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Some thoughts on automatics

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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Some thoughts on automatics

Unread postAuthor: judgment_arms » Mon Apr 28, 2008 11:05 am

Hey all,
I, like a lot of other people, am working on an automatic cannon and have compiled some interesting notes:


Gas operation:
First off, contrary to popular belief, gas operation works in low pressure, -100psi, cannon.
I built a LPHV (low pressure, high volume) sprinkler valve cannon:
Chamber was approximately 13 inches of 1 inch SCH40 PVC pipe.
Barrel was 24-28 inches of ¾ inch SCH40 PVC pipe.
Gas port was half way down the barrel and was made of a ¾ inch SCH40 tee.
Gas cylinder was a 4 inch long piece of ¾ inch SCH40 PVC pipe.
Gas piston was a piece of all-thread with three rubber washers sandwiched between four steel washers (S-R-S-R-S-R-S).

At 40psi with no projectile gas system pushed bolt back ~1/8 inch
At 100psi with no projectile gas system pushed bolt back ~1 inch
At 40psi with a projectile of wet paper towel the gas system pushed bolt back ~ 1 inch
At 100psi with a projectile of wet paper towel the gas system pushed bolt back ~2 inches

I upgraded the gas cylinder to a piece of 1.5 inch SCH40 PVC pipe, the performance improved as follows:
At 40psi with no projectile gas system pushed bolt back ~1 inch
At 100psi with no projectile gas system pushed bolt back ~3 inches
At 40psi with a projectile of wet paper towel the gas system pushed bolt back ~ 2 inches
At 100psi with a projectile of wet paper towel the gas system pushed bolt back ~3 inches

NOTE: 3 inches is the maximum amount of travel available to the system.

Another form of gas operation, the Gas Trap, would be another system which deserves testing.


Blow-back:

Blow-back, well simple, offers very little of anything in low pressure cannon.
For more information on my blow-back prototype see HERE

Recoil Operation

This one I have yet to check, but I see no reason that, given a large enough cannon, that this couldn’t work.




Auto-resetting hammer valve:
Since most paintball guns use this I’d say it works, Ant has made a few also.

What I’ve noticed is that at low pressures the hammer valve can only perform one operation; either resetting or firing.
So, as Ant put forward, you use two hammer valves.

I have bean tossing around the idea of a flywheel powered paintball heavy machine gun, utilizing one hammer valve acting as an “air engine” to run the flywheel and having a couple of rods come off the crank shaft, one acts as a hammer and the other moves the bolt.
An interesting side effect of using the flywheel to power this is that I could potentially have multiple barrels and valves perfectly timed to go off one right after the other, or timed to fire all at the same time.
In addition, one could disengage the engine and hand crank it Agar or Gatling style (useful for paintball games since certain fields don’t allow fully automatic weapons).
The design is kind of like a chain gun in the sense that it uses a motor to operate but I decided that sense it’s a hammer valve cannon id put it under that section.


Chain guns:
On a principle similar to the above flywheel/air engine driven MG, the thought of running it off a weed-eater engine or a large drill or a high RPM router has crossed my mind, the biggest problem being designing a feed mechanism that could keep up with the 1000-2000+rpm that such designs could produce.

Using chain operation to cycle a bolt is an obvious choice; for those inclined to do so, picture a similar action to that of an airsoft AEG.

Also, on this subject was an idea put forward by my dad of having a large disc with holes in it that acted as both valve and breach.
As the disk spun it lined up with a tube the pushed a paintball into a hole in the disk, as it continued to rotate it lined up with the chamber and barrel, the air would dump from the chamber, though the disk, and push the paintball out the barrel.
Obvious problems with this design include the need to a rotating disk and that, if not spinning vary fast, the valve would open painfully slow.

Blow-forward bolts:
Interesting concept, but not a good choice for larger or long (think cartridges) projectiles.
One major advantage of this type of bolt is it’s ability to keep up with the valve, no matter how fast it cycles.


Valves:
This is where I have the most trouble: finding a valve the is capable of keeping up with the cyclic rate of a cannon, with out the valve cycling faster than the cannon can (hammer valve cannon excluded).

HEAR valves:
Genius, pure genius, it wouldn’t be to hard to add an additional sear to it to allow it to only fire when the bolt was closed.

QEVs:
Expensive, but a very good option if one can afford them, or find them.

Piston “tee” valves:
Slow reset times, other than that they are plenty powerful and cheap and, somewhat, easy to build.

