Re: ASRG & clarification of "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>

Terry B., Terry F., Dan McC., Steve C., Matt D., Malcolm, et al:

Thanks for your comments and replies to my original post; it's encouraging 
that so many people are taking the time to formulate serious responses.

A few clarifications about my comments on the "propeller" rotary gap concept:

1. The baseline "conventional" RSG against which the propeller design was 
compared was assumed to have a rotor disk made from either one of the 
epoxy/fiberglass composite materials (G-10, Garolite, etc) or 
linen-reinforced phenolic. These materials will NOT "shatter" and fragment 
under any reasonable (3600 RPM maximum) rotary gap usage, even if a flying 
electrode is shed or there is an impact between flying and stationary 
electrodes. Any design that uses a rotor fabricated from an un-reinforced 
material will be dangerous also, as acrylic ("plexiglass") or Lexan WILL 
completely shatter under shock loads, especially if stress risers like 
electrode holes, etc are present. However, the fragments from a burst rotor 
will have less sectional density than a piece of tungsten rod, and will 
have far less kinetic energy and penetrating power.

2. The word "makeshift" did not imply poor workmanship or stupidity, it 
meant not having the correct tools available to do the job in the proper 
manner. The implication is that this type of rotary gap could be quickly 
built at home with nothing but a hack saw and a hand drill.

3. My comments were not meant to be "destructive" criticism; they were a 
warning that this design would not meet conventional design or safety 
standards for rotating machinery.

4. Terry B., your analysis of the actual forces involved is very useful to 
help see the "theoretical" safety margins of your particular gap. Your 
measured "slip" load of 20 lbs is also interesting. I believe that in the 
US, many builders would use 1/8" tungsten rod, which is generally the most 
commonly available diameter, rather than the 5/32" rod used in your 
calculations. This would increase the "pull-out" loads acting on the rod as 
a result of imbalance. Substitute 1/8" rod in your analysis, and the safety 
factor is further reduced beyond the 2X factor due to the 1/2*L error in 
your formula.

5. I would challenge anyone who has made one of these gaps to run a simple 
test: will the gap run continuously for 1 week without self destructing? I 
don't mean commutating an operating Tesla coil, but just sitting alone in a 
corner behind a shield with the motor running.  This might seem extreme at 
first, given the duty cycle of a Tesla coil, but certainly a rotary gap 
could be expected to see several hours of cumulative run time over the life 
of a coil. Demonstrating a survival time of 20X actual run time (or 40 
hours) is not unreasonable, given the possible consequences of failure.

Again, my comments were meant to highlight the fact that this type of 
rotary gap has some additional risk factors not present in conventional 
disk-type rotors, and that suitable protection for any rotary gap needs to 
be in place to deal with a worst-case failure. I have seen more rotary gaps 
run without "scatter shields" than with, and everyone running a rotary 
needs to consider shielding an integral part of the design, not an 
accessory to be added "sometime later after everything is running OK".

BR,
Scott