DC BRUSH COMMUTATED VS. BRUSHLESS MOTORS

Theory
  Each of these DC motor types convert electrical energy into mechanical energy through the interaction of magnetic fields. This discussion will be based on the latest technology whereby one of those fields is produced by a permanent magnet and the other field is generated by passing an electric current through the motor windings.

  In the case of brush motors, the stationary field [stator] is generally created by permanent magnets interacting with a rotating field [rotor] which contains the motor windings, see Figure 1 below. The brushless units are just the opposite in that the stator field is the wound member and the rotating field is the permanent magnet, see Figure 2 below. In both cases, the interaction of these fields produces a torque which turns the rotor. As the rotor turns, current in the windings is switched, or commutated, to produce a continuous torque. The brush commutated unit typically uses brushes made of graphite that ride on metal bars [the commutator] that are connected to the rotor coils as shown in Figure 1. As the rotor turns, the brushes transfer current to one set of coils to another. The brushless units rely on their commutation through the use of a shaft position sensor sending a signal to an external winding switching circuit. Each of these methods of producing torque has its advantages and weaknesses. The following is an examination of the various factors for consideration in the selection process.