From RC Helicopter Wiki
A type of electric motor employing a rotating armature (also called a 'rotor') that gets its power through a set of small contacts called brushes. These brushes remain stationary and ride on a portion of the rotating armature called the "commutator". The armature has a number of coils of wire wrapped around it that, when energized, interact with magnets held stationary in the motor's body (or can); the interaction of magnetic fields causes the armature to turn.
A brushed motor has two power leads and the speed is controlled by the electronic speed controller varying the amount of power delivered to the motor. This can be done via a simple resistive current limiter; or more efficiently by delivering the motor's power in short, rapid pulses and controlling the power by varying the amount of time the motor is powered compared to how much it is not powered.
Brushed motors tend to be relatively inefficient for a number of reasons. The timing of when the coils are energized relative to the magnets are fixed by the commutator, and the brushes themselves cause friction and electrical resistance, and the motors wear out, often sooner rather than later. For these reasons, for most helicopter power purposes, a brushless motor is a far better (if more expensive) choice.
- Brushed DC electric motor on Wikipedia.
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