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Can anyone tell me how this works?

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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Can anyone tell me how this works?

Unread postAuthor: killerbanjo » Sun Jan 29, 2012 8:08 pm

Well after trying to draw this out for a while im stumped :V I dont know if I am being silly or somthing but can somone else have a look for me?

http://www.youtube.com/watch?v=4h8wNlNW ... ature=plcp

wouldnt mind a picture :)
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Unread postAuthor: POLAND_SPUD » Sun Jan 29, 2012 9:19 pm

damn it works quite well :)

It uses an unbalanced QDV.... ever seen technician's QDV ? Now imagine one that isn't balanced - when the gun is presurised there is some force acting on the piston/spool

a simple mechanical sear (or use any other way to keep the valve in place - I think that in case of this prototype it's just a spring) keeps it in place... when the sear is released the valve opens
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Unread postAuthor: jackssmirkingrevenge » Mon Jan 30, 2012 2:37 am

I would say it's balanced, but spring loaded. Note how he has to let go of the trigger for it to reset.

Nice little project :) Damn French being all innovative and better as usual! :D
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Unread postAuthor: killerbanjo » Mon Jan 30, 2012 10:00 am

Either that or he has to let go of the trigger because if he doesn't it blowbacks and wipps his finger? I sort of understand but a diagram would be nice :) this is just the thing i have been looking for!

Also would like it if a mod moved this to pneumatic section, posted this in the wrong place...
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Unread postAuthor: jrrdw » Mon Jan 30, 2012 10:21 am

Topic moved and sorry I don't have the blue prints to the cannon in the video, but if you pause it and study the parts when pictured it's easy to figure out. Looks like he's using butane but he doesn't show the entire canister...
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Unread postAuthor: jackssmirkingrevenge » Mon Jan 30, 2012 11:37 am

Maybe someone active on patator (al-xg?) can share some diagrams if this is featured there?
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Unread postAuthor: killerbanjo » Mon Jan 30, 2012 11:45 am

Its from GMAN on this forum, he made the PACa MkII which is my favourite airgun of the forums :) and im not sucking up :P

The dude is a legend. Check out his video of the PACa Mk III.2 its a mini Mk2

I have an account of patator forum but it wont let me access the bit i want... dont know why :?

So Gman PLEASE READ THIS AND HELP!! :D
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Unread postAuthor: jackssmirkingrevenge » Mon Jan 30, 2012 12:00 pm

I tried to find it but no luck. Petitlu is also a member, you can ask him too ;)
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Unread postAuthor: killerbanjo » Mon Jan 30, 2012 12:07 pm

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Unread postAuthor: G-man » Mon Jan 30, 2012 1:57 pm

Hi guys, nice to see that my project got your attention ^^
I was actually working on a new project using the same QDV, but made in steel, working 40-50bar.
There's a good amount of work remaining (I was studying for my finals), but it's on a good way.
The main problem is the machining of the steel piston, I have to find someone to do it for me.

For the explanations, I guess a picture will do the work better than me :)

Image

I hope it's clear enough, ask me if you want details !

Note that I won't finish this thing.
It was my first try at differential qdv design, and even if it works quite well (except some jams), I don't like how it's made.
The breech is really bad designed, and I never figured how to keep the piston from rotating.

As you can see, the barrel is attached to the piston, which means a 25cm long moving part. It needs a lot of oil to work correctly, and it was really boring to ajust.


The pressure source used is propane (not butane, which only produces 2bars at 20°C).
It's an interesting pressure source since it can gives you a lot of autonomy, and it's really easy to reload.
(maybe I should make a video of how I made the adapter to refill airsoft bottles)

But the cooling effect of the gas discharge is quite a problem.
The copper structure loses a lot of temperature, which means less pressure.


Thank you really much for the nice comments, it really counts for me :)
And it motivates me to work on new projects !
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Last edited by G-man on Mon Jan 30, 2012 2:01 pm, edited 2 times in total.
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Unread postAuthor: killerbanjo » Mon Jan 30, 2012 2:00 pm

Great thanks so much! What was confusing me was the way the barrel was attached to the piston :V.

Cheers! :D

Be sure the post the steel one when ready :)
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Unread postAuthor: wyz2285 » Mon Jan 30, 2012 2:08 pm

Ah now I get it, very nice.
The rotation problem could be solved by a lock pin attached on the barrel, but there are other ways too.
Looks like it works well, but it´s not semi auto yet right? I can see how it works in semi auto but in that case can you show me your trigger mechanism?
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Unread postAuthor: G-man » Mon Jan 30, 2012 2:21 pm

It is a semi-auto, the pressure inlet was supposed to be a super thin hole, which would have let me the time to release the trigger, whithout spending all the gas while the piston is open.

The trigger is attached to the grey part you see moving first in the schematic, and there's a spring in the right end.
I totally forgot to show them:

Image

Also the propane reserve was way too small I think.
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Unread postAuthor: wyz2285 » Mon Jan 30, 2012 2:24 pm

Oh I see.
Well it´s not a good way for semi I think, to many gas lose and the trigger pull would be hard as the spring need to be strong enough for decente pressure.
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Unread postAuthor: killerbanjo » Mon Jan 30, 2012 2:28 pm

The trigger mech is attached directly to the bolt, check the video - He pulls back the bolt and it starts the process... thats why he has to take his finger off it quickly, because if he doesnt it will interupt the "spring back"

Correct G-Man?

Also the propane reserve im sure would be fine if you filled it up with liquid gas.
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Last edited by killerbanjo on Mon Jan 30, 2012 2:38 pm, edited 1 time in total.
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