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Re: The Geek Group Slingshot Resistor
Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Pyrotrons-at-aol-dot-com>
> an interesting varible resistor could be made by having a pair of
> copper bars with holes drilled along their length and bungee-cords
> strung between them. By making a variable mount to pull them tighter
> you would change the length and cross-section, changeing the
Yes, the rubber WILL change resistance as length and cross-section change.
Great idea, but off the top of my head I see two problems for this
"slingshot" resistor, lol.
1. Black rubber tubing has too much resistance to be used in this manner. It
is darn near an insulator for all practical (NOT tesla coil!) purposes. There
IS some stuff that gets close to what you're talking about, my dad was
playing around with this special "conductive rubber" for medical uses, but
unfortunately it has kohms worth of resistance (way too much for current
limiting) for a 5" x 5" pad of it, 1/4" thick or so.
2. Supposing you COULD get the stuff down into the 4 ohm(big coils) to 12
ohm(little coils) range, the resistance would change drastically as a
function of temperature. If you got it TOO hot, you have a nice flash of
light, then there would be no more current flow ; ) Heating in the rubber in
Watts would be equal to I^2 * R. I is the current in amps, R is the
(BTW, I just clamped a black rubber bungee cord in the vise for good
connection, and measured it with a precise ohm-meter. There was no
I always seem to throw in a little extra, I guess this is okay. As long as it