Due to their mechanical commutation, brushed dc motors have a limited operational lifetime and are confined to low operating speeds typically less than 12K rpm. This makes them not particularly suitable for certain medical and industrial tool applications. Electronically commutated miniature motors continue to gain interest due to their simple construction and long operational lifetime.
Fig. 1 shows the cross-sectional view of a Brushless DC (BLDC) motor. In slotted BLDC motors (as shown in Fig.1 a), the presence of stator teeth prevents the overall size of the motor from being minimized. Moreover, the winding process becomes progressively more difficult as the motor shrinks in size [1]. On the other hand, the slotless BLDC motor (as shown in Fig.1 b) has either skewed or axial type windings fixed on the cylindrical stator iron core providing several advantages as well as small size.