On Aug 22, 2009, at 4:23 PM, Kyle Mcallister wrote:
V,
Hey kids, what time is it?
"Howdy Doody time!"
No, actually, it's ball-bearing motor time again. The old motor was
disassembled and remade into a more nimble form. The spacing
between the bearings was halved, thus reducing resistance. Also,
the wobbly allthread shaft was replaced with a much more balanced
smooth steel shaft, with a copper spacer to keep the bearings
separated and give a bit less unit resistance. The pulley was
mounted this time with an allen setscrew, which again made things
run truer.
Turns on the transformer secondary were doubled. Now the whole set
of jumper cables is being used! Open circuit secondary voltage is
now 7.26VAC.
With this connected across the motor, giving it a gently spin with
my hand now causes it to rapidly accelerate. It ends up going at
what I would estimate is at least 1000 rpm.
Nice job!
I've had that running for a few minutes at a time, and there was no
evidence of the bearings trying to seize; it doesn't begin to slow
at all. The only limit I can see is how long the insulation on the
wires can stand the heat generated. The advantage to the
transformer over the battery is pretty clear to me, at least: no
killing of an expensive battery, no (effective) limit on run time,
relatively steady current, no risk of hydrogen explosion/acid
shower. The only disadvantage is that we are out of the DC realm.
Still, this can be alleviated to a degree by using a bridge
rectifier made with high current diodes. I might have enough diodes
of high current capability to do this. Have to look.
Note: these are with the bearings still packed with the original
grease; removing that, cleaning everything carefully, and perfoming
Horace's graphite powder treatment (do have graphite powder) would
be interesting to see.
I would recommend holding off on the graphite until you get a chance
to take some measurements first. The graphite messed up my motor to
some degree as far as measurements are concerned. I just went to
Anchorage today to buy a couple more bearings just to have some clean
of graphite. I'll put them in gasoline wash for a day and then wash
with acetone. Maybe I can get some more meaningful current drop
measurements across those bearings than I did with the graphite
coated bearings.
I am stunned that your motor runs with grease in the bearings.
Perhaps the grease has graphite in it? Or maybe just carbon? I'm
just amazed it can run at all. If you clean it throughly it might
start arcing (making a grinding sound) like mine did, and then
graphite cures that without adding much friction. However, the "brush
drop" the graphite adds makes measuring back emf much more
difficult. I don't think it can't hurt much to attempt some voltage
drop (across the motor) measurements before adding the graphite,
given all your bearings have been through so far.
Horace: I will go back over your first response to this thread and
see what I can do for some measurements.
--Kyle
Best of luck and may the anomalies be with you!
Best regards,
Horace Heffner
http://www.mtaonline.net/~hheffner/
