Servo motor

Understanding Servo Motor

A servo motor is a type of motor that has a high degree of precision in rotation. Servo motors often have a control circuit that provides feedback on the current position of the motor shaft; this feedback allows them to rotate with great precision. A servo motor is used when you wish to spin an object at a specified angle or distance. It consists of nothing more than a simple motor connected to a servo mechanism. A DC servo motor is one that is powered by a DC power supply, whereas an AC servo motor is one that is powered by an AC power supply.

In this article, you’ll learn the definition, applications, construction, parts, diagram, types, working principle, mechanism, advantages, and disadvantages of a servo motor.

Servo motor


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What is a servo motor?

A servo motor is a linear or rotary actuator that enables precise position control in closed-loop applications. Servo motors are not suitable for continuous energy conversion when compared to huge industrial electric motors. Because of the inertia, these motors have a high-speed reaction and are constructed with tiny diameters and large rotor lengths.

The speed and ultimate position of servo motors are controlled by a mechanism that uses position feedback. A servo motor is made up of a motor, a feedback circuit, a controller, and another electrical circuit on the inside. Smaller applications are best suited for these motors. Because of their high precise control, AC servo motors are becoming more popular as microprocessors and power transistors progress.


The applications of servo motors are common in industries due to their high-speed reaction. The followings are some applications of a servo motor:

  • The servo motor is built into the camera to improve out-of-focus photographs by correcting the lens.
  • This motor is used to control the robot wheels of a robotic vehicle, producing enough torque to move, start, stop, and control the vehicle’s speed.
  • In robotics, the servo motor is utilized to actuate movements and give the arm its precise angle.
  • These are used to start, move, and stop conveyor belts that transport goods through multiple stages. Labeling, bottling, and packaging are just a few examples.
  • Servo motors are also used in solar tracking systems to fix the angle of the solar panels so that they all face the sun. Additionally, these are employed in metal forming and cutting equipment to provide milling machines with precise motion control.
  • Textiles use servo motors to control spinning and weaving equipment, as well as knitting machines and looms.
  • Automatic door openers, such as those seen in supermarkets, hospitals, and theaters, employ servo motors to control the door.
  • Servomechanism is utilized in power steering, brake systems, and cruise (speed) control in automobiles.


A servo motor provides speed and location feedback via an encoder or speed sensor. The error signal is produced when the feedback signal is compared to the input command position (the desired position of the motor corresponding to a load) (if there exists a difference between them).

The error signal provided at the error detector’s output is insufficient to run the motor. As a result, the error detector, in conjunction with a servo amplifier, enhances the voltage and power level of the error signal before turning the motor shaft to the intended position. Servo motors are classified into AC and DC servo motors based on the power source they need to operate. Because of their low cost, efficiency, and ease of use, brushed permanent magnet servo motors are utilized for simple applications.


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Diagram of a Servo motor:

Diagram of a servo motor

Parts of servo motor

The followings are the major parts of a servo motor:

  1. Housing
  2. Motor shaft
  3. Bearings
  4. Rotor
  5. Stator
  6. Brake
  7. Snap ring
  8. O ring
  9. Bearing keeper
  10. Encoder


This part is a 1 inch thick coated aluminum casing that protects the inner workings of the servo motor from extraneous contaminants. The housing of the motor is designed to be disassembled and reassembled quickly and easily.

Motor shaft

It functions similarly to a prime mover, except that the gearbox or belt and pulley system to which it is connected can utilise that energy to boost the motor’s torque while lowering its speed. In most cases, the motor is built of cold or hot-rolled steel.


The motor might benefit from bearings since they give great precision and minimal vibration. As a result, the functioning is very smooth and cool. The use of new greases and ways to reduce fret will enhance bearing life.


The rotor is normally attached to the motor’s shaft and is held in position by two bearings. The rotor is the servo motor’s moving portion. The rotor of the motor rotates in the appropriate direction with the specified voltage until the error is zero.


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This part is the servo motor’s stationary portion. The stator’s job is to create a rotating magnetic field that efficiently generates torque. It normally consists of 12 separately wrapped winding segments that are joined by a single copper wire.


Brakes are made up of merely a few parts and are used to hold objects in place when the machine is shut off or the E-stop is triggered. Keep in mind that when voltage is provided, the spring will let go, so be careful when releasing the brakes because the motor will fall.

Snap ring

After a direct hit or nudge from an undesired force, a snap ring prevents 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

To prevent fluid from entering, an O-ring is put between the two pieces to form a seal. Servo motors are made up of several o-rings, which are constructed of plastic polymers.

Bearing keeper

A bearing keeper is a portable plate that keeps the bearing from slipping out of place near the pulley end.


An encoder is an electromechanical device that communicates the motor’s speed and direction to the drive. This gives the operator the ability to monitor and alter certain parameters on the fly. These are light in weight and small in size.

Servo motor Diagram 2:



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Types of servo motors

The followings are the various types of servo motor:

  1. DC servo motor
  2. AC servo motor
  3. Positive rotation
  4. Continuous rotation
  5. Linear servo motor

DC servo motor

In the fields of winding and armature winding, these types of servo motors employs seperate DC sources. A tiny DC motor, feedback potentiometer, gearbox, motor drive circuit, and feedback control loop are all parts of a DC servo motor. It’s very similar to a standard DC motor.

