Rotary Gap Construction?

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Matt Woody Meyer by way of Terry Fritz <twftesla-at-qwest-dot-net>" <meyerml-at-stolaf.edu>

Hello hello,
	My last coil used a static spark gap with marginal results at best, so I'm
planning out a means of building a rotary gap.  Since many of you seem to be
experts in construction, I was wondering if anybody would mind throwing in a
few engineering suggestions.  I'm open to anything, and have a substantial
budget to work with.  I'm looking around for 2400-4800rpm variable motors
(most of them I can just control the angular velocity with a variac, right),
I'm assuming that this should be enough if I have about 6-8 presentations
every rotation.

What I'm having difficulty with, as of now is:
1) My idea calls for using a conductive circle with bolts attached as the
electrodes.  I would then have two stationary electrodes (one at the 9:00
and one at the 3:00 position).  The problem I see in this is that the
charge, as it passes through the metal disc, will also partially hit the
motor.  This is bad.  Is there a way to, say, using electrical tape, wrap
the circle around the center with tape, or would this not work?

2) This would be slightly more complicated, but I suppose I could use a
belt, run off the motor and connected to the electrode plate, thus the motor
would be insulated from the electrode plate.

3) I'm also worried about the heat from the sparks melting the bolts... I
don't think those viewing the demonstration would appreciate a "hot dross
bath"... is there something (like tungsten?) that I should coat the
electrodes in?

As of now, I'm looking at the following for my setup:
a combination of the following transformers:
One 15kV 60mA neon
Two or three 12kV 30mA neons
Combination of the above... suggestions welcome here too.
Everything through a 20A 0-120V variac.

2 .018uf capacitors (in parallel)
12 turn flat primary spaced 1/2"
8" x 32" secondary, 24AWG topped with a 14x4 aluminum toroid (may build a
larger toroid).

The circuit is in the simplest design... Vac through primary transformer in
parallel with main spark gap. (two chokes to protect transformer).  Tank
circuit standard.

Thanks much, I'm still fairly new to coil construction, so I apologize in
advance for my ignorance :).  Strangely enough, none of the professors here
have had much HV experience, so I'm more or less on my own with this
project.

><>Matt Meyer
meyerml-at-stolaf.edu

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Matt "Woody" Meyer         Ellingson 120       507-646-2883 (CUTE)

St. Olaf College Physics Major
St. Olaf Admissions Tour Co-Coordinator
2001-2002 Ellingson Hall Residence Life Junior Counselor

"Physics is like sex. Sure, there's some practical application,
but that's not why we do it."   -Anonymous

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