Electric motors – DC Servomotors

Nowadays, the electric motors are playing a major role as actuators in the robots. It is said so because they deliver high controllability with less maintenance. One of the most commonly used electric motors in the robots is DC servomotors.

DC Servomotors:

DC servomotors can be classified into two types such as:

  • Brushed DC servomotors
  • Brushless DC servomotors

Brushed DC servomotors:

A brushed DC servomotor consists of two major components such as stator and rotor. The stator is incorporated with brush assemblies and a permanent magnet, while the rotor has commutator assembly and an armature.

At first, the current is passed through the armature windings in which a magnetic field is set opposite to the field placed by the magnets. This process leads to the generation of torque in the rotor.

The armature gets current from the commutator and brush assemblies when the rotor starts rotating. As a result, the field will stay opposite to the field placed by the magnets. Similar operation provides a constant torque all over the rotation.


  • Less expensive than brushless DC servomotor.
  • Simple variable resistors like rheostat or potentiometer will be sufficient for regulating the motor.


  • It is not highly efficient than brushless DC servomotor.

Brushless DC Servomotors:

A brushless DC servomotor includes a rotor with permanent magnet and an electromagnetic stator. Moreover, it has electronically controlled commutator instead of brushes. It is assembled similar to an inside – out DC servomotor.

A DC current is used to power the system. The poles in the permanent magnet are attracted to the opposing magnetic rotational poles, which is available in the stator. This operation produces a torque.

This type of electric motor also includes linearly connected torque, rpm, voltage, and current.


  • Electromagnetic interference is decreased.
  • Improved reliability
  • Highly efficient
  • Long lasting life-time
  • Less noise


  • Complex systems are required for controlling the speed.
  • Very costly
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