Brushless Motors 

When Less Is More...
This month, I'd like to talk about the advantages of brushless DC motors over brush DC motors and when it makes sense to go brushless.

Brushless Motor Construction
The brushless DC motor turns the construction of the brush DC motor inside-out.  It places the magnets on the rotating shaft and the coils of wire on the stationary motor housing.  The brushless motor does not have a commutator or brushes.  Instead, brushless motors require a method of measuring the position of the magnets on the shaft as they rotate.  The three most commonly used methods are Hall Effect Sensors built into motor, an encoder mounted external to the motor, or special electronics that measure the position of the magnets as the motor spins, known as back-EMF commutation.  In all three cases, brushless motors require control electronics that read the position of the rotor and energize the correct set of coils to rotate the rotor and create torque.

Less Is More...
By eliminating the brushes and the commutator, brushless motors are both more reliable and more efficient than brush DC motors.  Typical DC motor brushes can wear out in about 1,500 hours of use or less, depending on the load and other factors.  Without brushes and commutators to wear out and fail, brushless motors can last much longer than brush DC motors.  Eliminating the commutator also eliminates its associated power losses, making the brushless DC motor more efficient.  This is especially important in battery-operated systems since improved efficiency results in longer battery life.  Brushless motors typically have higher power density when compared to brush DC motors, so you can use a smaller brushless DC motor to do the same job as a larger brush motor.  Because the coil of the brushless motor is in direct contact with the housing, brushless motors are better able to conduct heat away from the coils, allowing higher power levels without damaging the coil.

...But Nothing Is Free
If brushless DC motors are more efficient and last longer, how come we don't see more of them?  The answer is a combination of cost and complexity.  A brushless DC motor is more expensive to manufacture than a brush DC motor.  The typical brushless motor requires 8 wires instead of the simpler 2-wire connection for brush DC motors.  Brushless motors also require more complicated control electronics, which increases the total system cost compared to brush DC motor systems.