Boom! The classic potato gun harnesses the combustion of flammable vapor. Show us your combustion spud gun and discuss fuels, ratios, safety, ignition systems, tools, and more.
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brplatz
- Specialist 2

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Thu Apr 17, 2008 4:44 pm
here is my new cannon. took about 2-3 days and multiple Lowe's runs to get er' done. Paint coming soon. 70"by 2" barrel and about a 20" Chamber. spark strip, chamber fan and Grill ignitor.
Almost done!

"Any problem on Earth can be solved with the careful application of high explosives...the trick is, not to be around when they go off" Col. Mertz Von Quiriheim
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STHORNE
- Sergeant 3

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Thu Apr 17, 2008 4:46 pm
wow, very nice job. damage pics?
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starman
- Sergeant Major


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- Location: Simpsonville, SC
Thu Apr 17, 2008 6:14 pm
Looks like a powerful cannon you have there...lots of chamber, lots of barrel...metered fueling...nice effort!
You should get yourself back down to Lowe's one more time and pick up some hose clamps to replace that duct tape. Also, it looks like you have forever sealed your spark system and fan inside your chamber with no way to service them if needed. Something to keep in mind for future combustions.
Have you shot the thing yet?
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STHORNE
- Sergeant 3

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Thu Apr 17, 2008 6:37 pm
yeah man...thats about the most unique ball valve i've ever seen (never seen it b4).
I haven't seen them at lowe's, so you got them somewhere else?
Forum Rules - follow them or else!
“Happiness is the meaning and the purpose of life, the whole aim and end of human existence”
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brplatz
- Specialist 2

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Thu Apr 17, 2008 6:52 pm
@starman
thanks i plan to get that duct tape off of there but it was much better that the bulky wood supports i made before. And no i have not been able to get it to fire yet. one calculator said about 85 PSI with my metering system but it didn't ignite. i must have tried it 5-6 times. so i tried another calculator and it gave me 50 psi to put in but i haven't tried it yet.
the ball valve you see there is one i found at Lowes right next to the one like
http://img.diytrade.com/cdimg/430486/40 ... 526668.jpg
i had one like that but it was a B!&@% to open and close. so i found this one and it is extremely easier.
COST me $90 bucks to make ugh! most expensive for me yet lol. Where can i get new propane tanks like the one pictured? i found that one in a cabinet in my garage lol
"Any problem on Earth can be solved with the careful application of high explosives...the trick is, not to be around when they go off" Col. Mertz Von Quiriheim
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brplatz
- Specialist 2

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Thu Apr 17, 2008 9:26 pm
anyone have an opinion on the PSI i should inject the propane at that would be great!
thanks
EDIT: forgot about double post sorry
"Any problem on Earth can be solved with the careful application of high explosives...the trick is, not to be around when they go off" Col. Mertz Von Quiriheim
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starman
- Sergeant Major


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Thu Apr 17, 2008 9:36 pm
brplatz wrote:anyone have an opinion on the PSI i should inject the propane at that would be great!
Be sure you are taking into account the volume of your rear elbows as part of the tank volume...all the way around to the potato breech. Also, your meter looks a tad bit smallish for your tank size, just eyeballing it from here...even using 1/2" pipe..maybe not. Check that again. If not you should have to be running a fairly high meter pressure to get the right amount. Check out Pat123's meter calc here:
http://www.spudfiles.com/forums/viewtop ... tml#169995
ALSO, one ugly thing I just noticed. You've got your propane tank mounted where it will essentially be upside (or tilted downward) most of the time...not good, will tend to liquidize and "flood" your meter plumbing. Turn it around the other way.
Last edited by
starman on Thu Apr 17, 2008 9:57 pm, edited 2 times in total.
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brplatz
- Specialist 2

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Thu Apr 17, 2008 9:47 pm
i tried it at 90 psi and nothing. im thinking my spark system is failing. i might have to go get a more powerful ignitor like a stungun and such.
the Propane tank is like that just for the pictures. its usually the other way around.

"Any problem on Earth can be solved with the careful application of high explosives...the trick is, not to be around when they go off" Col. Mertz Von Quiriheim
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DYI
- First Sergeant 5


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Thu Apr 17, 2008 9:48 pm
Just take the 5 minutes and do the meter calculations yourself. It won't kill you, and it might do a lot more good than all these "calculators" people are using.
Spudfiles' resident expert on all things that sail through the air at improbable speeds, trailing an incandescent wake of ionized air, dissociated polymers and metal oxides.
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starman
- Sergeant Major


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Thu Apr 17, 2008 9:51 pm
brplatz wrote:i tried it at 90 psi and nothing. im thinking my spark system is failing. i might have to go get a more powerful ignitor like a stungun and such.
the Propane tank is like that just for the pictures. its usually the other way around.
OK I get you on the upside down tank...hose is a bit long then. Also check with the calculator I edited into my last post.
Also, you should be able to hear a spark in there...and see one if you open the rear intake valve. Make sure you air it out good first...
IMO, it's hard to beat a stun gun for advanced combustions...
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BlackH
- Private 4

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- Location: Cape Town, South Africa
Fri Apr 18, 2008 1:46 am
Yes lose the calc go to
http://www.burntlatke.com/lp.html here is all the stuff you need to work out the stuff.
And here is a spark strip i made myself that has never let me down.
http://www.spudfiles.com/forums/my-new- ... 14078.html
O ps I don’t know if those gas bottles you use (I could not find a tap fitting for them here in SA) can work upside down make sure you hold the gas bottle upright if you load, I had that prob. and it floods your meter system. (This happened to me and uses a lot of gas.)
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brplatz
- Specialist 2

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Fri Apr 18, 2008 7:55 am
ok burnt latke gave me a Psi of about 53 so ill try that today. i was hitting 90ish on my first attempts. Burnt Latke has some great info and tools!
i make the spark strip like yours but less gaps because its just a regular BBQ lighter. im thinking i dont have enough power to jump the gaps. ill see if i can go find a electronic one or a stungun somewhere also.
"Any problem on Earth can be solved with the careful application of high explosives...the trick is, not to be around when they go off" Col. Mertz Von Quiriheim