A brushless DC motor is an electric motor that operates like a DC motor, but with the roles of the rotor and stator reversed. The rotor consists of a set of
permanent magnets and the stator consists of electromagnets. The motor has no brushes and no commutator in the traditional sense, but the role of the commutator is played by an electronic circuit, that switches the current to the different stator coils at the appropriate times. There exist integrated circuits specially designed for this purpose. Many brushless DC motors contain Hall effect sensors, so the electronic circuit knows the rotor position and can switch the current in the stator coils accordingly. Some brushless DC drive circuits use the back EMF in the undriven coils to sense the rotor position, so they do not need the Hall effect sensors. The "brushless DC" motor has a trapezoidal backemf, while the "brushless AC" motor has a sinousoidal backemf.
The advantages of brushless DC motors over conventional DC motors are high reliability, no production of sparks and decreased production of electromagnetic interference when compared to traditional DC machines. The disadvantage is higher cost due to the increased complexity of electronics and controls.
Applications
High power brushless DC motors are used in electric vehicles, industrial applications and robotics. Low power brushless DC motors are used in hard disks, CD players, PC fans and electric tools.
Low speed, low power brushless DC motors are used in direct-drive turntables.
Many hobbyists are recycling the brushless DC motors from CD and DVD drives for use in radio controlled planes.
