Re: The Geek Group Slingshot Resistor

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

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Pyrotrons-at-aol-dot-com>

Heey Duck.

> 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 
> resistance.

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 
resistance. 

(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 
measureable resistance.)

I always seem to throw in a little extra, I guess this is okay. As long as it 
helps.

Later,

Justin Hays
KC5PNP
G-3 #1150
Email: pyrotrons-at-aol-dot-com
Website: www.hvguy-dot-com