Servo Motor

What is the Servo Motor?

A servo motor one of the most important electrical motor which can rotate an object with high accuracy and speed which has lots of applications. But this motor differs from other motors because it does not rotate in full rotation (RPM) The basic function of the servo motor rotate the object at one or more specific angles. A servo motor is simply a DC motor or AC motor but with the controller to get specific angles. The servo motor is used in cars and aircraft, for example, to control the rudder, elevator,  ailerons, and flaps we use servo motors. Usually, Servo motors are rated in kg/cm which means how much loads or weight can servo motor lift at a specific distance. If your servo motor rated at 12kg/cm servo motor should lift the weight of 12 kg away from the shaft of your motor.

Servo Motor components

The servo motor consists of an electrical and mechanical system and the components are: 

  • Controller (To control the angles).
  • Closed-loop system (sensor and control process).
  • Gearbox (To convert torque and speed) reduce RPM and to increase Torque.
  • Three wires (Vcc, Ground, Signal). 
  • Hard case (To save internal componets).

the servo motor is a closed-loop system where it uses control theory (feedback) system to control the position of the final rotor shaft, from comparing output signal and input signal we can error signal to control servo motor.


Note that: In the control systems, we compare the input and output and based on the new value we control the motor accurately.

How is the servo controlled?

All servo motors have three wires.  which two will be used for Supply (Vcc and Ground) and one used for the signal (PWM) that is to be from the Arduino or any hardware controller. Servo motors can rotate 180, others can rotate with 270 or 360 degrees.

when we control servo motor de don’t use digital or analog signal but we use PWM (Pulse with Modulation) from Arduino or RC Reciever unit for any aircraft, The pulse value control changes the angle of the servo motor. 

In this example to control the servo motor we need a pulse value from 0 to 2 when the pulse value is 1.5, the servo moves 90 degrees, at pulse value is 1 the servo stays in 0 degrees and pulse value is 2 equal to maximum position 180 degree, The following picture shows the above: 

Servo Motor Specifications

The choice of servo motor is different from the choice of other motors such as brushless DC motor. In our servo motor we focus on torque more than the number of rpm. Generally these are the characteristics that should be considered when choosing a servo motor:


  • Weight and dimensions, certainly all engines share these two Specifications.
  • Speed, it should be noted that the speed of the servo motor varies depending on the voltage of the motor.
  • Accuracy is an important criterion for choosing a servo motor because the main objective of the servo motor is to rotate in angles for the purpose of precision.
  • Torque, before buying a servo motor should know exactly how much weight is expected to be lifted and know the distance expected to be shifted.
  • Operating currents – There are usually two types of currents for servo motors, the first standby current (No-Load Current) when the motor is free of loading, and the second current (working current), which is the lowest current needed by the servo motor to start roate.
  • The type of current in which the servo motor operates (DC or AC).
  • The width and duration of the electrical pulse used to control the motor.
  • The ideal operating temperature is an important and common characteristic of all electric motors.

Advantages and disadvantages of Servo Motor

Servo Motor due to its many uses but there is Advantages and Disadvantages we will mention the most important of them to be considered when you buy the Servo Motor.


  • Servo motor is a precise motor.
  • Suitable for applications that need tilt control.
  • It can give high torque.
  • Fast response.


  • Limit angles 180, 270 or 280.
  • There are electronic parts inside and a lot of gears which means more maintenance.

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