How Electric Motors Work

Electric motors are everywhere! In your house, almost every mechanical movement that you see around you is caused by an AC (alternating current) or DC (direct current) electric motor.

A simple motor has six parts:

• Armature or rotor
• Commutator
• Brushes
• Axle
• Field magnet
• DC power supply of some sort

The armature of a typical DC motor

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.

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 a computer (connected to high-power transistors) to charge up the electromagnets as the shaft turns. This system has all sorts of advantages: