Sync motor modification

From:  FutureT [SMTP:FutureT-at-aol-dot-com]
Sent:  Wednesday, January 28, 1998 9:34 AM
To:  tesla-at-pupman-dot-com
Subject:  Re: Sync motor modification

In a message dated 98-01-28 09:23:38 EST, you write:

> I'm just about ready to test out my sync RSG with a 15KV/60mA NST.  For a
> motor, I bought a 1/8 HP 1725 RPM motor for $4.95 from H&R Surplus.  This
> unit has a 3.5" dia rotor.  I milled four flats onto it, each being
> 1.00".  While the flats should have been 1.30" to each cover 1/8 of the
> circumference, I thought it safer to remove less and see if it works.  It
> sync's right up so I'll stick with the 1" flats.  Only problem is, there
> are four angular positions, each 90 deg apart, from which the motor will
> stall if started there.  

Gary, all,

I don't think the 1/8 of the circumference is a hard and fast rule, in
fact, I don't really know what the best proportions really are.  I've
been using basically what I've happened to try and what happened
to work.  That is very interesting about the stall spots.  I've never
seen this in my motors...maybe I was lucky the motors never
stopped at these spots?  I've never heard the stall problem 
mentioned before, has anyone else seen the effect?  Good price
on that motor!

>Perhaps if the RSG works out well, I'll buy
> another motor and remove more material and see if that resolves the
> stalling.

I don't see offhand how that would fix the problem, but you never know.
Again, maybe someone else has seen and solved the problem?
> A question on adjusting the phase of a sync RSG.  It would be best if I
 >could do this without attempting the subjective test of when I have the
>longest spark, turning off power each time.  I did a dry run last night
> without my secondary installed, and as I rotated the motor case, saw a
> clear point of maximum gap arcing.  Is this a valid indicator of the
> correct rotor phase for when the TC is completely assembled?

I guess it would be close.  I assume you kept your input voltage 
very low during the test?  Without an installed and tuned secondary,
the voltage can rise higher than usual and maybe harm the caps.
Also in general, if you're using a resonant charging sized cap, it may
see quite a high voltage even when the secondary is installed and
tuned.  In my 12kV, 30ma neon powered TC, I obtained about 32kV
peak on my caps.  So the caps need to be adequately rated voltage-

Can you attach a long plastic pole to the gap, and use it to adjust
the phase during coil operation, or rig up some sort of gear-motor
to provide remote phase adjustment during operation?

John Freau
> Gary Lau
> Waltham, MA USA