How Brushed Motors Work  What makes motors work is basic electromagnetism which states that whenever electrical current flows through a conductor, it produces a magnetic field. Conversely, whenever a conductor moves through a magnetic field, a voltage is induced in that conductor, this is often referred to as back-EMF in motors.
To prove this to yourself hook up a volt meter to your favorite motor and spin the shaft, notice the volt meter jump. The permanent magnets are inducing a current flow in the coils as they pass through the magnetic field.  The type of electric motor used in R/C racing is a DC, permanent magnet, 3 pole motor. The permanent magnets are mounted in the can, and three coils of wire, the windings, are mounted on the armature. Click on the image for and exploded view of a motor and its parts.
 When you connect power to the motor, current flows through the brushes onto the commutator and into the coils on the armature. This causes a magnetic field to form in the coils which will attract one permanent magnet while repelling the other causing the armature to rotate. The commutator determines the polarity of each coil which makes it attract and repel the appropriate magnets at the appropriate time. The polarity is based on which brush (+ or -) is in contact with which coil/comm segment.
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