On Sep 1, 2009, at 10:29 AM, 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?
See:
http://www.mail-archive.com/[email protected]/msg33690.html
http://tinyurl.com/melx3v
Watch the movies of the experiments. They are very short.
Steel - rotates at about 110 amps, even when arcing can be heard,
i.e. without graphite.
Stainless - decelerates even faster than when coasting down, due to
arcing.
Write-ups to date with data, scope photos and pictures:
http://www.mtaonline.net/~hheffner/HullMotor.pdf
http://www.mtaonline.net/~hheffner/HullMotor2.pdf
Glad to hear more experimentation might be done! I'm off on other
things for the moment.
Best regards,
Horace Heffner
http://www.mtaonline.net/~hheffner/
In any case, I looked it up and you can buy single race ball
bearings made of 316 (non-magnetic)stainless steel. Iron wire for
hanging picture frames can be had at hardware stores.
Soldering to stainless steel can be done fairly easily if you know
how. Soldering to any steel is difficult unless you use tinner's
fluid, an acidified zinc chloride solution modified with ammonia.
Soldering to stainless steel is something I discovered myself, and
if no one thought of this before me, then you heard it here first.
You treat the stainless steel with ferric chloride solution
(circuit board etchant), rinse, then wipe with tinner's fluid and
then ordinary electronic solder can be used. This works like a charm.
I may start a few experiments along these lines myself, if I can
find the time.
M.
--- On Tue, 9/1/09, Stephen A. Lawrence <[email protected]> wrote:
From: Stephen A. Lawrence <[email protected]>
Subject: Re: [Vo]:BB motor -- explanation (maybe not!)
To: [email protected]
Date: Tuesday, September 1, 2009, 9:42 AM
Here is another possible experiment
which could indicate definitively
whether the inductance of the outer bearing race is playing
a role.
Unfortunately it also seems likely to be harder than it
appears at first.
Run the experiment with stainless (non-magnetic) bearings,
and
(hopefully!) observe that the motor doesn't go.
Next, wrap many turns of uninsulated iron wire (obtained
where, exactly?
um) around the outside of each bearing race. The
tricky bit is that the
wire must make good electrical contact with the bearing
race all the way
around, because the idea is to increase the effective
permeability of
the race without messing up the current pattern in it.
An obvious way to make sure everything's in good contact
would be to
*solder* the wire in place all the way around, but
soldering to
stainless steel isn't something I've ever done and I don't
have the
impression it's straightforward.
Anyhow, if one can get the wire stuck to the bearings at
all, then one
should wind *enough* wire so that the magnetic properties
of the wire
are likely to make a gross change in the behavior of the
outer race.
Dunno how much that might be -- presumably, one would want
the layer of
wire to be at least as thick as the bearing race.
Now, re-run the experiment. If it still doesn't go,
then we haven't
learned anything, because there could be any number of
reasons why
winding iron wire around the outside isn't the same as
making the
bearings from iron to start with. But, if the motor
*does* go, then we
will have demonstrated that it is the magnetic property of
the iron, not
its thermal properties, that is having the effect, /and/ we
will have
demonstrated that it's the magnetic properties of the
*outer* *race*,
rather than the balls or the inner race, which is
important.
Whatever; this is another one which would be time consuming
and might or
might not show anything...
