On Sat, 27 Jun 2009, John Berry wrote:
> However if the current cuts across both poles then it encounters as much
> magnetic field exiting as entering over it's length resulting in opposite
> twists at each end.
Faraday motors have a subtle feature: we need to look at relative
torques between the two movable metal parts. To find differential torque,
calculate the disk torque, then subtract it from the torque upon the
sliding-contact/external-circuit. For the simple Faraday disk, depending
on how the b-field is shaped, we might find zero torque on the disk, but
significant torque on the battery circuit. Electric motors only respond
to relative torque, so if we grab the Faraday disk and prevent its
turning, the battery circuit still tries to spin.
Also: if we do as you suggest and magnetize the shaft, then perhaps a
shorted-out Marinov motor will produce a measurable electric current! This
would certainly demonstrate that HPG (Homopolar Generator) effects cannot
be ignored. (With two ball bearing races, the shaft needs to be magnetized
tripole: NSN or SNS. Just stick a couple of supermagnet disks or rings
in the right place.)
Also:
Radial current path for four balls touching a central shaft (balls
not shown):
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|------( )------|
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Current path if a corrosion layer invades the leading edge of the contact
points, w/shaft rotating CW:
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__ | __
|__-- ( )__-- |
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|
Note that these issues are quite similar to the "thermal humps"
explanation: it takes time for steel surface at the contact point to
expand, so the rising hump is always lagging behind, which puts it in a
position where it accelerates the spheres and the shaft.
Also note: lots of FE hobbyists claim that Faraday generators are
anomalous. If ball bearing motors are Faraday motors, then they
offer a form of high-speed Faraday generator for the anomaly-hunters.
(((((((((((((((((( ( ( ( ( (O) ) ) ) ) )))))))))))))))))))
William J. Beaty SCIENCE HOBBYIST website
billb at amasci com http://amasci.com
EE/programmer/sci-exhibits amateur science, hobby projects, sci fair
Seattle, WA 206-762-3818 unusual phenomena, tesla coils, weird sci
