Each armature stack is energized twice per rotation in a sequential mode at alternating points. The degrees at which the stack fires equals the timing degrees of the armature. The stack and the magnet repel each other at the point of fire. So by placing the strongest edge of the magnet at the point of repulsion will increase torque. (See Note)
The figure shows the deferent points of degrees, where the center of the stack falls during the time of fire. This point of degrees depends on the timing of the armature. The degree of time that a stack stays energized from start to end, solely depends on the circumference of the commutator and the size of the brush face.
Note: The torque of the motor is in direct proportion to its field strength and the armature current.
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