What is a brushless motor, and why is it marked as a good thing? Are “brushed motors” common?
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A brushed motor is cheap, simple and does not require any electronics to make it run. Attach DC directly to the motor and it spins. Typically starters for cars and tractors are brushed, and simple consumer applications.
Downside is that the brushes wear out and needs replacing, and it’s a bit complicated to vary the speed. So in an electrical car where the motor runs all the time, they aren’t used (*). Instead, brushless motors are applied. There are two main popular solutions, one is using strong permanent magnets in the rotor (that’s spins the wheel) and electronically vary the field in the stator (that’s attached to the engine bay). These are very efficient and do not wear out. The magnets are expensive and a bit heavy, though. This is a DC permanent magnet motor.
Other option is an AC induction motor. It’s about of magic, as the magnetic filed of the rotor is generated by *induction* from the stator. It’s a very simple and reliable design, used for heavy industrial applications for ages. The control electronics gets a bit complicated, and it’s not as efficient as a permanent magnet motor.
(*) There’s a type of motor that uses a brush instead of induction to generate a magnetic field in the rotor. Does not require expensive and heavy magnets, and is more efficient than induction motor. As the brush does not switch any currents, it’s more of a slip ring. It’s supposed to work for the life of the car without replacing. BMW uses this, for instance.
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