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Re: synchronous gap help (fwd)

---------- Forwarded message ----------
Date: Tue, 10 Jul 2007 16:31:46 -0700
From: Ed Phillips <evp@xxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: synchronous gap help (fwd)

Subject: RE: synchronous gap help (fwd)

I think you're going to run into a problem using your relatively small
teletype motor to spin-up such a heavy 3/8" thick disk.  I was barely
able to get such a motor to spin a 09" thick x 6.12" diameter G10 disk
with just 4 brass acorn nuts electrodes, and it utterly failed to sync
with anything larger.  I'd strongly recommend using a propeller gap if
using a Teletype motor.  My SRSG page:
http://www.laushaus.com/tesla/sync_gap.htm, and Terry Blake's:

Regards, Gary Lau

	Many, many years ago I was involved in a project where we wanted to spin a 36" diameter disk at 3600 RPM.  I had an old NACA report which gave the windage torque of a disk as a function of diameter and speed.  I believe it goes up as the fifth power of the diameter and the cube of the speed but could be the other way around - report is long lost; width of the disk up to an inch or so had negligible effect.  Anyhow, even with a three phase 5 hp motor we never got that thing up to speed - motor would hunt violently - and ended up driving it through a mercury clutch which let the motor get started and run OK at around 3200 RPM.  At one point in the learning process we built a wrapping-paper covered frame around the motor and disk, filled same with helium and turned on the power.  Instant disaster as anyone with his thinking cap on should have anticipated.  The stream of air off the perimeter of the disk was accompanied by air rushing in at the center with the result that the frame was sucked into the disk and the pieces flung around the lab at alarming speeds - the thing made a very powerful air pump with a prodigious flow off air off the rim.  Fortunately no one was hurt.................

	Bottom line is that it would be a good idea for anyone planning an RSG with a synch motor jury rig a rotor of just about any material (even cardboard probably) and test to see if the motor could start and run.  I think the drag of the electrodes might be of second order importance but still something to be considered.