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Semi-Automatic Combustion Cannon Concept

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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Semi-Automatic Combustion Cannon Concept

Unread postAuthor: Bowman » Sat Apr 14, 2012 8:37 pm

Well I'm new to the world of spud guns so I am not really sure of what would be the proper materials for a build such as this. I've been toying around with the idea of a semi-auto combustion cannon. And all I want to know is what type of materials would be safe to use. To see what the design looks like look below.

NOTE: I created a rough "drawing" of the design in adobe flash but now it won't let me put it in this post..Any help? *FIXED*

Ok so here's a basic lowdown on how it works. You prime to gun once by pulling back on the bolt thus loading a ball from the spring loaded magazine while simultaneously pumping fuel into the chamber. The trigger mechanism is hooked up to a piezoelectric BBQ ignitor that ignites the fuel pushing it through the "inside" of the bolt. Once the expanding gases reach the end of the bolt it pushes the ball forward once the ball gets to a certain point in the barrel the gas operated reloading system moves backwards due to the gases already behind the ball. When it moves back it pumps more fuel into the combustion chamber and loads another ball. After all that happens all you have to do is pull the trigger another time to ignite the fuel once more thus repeating the cycle of operation.

The main point of this thread was to get some ideas for what materials would be safe to build something like this with. The only reason I'm asking is because I realize how dangerous this build could be if not assembled correctly.

Color Guide:
silver - magazine
teal - lower receiver
red - combustion chamber
green - bolt housing
blue - bolt
black - trigger mechanism
yellow - gas reload system
orange - fuel chamber with integrated pump
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BC-2 spud gun.jpg
BC-2 spud gun.jpg (14.66 KiB) Viewed 2385 times
Last edited by Bowman on Sat Apr 14, 2012 11:07 pm, edited 3 times in total.

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Unread postAuthor: Crna Legija » Sat Apr 14, 2012 8:42 pm

You could use PVC but only issue is it could over heat so id say best off using thin steel or aluminium.
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Unread postAuthor: pneumaticcannons » Sat Apr 14, 2012 9:04 pm

What error message are you getting? have you lowered the quality enough so that the image takes up less than 350 KB?
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Unread postAuthor: Bowman » Sat Apr 14, 2012 9:38 pm

@Crna Legija that was my first idea for a material but I have no idea where to get them.
@pneumaticcannons no I have the file saved on my desktop so when I was making my post I clicked on the "browse" button and found the file then I tried submitting the post it says does not allow ".fla" and I don't really understand how you can lower the quality of an image....But that's not important I have and idea. Do you know how to convert .fla to a .jpg? Maybe it will let me post it if it's in a different format?
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Unread postAuthor: Gun Freak » Sat Apr 14, 2012 9:56 pm

.fla is only recognized by the program you made it on. You need to export it as another file type.
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Unread postAuthor: Bowman » Sat Apr 14, 2012 10:44 pm

Ok got it all figured out. I edited the first post.
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Unread postAuthor: jackssmirkingrevenge » Sat Apr 14, 2012 10:51 pm

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Unread postAuthor: Bowman » Sat Apr 14, 2012 10:55 pm

I don't understand what that link has to do with my concept? I mean mine is semi-automatic, from what I could tell his was a pump action paintball gun that he modified to run off of propane.
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Unread postAuthor: jackssmirkingrevenge » Sat Apr 14, 2012 11:09 pm

It's a semi-automatic combusion which works, sufficient to be a commercially viable paintball makrer. To my knowledge, no one on this forum has ever made a true semi-auto combustion, unless you count this awkward robot. While not strictly semi-automatic, I would also count this brilliant effort by ijahman.

