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3/4" inch cannon how to

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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3/4" inch cannon how to

Unread postAuthor: bangmikkelbang » Fri Jan 04, 2008 1:05 am

does anyone know of a link that has plans to build a standard 3/4" or 1" cannon to shoot marbles and paintballs and whatnot. the kind of cannon with a sprinkler valve and blowgun trigger. thanks
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Unread postAuthor: elitesniper » Fri Jan 04, 2008 1:07 am

look in the how-to section :D
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Unread postAuthor: bangmikkelbang » Fri Jan 04, 2008 1:16 am

i looked through it and only saw how to mod a sprinkler valve. im not really sure where to go from there
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Unread postAuthor: rna_duelers » Fri Jan 04, 2008 1:21 am

Look at other cannon designs and use your brain to construct a style you would like.It's not to hard to use your brain and a bit of time to design and build a working gun.
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Unread postAuthor: TurboSuper » Fri Jan 04, 2008 8:39 am

1:1 is a good chamber to barrel ratio for a pneumatic.



Gogogogogo....
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Unread postAuthor: DYI » Fri Jan 04, 2008 11:07 am

To expand on Turbosuper's comment, 0.2:1 is perfect for a cannon running on 120-150 psi, assuming a fixed chamber size. If the barrel size is fixed, increasing chamber size will always increase power.

If you already know how to mod a sprinkler valve, then you just need to attach a pressure chamber to one side (obviously must be rated at or above your intended working pressure), and a barrel to the other side. Since you now know the volume ratios needed, you just need to decide on the size you want, and your fill valve.

Firstly, the barrel size: Paintballs are supposedly 0.68" OD at room temp. So you need a barrel as close to .68" ID as possible for paintballs. Looking at the specs on McMaster-Carr.com should help you to choose the best barrel possible. For marbles, it all depends on their size. Measure the kind you intend on using with a vernier caliper, and then choose whichever type of tube is best suited to your purpose. Tighter bores mean less deviance from straight firing, which can be further helped by adding a simple hop up. Again, McMaster is your friend.

As far as a fill valve: although many people use shrader valves (bike tyre valves), quick disconnect hose couplings (the kind found on air compressors), are a far better choice; they are less prone to breaking, easier to find, and waste extremely little air on connection and disconnection. They can be attached to a bike pump by cutting off the female shrader, and inserting the proper size of threaded hose barb on to the end of the hose.

For a propellant gas, I would recommend air for a beginner. It is completely free, as all you have to do is compress it. Avoid CO2. It is denser, and therefore not as good a propellant, and requires decent engineering skills (which I assume you don't have, based on the fact that you made a post on such a simple topic) to make it safe. Low density gases are better, but then you have to lug around a tank of some sort, which you probably don't want to do.

Unlike the other posts here, I have answered this post to the best of my ability, because I feel that it is essential to provide comprehensive information to beginners, to decrease accidents and increase the membership, and because this is only your second post. I wish you luck with your cannon, and strongly encourage you not to post a topic like this again.
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Unread postAuthor: Ragnarok » Fri Jan 04, 2008 11:13 am

DYI wrote:Firstly, the barrel size: Paintballs are supposedly 0.68" OD at room temp. So you need a barrel as close to .68" ID as possible for paintballs.

To expand very slightly on DYI's excellent post - as close ABOVE 0.68" as possible.

0.72" might be further from 0.68" than 0.65", but you won't be able to get paintballs down 0.65" without smashing half of them.
Marbles of course have no give at all, so it's above, or you're not firing them.
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Does that thing kinda look like a big cat to you?
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Unread postAuthor: DYI » Fri Jan 04, 2008 11:23 am

Ah, yes, above...

You have to assume that he has at least a partially functioning mind. If he can't figure that out himself, then he probably shouldn't even be building this to start with.
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Unread postAuthor: Ragnarok » Fri Jan 04, 2008 12:31 pm

DYI wrote:You have to assume that he has at least a partially functioning mind. If he can't figure that out himself, then he probably shouldn't even be building this to start with.

Not necessarily, sometimes people's brains just don't handle numbers properly: http://forum.pcformat.co.uk/viewtopic.php?t=54621
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Unread postAuthor: DYI » Fri Jan 04, 2008 1:59 pm

WOW...
But I think that guy's method of thinking would say that .68>.65, so it's all good. Until you get up to .7, that is :roll:
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Unread postAuthor: jrrdw » Fri Jan 04, 2008 5:25 pm

Have you checked the Wiki? Very self explanatory instructions there. Just substitute the pipe diameters, scale down or up as needed. The Wiki button is at the top of the web page, in between the Cannons and Album buttons. Welcome to Spudfiles.
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Unread postAuthor: Novacastrian » Fri Jan 04, 2008 5:39 pm

"Well because i said that the blank disc i want to put it on is only 4.7GB in size, and the file i want to go on that is 4.24GB, and if my math serves me correctly 4.24GB, is bigger than 4.7GB, so theres not gonna be room left over. so i need a way to compress it to fit, but doesnt matter, i'll just split the file over 2 discs." (some loser from some site)

Hahahaha Lol :scratch: :scratch:
That has to be the funniest thing i have read all year Rag, thanks for the link.
What an idiot :lol: :lol: :P
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Unread postAuthor: Eddbot » Fri Jan 04, 2008 10:32 pm

basic decimals, gotta love 'em :roll:
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Unread postAuthor: TwitchTheAussie » Fri Jan 04, 2008 11:18 pm

Im confused. But even I am not that stupid. Also 1/2 pipe fits marbles/paintballs/sinkers pretty good. I'm sleeving mine in 3/4 to fit a valve. That and basically all you need is 3-4 pipes, some pvc glue and epoxy and of course some bloody common sense to make a simple pneumatic cannon for marbles.

Am I a genius or what? :lol:
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