In the item on the power generating function of a motor, I explained that the torque constant and back-emf constant are basically the same thing. Here, if we review Fig. 2.8, we will understand that the counter-electromotive force is also generated from a slotted core motor for models.
Rather than thinking that the wire is cutting across the magnetic field, we can think that counter-electromotive force is generated as a fraction of chronological changes in the magnetic flux that interlinks the coil as Fig. 2.20 shows, and then it is rectified by the brushes and commutator (AC/DC conversion) and observed as the counter-electromotive force of the direct current.
As we studied in equation (2.9), KE and KT are the same thing. Therefore, we will observe the counter-electromotive force instead of analyzing torque, and we let the obtained KE be KT as is, then torque calculation becomes possible. This is the second method of explanation.
Now, how should we consider cogging when applying this method? Simply speaking, you just add this element to the calculation.
There are several methods for calculating cogging torque, but they all require complex mathematical expressions that are difficult to understand.
This book will not go into detailed description of the above method but only mention it for your information that it can also figure out the torque of a cored motor. For more details, please refer to reference material .
 Kenjo and Nagamori; New Brushless Motor, Chapter 5, Sogo Denshi Shuppansha
The theory developed in said book is part of the basics, however, we believe this is the only book that has yet been published that describes basic principles yet unknown to specialists in this field. This book may be a little difficult for novices to tackle, but those aspiring to be motor specialists will hopefully attempt to read it.