Rotary gaps

["Richard Barton" <richardbarton-at-caving5.freeserve.co.uk> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Hi there
	People may be interested in a method I have used that enables me to
increase the number
of spark contacts on the edge of my rotary gaps. (I'm talking about the type
that has a simple bolt
through the wheel edge, to bridge across two stationary electrodes)
I have used four pairs of stationary electrode, positioned at 12/3/6 and 9
o'clock around the disc.
I then drill and fit bolts at an odd number of positions around the disc
(but equally-spaced). The
exact number you can fit in depends upon the diameter of the disc. If you
get this right you find
then that each consecutive spark is staggered in relation to the previous
spark by at least 90
degrees, so you don't get a bad quenching situation at high speeds, with the
arc carrying over
between electrodes. I used a 12" diameter disc and got around 12 bolts at
its edge.
This disc was driven by directly mounting on a vacuum-cleaner motor,
controlled by an ordinary
dimmer-type switch on my control console. The whole disc assembly was
mounted in a perspex
box, and blown through by a second vacuum-cleaner motor, via a flexible
rubber hose.

											Richard.