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16' Coaxial cannon

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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16' Coaxial cannon

Unread postAuthor: ElDuderino » Thu Dec 29, 2011 10:36 pm

I built this thing a number of years ago, and repaired it this week. It kicks @$$.

16' x 2" barrel
6"x 7.5' tank
4" ported quick exhaust valve
Piston made from 3" coupler sanded down, metal face with reinforced gasket material
Sprinkler valve pilot actuated, solenoid actuated off truck battery (formerly 9v's and a doorbell)
Nice stand built from sawhorses, fence boards and stakes.

I've been launching 1 1/4" PVC darts with 2 D cells glued in the head. I can't seem to get anything that flys straight, most everything tumbles. Some of my PVC darts actually spent most of the flight backwards!

Today was a test day for both the launcher and a rocket. I will be launching a 3' fiberglass rocket with a G motor launched vertically via a pusher rod and a slotted cup to hold the rocket. The motor will be air started by an onboard G-switch as soon as it leaves the barrel.

Image
IMG_9969 by arendtj, on Flickr

And here's a video of me accidentally launching the barrel!
http://www.flickr.com/photos/17071948@N05/6598312779/

The 8' barrel extension screws on the front of the 6" chamber by male/female threaded adapters. I was using a 1 1/4" cap as a sabot to launch a smaller dart when the the cap was cocked in the barrel, causing it to momentatily seal. the result was pressuring the barrel and blowing out the barrel from its glued joint!

Image
IMG_9991 by arendtj, on Flickr
This is all that is left from a D Cell battery wrapped in Duct tape and hammered into a piece of 1 1/4" pipe

Image
IMG_9992 by arendtj, on Flickr
The piston is made from a 3" coupler and inserted into a short section of 4" PVC pipe. The back cap is a 4" cleanout with the filling port and pilot valve.

Some videos are on the way, youtube is being a pain
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Last edited by ElDuderino on Thu Dec 29, 2011 11:34 pm, edited 5 times in total.

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Unread postAuthor: squnto » Thu Dec 29, 2011 10:42 pm

thats hella large my friend :O
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Unread postAuthor: iisthemuffin » Thu Dec 29, 2011 10:42 pm

I havent been into building for a while now, but last i heard, clean outs were bad. Especially on pneumatics. I would be careful with that thing. Possible replace it.

But, i could be wrong.

Otherwise, nice cannon. I bet it makes some noise eh?

Oh an your pictures arent displaying correctly. Atleast for me anyway. Just a heads up.
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Unread postAuthor: ElDuderino » Thu Dec 29, 2011 10:47 pm

Yeah the cleanout sucks, I loaded it with teflon, it will leak down from 100 psi to 80 psi in maybe 2 min. I glued a coupler on the back side of the hole drilled into the cleanout so that the pilot valve nipple has something to bite into. Not the same for the 1/4" nipple, I just drilled a hole and let the pipe cut the threads, then used liberal teflon.
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Unread postAuthor: ElDuderino » Thu Dec 29, 2011 10:48 pm

I have some videos, they will be up as soon as i get around to it

and here's another video:
http://www.flickr.com/photos/17071948@N05/6598395263/
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Last edited by ElDuderino on Thu Dec 29, 2011 11:46 pm, edited 2 times in total.

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Unread postAuthor: Fnord » Thu Dec 29, 2011 10:52 pm

Yeah, cleanouts are generally a weak point, especially when you're hitting them with a piston. Replace it with a plug or reinforce any way you can. Fiberglass or even bondo will help.


vv edit, nevermind, I see you figured it out.
The [img] tags only work with a .jpg url.
try it with this: http://farm8.staticflickr.com/7161/6597 ... 2502_b.jpg
To upload photos directly to spudfiles, hit the edit button in the upper right corner of your post. Look down though the options and you'll see an 'add attachment' button. Pick the image from your computer and make sure it's compressed enough to fit the size limit (350k I think).

But anyway, that looks rather good. I wish I had your shooting range.
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Unread postAuthor: iisthemuffin » Thu Dec 29, 2011 10:58 pm

Well leaking isnt my main concern. Like Fnord said, its a weak point. Especially with that piston slamming into it. Could potentially break or pop off the cannon.

Could be bad news. But, seeing as how you fire it with it facing the ground, i guess it couldnt cause too much damage if it fails. But i would be cautious of it.

Anyway, I think i see a coupler near the top of your chamber? Is this where you connect 2 barrel pieces to get 16'? Or did you somehow get a hold of a 16' piece?
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Unread postAuthor: jackssmirkingrevenge » Fri Dec 30, 2011 12:39 am

Always nice to see a larger cannon, nice.

I can't seem to get anything that flys straight, most everything tumbles. Some of my PVC darts actually spent most of the flight backwards!


Some advice on optimised projectiles here.
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Unread postAuthor: Technician1002 » Fri Dec 30, 2011 9:59 am

I had to switch from PVC to ABS on a similar design as the PVC eventually cracks and shatters. Use a really good bumper and keep clear of the breech.

Image

I eventually scrapped that cannon and built the ABS test cannon. See my sig for the link.

This PVC breech broke after about a year of use.
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