“Toolies” style valve:
Basically a non-automatic HEAR valve, although I am currently experimenting with this type of valve and find that a rather appreciable ROF can be achieved.

Sprinkler valves:
Only good for half-auto prototypes; slow and poor flow, not very good for anything.



Feeding:

Gravity:
Hopper feed is by far the simplest method available; unfortunately it has a limitation of only being able to feed up to about 600-800 rounds per minute, the larger the projectile the more likely it will be able to feed at the higher RPMs.

Spring tension magazine:
Detachable or not, this would provide very reliable feeding even at high RPMs, but either doesn’t hold many rounds, or becomes very large and cumbersome.

Belt:
Very nice looking, very fun to watch run, but is also very complex.
Would require either a short belt or a strong advance mechanism, particularly once you get to the larger projectiles.
It is a good way to feed a gun a large amount of ammunition, with out having a large box on it.
Besides, who wouldn’t like a belt-fed automatic?

Force fed:
Derived from paintball feeders, uses a motor to push the ammunition down a tube and into the breach.
I came up with the idea of having a cylinder like on a revolver that is advanced by the bolt, you then have a spring tension magazine to force paintballs into the empty holes in the cylinder.




Well, that’s about it…

Does anybody out there (Jack, Ant, Ragnarok) have anything to add?

Questions and comments are more than welcome

Thanks!
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Unread postAuthor: jrrdw » Mon Apr 28, 2008 11:44 am

Also, on this subject was an idea put forward by my dad of having a large disc with holes in it that acted as both valve and breach.
As the disk spun it lined up with a tube the pushed a paintball into a hole in the disk, as it continued to rotate it lined up with the chamber and barrel, the air would dump from the chamber, though the disk, and push the paintball out the barrel.
Obvious problems with this design include the need to a rotating disk and that, if not spinning vary fast, the valve would open painfully slow.


Doesn't that depend on how fast you spin the disc? The air storage could be a pressurized magazine hooked to every other hole some how. Make any sense?
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Unread postAuthor: THUNDERLORD » Mon Apr 28, 2008 11:48 am

That covers a lot of information/topics Judge,
Well, I have been thinking about a gas piston assist similar so that was interesting.
However I think that would be more useful for mechanical actuation of events.
Something more simple could be used for electrical actuation like for example an photo cell type "opto isolation switch" jimmy101 was nice enough to post a pic of here:http://www.spudfiles.com/forums/digital-pressure-switchs-t14152.html That's a topic I did on digital (programmable) pressure switchs.
If a hole was drilled toward the end of the barrel a switch similar could be used and would use no gas venting.
Unless the hole became blocked with lubricant or debris.
That would be useful for constructing a shot counter also.

With the blow forward bolt like JSR's model it would be most useful for long projectiles in the case of a hybrid. And a smaller version could also be useful in pneumatics .

As far as gravity feed, if the barrels were being spun and the magazine was in the center the centrifugal force outwards of the shot would channel the shots into each feed hole, maybe stronger than a spring.
Also if it was spinning a seperate valve could be used for each barrel
A hammer rubbing on a cam to cock and release the hammer into each valve just like the action of a real Gatling gun.

You mentioned some possible motors, one that I think would have great potential for something like that is an electric boat motor.
They are waterproof, have a shaft output(where propellors attach) run on dc battery and are also designed to be quiet as possible. They have a lot of torque so if more rpm was desired they can be fitted with gear or pully.
They are slightly expensive but are sold used at pawn shops/classifieds
(As well as pneumatic power tools btw)
Well those are my main thoughts thinking of to share on that.
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Unread postAuthor: judgment_arms » Mon Apr 28, 2008 12:11 pm

THUNDERLORD wrote:As far as gravity feed, if the barrels were being spun and the magazine was in the center the centrifugal force outwards of the shot would channel the shots into each feed hole, maybe stronger than a spring...

Centrifugal feed, hummm… sounds good, wouldn’t be very practical in a hand cranked Gatling gun, but a powered unit…

The biggest problem in Gatling style cannon is getting air to the chambers, anybody got any ideas on how to do this? I was think of perhaps using a 3/8” swivel adapter or something.

Routers spin at something like 4000rpm, that could yield a ROF of 4000 rounds per minute, now imagine if you had it in a “quad” set up with four guns each shooting at 4000RPM,
That’s 16000 paintballs in one minute… nearly 270 every second! :shock:
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Unread postAuthor: THUNDERLORD » Mon Apr 28, 2008 12:39 pm

judgment_arms wrote:Centrifugal feed, hummm… sounds good, wouldn’t be very practical in a hand cranked Gatling gun, but a powered unit…

The biggest problem in Gatling style cannon is getting air to the chambers, anybody got any ideas on how to do this? I was think of perhaps using a 3/8” swivel adapter or something.

