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Small coaxial

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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Small coaxial

Unread postAuthor: rixth » Fri Oct 26, 2007 3:15 am

Hi guys,

I've modeled this gun in GGDT, and it seems good but I'm not sure.

Please note, the measurements are in metric (meters, grams etc), but I will convert to inches for you guys too. The ggdt file is attached too.

Chamber: 1 meter (3.3 ft or 39 inches) 50mm (2 inch) galvanized steel
Barrel: 1.4 meters (4.6ft or 55 inches) 20mm (3/4 inch) copper
The outer diameter of the barrel is 21.2mm (0.87 in).
It is a barrel sealing piston valve with a 20mm (3/4 in) ball valve pilot vent

At 60 PSI, with a 35g projectile (1.3 oz), the range would be 300m (328 yards, or 984ft).

This seems amazingly high.

Does this gun seem ok spec wise?
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GGDT file
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Unread postAuthor: jackssmirkingrevenge » Fri Oct 26, 2007 3:24 am

You have a long barrel, efficient valve and high C:B ratio so good performance is to be expected, and if shot at a 45 degree angle in a vacuum 300 metres seems like a feasible range. When you factor in air drag however (and I don't know if the GGDT calculator allows for this) , that figure will drop substantially.

Does this gun seem ok spec wise?


Yes, and given the heavyweight construction material, I hope you have more than 60 psi in mind as a working pressure ;)
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Unread postAuthor: Hubb » Fri Oct 26, 2007 3:24 am

I downloaded the file but it did not save right. Re-input into GGDT then take a screenshot so we can look at it.
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Unread postAuthor: rixth » Fri Oct 26, 2007 3:33 am

jackssmirkingrevenge wrote:Yes, and given the heavyweight construction material, I hope you have more than 60 psi in mind as a working pressure ;)


Hehe, my current air source (a footpump) can only go to about 60 before it starts leaking badly.

I've attached two screenshots.
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Unread postAuthor: Novacastrian » Fri Oct 26, 2007 3:53 am

What you essentialy have is an under powered combustion.
Up THA DANG PRESSURE BOY! and or girl.
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Unread postAuthor: Hubb » Fri Oct 26, 2007 3:57 am

Novacastrian wrote:...combustion...


??
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Unread postAuthor: Novacastrian » Fri Oct 26, 2007 4:01 am

What i mean is that pneumatics by nature should be more powerful than a combustion. 60 psi is less than what is produced by a basic combustion.
Again, UP THE PRESSURE :D
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Unread postAuthor: rixth » Fri Oct 26, 2007 4:10 am

Guess I'll get me this then: http://www.torpedo7.co.nz/products/ZFPUFNNA1
Max pressure: 203 PSI

So the gun shouldn't be underpowered? I was just worried when I saw people with coaxials with 4" diameter chambers, where as mine is only 2.
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Unread postAuthor: Hubb » Fri Oct 26, 2007 4:12 am

Or you could run it off of CO2 and obtain even higher pressures. And don't worry about your cannon being under powered.
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Unread postAuthor: Novacastrian » Fri Oct 26, 2007 4:15 am

Don't worry about your chamber size! That pump should do the job quickly and efficiently :)
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Unread postAuthor: rixth » Fri Oct 26, 2007 4:17 am

Stay tuned.... photos coming in a few minutes!
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Unread postAuthor: rixth » Fri Oct 26, 2007 4:28 am

As for pressures, the steel fails at.... who knows... probably a few hundred PSI. The copper at 350-400 if I remember right, the plastic fittings however, are only rated to 216.

http://i23.tinypic.com/2qd780j.jpg
Whole cannon, but missing the barrel (it will stick out the end a little over a foot)

http://i22.tinypic.com/hwbvo9.jpg
Closeup of the pilot. Here's how it will be filled:
    * End cap with Schrader valve screwed into ball valve
    * Ball valve opened
    * Chamber filled to pressure
    * Ball valve closed
    * End cap with Schrader valve removed


I did this for 3 reasons. First, it uses less parts (than getting a tee and making one side exhaust, the other fill). Second it would have a smaller pilot volume. Finally, because the chamber will be closed off when the air source is disconnected, there is no risk of the piston disengaging due to the puff of air that comes out.

I have a question though. Here is the reducer that is on the barrel end:
http://i20.tinypic.com/2hn1d9f.jpg
It is a 50mm (2 inch) to 25mm (1 inch) reducer. My barrel has an otuside diameter of 21.2mm. This leaves 1.9mm (about 1/16th of an inch) around the pipe. How would I secure it in there? Could I just epoxy it?
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Last edited by rixth on Fri Oct 26, 2007 4:35 am, edited 1 time in total.

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Unread postAuthor: Novacastrian » Fri Oct 26, 2007 4:34 am

I like it. You simplified the fill/fire procedure very nicely.
Kudos on a nice cannon bro :D
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Unread postAuthor: rixth » Fri Oct 26, 2007 5:01 am

What about how to attach the barrel?
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Unread postAuthor: jackssmirkingrevenge » Fri Oct 26, 2007 5:07 am

Wrap it hard with masking tape and use good quality epoxy ;) lookin' good by the way
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