On Sep 1, 2009, at 10:51 AM, Stephen A. Lawrence wrote:
Michael Foster wrote:
I haven't been following this thread very closely, so if my input
is repetitive, shoot me. Stephen's idea seems like a good test of
whether this phenomenon is thermally or magnetically driven. Has
anyone tried this with non-magnetic bearings?
Horace did, and as I recall he got a null result. His reason for
trying
it was specifically to test whether it's a magnetic or EM effect,
rather
than a thermal effect. Fly in the ointment is that stainless does
have
rather different thermal (and other) properties from plain steel which
could have accounted for the failure with stainless.
The effect is clearly magnetic. The current drop through the current
sense resistor when running vs not running, for the magnetic
bearings, clearly shows this. There is a back emf.
There is *no* sign of torque with the stainless bearings. If fact
they brake when current is applied, probably due to arcing. The
braking is somewhat reduced when graphite powder lubricant is used,
but there is still no sign of torque whatsoever for the stainless
bearings. It is apparent there is a similar braking action for the
magnetic bearings, but their torque clearly overcomes the drag
increase due to arcing.
I have a specific series of follow-up experiments planned, but am
doing other things at the moment.
Best regards,
Horace Heffner
http://www.mtaonline.net/~hheffner/