Routers spin at something like 4000rpm, that could yield a ROF of 4000 rounds per minute, now imagine if you had it in a “quad” set up with four guns each shooting at 4000RPM,
That’s 16000 paintballs in one minute… nearly 270 every second! :shock:


I think it would still work in a hand cranked because the rate of fire will be slower so also the feeding would be slower.
If it's spun faster(however it's spun) the centrifugal force on the shots outward would actaully help feeding if the magazine was in center of the barrels with a seperate hole for each feed tube.

I got the idea while replying to the guy who wanted to use seperate PB valves for each barrel (but he was planning to use tippman valves apparently not sealed?)

It would be a pretty simple design to have seperate PB valves for each barrel with a round canister magazine going into each feed tube (center of barrels).
If the air tank was in front of that (center of barrels)and spun right along with the barrel and magazine, The air would go to each valve through seperate hoses to each valve.

The "disc" they're mounted to would have a bearing (like for roller blade or skateboard wheels with each valve head going through holes in it.
Another disc behind that could have lobes or cams (ramps) that a hammer rubs against and releases to strike each hammer.

The axle connecting the two discs would be spun by hand crank or preferably an electric motor. Anyway that's the design I came up with by replying to (forget right now) post.
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Unread postAuthor: judgment_arms » Mon Apr 28, 2008 12:44 pm

Oh, I see, your design has onboard air.


On Gatling guns feeding is generally at the top, so for your idea to work you’ll have to have the bottom most barrel being the one that’s fed, and it fires when it hits the top.

All those Tippmanns will get expensive FAST, why not use a bunch of cheapo brass eagles? They can be had for 10 bucks on e-bay.
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Unread postAuthor: THUNDERLORD » Mon Apr 28, 2008 1:06 pm

judgment_arms wrote:Oh, I see, your design has onboard air.


On Gatling guns feeding is generally at the top, so for your idea to work you’ll have to have the bottom most barrel being the one that’s fed, and it fires when it hits the top.

All those Tippmanns will get expensive FAST, why not use a bunch of cheapo brass eagles? They can be had for 10 bucks on e-bay.


If I was to go as far and draw the actual design, I would't use PB parts at all.(unless it was to be used for PB or sold to a PB company)
Maybe just the hammer struck valve similar , but I'd go with JSR's blow forward bolt on each barrel (with the feed tube facing inward).

I only stated Tippman because that's what (Dang, didn't look up his name yet) was planning to use.

As far as loading, with use of a magnet or friction (and the centrifugal factor), each shot would enter each feed tube/fire in whatever position.

It's more a theme type gun design and I'm more interested in function.
I do find the Gatling design interesting and naturally look for it's advantages though.(which are obviously being used in military still) 8)

BTW if it didn't have onboard air some type of sealed but spinning linkage would be needed. I am going to look up that topic and edit or reply back.
EDIT: Here we gohttp://www.spudfiles.com/forums/rotating-seal-t14073.html it was )DEMON( 's post about rotating seal

EDIT2: Your gas assist would be very interesting if it could mechanically open say a valve piloting a piston.
Also that's interesting brass eagles can be obtained so cheaply.
Also, while reading this over, I do repeat the same concepts a lot but I was thinking for a faster rate of fire maybe a Gatling design could have one hammer per valve and fire all the barrels at the same time!!!
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Unread postAuthor: Antonio » Mon Apr 28, 2008 5:16 pm

Sounds like an interesting post. When i have time i'll c if I can add anything:)
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Unread postAuthor: clide » Mon Apr 28, 2008 5:26 pm

Very nice writeup.

Can you elaborate on the gas operation system. On the one you built was it completely functioning? As in, perfectly sealed breech and spring reset mechanism all in place and actually able to load ammo?

I've been considering trying a completely different loading mechanism on the GB Semi. Possibly a blow-back system delayed by the valve movement, or a gas operated bolt.
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Unread postAuthor: judgment_arms » Mon Apr 28, 2008 7:12 pm

Clide, the main spring was a couple of rubber bands, the bolt a ¾” coupler reamed out to slide over the pipe.
The prototype, as crude as it was, showed promise and cycled fairly reliably considering that I crapped it out in a matter of hours.

