Electrical – BLDC Motor – Reason for different number of pole pairs on rotor / stator

brushless-dc-motormotor controller

The figure below shows a BLDC motor (TSDZ2 Ebike Motor).
It has 18 stator windings (3 phase -> 3 pole pairs per phase)
and 16 poles on the rotor.
What are possible reasons for this design? Why is a lower pole count on the
rotor beneficial?

Is my assumption correct that the ratio between electrical and mechanical revolutions
is given by the rotor pole count? In this case there would be 8 electrical cycles
per mechanical revolution.

TSDZ2 BLCD Motor

Best Answer

The unequal numbers are chosen to minimize ripple. The rotating field is generated in the stator, hence mechanical rotation depends on the stator