Re: My first ARSG, or a Dangerous Design?

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

Original poster: "Stephen Conner by way of Terry Fritz <teslalist-at-qwest-dot-net>" <steve-at-scopeboy-dot-com>

At 08:00 23/01/03 -0700, you wrote:
>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 (snip)

I take your argument on board, but consider that the moment of inertia, 
hence stored energy available for doing damage if it bursts, is much lower 
in Terry's propeller design than any other RSG of the same diameter. The 
traditional design uses a large dense flywheel studded with chunky bolts 
all of which travel at the full peripheral velocity. OTOH, the "disk" of 
the propeller gap is 95% air. At higher speeds, the rod may tend to 
self-balance, but this can't be relied upon. If the unbalance is bad enough 
then there is definitely a risk of the rod slipping and hitting one of the 
fixed electrodes, in which case it might shatter, and the sh* would really 
hit the fan.

I still like the simplicity of Terry's design but I agree that positive 
location (ground flats and set screws) of the rod and motor shaft, also a 
hub made of phenolic or G10 rather than polythene, would be wise. I also 
wouldn't risk using a solid tungsten rod since it is so dense and brittle. 
If the rod were lighter and solidly fixed in place, I think the low inertia 
would make the propeller gap safer than many other homebuilt unbalanced 
RSGs. I intend to make mine from a 3/8" square aluminum bar (screwed to the 
hub) with platinum points from an auto contact breaker fixed to the ends.

Steve C.