q₋Index

Indicated by the symbol q, there is something that allows us to know the number of slots for each pole and phase as an index indicating the quality of the slot type winding.

where
S = number of teeth
m = number of phases
p = number of magnetic pole pairs

In a motor that utilizes rotation of a magnetic field generated by the stator (armature) like an induction motor, it is desirable that q is an integer of 2 or larger. For BLDC motors using strong permanent magnets, fractions with q being 1 or less are allowed. However, for designs that require efficiency and smoothness, q = 2 as in induction motors, is preferred. The photo below is an example of this.
The table on the next page summarizes the combination of S, m, p and q. This table shows the least common multiples of the number of teeth and the number of magnetic poles. The larger this value, the larger the number of cycles of cogging and the tendency for cogging torque to decrease.