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Re: shaft fasteners for RSG?



Original poster: DRIEBEN-at-midsouth.rr-dot-com 




 >
 > >Original poster: "Dr. Resonance" <resonance-at-jvlnet-dot-com>
 > >
 > >
 > >Don't consider Lexan for a large high power coil.  The heat will
 > start to
 > >melt the Lexan and send sparkgap shrapnel flying around.
 > >
 > >Use 1/2 inch dia. G-10 phenolic.
 > >
 > >A good design would be a 14 inch dia. G-10 rotor with 12
 > electrodes on a
 > >12.5 inch dia. circle.  Use a cheap surplus DC treadmill motor
 > (usually 2-3
 > >hp) with a pulley and belt for reduction in speed.  Most of
 > these motors
 > >top
 > >out around 3,000 RPM with a light load.
 > >
 > >Set the pulley reduction ratio to give you approx 600 pps
 > (maximum) from
 > >your rotor.  Power the DC motor with a standard 120 V 25 Amp
 > rectifier >block
 > >and use a healthy filter cap on the output for smooth DC power.
 > Use an RF
 > >"hash" choke between the DC output and your motor to choke off
 > any RF that
 > >might feed back due to any spikes or induced currents in the
 > sparkgap --
 > >motor case.  Use one on both pos and neg legs.
 > >
 > >The treadmill motors are $30-$75 range or less thru surplus houses.
 > >
 > >This allows you to adj speed and pps for best results with your
 > coil. >
 > >Have a machinst to the layout and setup on the rotor (.0005"
 > tolerance) and
 > >then static balance it.  Don't do this at home as a do-it-
 > yourself thing.
 > >The rotors are a dangerous part of a coil setup and a quality
 > machine shop
 > >will do an excellent job.  Safety first --- it's a bit expensive
 > but a lot
 > >cheaper than buying one of your neighbors a new eye.
 > >
 > >We can machine you a rotor hub if you need one.  I would need to
 > know the
 > >shaft size on your motor.  Then take this and your G-10 to a
 > local shop and
 > >have them do the rest.
 > >
 > >Dr. Resonance


Hi Dr.

Thanks for the info. I already have a 2.5 HP treadmill
motor that I obtained for the purpose of a possible
drive for an ASRSG. I built a rectifier out of (2)
paralleled FW bridge 200 PIV, 8 amp rectifiers from
Radio Shack and paralleled them for a 16 amp rating.
I have not used a filter cap during testing and the
motor seems to run great from 0 to 3500 (max) rpm
through a variac. I've tested current draw from the
motor and it only draws considerable current while the
speed is accelerating (i.e. turning up the voltage at
the variac). Once the speed has stablized (within a second
after the input voltage has stopped increasing) then
it tends to draw only about 2 amps at 120 volts input
with no load on the shaft. I am aware that a 12" or
14" dia, half-inch thick G-10 disc loaded with 8 to 12
12 tungsten rotary  electrodes will add a consider-
able drag load to the motor and the current draw will
be considerably more than 2 amps. BTW,  will a standard
power line filter work instead of the RF hash choke for
filtering the input leads to the motor? I already have
several 120/250 volt, 20 amps line filters.

I know that G-10 is the choice material for high powered
RSG rotors and although I did successfully employed lexan
discs in my previous design at up to around 9 kVA (accord-
ing to the meters) w/out a meltdown, but I know that I was
running on "borrowed time" :^O I also know that it's
just about imperative to have someone with professional
maching tools/facilities to turn down and drill the
rotory disc to keep the tolerances tight. I may
have to hold off on that aspect of it for the time
being as the budget is a little small at the time ;^(
For now, I'm still in the secondary coil construction
phase and will be winding #17 heavy build magnet wire
on a 12" (actual dia measurement colser to 13") card-
board concrete former. It is being coated with several
coats of spar varnish urethane. The spar varnish doesn't
seem to crack with temp changes like the plain urethane.
I will be winding about 44" of the tube with the wire
and the nominal dia. for #17 is about .045", so that
would translate to about 21 to 22 turns per inch.

Overall, I'm taking how ever much time that it requires
to make sure that I do this coil project right (as right
as a limited budget ameture can, at least). Some would
say that Cardboard is a poor choice for a secondary coil
former but I got great performance from the 12" cardboard
tube from my previous coil w/ 8 to 10 ft sparks from
a 38.5" long secondary coil (total winding length) with
#18 wire and a 9x30 Landegren toroid with around 7 to
8 kVA input.

This post is starting to get long so I'll cut it off
now.

David Rieben