Smudges permanent magnet motor discovery PDF

[Smudge]

Another issue to consider is the distance between magnets in the stator, as it modifies-deforms the natural shape of the mag field.

That deformation is simply the effect of the stator field adding (vector addition) to the rotor field.  By considering the magnet to be equivalent to a current loop, and in particular by considering rectangular loops, you can examine independently the separate forces on each of the four rotor current elements coming from each of the four stator current elements.  You are not faced with trying to understand the deformed field.

You find that the long edges of the stator do impose torque forces on the long edges of the rotor, but they are only cogging forces, they cancel out over a full rotation.  Then considering the long edges of the stator imposing forces on the short (end) edges of the rotor, those forces do not create torque, they only create compression or stretching forces on the rotor magnets.  That leaves only the short edges of the stator and the forces they impose on the four edges of the rotor.   By examination it is clear that the short edges of the rotor do get torque that doesn't cancel out over a full rotation.  The long edges also get torque that can negate that, and that is where I have had to build my computer model that integrates the forces along those long edges.

Note that my approach only applies to rare earth magnets where the magnetization does not change.  For other magnets where the magnetization changes on approach to other magnets the edge current model would require the currents to change in accordance with the magnetization change.

Good luck with your experiments.

Smudge