What Is a Brushless Motor?

By: Marshall Brain  | 
A diagram of the armature of a typical DC motor
The armature of a typical DC motor

When it comes to engineering electric motors, few stand taller than the brushless DC electric motor. But, what is a brushless motor, and what's so special about it anyway?

For starters, brushless motors operate with more efficiency, enjoy more longevity, and improved performance when compared to a brushed motor alternative [source: Beacham]. To begin, let's take a look at how brushed motors work, to better understand the operational differences between brushed and brushless motors.


Brushed DC Motors

The article How Electric Motors Work explains how brushed motors work in great detail. In a typical DC motor, there are permanent magnets on the outside and a spinning armature on the inside. The permanent magnets are stationary, so they are called the stator. The armature rotates, so it is called the rotor.

The armature contains an electromagnet. When you run electricity into this electromagnet, it creates a magnetic field in the armature that attracts and repels the magnets in the stator. So the armature spins through 180 degrees.


To keep it spinning, you have to change the poles of the electromagnet. The brushes handle this change in polarity. They make contact with two spinning electrodes attached to the armature and flip the magnetic polarity of the electromagnet as it spins.

This setup works and is simple and cheap to manufacture, but it has a lot of problems:

  • The brushes eventually wear out.
  • Because the brushes are making/breaking connections, you get sparking and electrical noise
  • The brushes limit the maximum speed of the motor.
  • Having the electromagnet in the center of the motor makes it harder to cool.
  • The use of brushes puts a limit on how many poles the armature can have.


Brushless DC Motors

The poles on the stator of a two-phase BLDC motor
The poles on the stator of a two-phase BLDC motor used to power a computer cooling fan. The rotor has been removed.
Public domain image

With the advent of cheap computers and power transistors, it became possible to "turn the motor inside out" and eliminate the brushes. In a brushless DC motor (BLDC), you put the permanent magnets on the rotor and you move the electromagnets to the stator. Then you use an electronic speed controller (ESC) to deliver electric signals that determine rotation speed and direction [source: Joner]. This system has all sorts of advantages:

  • Because a computer controls the motor instead of mechanical brushes, it's more precise. The computer can also factor the speed of the motor into the equation. This makes brushless motors more efficient.
  • There is no sparking and much less electrical noise.
  • There are no brushes to wear out.
  • With the electromagnets on the stator, they are very easy to cool.
  • You can have a lot of electromagnets on the stator for more precise control.

The only disadvantage of a brushless motor is its higher initial cost, but you can often recover that cost through the greater efficiency over the life of the motor.


The Evolution of Electric Motors

Brushless motors represent a leap forward in electric motor technology, offering advantages that include efficiency, durability, and low maintenance. Their versatility and performance make low power brushless motors suitable for a wide range of applications, from consumer electronics to industrial machinery.

As technology continues to evolve and advance, the use of BLDC motors is only expected to grow, further solidifying their position as a critical component in modern electrical and industrial engineering and design.


Frequently Answered Questions

What is meant by brushless motor?
A brushless motor is an electric motor that uses magnets instead of brushes to rotate the motor's rotor.