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Re: Disc Construction



Brian and Reinhard,
I'm fascinated by your discussion of how to reduce the dwell angle by 
offsetting the centerline running thru the three elements of the gap. I hope 
my 2-cents doesn't dumb-
down things too much. I assume you mean the centerline lying in the plane 
parallel
to the motor shaft. But there is also the centerline in the plane lying 
parallel to the disc and
perpendicular to the shaft--the radius. Brian, as you say, offsetting the 
fixed elements from
the rotating element will not unbalance the rotor. But in addition to 
offsetting the angular
displacement, why not offset the radial displacement, or in other words why 
not move the
fixed elements up or down? Sort of like instead of O-O-O make it a D-D-D in 
both planes -- sorta. The D is supposed to show 1/2 the area of the O. This 
ANSCII really sucks!
What is ROC?

Angular displacement:  D-O-D
  Radial displacement:  D-O-D

I'm afraid I have regained the lead in the bidding for stupid questions.

Ralph Zekelman

Subj:	 RE: Disc Construction
Date:	5/8/99 5:17:39 AM US Eastern Standard Time
From:	tesla-at-pupman-dot-com (Tesla List)
To:	tesla-at-pupman-dot-com

Original Poster: "Basura, Brian" <brian.basura-at-unistudios-dot-com> 

Reinhard,

You're comment about the start/stop of the actual spark not coinciding with
the mechanical dwell is correct.  

Note-This spreadsheet was intended as a tool to get the mechanical
components in the ballpark and not necessarily a representation of the
electrical behavior.

As for the offset. Let me see if I can explain it without resorting to
ASCII...  

Take a simple rotor, equally spaced rotating electrodes, and two fixed
electrodes (one on each side of the rotor).  The offset would be the
centerline difference (if any) in the two fixed electrodes. 

If the fixed electrodes are in line with each other then the mechanical
dwell will be maxed and determined by the speed of the rotating electrode
and it's diameter. If you offset the centerline of the fixed electrodes
(without changing any other parameters) you will reduce the dwell since the
overlap will be less. 

Regards, 
Brian D. Basura


-----Original Message-----
From: Tesla List [mailto:tesla-at-pupman-dot-com]
Sent: Thursday, May 06, 1999 7:17 AM
To: tesla-at-pupman-dot-com
Subject: Re: Disc Construction


Original Poster: "Reinhard Walter Buchner" <rw.buchner-at-verbund-dot-net> 

Hi Brian,

>Original Poster: "Basura, Brian"
<<mailto:brian.basura-at-unistudios-dot-com>brian.basura-at-unistudios-dot-com> 
>The RSG Dwell Time spreadsheet is now available at:
><http://fp2.hughes-dot-net/brianb/download.htm>http://fp2.hughes-dot-net/brianb/do
wnload.htm
 
 
I downloaded your XLS sheet. It is very similar to what I use in my
HBTC program. However there are two things:
 
1.) You make the assumption, that the arc start/stop takes up no dwell time.
This is a major problem (I donīt have a solution for it, either), because
the
arc will jump before the gaps line up and will continue after the gaps
seperate.
In order to consider this time "zero", you would have to incorperate a very
high rpm motor and / or big disk diameter (the speed of the electrodes has
to be VERY high). Otherwise, the arc time is much longer than your proggy
suggests. Finding the time that the arc stays on (= time before alignment+
time during alignment+time after alignment) isnīt that easy. It depends on
electrode size (the larger the ROC, the faster the time is) and shape. I
donīt know of any simple formula that will allow one to accurately calculate
this (although the Sim guys out there probably could make a simulation to
predict results),
 
2.) What do you mean by center to center offset? Do you mean this:
(use courier to view)
 
RSG A with no center offset:
 
  X
X   X
  X
 
RSG B with center offset:
 
  X
X   X
 X
 
Arrgh! I hate ASCii. It doesnīt come out like I want it to. In 
RSG "A" you can "connect" the electrodes to form a cross
where the lines intersect exactly in the center of the disc. In
RSG "B" the line intersection is not in the center of the disc.
Is this what you mean by offset? If so, I donīt think this
would be wise, because the disk will rotate off-balance and
you be getting different firing angles for each electrode. If
this isnīt what you mean, could you please explain what 
"offset" means.
 
Thanks and coiler greets from germany,
Reinhard 




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