Re: Revised analysis of propeller gap: reduced safety factors

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

Original poster: "Terry Blake by way of Terry Fritz <teslalist-at-qwest-dot-net>" <tb3-at-att-dot-net>

Hi all,

Thank you Scott and Russ for checking my math.  I had not cracked that
physics book in over 15 years, and was so concerned about the other
equations, I forgot that there were only 100 cm in a m (not 1000).  Arf.

I have revised all the caculations at my website and added some general
conclusions.  Russ has already checked my math and thinks it looks good.

It is still being refined (and checked for errors), but here it is for now.

http://www.tb3-dot-com/tesla/sparkgaps/safety.html

Any additional information that comes out of this discussion will be added
to this propeller gap safety page.

The general conculsions are as follows;
1) make an enclosure (then a rotor explosion will not be a big deal)
2) do your best to center the rod, as this will reduce the forces pulling it
appart
3) 1800 RPM looks like it is no problem.
     3600 RPM should be OK if you watch your rod balance.
     higher than 3600 RPM is possible, but it is getting kinda scary
4) It is worthwhile to check your friction grip to ensure some level of
initial confidence
5) Improve the rod to arbor grip in any way you can


I like this gap approach.  I have run the 1800 RPM gap and it clearly is not
moving fast enough to be much of a threat.  But at 3600 RPM, the whizzing
sound is a bit unnerving, and you could see how a misshap would be ugly.
The forces are still quite reasonable at 3600 RPM, and it should be OK.

Even though I have called my ARSG a 15,000 RPM gap, that is the unloaded
motor rating.  I am sure it would never get that fast.  Although I have not
actually measured it (add to my todo list), I don't think I have pushed it
beyond 3600 RPM.  That's 480 breaks per second, which is plenty for most
occasions.

The only thing left to do is a destructive test to determine if the rotor
actually blows up at the expected RPM.  I'm not ready to blow one up yet,
but maybe soon.

Terry Blake
Coiling in Chicago


----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Saturday, January 25, 2003 12:47 PM
Subject: Revised analysis of propeller gap: reduced safety factors


 > Original poster: "Scott Hanson by way of Terry Fritz
<teslalist-at-qwest-dot-net>" <huil888-at-surfside-dot-net>
 >
 > Terry B. -
 >
 > I finally had a few free minutes to look at your analysis of the forces
 > acting on the press fit of the tungsten rod into the hub of your
"propeller
 > gap", and I think there may be  a few errors that created the impression
of
 > a large safety factor. The actual loads are much greater (~100X) than your
 > calculations indicate.
 >