Earlier I wrote: "Ordinary brushes or slip ring brushes should not work at all." This is not correct.
The above should say: "Slip ring brushes should not work at all. Of possible interest is that contact point brushes might work on ordinary iron disks used in place of the bearings. The same circular M field wold be produced and hysteresis would allow that field to rotate into an effective position."
In other words, a shaft with bearings and two iron disks, with point brushes to the disks instead of the bearings, should also work. Replacing the disks with copper disks should not work. Even a shaft with a single iron disk and point brush, and an ordinary brush to the shaft, should work.
Best regards, Horace Heffner http://www.mtaonline.net/~hheffner/
