Re: My first ARSG, or a Dangerous Design?

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

Original poster: "Scott Hanson by way of Terry Fritz <teslalist-at-qwest-dot-net>" <huil888-at-surfside-dot-net>

Some time ago, when I saw the first proposal for a rotary gap based on this
design, I cringed but refrained from making any comments.

However, I feel that I must warn anyone who would consider this "makeshift"
type of rotor that it is unquestionably the most dangerous design concept
that I have ever seen proposed on the TCML. Please understand that this is
not a personal attack on anyone who has conceptualized, designed, or built
such a device; its just that this design is intrinsically incredibly
dangerous, and is contrary to all conventions and design standards that have
been established for high speed rotating machinery.

The single greatest weakness in this design is in the attachment of the
rotating electrode (tungsten rod) to the "hub". The only thing retaining the
rod in the hub is friction, whether it is obtained from a press fit of the
rod into the hub, or side load provided by a set screw, etc. The coefficient
of friction between any plastic and a smooth tungsten rod is very low.
Theoretically, if the hub and rod were somehow assembled with such
perfection that they were in a condition of perfect dynamic balance, the
centrifugal forces acting on each leg of the rod would cancel each other,
and there would be no load on the rod trying to move it axially through the
hub. In reality, the balance will never be perfect, and the unbalance forces
will try to fling the rod out one side of the hub. Now as soon as the rod
slips a few thousandths of an inch, the unbalance forces will increase
greatly. In a few microseconds, the rod is shot out of the hub at very high
velocity. The tungsten rod has scores or even hundreds of times the
sectional density, and penetrating power, of a nut and bolt or short section
of tungsten rod that might be shed by a conventional disk-type rotary-gap.
While a heavy Lexan shield can usually contain electrode parts from a
conventional gap, there is a much higher probability of penetration by a
projectile with high sectional density (that's why almost all
current-technology gun-fired anti-tank projectiles are long, thin
high-density kinetic energy "penetrators" of tungsten carbide or depleted
uranium).

By itself, that's bad enough. But there's much, much more wrong with this
design. First, all plastics "creep" to release internal stresses. A good
"press-fit" of the rod into the plastic hub the day its made will be looser
next week, and even looser next month as the plastic "cold-flows" and loses
its grip on the rod. If a set screw is used, the threads in the plastic
slowly deform and creep, and the clamping pressure of the screw against the
rod decays with time. In the end, no matter how tight a fit the rod is in
the hub initially, it will inevitably get looser with time.

Now, add the potential problem of heat conduction through the rod to the
plastic hub, either causing the plastic to heat up and expand very slightly,
or in more severe cases to start to melt. Again, the rod is in danger of
being shot out of the hub as if from a gun.

Further, all these considerations are also applicable at the attachment of
the hub to the motor shaft, which is also very weak in this design.

The bottom line is that this type of rotor construction may run for several
hours, or it may self-destruct before the motor ever reaches operating speed
the first time it is powered up. The probability of failure, and the
consequences of failure, are much more severe with this type of rotor
construction, compared to a conventional disk rotor with multiple flying
electrodes.

Unfortunately, the construction requirements for a high speed rotary gap
(1,000 RPM or greater) are not easily improvised in a home workshop. If you
lack the right equipment (lathe, milling machine & precision rotary table)
to make a high quality disk-type rotor with multiple flying electrodes, you
will not be able to make a safe "propeller" type rotor either.

Dan, the construction quality and attention to detail in your rotary gap is
apparent from your photos. Unfortunately, the basic design is severely
flawed. If you actually intend to power this rotor up, PLEASE equip it with
a multi-layer safety shield/enclosure of Lexan,  3/4" plywood, or steel
pipe, etc that can stop the rod when it separates from the hub.
Additionally, I'd orient the gap vertically, and stay out of the plane of
the rotor when its operating.

As for others contemplating the construction of this type of gap, I'd
emphatically urge "DON'T DO IT". The risks are just too high.

Regards,
Scott Hanson





----- Original Message ----- type
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Wednesday, January 22, 2003 7:50 PM
Subject: My first ARSG - Tribute to Terry Blake !


 > Original poster: "by way of Terry Fritz <teslalist-at-qwest-dot-net>"
<dhmccauley-at-spacecatlighting-dot-com>
 >
 > I just finished my first ARSG and to my knowledge, I think I am the first
to
 > follow in the footsteps of Terry Blake's Propeller-Rotor design.
 > Thanks to Terry Blake's ingeniusness, we individuals who lack the
machining
 > equipment to make a precision balanced rotor can now have a
 > top quality rotary spark gap.
 >
 > Here is a picture of my ARSG:
 >
 > http://www.spacecatlighting-dot-com/images/arsg01.jpg
 >
 > Here is the complete webpage:
 >
 > http://www.spacecatlighting-dot-com/teslacoil9.htm
 >
 > And here you can see the genius himself at work creating a wide variety of
 > different Propellar-Rotor sparkgap designs:
 >
 > http://www.tb3-dot-com/tesla/sparkgaps/index.html
 >
 > Thanks again Terry for the help!!!  Lets hope it works as good as it
looks!
 > Better wear those safety glasses!
 >
 > Dan
 >
 >
 > ---
 > [This E-mail scanned for viruses by SURFSIDE INTERNET]
 >
 >

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