Paul your physics are sound with regard to torque couples.
I am however in agreement with Elvo that position on the fast rotating mass of the armature assembly .... particularly when there are large near instantaneous changes in it's speed of rotation.
Again, with Elvo ...... late, heavy day and not exactly firing on all cylinders ... was early when I made my first post.
As I say ... going to have to think about it some more.
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