This is my first time here and I hope to seek some advice from more experienced launchers.
I built my first potato cannon two weeks ago out of PVC piping.
I have a 4" x 2 ft combustion chamber with a 2" x 4 ft barrel.
The chamber volume is 96*(pi) inches^3 and the barrel is 48*(pi) inches^3
Yes, I don't have the ideal 1.5:1 volume ratio for chamber to barrel but my gun has fired successfully in the past so I don't think that's the issue.
The problem I'm having right now is that I cannot get a detonation to occur within my chamber. I had originally been using a BBQ igniter wired externally in this circuit diagram:
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[[BBQ (+)]] ~~~~insulated copper wire tie~~~~~ (screw head leading into chamber)
[[BBQ (-)]] ~~~~direct contact~~~~ (second screw head leading into chamber)
Internally the screws form approx. a 90deg angle with <1/8" space between for an arc.
This worked for awhile, with a small arc of electricity occurring across the screws when I pressed the igniter. Then, either dropping it in the sand (I live on the beach) or successive use diminished the power of the igniter and now I can barely get a spark to work under the most ideal of conditions (touching the two contacts together outside of this circuit).
So, not wanting to pay 15$ every few attempts at firing this gun, I bought a 100,000v stun gun off eBay thinking that I'd get more life out of my trigger mechanism. With a constant stream of electricity, I wouldn't have to worry about pressing that resistant red button a few 100 times to get a shot off.
I have -yet- to get the spud gun to fire with the taser, but understand that two weeks have passed since I've had a successful launch.
Interventions taken so far
Besides buying a taser for a better trigger mechanism, some things have been done since I've had a successful launch.
I've changed out the screws which had a dark black tint to them (note I did not use hairspray ever for the gunking reason; did my homework first). I figured they may have lost some conductivity from the 5-6 launches I've done.
I've greased the threads of my male and female end caps for the chamber with non-flammable pool pipe (PVC rated) lubricant.
I've hosed out the entire apparatus to clear any residual burned fuel and potato remnants (this was a different day, it was perfectly dry with each attempt to fire it).
As mentioned, I never once used hairspray because of what some of the veteran launchers said about what it does to screws and the interior of the chamber.
I've used right guard deodorant spray which has been successful in the prior launches.
I've also -tried- TAG body spray but I have been unsuccessful with that since this problem started.
I live on long island; temperate climate. But since it's summer, temperatures average about 75-80deg Farenheit daily.
I'm sorry for the huge story, I just wanted to provide as much background as possible for anyone who wishes to assist me.
Thank you for reading!