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The most basic source of cogging torque is the interaction or attraction of the permanent magnets and the steel structure of the stator as the motor rotates. These attractions and overcoming them prevent the rotor from turning smoothly. Another source is the interaction of the rotor magnets and the stator winding when it is energized, due to harmonics. Cogging is often an undesirable feature, causing noise, vibration and non-uniform rotation, so during product development, minimizing this effect was a design “CTQ” (Critical To Quality). As a result, DEC Star® motors have extremely low cogging torque, resulting in smoother operation at all speeds, virtually eliminating torque and speed “ripple”.