These are outer rotor type brushless DC motors that achieve high efficiency, long life, and low noise levels.
Brushless DC motors are energy-saving DC motors that do not need the commutators and brushes that are the disadvantages of brush motors and provide superior service life, noise levels, quietness, and efficiency. The outer rotor type has the stator positioned within the cup-shaped rotor. The inertial moment is large and the drive torque can also be made large, so they have superior speed constancy that contrasts with the inner rotor type. This speed constancy is utilized to drive optical disk drives and hard disk drives. Also, because they have such high torque for being lightweight, they are also used for direct propeller drive of model airplanes.