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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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Hubb
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Thu Apr 15, 2010 6:33 pm

Okay. For the past year, I've been "building" a combustion launcher. I figured I would start this topic to display what I've done with it so far in hopes that it motivates me to finish it. It will be made to shoot potatoes, golf balls, and tennis balls.

I plan on having several features to this launcher that are not normally seen. I will not discuss them just yet, but will update this thread with them as they are built.

Below are images so far. I want the final design to be aesthetically pleasing as well as powerful.
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This shows how the vent valve will fit in the chamber.  It is not glued in yet, as I may change the look before it is finished.
This shows how the vent valve will fit in the chamber. It is not glued in yet, as I may change the look before it is finished.
0415101805a.jpg (6.86 KiB) Viewed 3309 times
This shows the ball valve vent system.  It is designed so that it can be removed in case maintenance is needed.
This shows the ball valve vent system. It is designed so that it can be removed in case maintenance is needed.
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This picture shows the elbow portion of the launcher.  Notice how the fittings are countersunk in the breech end and chamber end.
This picture shows the elbow portion of the launcher. Notice how the fittings are countersunk in the breech end and chamber end.
0415101759a.jpg (6.11 KiB) Viewed 3309 times
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Gun Freak
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Thu Apr 15, 2010 6:36 pm

Can you post a diagram of the final product?
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Thu Apr 15, 2010 6:50 pm

Are you using 3" fittings in 4" pipe for the chamber?

Slick. :)

What size is the camlock?
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Hubb
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Thu Apr 15, 2010 7:01 pm

Gun Freak wrote:Can you post a diagram of the final product?
Yes I can. It is below.
mark.f wrote:Are you using 3" fittings in 4" pipe for the chamber?

Slick. :)

What size is the camlock?
Why, yes. Yes I am. The power of Gort discovered this little tidbit a while back. And my sleeving calculator discovered that if you sleeve 3" thinwall pipe into 3" Sch40 pipe, it fits snugly around 2" fittings, which is what I've done to support the camlock in the image above.

Those pictures were taken with my phone, but the next set of pics will be taken with a better camera so that it can capture more detail for you guys.
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Gun Freak
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Thu Apr 15, 2010 7:45 pm

That looks pretty nifty, I like the slanted style. Where's the sparker going?
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Hubb
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Thu Apr 15, 2010 7:53 pm

I plan on actually having two spark strips in the chamber, one on each side of the interior wall. This will generate six sparks simultaneously, which will launch six flame fronts to travel from the outside . In theory, it should function the same as centrally placed three spark system without having any obstructions in the center of the chamber.

It may or may not work, but I plan on firing it with a stun gun and it will easily fire six sparks with the strips I have in mind (which are very similar to starman's spark strips).
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mark.f
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Thu Apr 15, 2010 8:09 pm

Hubb wrote:...And my sleeving calculator discovered that if you sleeve 3" thinwall pipe into 3" Sch40 pipe, it fits snugly around 2" fittings...
Quite a useful tidbit there. Especially when making a piston valve in a 3" tee... hmm...
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Hubb
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Thu Apr 15, 2010 8:59 pm

Yeah, I use that sleeving calculator quite often for a lot of different projects, including paintball and nerf.
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Thu Apr 15, 2010 10:05 pm

I love fitting shortcuts, did you do something special to attach the 3" threads on the ball valve?,

I believe you intended to design this to be special, but now that you posted it someone else is probably gonna try these techniques, and if you don't finish this by then, your cannon wont be the first and wont be as special so you wont be able to enjoy the secret gratification of being the first to employ a concept that many of us secretly strive for. So there's your motivation for posting this, now go build it!
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Thu Apr 15, 2010 11:20 pm

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Fri Apr 16, 2010 1:31 am

That is a very attractive design! I really like that a lot. Good luck with getting it finished. I'm looking forward to it. Oh, if anyone builds one like it before yours is finished, I will know who I saw it from first.
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Hubb
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Fri Apr 16, 2010 7:20 am

iknowmy3tables wrote:...did you do something special to attach the 3" threads on the ball valve?...
Everything I do is special :lol:
I cut a hole into the 3" cleanout so that a 1.5" pipe would fit through it. I glued the 1.5" ball valve to the pipe, then inserted the pipe into the cleanout. I trimmed the pipe enough so that I could fit a coupling over the pipe and it rest against the inside edge of the cleanout. I then trimmed the coupling so that it would be flush with the threads.

It sounds more complicated than it actually is, so I'll try to get some pics of it up to better explain.

SpudBlaster15 wrote:...What are the final dimensions (Chamber volume and barrel length) you have planned for this launcher
I'm gonna go for about a 1:1 ratio with all three barrels, so each one will have a different length. The chamber is (without the slant cut in it) is just under 450 cu in (this includes the fittings).


To everyone else: Yeah, this is going to be unique. It's one of the objectives I was going for. Thanks for the positive feedback. I plan on getting a great deal of it done over the weekend.
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Hubb
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Sun Apr 18, 2010 11:34 am

I'm almost finished with the breech and barrel support section of the launcher. I wasn't able to cut the chamber at an angle, mainly because my miter saw wouldn't stretch that big comfortable, but I'll say it's because it would have sacrificed too much chamber volume.

I'm also thinking about dropping the camlock fittings as well. The camlocks are nice, but they are a bit bulky and this means that I'm gonna have to trim up on some of the launcher (which I really don't want to do) to make them work comfortably.

Stay tuned...
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This is a picture of the 3" support for the breech.  3" SDR was sleeved into the Sch40 to form a nice fit over 2" fittings.  The same is done for the barrel support.
This is a picture of the 3" support for the breech. 3" SDR was sleeved into the Sch40 to form a nice fit over 2" fittings. The same is done for the barrel support.
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