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 advantages of brushless DC motors over conventional DC motors are high reliability, no production of sparks and no production of electromagnetic interference. The disadvantage is higher cost due to the complex electronics.
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.
The poles on the stator of a two-phase BLDC motor.
In the 'outrunner' configuration, the radial-relationship between the coils and magnets are reversed; the stator coils form the center (core) of the motor, while the permanent magnets spin on an overhanging rotor which surrounds the core.
In all BLDC motors, the stator-coils are stationary.
The brushlessDCmotor of claim 9 wherein said means for preventing comprises at least one spacer coupled to said shaft, said at least one spacer having a surface in contact with a surface of said multi-pole composite magnet.
The brushlessDCmotor of claim 25 wherein said means for preventing comprises at least one spacer coupled to said shaft, said at least one spacer having a surface flush to a surface of said multi-pole composite magnet.
The brushlessDCmotor comprises a multi-pole, composite magnet which functions as a portion of a rotor, at least one stator member which determines the angular position of this composite magnet, and means for positioning the composite magnet and the stator member on a common axis.
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