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constant flow full auto :)

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: VH_man » Wed Jan 07, 2009 8:49 am

Where can I get one of theese!

Thats kinda sick........
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Unread postAuthor: jimmy101 » Wed Jan 07, 2009 1:02 pm

Looks promising. From the video it looks like the cyclic rate is a couple per second, so the ROF is a couple hundred RPM, much more practical than standard BBMGs ROFs of a couple thousand RPM.

Put a chamber behind the valve that is a couple times bigger in volume than the barrel and you should be able to get the barrel pressure up near the air supply pressure. That should give pretty good performance in terms of muzzle velocity since the whole thing isn't being limited by the rate the air supply hose can supply air (like it is in a vortex or cloud).
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Unread postAuthor: jackssmirkingrevenge » Wed Jan 07, 2009 1:27 pm

I've had a bit of a play and it's become clear what a hopeless cause trying to achieve full auto by fiddling around with blow forward valves as I've done in the past - the thing is so incredibly sensitive to spring strength, pressure and feed rate as well as exhaust restriction it's ridiculous.

[youtube]http://www.youtube.com/watch?v=dxCTdwr2Ufs[/youtube]

Here's a video of it hooked up to the blow-forward breech, working beautifully. I then remove the valve from the breech and at the same pressure, it behaves in a completely different way. I then adjust the spring (off camera) to get it performing at a good ROF, and vary the blowgun trigger to show how high flow gives *dakka dakka dakka dakka dakka* and low flow gives *braaaaaaaaaap!*

Fascinating stuff :) as to the next step, I'm thinking...
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Unread postAuthor: sputnick » Wed Jan 07, 2009 1:36 pm

That does look like you have found the perfect valve, Kudos!

I am really looking forward to seeing the finished product!

Just as some clarification, What pressure would you run it at, what kind of feed are you considering(hopper, magasine tube, other) and what about pellets? they were always out of reach for full auto because of the vortex block, but this makes it very possible... all you would have to do is replace the tube magasine with a square one, and take a little longer to load.

And one last thing, what are they called exactly? (brand, make, model) that way everyone could build a constant flow gun :twisted:
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Unread postAuthor: ALIHISGREAT » Wed Jan 07, 2009 1:46 pm

LOL the *braaaap* sounds like a fart :D

but its nice to see it working....

(p.s. have you realised you attached the barrel on pointing the wrong way :wink: :D )
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Unread postAuthor: jackssmirkingrevenge » Wed Jan 07, 2009 1:51 pm

Not exactly what I had bought but this should be pretty much the same thing ;)

The whole point of making the blow-forward breech etc was to be able to use pellets as ammo. I always though I would have a gravity fed hopper instead of a magazine to allow for long bursts.

With this one however, I'm not sure if the blow forward breech is the best idea - it's quite a wasteful system in terms of efficiency, and since the valve is giving off relatively short bursts I don't think it can be afforded.

ALIHISGREAT wrote:LOL the *braaaap* sounds like a fart :D


Very much, I must confess to spending a good 5 minutes playing around making extended fart noises *sigh*

And yes, it's a side-firing gun :P
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Unread postAuthor: sputnick » Wed Jan 07, 2009 1:56 pm

If your little animation is to scale, then I would not be worried about lost air, there looks to be not much lost energy in there, and not much room for expansion (unless it leaks, that is) It seems to work fine, so why not just stick with it for now, and be proud of what you have found :wink:
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Unread postAuthor: jackssmirkingrevenge » Wed Jan 07, 2009 1:59 pm

sputnick wrote:so why not just stick with it for now, and be proud of what you have found :wink:


... because I tried a few single 0.20 BBs through it, they will go through a cardboard box but not much else, and MOAR POWER! is required ;)
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Unread postAuthor: sputnick » Wed Jan 07, 2009 2:02 pm

What are you using as a barrel? because if it is 1/4 inch brakeline, then it is not lack of airflow, it is blow-by, bb's do not even come close to filling brakeline, and you should look for a more suited barrel.
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Unread postAuthor: jackssmirkingrevenge » Wed Jan 07, 2009 2:07 pm

6mm brass tube through which I got well past 1,000 fps for airsoft BBs from a burst disk, trust me it's very tight ;)

The fact is that the valve stays open for a very short time, so it's never going to be as powerful as a normal piston valved cannon.
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Unread postAuthor: sputnick » Wed Jan 07, 2009 2:13 pm

Hold on, so you are firing AIRSOFT bb's? ok my mistake, I thought you meant steel bb's, which are much smaller.

If it does not work with a tight fit, I do not know what to tell you, probably that the valve is not giving enough pressure for real power, unless you up the pressure (speaking of which, you never did tell me what pressure you are using) and that will likely require more adjusting of the valve.
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Unread postAuthor: jackssmirkingrevenge » Wed Jan 07, 2009 2:17 pm

That was my point, the small bursts of air are not sufficient for real power at the pressures I'm using (8 bar - 116 psi by the way) - unfortunately, that's what my compressor can manage so I have to make do with that.

I might not use it as a main valve after all, but a large calibre pop-off piloted launcher might be on the horizon :)

That, or I could marry the concept to this idea and have brass flying all over the place :D
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Unread postAuthor: ALIHISGREAT » Wed Jan 07, 2009 2:49 pm

I would do a BtB style QEV mod and stick a spring in it then you could use the pop-off as a pilot... although the performance still may not be too good in terms of ROF.
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Unread postAuthor: jackssmirkingrevenge » Wed Jan 07, 2009 2:54 pm

ALIHISGREAT wrote:although the performance still may not be too good in terms of ROF.


If it's from a 3/4 inch shell ejecting cannon, I wouldn't be bothered with one round per second :)
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Unread postAuthor: ALIHISGREAT » Wed Jan 07, 2009 3:00 pm

jackssmirkingrevenge wrote:
ALIHISGREAT wrote:although the performance still may not be too good in terms of ROF.


If it's from a 3/4 inch shell ejecting cannon, I wouldn't be bothered with one round per second :)


DO IT! DO IT! DO IT! that would be BEAST!

and please make sure it works first time :wink: :D
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