Brushed vs Brushless DC Motors

Electric vehicles are all powered by some sort of electric motor. It can be either a brushed motor or a brushless motor. Brushed motors can be found in everything from car starter motors to children’s’ toys. They have been around for over a 100 years. Brushless motors are a newer invention. What is the difference? Why would one want a brushless motor? Well, to answer those questions, one must understand their operation.

A brushed motor has a rotating set of wound wire coils (armature) which acts as an electromagnet with two poles. A mechanical rotary switch (commutator) reverses the direction of the electric current twice every cycle, to flow through the armature so that the poles of the electromagnet push and pull against the permanent magnets on the outside of the motor. As the poles of the armature electromagnet pass the poles of the permanent magnets, the commutator reverses the polarity of the armature electromagnet. During the instant of switching polarity, inertia keeps the motor going in the proper direction.

A brushless motor uses a permanent magnet external rotor, three phases of driving coils, one or more devices to sense the position of the rotor, and the associated drive electronics. The coils are activated, one phase after the other, by the electronic speed controller as cued by the signals from the rotor position sensors. The absence of the mechanical rotary switch vastly reduces friction allowing it to operate more efficiently and at higher rpm’s compared to the brushed motors. The only downside of brushless motors is the fact that they cost more due to their need for an electronic speed controller. If the cost of ESC’s can come down, brushed motors will go the way of the Dodo bird. Dyson is already powering their vacuum cleaners with brushless motors to boost performance.

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