RSG Treadmill Motor

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Original poster: "S&JY" <youngsters@xxxxxxxxxxxxxxx>

Happy New Year,

For those contemplating building an asynchronous rotary spark gap, the
following may be useful:

I bought one of the new $10 surplus treadmill motors from Surplus Center
(www.surpluscenter.com), Item # 10-2167, and I am most pleased with it.  It
is a permanent magnet DC motor rated at 2.25 HP at 260 volts and 5 amps.
The bearings are tight with inperceptable end play.  It comes with a 6 inch
diameter combination flywheel, cooling impeller and pulley that is perfectly
balanced.  The temptation to use it as-is as an arbor for the RSG rotor was
too much, so that is what I am using.  As there are 11 impeller blades, I
had to drill 11 mounting holes between the blades through the rim to attach
the rotor.  Any other number of bolts would result in imbalance.

With the hub at 6 inches, the rotor must be 12 inches in diameter to allow
enough space between the electrodes (mounted at 11 inch diameter) and the
"arbor" rim.  This is not a problem - there is power to spare to turn this
relatively large rotor, a 12 inch x 3/8 inch piece of GP03 (electrical grade
fiberglass) from McMaster Carr (8549 K47), cost about $13.

A small 0 - 120 VAC variac powers a full wave bridge rectifier with a 1,000
uF filter capacitor.  Here are some test results:

Rotor RPM    AC Volts   AC Amps
1000                       30          0.6
2000                       56          1.1
3000                       82          1.9
4000                      106         2.8

At 4,000 RPM, the motor power needed is only about 0.4 HP, and it runs cold
and is very quiet.  I will be using 12 rotor electrodes, so at 4000 RPM, the
break rate will be 800 which is more than adequate for most purposes.

Bottom line - this is a winning combination, and I commend it to anyone.

--Steve Y.