SpudFiles

Hello guys,

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

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:
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).

Fuel Used

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!
[/code]

hmm... I'm not shure what greasing the threads would do exept completely insulate them. try another pair of screws, or a different ignition like this one: http://www.spudfiles.com/forums/idea-fo ... t8727.html -make shure to read all the pages as there is a lot of info to help make that technique work.

Hope this helps

have you disconnected the taser to see if works w/o being hooked up to the gun?

Spedy wrote:hmm... I'm not shure what greasing the threads would do exept completely insulate them. try another pair of screws, or a different ignition like this one: http://www.spudfiles.com/forums/idea-fo ... t8727.html -make shure to read all the pages as there is a lot of info to help make that technique work.

Hope this helps

I just thought I'd mention that I greased the threads of the male/female end cap, it shouldn't be preventing combustion of the gas.

Are you saying that the 9v battery isn't producing a strong enough current in the stun gun? That's something my father (who is in the electrical business) mentioned, that the BBQ lighter creates a spark across the screws while the taser is just a steady stream of electricity.

In any case, I'm going to Home Depot tomorrow morning to buy a new BBQ lighter and will test that to rule out the taser as the problem.

If the 9v thing is what you're thinking, because the taser is 100,000volts it only uses one 9v battery while some other stronger tasers use 2, 3 or 4.

Merged:

sandman wrote:have you disconnected the taser to see if works w/o being hooked up to the gun?

Yes, it works perfectly fine... it's not permanently connected when I'm firing.

I'm basically holding the (+) and (-) electrodes of the taser to the two screws and pulling the trigger. I know it's sparking inside because I hear the sparking muffled by the PVC as opposed to the louder buzz when I test it outside.

ok, then how long of a burst of deodorant did you put in

I thought plenty... even excessive amounts at times.

I ranged anywhere from 5 one thousands to 10 one thousands...and then on some attempts I waited 2-3 seconds for some oxygen to get in before immediately sealing the cap.

Note that 5 one thousands of deodorant and the BBQ spark has been sufficient in the past.

ok even though you said it was sufficient in the past i would say try a 1-2 second burst depending on chamber size, and let it set for 10 sec to mix, and then try to fire
but thats all the info that i can give you, hope it helps

arthasmenethil wrote:

Spedy wrote:hmm... I'm not shure what greasing the threads would do exept completely insulate them. try another pair of screws, or a different ignition like this one: http://www.spudfiles.com/forums/idea-fo ... t8727.html -make shure to read all the pages as there is a lot of info to help make that technique work.

Hope this helps

I just thought I'd mention that I greased the threads of the male/female end cap, it shouldn't be preventing combustion of the gas.

Are you saying that the 9v battery isn't producing a strong enough current in the stun gun? That's something my father (who is in the electrical business) mentioned, that the BBQ lighter creates a spark across the screws while the taser is just a steady stream of electricity.

In any case, I'm going to Home Depot tomorrow morning to buy a new BBQ lighter and will test that to rule out the taser as the problem.

If the 9v thing is what you're thinking, because the taser is 100,000volts it only uses one 9v battery while some other stronger tasers use 2, 3 or 4.

Oh.. I got confuzed. I thought you sprayed the spark gap. lol. The current shouldn't be a problem in the stungun, and the only difference in the sparks of the bbq igniter and stun gun is that the stun-gun has higher voltage and that the stun-gun spark is a continuous arc..

Alright, well 1-2 sounds a little light but it's something I haven't tried yet and is worth an attempt.

Thank you for trying to help.

Merged:

Spedy wrote:

arthasmenethil wrote:

Spedy wrote:hmm... I'm not shure what greasing the threads would do exept completely insulate them. try another pair of screws, or a different ignition like this one: http://www.spudfiles.com/forums/idea-fo ... t8727.html -make shure to read all the pages as there is a lot of info to help make that technique work.

Hope this helps

I just thought I'd mention that I greased the threads of the male/female end cap, it shouldn't be preventing combustion of the gas.

Are you saying that the 9v battery isn't producing a strong enough current in the stun gun? That's something my father (who is in the electrical business) mentioned, that the BBQ lighter creates a spark across the screws while the taser is just a steady stream of electricity.

In any case, I'm going to Home Depot tomorrow morning to buy a new BBQ lighter and will test that to rule out the taser as the problem.

If the 9v thing is what you're thinking, because the taser is 100,000volts it only uses one 9v battery while some other stronger tasers use 2, 3 or 4.

Oh.. I got confuzed. I thought you sprayed the spark gap. lol. The current shouldn't be a problem in the stungun, and the only difference in the sparks of the bbq igniter and stun gun is that the stun-gun has higher voltage and that the stun-gun spark is a continuous arc..

Well from what I understood about both devices:

The stun gun emits an extremely low current, with extremely high voltage in a constant stream of electricity.

The bbq ligher uses pressure on a crystal to generate a high voltage spark across its electrodes.

I'm not sure whether there's a difference between a short powerful spark and a constant arc of low current high voltage electricity but all I know is that it HAS fired from the BBQ lighter but NOT from the taser.

Merged:

Ok... 2 seconds of fuel did it. Wow that was really loud.

Merged:

Thank you very much for both of your help .

I honestly thought that 5 one thousand-10 one thousand of fuel was optimal for the volume of my chamber but I guess more fuel doesn't always mean more power.

yah, more fuel doesn't mean more power. you could have found this throughout the forums. Btw, glad to hear your cannon is working.

Hi,

OK cool you got it to fire.

The extremely high voltage and low current that you mention are true. That also means you do not have to worry about condictivity or your wires and screws. The current can go right through many kOhms with only a little voltage drop -- and there is plenty of voltage drop to afford.

Did you consider propane? You get a little more power, it's very clean to work with and it will never wet your ignitor.

Regards
Soren

glad that i could help, and now it sounds like your getting better performance

dongfang wrote:Hi,

OK cool you got it to fire.

The extremely high voltage and low current that you mention are true. That also means you do not have to worry about condictivity or your wires and screws. The current can go right through many kOhms with only a little voltage drop -- and there is plenty of voltage drop to afford.

Did you consider propane? You get a little more power, it's very clean to work with and it will never wet your ignitor.

Regards
Soren

The question of whether the current of the taser had the ability to ignite the gas was answered last night with a bang (so to speak).

I did not consider propane because when I think of propane, I think of those large containers for gas grills and then the thought of working with valves and stuff seemed to be undesirable for me and my friends who want our spud gun to be portable and easy to use. How hard is it to buy some Right Guard from CVS, spray a little inside and close the cap and fire? You can see why I ruled out propane.

I'm not worried about my igniter getting wet considering it's manually ignited from the outside (making contact with 2 screws and pressing the taser trigger). I do worry about the part of the screws that are on the inside getting gunked up but so far Right Guard has proven to be relatively clean (and fresh smelling, even after it burns).

Sandman:

I wish I saw how far the potato went, but it was very dark out and I was taken aback by the apparatus working and didn't even think to listen for a "thud." But based on the sound of the launch, it probably went super far.

Actually, propane is much more efficient. You can just get the smaller containers and strap it to the side of the cannon.

You can also use a $1 syringe and a disposable butane lighter like this. Even without the syringe, a butane lighter is a little more reliable than a spray can since the lighter puts out gas as a slow stream instead of a big blast. The lighters I've mod'd put out about 5cc/second, a tiny fraction of what a can of Right Guard (or whatever) puts out. Makes it a lot easier to get the right amount of fuel.

With a decent fueling system, and a chamber fan, the gun should fire every time.