Cogging torque
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Cogging torque of electrical motors is the torque due to the interaction between the permanent magnets of the rotor and the stator slots of a Permanent Magnet (PM) machine. Also termed as detent or 'no-current' torque, it is an undesirable component for the operation of such a motor. It is especially prominent at lower speeds, with the symptom of jerkiness.
[edit] Reducing cogging torque
A summary of techniques used for reducing cogging torque:
- Odd - Even number of stator coils (15) and magnets (16) - See Muller Motor
- Skewing stator stack or magnets
- Using fractional slots/pole
- Modulating drive current waveform
- Optimizing the magnet pole arc or width
Almost all the techniques used against cogging torque also reduce the motor Back emf and so the resultant running torque.
Here to mention, a slotless PM motor does not have any cogging torque.
[edit] Model railway motors
Model railway motors usually have a 2-pole permanent magnet and 3, 5 or 7 poles on the armature.
