Everything You Need To Know About Servo Motors

Electric motors are used in almost every industry and in a wide range of applications. Electric motors are available in a wide range of sizes and types. These motors can be selected based on their functioning, voltage, and applications. Using the proper motor with high-quality parts and performing regular maintenance keeps your motor running smoothly and protects endpoint equipment from wear and power spikes.

In this article, we are going to discuss what is a servo motor, the basics of servo motor, advantages, disadvantages, applications, and construction of servo motor.


A Servo motor is a rotary actuator or linear actuator. Servo motors are motors capable of providing very precise angular or linear control. It comprises a suitable motor coupled to a sensor for position feedback.

A servo motor system’s feedback detects the difference between the actual and desired speed or position so that the controller may rectify any deviation from the target position. The two primary types of servo motors are positional rotation and continuous rotation.

The servo motor consists of a DC motor. DC motors spin at high rpm and very low torque. However, inside a servo motor, there is an arrangement of gears that will take the high speed of the internal DC motor and slow it down, while at the same time increasing the torque. Thus, the gear design rotation speed of the servo is much slower but with more torque. 

A servo contains a positional sensor, or encoder, on the final gear. Based on closed-loop control, the microcontroller compares the actual position of the rotor to the desired position and generates an error signal. This error signal is then used to generate the appropriate control signal to move the rotor to the final position. More sophisticated servos also measure speed to provide more precise and smoother movement.Some of the features of servo motor are:

  • The inertia of the servo motor should be less for precision and accuracy
  • It should have a fast response which can be obtained by keeping high torque to weight ratio.
  • The torque-speed characteristics should be linear
  • Four quadrant operation is desirable by using further converters.
  • Stable operation
  • Robust nature.

Servo motors are measured in kilograms per centimeter (kg/cm), with the majority of hobby servo motors rated at 3kg/cm, 6kg/cm, or 12kg/cm. This kg/cm value indicates how much weight a servo motor can raise over a certain distance. Consider the following scenario: If the load is suspended 1cm from the motor’s shaft, a 6kg/cm Servo motor should be able to lift 6kg; the greater the distance, the lower the weight bearing capacity. A servo motor’s position is determined by an electrical pulse, and its circuitry is located beside the motor.

Types of Servo Motors

Servo Motors are classified into different types based on their application, such as the AC servo motor, and DC servo motor.

AC servo motor: This type of servo is currently used today by most companies. AC servo motors are mostly used in industrial fields. AC servo motors are typically seen in industrial settings. AC servo motors are AC motors that use encoders to control their speed. These servo motors are controlled by controllers that provide feedback and closed-loop control. They are well-known for their exceptional accuracy and ease of control.

DC servo motor: Fuji Electric employed these types of servo motors in the past, but they are now rarely used because AC servo motors are easier to use, more effective, advanced, and reliable.

Construction of Servo Motor & Working Principle 

A servo consists of four things:

  • Normal DC motor- That is in charge of generating the motion through its shaft.
  • Gear reduction unit/gear box
  • Potentiometer
  • Control circuit

Gear assembly is used to reduce RPM and to increase torque of the motor. The initial position of the servo motor shaft and the potentiometer knob is such that no electrical signal is created at the potentiometer’s output port.

An electrical signal is now sent to the error detection amplifier’s other input terminal. Now, the difference between these two signals, one from the potentiometer and the other from other sources, will be processed in a feedback mechanism, and an error signal will be output. This error signal is used as the motor’s input, and the motor begins to rotate. The potentiometer is now linked to the motor shaft, and as the motor rotates, the potentiometer will generate a signal. As the angular position of the potentiometer varies, the output feedback changes as well.

After a while, the position of the potentiometer reaches a point where the output of the potentiometer is the same as the external signal. As there is no difference between the external applied signal and the signal created at the potentiometer, there will be no output signal from the amplifier to the motor input in this condition, and the motor will stop rotating.


  • High efficiency
  • High output power relative to their size
  • More constant torque at higher speed
  • Closed-loop control
  • Quiet operation
  • Highly reliable
  • High ratio of torque to inertia
  • High acceleration
  • High-speed performance
  • Torque control
  • Smooth running
  • High accuracy
  • Small in size
  • Well suited to varying load applications


  • More complex control – tuning required
  • Position feedback required
  •  Higher overall system cost

What are Servo Motors Used For?

Servo motors are used in a wide range of applications. Because of the benefits described above, servo motors are increasingly being employed in industrial applications to replace traditional AC and stepper motors, as well as hydraulic and pneumatic systems. Servo motors are advantageous in a variety of applications

  • Machine tools where high accuracy is required.
  • Robotics applications where high accuracy, power and speed are required and low weight and size is an advantage.
  • Conveyer and handling systems where speed and accuracy, as well as high torque, is required.
  • Antenna positioning systems typically need high torque and very high accuracy.
  • Simulation applications where speed, torque and smoothness are important.
  • Renewable energy applications where performance and efficiency are needed.
  • Printing Press where accuracy, speed and reliability as well as low cost is an advantage.

Servo motors, due to their brushless design have advantages in applications in harsh and demanding applications such as:-

  • Food and beverage where motors have to cope with washdown and temperature fluctuations.
  • Defence applications where high shock loads and temperature ranges are seen while high performance is required.
  • Subsea and Oil & Gas application where high pressures and temperatures are seen as well as explosion-proof requirements.

Conclusion:Servo motors are one of the most important devices on the world today. Choosing the proper motor is entirely dependent on the application and the designer’s expertise. Hope all of you find this article informative. For more queries, contact our online store-MATHA ELECTRONICS

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