their position and prevent them from slipping out of place near the pulley end.


The servo motor has an encoder which is an electromechanical device that communicates the speed of the motor and guides the direction of the drive. 

The use of an encoder gives the operator the ability to monitor and alter some parameters during the run. These encoders are light in weight and small in size so there is no issue in using them.

Gear System

Servo motors have a gear system, the gear system of a servo motor is responsible for the delivery of the output of the motor to the servo arm using a servo spline. The gear is generally made up of plastic for standard servo motors while for high-power servos it is made up of metal. 

Working Principle OF Servo Motor

Servo motors generally consist of a DC motor, a gearbox, a position sensor, and a circuit.

The DC motor gets power from the battery and it starts running at a higher RPM which results in lower torque. The first thing we will do here is to reduce the RPM(Revolutions Per Minute) using a gear system which ultimately helps in increasing the torque. 

Now, the position sensor starts sensing the position of the shaft and delivers the information to the control circuit. Then the control circuit starts decoding the signals received from the position sensor and then it starts comparing the actual position of the motor with the desired position if the position is not the same as required then it accordingly controls the direction of rotation of the DC motor to get the required position. 

Working of A Servo Motor

How TO Control Servo Motor?

As we all know every motor has 3 wires coming out from them. From these 3 wires, two of them are for power supply i,e. One for positive and another one for negative supply and the third wire is used for sending the signal which is to be sent from the microcontroller. 

The three wires coming out from the servo motor are of different colors which are

Wires of the servo motorColor of the wires
Vcc PinRed
GND or Ground PinBrown
Pulse Width Modulation PinYellow or Orange

Servo motors are controlled using pulse width modulation or PWM pins. Different types of pulse are sent for a fixed amount of time. The pulse which is being transmitted can be a minimum pulse, a maximum pulse, and a repetition rate. 

As we know servo motors can rotate up to 90 degrees in either direction from their neutral position. Servo motors check for a pulse every 20 milliseconds (ms) and the length of these pulses will determine how far the motor turns.

The pulse Width Modulation(PWM) principle is used for controlling the servo motor i,e. The angular movement of the motor is controlled by the value of the pulse and the duration for which it is applied. 

Suppose that if a servo motor rotates 90 degrees for a 1.5ms pulse then if we increase the pulse from 1.5ms then the motor will rotate 180 degrees. Similarly, if the value of the pulse is less than 1.5ms then it will turn to 0 degrees. 

Well explained in “flex sensor working and Arduino Interface

Advantages and Disadvantages OF Using Servo Motors

The advantages of using servo motors are listed below

  1. Servo motors can provide a huge amount of output power.
  2. If the load is heavy then the driver will increase the current to the motor coils for rotating.
  3. High efficiency(90%) for light weights. 
  4. Have high torque to inertia ratio.
  5. Able to accelerate quickly.
  6. It is possible to perform high-speed operations.

The disadvantages of using servo motors are listed below

  1. Needs adjustment for making the feedback loop stable.
  2. Costly.
  3. If stopped the motor’s rotor kept on moving forth and back one pulse which is not suitable for preventing vibration.
  4. It becomes unreliable if something breaks.

Application OF Servo Motors

Applications of servo motors are as follows

  1. In industries, servo motors are used in machines.
  2. Used in radio-controlled airplanes.
  3. Used in robots. 
  4. Used in CD/DVD players.
  5. Used in automobiles etc.

Frequently Asked Questions

Q1 – Can servo motors rotate 360?

Ans – No, the servo motor can only rotate up to 180 degrees however if you need 360-degree rotation then you can use continuous servos that can rotate through the full 360 degrees.

Q2 – Can the servo motor rotate in both directions?

Ans – Yes, servo motors can rotate 90 degrees in both directions.

Q3 – Servo motors are ac or dc?

Ans – Servo motors can be of both types depending upon the type of supply it gets. 

Q4 – Do servo motors have Encoders, Drivers, and Brakes?

Ans – Yes, servo motors have encoders, drivers, and brakes.

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