Re: mot's

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

Original poster: "Jason Johnson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <hvjjohnson13-at-hotmail-dot-com>

Well my rotary is as precise as you can get with a jigsaw, file, and $40
drill press (cheap chinese made ebay variety), but doesn't really run at
very high speed. It runs at 3450 rpm, just on a normal 1/4 horse 2 pole
motor, but you're right, there is virtually no play in the bearings
whatsoever. It was like that when I bought it for $16 at a local
junk/surplus/hardware store. There are eight 1/2" square tungsten carbide
cutting inserts (ebay, 7.00 for 20) for the spinning electrodes, and two
pieces of  1/4" brass threaded rod for the stationaries (by the way the
brass electrodes have less than 1/4" erosion over the entire runtime of this
gap), adding up to a total of 460 BPS. The only place you can see it online
is the geek groups page for the MI teslathon,
http://www.thegeekgroup-dot-org/teslathonmain.htm
scroll down and click on the
link that says "Click to see Jason's Coil" right under my picture. There is
a safety gap that comes up REAL close to the rotor, but I have never seen it
fire, except for the time I forgot to hook the coils ground up, and even
then all it was was a few very faint sparks, looked much like a shock from
static electricity. The electrodes are normally adjusted to about 1/32" gap
on each side for a total of about 1/16". The rotor is 6" in diameter and
1/8" thick, I don't know what type of aluminum, but I'm guessing 6061 from
the way it cut . Almost any aluminum should work just fine for something the
size of mine. FWIW the motor is floating, the cord has only 2 prongs, it is
a GE type, thermally protected, 1/4 HP, 3450 rpm, ball bearing, capacitor
start/induction run type (though I don't have the capacitor hooked up right
now, it pulls the disk up to speed just fine over a few seconds), don't know
the service factor off the top of my head. This gap has also eliminated
interference from my coil, I run it 30 yards from a 6 (sometimes more)
computer network, 3 TVs, our directv box, and then all of neighbors stuff,
and theres not so much as a line or snow of any kind (with the airblast
there was some interference).

As far as performance goes, this gap has entirely replaced my airblast gap,
added a foot and a half of spark length, halved the current draw, and made
the sparks look MUCH cooler. The BPS still wants to be higher, the sparks
are still really hairy looking and have 2 or 3 main branches, the best
performance over this whole range is at the max speed of the gap, and when I
let the gap spin down spark length drops as the speed drops (much like a DC
coil). I've measured the voltage to ground from the center of the rotor
while the gap was firing with a small MOT (just the MOT) and it bounced a
bit but never went above 3 or 4 volts. With a MOT bank the discharge tracks
all the way around the disk (looks like a purple flame), and I have never
measured the voltage to ground with this setup, but the second you throw a
capacitor in the mix there isn't a single problem and voltage on the shaft
of the motor is nill. Of course it could just all be that I got incredibly
lucky and all of this works for me every time without a hitch...., (looks
back on junk pile from misc. previous ideas and experiments) on second
thought, no it didin't happen like that :-)

I don't see any reason why this type of gap couldn't be the norm, I'm only
15, I've never even been in a machine shop, don't own or have access to any
precision machine equipment, and I built this gap for under 25 dollars in 2
days. Most anyone with some patience could build this gap. However, its
looking like people won't have too, the way triggered gaps are
progressing...

<< Jason R. Johnson >>
G-3 #1129
The Geek Group
http://www.thegeekgroup-dot-org/


----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Thursday, August 09, 2001 2:23 AM
Subject: Re: mot's


> Original poster: "Gregory Hunter by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <ghunter31014-at-yahoo-dot-com>
>
> Hi Jason,
>
> Straw man argument. High-precision, high-speed, low
> firing voltage asynchronous rotary spark gaps are the
> exception, not the norm. For 99% of hobby-level
> coilers, a 15A breaker is inadequate for two
> unballasted MOTs. I saw a guy at the 1st UK teslathon
> running a 10,000RPM ARSG with an unballasted (!) 5KVA
> pole pig, but that doesn't mean it's a common setup or
> even a very good idea.
>
> I'm pleased to hear your ARSG works so well. I'm
> inspired to contemplate building a copy, since I work
> with MOTs quite a bit. I've got a nice chunk of .125"
> Aluminum sheet stock in my junk box. I don't know the
> exact alloy, but it is hard, flat, and mirror smooth.
> I bet it would make an excellent rotor for an ARSG
> along the lines of yours. Now I just need a motor with
> near-zero play in the bearings. Do you have a link
> where I can have a look at yours?
>
> Best Regards,
>
> Greg
> http://hot-streamer-dot-com/greg
>