Controlling the armature current or the field current to control the motor. Because of the low armature inductive reactance, these give a very precise and quick reaction to the start or stop command signal. These motors are utilized in numerically controlled devices that are computerized.

AC servo motor

Encoders are built into AC motors and used in conjunction with controllers to provide feedback and closed-loop control. This motor has a high design tolerance and may provide great accuracy. Higher voltages are also used in some designs to increase torque. Because of the great degree of accuracy and versatility required, they are utilized in automation, robotics, CNC machines, and other applications.

Positive rotation

The motor’s output shaft rotates 180 degrees in this type of servo motor. Physical brakes in the gear system prohibit the rotation sensor from turning, which is the main component of the motor. These can be found in radio-controlled water, radio-controlled automobiles, planes, robotics, and toys, among other things.

Continuous rotation

These are conventional types of servo motors that have been modified to provide open-loop speed control rather than the closed-loop position control that they normally provide. Rather of determining the servo’s position, the control signal is interpreted as the speed and direction of rotation. Servo to rotate clockwise or counterclockwise at varied rates in a spectrum of available command sources. The application can be found in a mobile robot’s drive motor.

Linear servo motor

Linear servo motors are similar to positional rotation servo motors, but they have an extra set of gears to convert the O/P from circular to linear. These servo motors are uncommon, however they are occasionally employed as actuators in larger model airplanes.


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Servo motor mechanism

Mechanism of a servo motor

A controlled device, an output sensor, and a feedback system are the three essential components of a servo system. This is a closed-loop control system that operates automatically. Instead of using a variable input signal to operate a device, a feedback signal generated by comparing the output signal and the reference input signal is used to control the device.

When a reference input signal or command signal is applied to the system, it is compared to the output sensor’s output reference signal and a third signal created by the feedback system. This third signal is the controlled device’s input signal. As long as there is a logical difference between the reference input signal and the system’s output signal, this input signal to the device is present.

There will be no logical difference between the reference input signal and the system’s reference output signal once the device achieves its desired output. Then, until the next input signal or command signal is applied to the system, the third signal produced by comparing these above signals will not be adequate to operate the device and produce a further output of the system.

As a result, the fundamental function of a servo mechanism is to keep a system’s output constant in the face of disturbances.

Working Principle

The working of a servo motor is less complex and can be easily understood. The pulse width modulation approach is used to operate a servo motor. The duration of the applied pulse to its control pin controls the angle of rotation in this case. A servo motor is essentially a sort of DC motor that is controlled by a variable resistor (potentiometer) and a set of gears. see working diagram below:

working diagram of a servo motor

A DC servo motor is made up of the following components: a DC motor, a position sensor device, a gear assembly, and a control circuit. A tiny DC motor is used in the DC servo motor to drive the loads at a precise speed and location. A DC reference voltage is now connected to the desired output. Depending on the control circuitry, this voltage is provided to the voltage converter via a potentiometer by adjusting the pulse width or by a timer. The potentiometer’s dial generates a voltage that is subsequently applied to the error amplifier.


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A pulse control method is used in some circuits to provide a DC reference voltage that corresponds to the intended position or speed of the motor. The pulse width is then applied to the voltage converter. When the pulse is high, the capacitor begins to charge at a consistent rate through this converter. When the pulse is low, the charge on the capacitor is sent to the buffer amplifier, and this charge is then delivered to the error amplifier.

As a result, the voltage provided to the error amplifier as the appropriate voltage to create the desired speed or position is determined by the length of the pulse. A position sensor is used to receive the feedback signal corresponding to the load’s current position. Normally, this sensor is a potentiometer that provides voltage proportional to the absolute angle of the motor shaft via the gear mechanism.

Watch the video below to learn more about servo motor working:

Advantages and disadvantages of servo motor


The followings are the benefits of  servo motors in their various applications:

  • They have the ability to provide a large amount of output power considering their size and weight.
  • It has a high efficiency rating of up to 90% under light loads.
  • The motor has a high torque-to-inertia ratio and can quickly accelerate loads.
  • It has the ability to operate quietly, smoothly, and with excellent accuracy.
  • In comparison to other DC motors, the position of servo motors may be controlled more precisely.


Dispite the advantages of servo motor, some limitations still occur. Below are the disadvantages of servo motors in their various applications:

  • The servo motor’s disadvantage is that it requires adjustment to keep the feedback loop stable.
  • The motor will be unreliable if something breaks. As a result, a protective circuit is necessary.
  • Because feedback components are required, the overall system cost and installation cost are more than for a stepper motor.
  • To offer the encoder and electronic assistance, a complicated controller would be required.


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A servo motor is a motor that rotates with a high degree of precision. Servo motors frequently have a control circuit that provides feedback on the present position of the motor shaft, allowing them to revolve with great precision. Servo motors are utilized in a variety of industries and offer a number of benefits, as we’ve already described. They have qualities that make them powerful and efficient, as well as a variety of mechanical solutions.

That is all for this article, where the definition, applications, construction, parts, diagram, types, working principle, mechanism, advantages, and disadvantages of a servo motor are been discussed. I hope you learned a lot from the reading, if so, kindly share with other students. Thanks for reading, see you around!