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Only shoots once!

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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Only shoots once!

Unread postAuthor: alkapwn1 » Mon Jun 14, 2010 7:37 pm

Hi, I decided to take it upon myself a year ago to start my first potato cannon. I have now completed it with various add-ons and features including three spark gaps, a bolt action breech-loading mechanism and a PC fan to circulate the air within the combustion chamber. While The fan was blown out on the first shot, all other systems still work.

The problem lies in the ignition. I can go out, fire it, then any other immediate attempts to shoot completely fail. I don't use hairspray, (use Old Spice) and can clearly see sparks igniting from the only spark gap I can see (therefore a complete working electrical connection, no?).

Is it because the spark gaps are too large for the little click BBQ ignitor? I have thought of getting an electric ignitor to possibly 'boost' the power of the sparks. I spent so much time on this cannon (including burning a fair sized hole on my forehead) I cannot give up now and say it doesn't work!

If anyone could please help me I'd sure appreciate it thanks!

Topic title edited by MrCrowley: Don't post in ALL CAPS.
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Unread postAuthor: Technician1002 » Mon Jun 14, 2010 8:25 pm

For combustion, fresh fuel and AIR is required. Simply shooting in another load of fuel and not bothering to completely change the air will do this every time.
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Unread postAuthor: sgort87 » Tue Jun 15, 2010 2:49 am

If you are allowing the chamber to vent properly then your problem is what you suspected.

BBQ sparkers have the tendency to spark once and kinda burn out for a while if the gap is too big. You can reset the sparker by shorting the gap. (I usually use my fingers. :P) This will keep happening unless you tighten up your gaps.

I recommend taking one of the gaps out completely. Sure, it's not as "cool", but it will be MUCH more reliable.
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Unread postAuthor: Technician1002 » Tue Jun 15, 2010 3:20 am

Sometimes a product of combusion, which is water, will condense in high humidity and provide an electrical short. Make sure you don't have steam condensation in the chamber.
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Unread postAuthor: jrrdw » Tue Jun 15, 2010 9:58 am

Also I have read hear before that the multiple gaps can not ad up to more then the original intended gap of the igniter. I'm sure this can be changed a little, but how much would involve some trail and error.
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Unread postAuthor: sgort87 » Tue Jun 15, 2010 12:10 pm

Technician1002 wrote:Sometimes a product of combusion, which is water, will condense in high humidity and provide an electrical short.

After one shot? No way. Worry about the gap.
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Unread postAuthor: ukejosh » Tue Jun 15, 2010 4:43 pm

i just made my cannon yesterday too, and if you can see that the spark is going off then your problem is probably the same as mine was, your not venting it properly, so my advice is to blow really hard into it after every use, the exhast from the first shot just sits in the combution chamber stopping the primary ingredient of combustion to enter the chamber( O2 )

so, basically just blow in it a few times after every use to let O2 in
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