The hard part is reseating actually, it opened fine, but the rubber bands had trouble overcoming all the friction, but if you used o-rings on a piston it would undoubtedly perform better.

I experimented with a hopper, but the gun cycled to fast to allow a paintball to drop in.
I would take pictures of it, but I’ve already scraped it.

My advice is, use as large a diameter cylinder as you can, more surface area means more force.

Sorry for the random order, that’s just how my brain works…
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Unread postAuthor: brogdenlaxmiddie » Mon Apr 28, 2008 7:59 pm

Have you thought of using a piston valve, a smaller one, maybe about 1.5" and using a pressure saftey release valve on the exhaust side of the piston? You could set up your air compressor to it via a female quick connect and have a smaller air chamber. You could set your saftey valve at say, 50 PSI and you could probably get a rather nice ROF. All you would have to work on would be an ammunition/feeding system.
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Unread postAuthor: judgment_arms » Mon Apr 28, 2008 8:39 pm

brogdenlaxmiddie wrote:Have you thought of using a piston valve, a smaller one, maybe about 1.5" and using a pressure saftey release valve on the exhaust side of the piston? You could set up your air compressor to it via a female quick connect and have a smaller air chamber. You could set your saftey valve at say, 50 PSI and you could probably get a rather nice ROF. All you would have to work on would be an ammunition/feeding system.


Yes, but I don’t like the having the main valve dictating when the gun fires, rather, I prefer having the bolt do that.
Then it’s not a matter of getting bolt that can keep up with the valve, but a valve that can keep up with the bolt.

I look at the valve/chamber as the powder charge/firing pin on a firearm, the firing pin doesn’t decide when the bolt moves, the bolt decides when the firing pin moves (actually it’s the trigger group, but you get the picture).
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Unread postAuthor: brogdenlaxmiddie » Mon Apr 28, 2008 8:42 pm

Unfortunatly, I don't. Could you further describe your bolt system?
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Unread postAuthor: judgment_arms » Mon Apr 28, 2008 8:51 pm

brogdenlaxmiddie wrote:Unfortunatly, I don't. Could you further describe your bolt system?


Okay, on a blow-forward gun the mechanism is operated by the valve firing, there for the valve dictates the cycling and firing of the gun.
My preference is to have the bolt open the valve upon closing; for example, using a slide valve to pilot a QEV, a line would be attached from the slide valve to the bolt, and having a spring to return the slide valve closed. When the bolt closes it pulls on the line opening the slide valve and piloting the QEV.
When the bolt rests the tension on the line is released and the spring returns the slide valve to close and the QEV seals back up.
The steps are then repeated.

You got it?
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Re: Some thoughts on automatics

Unread postAuthor: Ragnarok » Mon Apr 28, 2008 9:00 pm

Sounds like a pretty decent write-up.
I've never been too keen on the conventional methods of auto-loading myself.
Most, other than the obvious blow-forward bolt, are all designs developed for firearms, and although some can be operated successfully on spudgun pressures, my choice would be to use a different loading mechanism.
None of the conventional designs will get away without affecting a launcher's power, and when scarce little is available to begin with anyway, losing some to a loader isn't very tempting.

I developed one a while back, which got dubbed the Jackhammer design. It involved a pneumatic cylinder directly connected to the chamber in such a way that the loader was held shut when the system was under pressure.
When the pressure fell (i.e. after firing), a lower pressure fed to the other side of the cylinder would push it open again. Re-pressurizing the chamber would close the bolt again.

If the design was well calibrated, it could have minimal effect on a launcher's power and efficiency - perhaps even to the extent of no change at all.
Many of my automatic designs are based around similar concepts, with cylinders driven off by chamber pressures rather than other methods.

judgment_arms wrote:the biggest problem being designing a feed mechanism that could keep up with the 1000-2000+rpm that such designs could produce.

I did design such a thing for an airsoft minigun, which could have practically loaded BBs at well over 6000 rpm, partly by using the barrel's spinning motion, partly by use of a modified injector concept.

Basically, this used the Bernoulli principle to draw in and feed BBs from a hopper at nearly unlimited rates. These BBs were then fed to a feed port, where they'd be drawn in by the rotary barrel movements.

The condensed version makes it sound a little simple - the principles behind it are, there is only one moving part per barrel (plus the rotary barrel assembly itself).
But the simplicity doesn't translate well into production - in reality it would be ungodly complex to make, which is part of the reason I haven't. My building skills, although decent, are not up for this task yet.

I would say more, but it's 3 in the morning, so I gotta go.
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