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Need Help/Advice On my First Cannon Build for School Please!

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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Unread postAuthor: MaxuS » Sun Oct 14, 2007 4:26 pm

You most definately wont be launching pumpkins 250+ yards with a 1" sprinkler valve, even if it is indeed modified.
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Unread postAuthor: DYI » Sun Oct 14, 2007 4:43 pm

A "perfect ratio" at 100 psi is around .25:1, not 4:1. This means that you could make your barrel up to 8 times longer and still be gaining power.

He isn't using a 1" sprinkler, he is using a 2" ball valve, and if he makes a 3" barrel about 12' long (or more), he could easily shoot a small pumpkin more than 300 yards at 100 psi.
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Unread postAuthor: bruno6491 » Sun Oct 14, 2007 5:08 pm

what if i already used the primer purple stuff and cement glue, is there a way to get it out of the ball valve or just when i build another one?? Can i use a 2" coupler and just add more 2" pipe?

I thought it was a 4:1 just volume, never anything pressuirzed

Any ideas on the ball valve spring idea, that seems like the only way to increase distance?
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Unread postAuthor: DYI » Sun Oct 14, 2007 6:54 pm

I already made a post telling you how to spring load the ball valve.

If you applied some logical thinking to the problem of C:B ratios, you would realise that a chamber of a given size at 200psi will contain twice as much air as a chamber of the same size at 100 psi. It should follow that since the amount of air pushing the projectile is doubled, then you should be able to increase the barrel length. If everyone just took 30 minutes and downloaded GGDT, we wouldn't need to have these discussions anymore.

The only reason that the C:B ratio for combustions is fixed is that they all produce essentially the same pressure.

Why would you make a gun with a permanent barrel? The best solution would be to cut the barrel pipe down to about 4", and then cement on a threaded adapter. Then you could use any barrel you like.
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Unread postAuthor: Fnord » Sun Oct 14, 2007 7:10 pm

If you make a combustion with a 3"x10' barrel, you can shoot something the size/weight of a baseball at least 300 yards. I know because I have one, and I just have to get it in posting shape before anyone sees it.
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Unread postAuthor: bruno6491 » Mon Oct 15, 2007 1:40 pm

So is my chamber too big or too small when i pressurize it?

I will be adding a threaded piece so i will have interchangeable barrels, just slipped my mind yesterday at HD

I saw the post on the spring loaded vlave, but could not follow what you were saying. If there was a diagram or even a more deatiled way i may be able to understand.

thanks again o everyone, and i have used GGDT but that doesn't tell you about chamber to barrel ration unless i missed something
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Unread postAuthor: DYI » Mon Oct 15, 2007 3:38 pm

For one, there is no such thing as a chamber being too big on a pneumatic, but a chamber the size of yours is a waste of air. I'm not suggesting to cut down the chamber, just make the barrel longer so you can use more of that air.

I'd post a diagram for a spring loaded ball valve, but my scanner crapped out on me and I don't feel like drawing it up on paint. Honestly, you should be able to figure it out yourself anyway.
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Unread postAuthor: bruno6491 » Mon Oct 15, 2007 6:02 pm

I did add another 3 feet to my barrel and noticed an improvement in distance

Thank you for your efforts in trying to post a diagram but i have looked it over read it many times and asked people but still confused

If you can post a diagram, i am thankful, just want to have it done by the 25th, when its due.

Thanks once again to all

Bruno
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Unread postAuthor: DYI » Mon Oct 15, 2007 7:02 pm

The spring is tensioned and held back with a pin which is held straight by a holder on the frame of the launcher . A wire connects the handle of the BV to the spring. When the pin is pulled out, the spring snaps back and pulls the wire, opening the valve.

For some reason, spudfiles won't let me post the picture, even though it is the right size.
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Unread postAuthor: bruno6491 » Tue Oct 16, 2007 1:28 pm

you can send it to my email bruno6491@yahoo.com if you want and im still confused how a wire and pulling a pin will have enough force to open the valve
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Unread postAuthor: MaxuS » Tue Oct 16, 2007 4:06 pm

*Smacks head* Its the spring that will be opeing the valve, the wire and pin are just to release the spring..
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Unread postAuthor: DYI » Tue Oct 16, 2007 4:39 pm

If you can't figure out from the descriptions, I'm not sure I'd trust you with a spring, much less a pneumatic cannon...
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Unread postAuthor: bruno6491 » Tue Oct 16, 2007 4:47 pm

well, i have asked people but if it is something that if you have never done before or used before you don't know how it works.

I have built many others things like trebucheuts that were 25 feet tall and this came up as a school project.

If you want to send it to me you can, but i really don't undertand how everything works, and im not going to try it without a better idea how to do it

Thanks to everyone Bruno
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Unread postAuthor: bruno6491 » Tue Oct 16, 2007 5:36 pm

What type of spring should be used?

i tried searching google for spring loaded ball valve and got nothing
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Unread postAuthor: Insomniac » Wed Oct 17, 2007 1:59 am

Thats because it is simply a normal ball valve that is slightly modified.
Here is a diagram of a simple setup (it wouldn't work without a little reinforcing)

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The spring tries to pull the valve handle to the left, but it can't because the blue pin is holding the string to the thing attached to the pipe. When the blue pin is pulled, the string goes loose and the spring is able to pull the handle. There are many better setups but all use the same basic idea.
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