What's the difference between a brushless motor and a brushed motor?

brushless motor and brushed motor
  • Construction Differences

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 encoder, such as an optical encoder.

Windings are on the rotor (rotating part of motor) for brush motors and on the stator (stationary part of motor) for brushless motors.

By positioning the windings on the outside stationary portion of the electric motor, the need for brushes can be eliminated.

  • Brushed motor Advantages:

Simplified wiring: Brush motors can be wired directly to DC power and control can be a simple as a switch;

Low cost.

Brushed Motor Disadvantages:

Less efficient;

Electrically noisy: The switching action of the commutators constantly creating and breaking inductive circuits creates a great deal of electrical and electromagnetic noise;

Lifespan: As they are in perpetual physical contact with the shaft, brushes and commutators wear out.

  • Brushless Motor Advantages:


Long lifespan: No brushes to wear out;
Low maintenance: No brushes to replace;
High efficiency.

Brushless Motor Disadvantages:

Higher initial cost compairing to brushed motor.

Brushless Motor vs Brush Motor Efficiency:

Brushless motors are typically 85-90% efficient whereas brushed DC motors are around 75-80% efficient.

This difference in efficiency means that more of the total power used by the motor is being turned into rotational force and less is being lost as heat.

 

  • In conclusion :

Brushless motors offer several advantages over brushed DC motors, including high torque to weight ratio, increased efficiency producing more torque per watt, increased reliability, reduced noise, longer lifetime by eliminating brush and commutator erosion, elimination of ionizing sparks from the commutator, and an overall reduction of electromagnetic interference (EMI). With no windings on the rotor, they are not subjected to centrifugal forces, and because the windings are supported by the housing, they can be cooled by conduction, requiring no airflow inside the motor for cooling. This in turn means that the motor's internals can be entirely enclosed and protected from dirt or other foreign matter.

Brushless motor commutation can be implemented in software using a microcontroller, or may alternatively be implemented using analog or digital circuits. Commutation with electronics instead of brushes allows for greater flexibility and capabilities not available with brushed DC motors, including speed limiting, microstepping operation for slow and fine motion control, and a holding torque when stationary. Controller(ESC) software can be customized to the specific motor being used in the application, resulting in greater commutation efficiency.