Chapter 2

Types of DC Motors


Traditional Brushed DC Motors

In a brushed DC motor, the DC current passing through the coil windings of the rotor generates an electromagnet with the poles as seen in the below animation. These rotor magnetic poles interact with the poles of the fixed permanent magnet, called the stator, to make the rotor spin.

  • After every half turn the rotor, to keep the motor spinning, the rotor poles need to be flipped by switching the polarity of the current in the coil windings.
  • This switching of current polarity is called commutation.
  • Commutation occurs mechanically: Every half turn electrical contacts, called brushes, complete a circuit to the other half of the commutator on the rotor as it spins.
  • Due to this physical contact, brushes wear out over time, preventing the motor from working.

Brushless DC Motors

BLDC motors overcome the shortcomings of brushed motors by replacing mechanical commutation with electronic commutation. To better understand this, it is useful to take a closer look at the BLDC motor structure.

A BLDC motor is a kind of flipped version of a brushed motor because the permanent magnets are installed in the rotor, whereas the coil windings become the stator.

There are motors with different magnet arrangements where the stator may have different numbers of windings and the rotor may have multiple pole pairs as can be seen in the following animation.

Rotor and stator of a brushless DC motor

A type of similarly structured motor is the permanent magnet synchronous machine, or PMSM. The next chapter discusses the differences between BLDC and PMSM motors and the type of control algorithm required to operate these motors.