The brushless DC motor
1）These motors contain permanent magnets on the rotor, and the position of them must be known so that the nearby coils are energized at exactly the right time to cause magnetic forces that spin the motor. Three-phase sensor brushless DC motors use three Hall sensors that toggle and tell the controller when to commutate the coils.
2)And there’s also a second use for Hall sensors in motors. If a magnet is attached to the shaft or the driven gears, a nearby Hall sensor can be used to detect the speed and direction of the turning.