Re: Rotary Spark Gap - Construction Questions

["Mark Broker" <broker-at-uwplatt.edu> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Ross,

I don't know too terribly much about motors.  But, I know that one can make
an
adjustable speed AC motor but modifying the input frequency.  This will
also
adjust the torque, but I never really got an explanation of that.  But, I
believe (more guess than fact) that this frequency controller is not
incredibly
easy to build, and is a bit expensive to purchase.

A 3600RPM motor with this type of controller may get you to your desired
speed.
I'd talk to a buddy at work about it, but he's going to Wyoming on business
next
week, and I don't know of anyone else who know's anything about this type
of
motor control (all DC at work.  For those who don't konw, which is all but
about
3 of you, I work at P&H Mining Equipment, which makes huge electric shovels
for
open pit mines.  I've seen my fair share of 1600HP DC motors on the shop
floor
:-)

Perhaps not the best solution for your needs, but I thought that I'd throw
it
out there for consideration.  For motor sources, try rockwell-dot-com (some
subsidiary makes good motors).

Good luck

Mark B.


> I'm looking for nice speed controlled gap from 0 to about 800 breaks per
> second.  I'm half-way basing my desgin Kevin Ottalini's DC coil that does
> well all the way out to 700 bps.  After reading lots of TCML archives, it
> appears that the ideal motor for such a task is a 1/2 to 1 HP "Universal
> Motor" that apparently can be run on either AC or DC.  Chip mentions that he
> uses one of these on his gap
> http://bhs.broo.k12.wv.us/homepage/chip/details.htm
>
> I don't know anything about this type of motor.  Can someone suggest
> sources/costs for such a motor?  I will probably wind up using a phenolic LE
> rotor with 3/16" tungsten rod electrodes.  Looks like 6000 RPM with 8
> electrodes can get me the 800 bps I desire.  Don't worry with sending the
> usual safety alerts - all will be cut on a good mill, statically balanced,
> contained, etc.  I can use any advice/links on high speed ASRGs and
> universal motors.