In short, you've got your work cut out so a bit of inspiration won't hurt ;) I recommend cartridges :D
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Unread postAuthor: Crna Legija » Sat Apr 14, 2012 11:21 pm

Bowman wrote:I don't understand what that link has to do with my concept? I mean mine is semi-automatic, from what I could tell his was a pump action paintball gun that he modified to run off of propane.


nope its a store bought semi auto paint ball gun power by combustion of propane.
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Last edited by Crna Legija on Sat Apr 14, 2012 11:42 pm, edited 1 time in total.
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Unread postAuthor: Bowman » Sat Apr 14, 2012 11:28 pm

I was wondering if you could point me in the direction of a good fuel for sustainable fire because in the design I have in the first post it's running off of hairspray....But I do have an alternate fueling system for propane I imagine that would be better than hairspray (duh)... I'm not sure what you mean by cartridges... I assume you mean a shell that houses the projectile like in a real gun, but that would require a shell ejection system which I don't really plan on building if I don't have to.... Could you elaborate more on those "cartridges" you were talking about? I'll go through your thread again more carefully to see if I can understand.
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Unread postAuthor: jackssmirkingrevenge » Sun Apr 15, 2012 12:40 am

Bowman wrote:I was wondering if you could point me in the direction of a good fuel for sustainable fire because in the design I have in the first post it's running off of hairspray....But I do have an alternate fueling system for propane I imagine that would be better than hairspray (duh)...


On this level I think you need to read up a bit more about the issues involved.

Projectile loading inside, you need to do the following things:

1) bring fresh air into the chamber

2) inject the correct amount of fuel

3) ignite the mixture

... and repeat.

The pump action of the Tippman C3 carries out the first two functions:

Image

The piston vents the chamber and at the end of its stroke, opens a valve that allows a measured amount of fuel into the chamber.

Doing this automatically (without using a manual pump action) is rather more challenging.

I'm not sure what you mean by cartridges... I assume you mean a shell that houses the projectile like in a real gun, but that would require a shell ejection system which I don't really plan on building if I don't have to.... Could you elaborate more on those "cartridges" you were talking about?


The idea of using cartridges has the advantage of removing the mix problem, because you have a pre-filled cartridge that is already fuelled. Fuelling it would be very easywith a syringe. Some more infohere.

Image

Making a shell ejecting system is not easy, but far easier than making a semi automatic self-venting and self-fuelling combustion ;)
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Unread postAuthor: Bowman » Sun Apr 15, 2012 12:45 pm

1) bring fresh air into the chamber

2) inject the correct amount of fuel

3) ignite the mixture


Well, I had an idea of having a fan in the rear of the chamber that will pretty much be on all the time that way it will vent in between shots and provide air to mix in with the fuel. Like I said this is a basic design it's no where close to what it actually is going to look like, I'm in the process of designing a "fuel injector" if you will. And obviously I would need a way to ignite the mixture (which I already have). I was thinking about using just a piezoelectric BBQ ignitor just for the sake of simplicity but my only worry is that if I use thin steel or aluminum the chamber itself will short out the circuit due to it's material. So then I thought of maybe using a spark plug, which would work, so I got the ignitor I want to use.

Making a shell ejecting system is not easy, but far easier than making a semi automatic self-venting and self-fuelling combustion


True....When you mentioned yesterday I fought with the idea of it because I wanted it to be simple... But then I realized I would have to have a shell ejection system if I wanted it to be simple.... Overwhelmed with curiosity I started the design last night. Still a WIP....
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Unread postAuthor: al-xg » Sun Apr 15, 2012 1:16 pm

http://home.howstuffworks.com/nail-gun3.htm
Any one seen one of these up close ?

Cartridges are probably one of the easier ways to get rapid fire but also involve quit e a bit of bulk, unless the power density is increased.

For these pump action designs, I reckon one could use the fuel pressure to operate the pump while at the same time providing volumetric metering.

The fuel could also serve to keep the chamber cool if required.
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Unread postAuthor: POLAND_SPUD » Sun Apr 15, 2012 1:39 pm

it's 100% possible to build a semiauto combustion... no one has ever attempted it - that's the point

get 2 or so DCVs a microcontroller and you're done
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