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Built a pneumatic cannon? Then post it here! This section is for completed, finished cannons that you have built. Please include pictures and information.
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Unread postAuthor: PCGUY » Mon Jan 31, 2005 12:31 am

<div align="center">MCPAC

Provided By Fiebig - <a href="http://www.geocities.com/fiebigspudguns/">http://www.geocities.com/fiebigspudguns/</a>

This is the MCPAC. Its a coaxial piston cannon. Meaning that the barrel runs through the chamber where it meets a piston on a spring which stops air from entering the barrel. You pressurize the chamber as well as behind the piston then release the air behind the piston very quickly which creates a relative vacuum and the piston moves back and allows all the air to enter the barrel to shoot... stuff... far. The MCPAC has gone through a few design changes to increase performance, or even just to get it to work at all. The original design is below. I had a blowgun as the trigger valve. I laugh at this now because blowguns have horrible airflow, that plus I had 1/4" pipe leading to it, this is all way too constricting to let the air vent properly. Also I used this cheap plumbers epoxy stick junk to seal around the barrel because Sears didn't have JB Weld. This crap was crap. It leaked horribly. Needless to say I had a lot of work to do...

Provided By Fiebig - <a href="http://www.geocities.com/fiebigspudguns/">http://www.geocities.com/fiebigspudguns/</a></div>
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As of now the main ammunition for the MCPAC is 3/4&quot; dowel rod pieces. These are good to use because they are cheap and easy to retrieve. At only 20 PSI the MCPAC can shoot one of these little rods over 50 ft. At close ranges they are good at devastating coffee makers and monitors. The MCPAC is so small it can easily be pumped up to 20 PSI with a hand pump.
This is the current final design of the MCPAC. Since the sprinkler valve was still constricting the airflow a bit, I put a 3/4&quot; ball valve in its place. I also put an elbow in. This design is the most efficient and I will probably leave it like this. Below is a pic of the rear of the gun.
MCPAC_2-29.jpg (17.8 KiB) Viewed 4269 times
This is the first design that actually worked. It has a male adapter JB Welded into the end cap with a tee on that. The tee leads out on one side to a sprinkler valve and on the other side to a Schrader valve. This design worked but still constricted the airflow a little. Below is a close-up of the rear of the gun.
This is the piston. Actually its the parts of the piston. Its very simple, just a .75&quot; PVC coupling with a plug in the end and a rubber washer bolted on.
The duct tape wrapped doohickey is the piston itself.
Next comes a short 3&quot; piece of 1.25&quot; pipe. this is the actual sleeve
This shows the chamber with the first piece of pipe sleeved in. It is a 1.25&quot; repair coupling wrapped with a few layers of duct tape to fit snugly. The gunky stuff around the chamber threads is plumbers putty.
This is the chamber of the MCPAC. You can see the barrel inside, there is a screw in the barrel to stop the ammo from going all the way through and firing early. Also you can see the barrel support a little farther down.
Next I upgraded to a 3/4&quot; ball valve but kept the 1/4&quot; pipe. Also I added a pressure gauge (just because these are essential for pneumatics).

I went to AutoZone to get some JB Weld to seal the barrel PROPERLY. This design didn't work either because the pipe leading to the trigger valve was still 1/4&quot; which is far to constricting!

I did however make a better piston for this design. I used to have a 1.25&quot; PVC end cap directly in the chamber with a rubber washer bolted on. The chamber is galvanized steel which is very rough on the inside.

The new piston was simply some PVC pipe sleeved inside the chamber with a new piston inside the PVC. This was much smoother the piston moved very well (by hand, I couldn't get it to move on its own)

There are some pics of the new piston below.
MCPAC_2-19.jpg (12.92 KiB) Viewed 4269 times
The original design.
MCPAC.jpg (13.99 KiB) Viewed 4269 times
Last edited by PCGUY on Mon May 08, 2006 9:16 pm, edited 1 time in total.
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Unread postAuthor: syco kilaa » Mon Jan 31, 2005 3:18 pm

wait, is that a metal plug screwed into the end of the sprinkler valve? why would you do that? now I understand why your sprinkler valve was constricting the flow, besides, sprinkler valves open up faster and more then ball valves ever will!!!!!, you should take that plug out of the sprinkler valve and use it instead of the ball valve, trust me it will work so much better. :wink:
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Unread postAuthor: theexp » Mon Jan 31, 2005 6:50 pm

OHHHH, so that is how pistons work, lol,
I make combustions, but that is awsome, I like how it is made of metal

Wait could someone describe a piston a bit further, i might want to make one eventualy...
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Unread postAuthor: fred_roux » Sat Apr 02, 2005 10:05 pm

...with the ball valve he can go with highr pressure than if he use a sprinkler valve wich is rated 125 psi......
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Unread postAuthor: spudshot » Sat Apr 02, 2005 10:44 pm

syko that looks as though it is a copper male adapter, perhaps he screwed it in and had trouble getting it out, so he left it in, it wouldnt bother the flow that much
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Unread postAuthor: Flinchy » Sat May 06, 2006 11:19 pm

interesting, thanks to the detailed pictures i understand pistons a whole lot more, if i can manage to get my hands on some pressure rated 4" pvc i think ill start constructing a tenis ball coaxial... :)
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Unread postAuthor: shud_b_rite » Mon Mar 26, 2007 5:26 am

I like the look of that gun, and the way you painted MCPAC along the chamber, it makes it look kind of (idk whats the word for it?) artillery. Looks like a pretty sweet coaxial, good job. I wish there was a place around where I live that sold that steel pipe cause you just sparked a wicked idea in my head.
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Airbeds... so many different uses
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Unread postAuthor: spudthug » Mon Mar 26, 2007 6:14 am

yo dont bring back old posts...
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4" piston valved cannon-half done..( i spilt my cement...)

Hybrid- 75% done. need to build propane holder and drill/tap sparkplug hole..
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Unread postAuthor: joannaardway » Mon Mar 26, 2007 6:53 am

Yo spudthug!

Rather than just adding a pointless and badly spelled post on as well, why didn't you just ignore it?
Often, the "Don't kick up dead topics" posts are more annoying than the posts that kicked up the dead topic - at least shud_b_rite's post was grammatically correct.

After your ranting and flaming in the other thread - I think you really don't realise that you are walking on eggshells, and you need to think carefully before each post.

Now, I'm not going to allow myself to get angry at you, but I can't guarantee that other forum members will do the same. I suggest that you don't give them the chance - clean your act up.
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Novacastrian: How about use whatever the heck you can get your hands on?
frankrede: Well then I guess it won't matter when you decide to drink bleach because your out of kool-aid.
...I'm sorry, but that made my year.
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