Stepper motor with adjustable cogging torque

A stepping motor has a rotor with a permanent magnet, a stator housing, and a plurality of stator coil assemblies provided in the housing. Each coil assembly has a bobbin, a bobbin wound around the bobbin, and two pole plates with pole fingers extending axially in the bobbin. The bobbin is disposed between two pole plates and defines a rotor receiving space. A number of magnetic detent plates are arranged around the permanent magnet rotor. Each magnetic detent plate has a rotor receiving central aperture and a plurality of inwardly extending projections spaced about the central aperture. The projections cooperate with the magnetic field of the rotor magnet.