What really is a brushless motor, and why are we using one?

As I’ve written about in previous blog posts, my Senior Design Project is a hybrid-powered race kart. For the hybrid component, we’ve chosen to use a high-power brushless DC motor. To explain why, I’ll first have to discuss what a brushless motor is and how it works.

If you’ve ever touched an electric scooter, a cordless drill, a drone, an RC car, etc., chances are you’ve used a brushless DC motor before. Brushless motors are more complicated to drive and expensive than brushed DC motors, but they have several advantages: precise control, higher efficiency, better reliability, and several more.

A typical brushless motor will have three separate conductors organized into windings. Each conductor shares an end with another conductor. With this layout, when any two wires have a voltage across them, a specific coil will become energized. This coil will then make the rotor align to it, and the motor will spin. By energizing specific coils at specific times, the motor gains speed. However, as a consequence of this layout, it is much harder to drive a brushless motor than a brushed motor as you cannot apply a voltage and expect it to spin. Typically, hobbyist applications involving brushless motors will use off-the-shelf speed controllers rather than custom-designed ones due to the relative difficulty of driving the motors.

image source: https://www.edn.com/hdd-bldc-motor

This operating principle is significantly different from a brushed motor, which uses carbon “brushes” to maintain contact with the rotor, so that the rotation of the motor itself acts as a sort of mechanical controller. Brushed motors only require a DC voltage across the terminals to spin continuously. The brushes inside a brushed motor can wear out over time and require the motor to be rebuilt, while brushless motors have no moving electrical parts; their main vulnerability is to overheating where the insulation around the windings can melt. The inherent lack of positional control also makes brushed motors much less precise, and they require an external tachometer to know the speed of the motor.

With so many advantages, it makes sense that these types of motors are so common in mobility applications where high torque, speed, and longevity are required.