In a typical DC motor, there are permanent magnets on the outside and a rotating armature inside. The permanent magnets are fixed, hence called the stator. The armature rotates, hence called the rotor.
The armature contains an electromagnet. When you supply electricity to this electromagnet, it creates a magnetic field that attracts and repels the magnets in the stator, causing the armature to rotate by 180 degrees. To make it rotate, you need to change the poles of the electromagnet. Brushes handle this change in polarity. They contact with two rotating electrodes attached to the armature and, as they rotate, they reverse the magnetic polarity of the electromagnet.
This setup works and production is simple and cheap, but it has many issues:
- Eventually, the brushes wear out.
- You get sparks and electrical noise because the brushes make and break connections.
- The brushes limit the maximum speed of the motor.
- Having the electromagnet in the middle of the motor makes cooling difficult.
- The use of brushes limits the number of poles the armature can have.
With the advent of cheap computers and power transistors, "inverting the motor" and eliminating brushes became possible. In a brushless DC motor (BLDC), you place the permanent magnets on the rotor and move the electromagnets to the stator. Then, you use a computer (connected to high-power transistors) to charge the electromagnets as the shaft rotates. This system has all sorts of advantages:
- A computer is more precise since it controls the motor instead of mechanical brushes. The computer can also account for the motor's speed in the equation. This makes these brushless motors more efficient.
- No sparks and less electrical noise.
- No brushes to wear out.
- With the electromagnets on the stator, cooling is very easy.
- For more precise control, there can be many electromagnets on the stator.
The only disadvantage of a brushless motor is the initial high cost, but you can recover this cost over the motor's lifetime with higher efficiency.
.png)
