Electric motors AC servomotors and Stepper motors

Apart from DC servomotors, other two commonly used electric-type actuator in the robots are AC servomotors and Stepper motors.

AC Servomotors:

The AC servomotors are incorporated with a large resistance and small-sized rotor, which is mostly used for obtaining a perfect and quick response.

The AC servomotors can be categorized into two different types such as:

  • Synchronous
  • Asynchronous

An AC servomotor is a reversible induction and two phase motor, which is transformed for performing the servo process. When there is a possibility of rapid reversals, stops, and starts, this motor use to deliver a low inertia.

Most importantly, the performance of an AC servomotor can be increased similar to a DC motor with the help of an appropriate electronics package.


  • When compared with DC motors, the manufacturing cost for AC servomotor is low.
  • It is capable of providing high power output.
  • It does not include any sort of brushes.

Stepper motors:

The stepper motors are classified under the brushless DC servomotor category, and it is also known as stepping motors. This type of actuator is currently employed in the computer I/O devices.

The stepper motors are generally incorporated in the robots, which require a light duty function. Moreover, it is mostly applied in the open loop systems when compared with the closed loop systems.

A sequence of discrete electrical pulses is used to power a stepper motor. The motor shaft is rotated to single step for each electrical impulse. As a result, it produces the discrete angular motion increments as the output.


  • It can support both digital and analog feedback signals.
  • It provides high dynamic torque with low pulse rates.


  • Less efficient
  • During high load inertia, it might require damping for avoiding oscillation.
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