The principles of the internal workings of both the brushless and brushed DC motor are essentially the same. When the motor windings become energized, a magnetic field is created that repels and/or attracts the brushes or coils against magnets. This force is transferred into shaft rotation, forcing the rotor to continually turn.
Brushes inside electric motors are used to deliver current to the motor windings through commutator* contacts. Brushless motors have none of these current carrying commutators. The field inside a brushless motor is switched via an amplifier triggered by a commutating device, such as an optical encoder.
Windings are on the rotor (rotating part of the motor) for brush motors and on the stator (stationary part of the motor) for brushless motors.
Brushless DC motor pro’s
- Less requires maintenance due to the absence of brushes
- High efficiency, no voltage drop across brushes
- High output power
- Higher speed range – no mechanical limitation imposed by brushes
- Low electric noise generation
- Electronic commutation based on Hall position sensors*
- Reduced size due to superior thermal characteristics
Brushless DC motor con’s
- Higher cost of construction
- Electric controller is complex and expensive – needed to keep the motor running
Brushed motor pro’s
- Two wire control
- Replaceable brushes for extended life
- Low cost construction
- Simple and inexpensive control
- Operates in extreme environments due to lack of electronics
Brushed motor con’s
- Periodic maintenance is required – possible new brushes required
- Speed/torque is moderately flat. At higher speeds, brush friction increased, thus reducing useful torque
- Poor heat dissipation due to internal rotor construction
- Higher rotor inertia which limits the dynamic characteristics
- Lower speed range due to mechanical limitations on the brushes
- Brush arcing will generate noise
*Commutator – a commutator is a moving part of a rotary electrical switch in certain types of electric motors and electrical generators that periodically reverses the current direction between the rotor and the external circuit.
* Hall position sensors – is a device that converts one form of energy to another.
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