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VARGAS Nitrogen (inert gas) powered cartridge gun system.

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: jagerbond » Fri Dec 17, 2010 4:02 pm

Ragnarok wrote:
jagerbond wrote:I think the noise you're referring to is the pilot volume venting.

... really? That gives a lock time of over 150 ms.

At best, that's an irritating inconvenience that'll affect accuracy (particularly on moving targets). At worst, it's giving your target a loud sixth of a second warning.

If it really has such a long lock time, I'd say that's a major problem.


You've really taken an interest here?

In fairness, we'd have to look at the sound file. How are you timing the pilot delay? The target is 90 feet away and at 450fps it should take 1/5 of second to reach. Maybe your mistaking the target impact with the actual shot sound?

Ragnarok wrote:I'd say that's a major problem.


Pretty offensive statement, especially without the data to back it up. My "major problem" got us invited to this JNLWD show. We demonstrated next to FN Herstal, Pepperball, Taser etc...
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Unread postAuthor: JDP12 » Fri Dec 17, 2010 4:23 pm

I would love to go to that show sometime. And I don't think rag is trying to be offensive, I wouldn't take it that way
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Unread postAuthor: Technician1002 » Fri Dec 17, 2010 5:09 pm

There is nothing wrong with a little hiss boom on a narrow ratio piston valve. They don't require a huge pilot to fire then. They do require bleeding off the pilot to a low pressure before it goes boom
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On one of my launchers you can see the hiss build as the pilot opens slowly, then drop off as the pilot pressure drops, then the main valve opens. With a good audio recording of the VARGAS, I would expect to see the same type of recording.

Much like a good firearm, tracking the target and squeezing until it goes off is normal.
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Unread postAuthor: saefroch » Fri Dec 17, 2010 5:12 pm

I'd also say that the amount of time to pilot that valve seems tremendous to me, since for me there is not distinguishing between the pilot "hiss" and the loud boom as the gas expands, all I hear is one loud BOOM!

EDIT: Isn't the duration of that hiss evidence of an oversized pilot volume though? Doesn't it allow time for the chamber pressure to drop during piloting, even if it is a pretty tight ratio?
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Unread postAuthor: Technician1002 » Fri Dec 17, 2010 5:33 pm

In a narrow ratio piston valve, the larger pilot is there to reduce the compression as the piston moves into the pilot space.

Say the piston opens at 30 PSI in the pilot and the piston tries to move into the pilot volume reducing it by 80%. The compression of the pilot gas is now 5X. In absolute pressure that is 1 atm for 0 PSI, 2 atm for 15 PSI, 3 atm for 30 PSI, etc. At that compression ratio, the piston to open will boot the pilot pressure to 3atm X 5 or 45 ATM. The piston would not fully open with a small pilot volume. It is true that while the piston is opening, some more air escapes the pilot, but not much due to the piston opening time.

As the chamber vents, the pilot pressure can slam the piston back closed as it bounces off the are spring in the pilot and the chamber pressure has dropped drastically. This breaks things. There is a bumper in the pilot, but not a good one on the valve seat. I have broken things with too small of a pilot. Piston deceleration is important to the design of a launcher if you don't want it to destroy itself. The kinetic energy must be safely dissipated. A good bumper and a pilot designed as a dash-pot helps.

I let the chamber pressure hold the piston into the bumper and let the pilot bleed the pilot while the chamber empties so the piston does not have high force at the end of the shot.

If the same were true and the pilot size is somewhere double in size..

3 ATM compresses to 6 ATM instead of 45. Piston slams open.

In my Mouse Musket, the original hollow piston and hollow pipe plug provided a pilot volume so the piston slamming back compressed it by only 1/3 it's volume, so the pressure rise is less than double.
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Unread postAuthor: velocity3x » Fri Dec 17, 2010 5:48 pm

jagerbond,
I've watched that video over and over. Damn if I hear a pilot hiss or notice a delay in firing. I think people are attempting to "fix" a problem that doesn't exist.
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Unread postAuthor: saefroch » Fri Dec 17, 2010 5:54 pm

Doesn't the slower pressure drop on the chamber side force the valve to stay open, and vent faster as the piston retracts? Just using some data from GGDT here, my piston valve opens fully in 1.25ms, but there is still about another 4.4ms before the projectile exits the barrel, and in that time the pressure only drops to 722 psi from 1,000psi. Wouldn't that amount of time with such a small pressure drop be more than enough to vent the rest of the compressed pilot volume?
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Unread postAuthor: Technician1002 » Fri Dec 17, 2010 6:06 pm

In reviewing the sound of my Mouse Musket, the hiss duration was 40ms prior to valve opening. Main discharge is over in about 7ms. Don't overestimate the rate of pressure drop in a small chamber with a short large bore barrel.

In relation to the rate the chamber vents, the pilot venting is at a snail pace.
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Unread postAuthor: Ragnarok » Fri Dec 17, 2010 6:16 pm

jagerbond wrote:How are you timing the pilot delay?

Downloaded from youtube, ripped sound from the file, then studied it in Audacity.

There are clear peaks for pilot, muzzle blast, and impact. All are quite clear sounds, but the report and impact can be identified doubly reliably by their timecode relative to the video.

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I can't determine exactly why there are two peaks for firing, but it may either be a minor echo off a nearby object, mechanical noise from the valve, or an artefact of the muzzle brake.
Either way, I'm measuring to the first peak.


The lock time is not always quite that long (in some cases, it's a little under half the ~150 ms of the slower cases), but I am confident that I'm measuring it correctly.

Pretty offensive statement

It's a statement of my opinion. If you found it offensive, then I apologise, but I'm not going to pussyfoot around sugar coating things when we're both mature adults.

... okay, I lie. I'm an immature adult. :tongue3:
Stupid jokes aside, criticisms are not always going to be completely sanitised.

If it's taking at times 150+ ms to vent and fire, then, yes, in my opinion there is a problem somewhere - it shouldn't really need to take that long.
In some of the situations this may be employed in, that may well multiply in to a bigger problem.

Were I working on this, I'd want to bring the lock time down. Whether you want to is entirely up to you.
(And I intend absolutely no subtext of my opinion being superior. It's not. But it's there if you want it.)
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Unread postAuthor: saefroch » Fri Dec 17, 2010 6:45 pm

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Recorded into Audacity from my speakers watching the video. Not exact, but a good approximation. IMO, it takes too long to pilot, but whether that is an issue or not is probably up to you. An old recording from a previous piston valve model:
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I don't see a hiss from the pilot valve at all, except for maybe that bit of shaky area just before the valve opens.

Ragnarok wrote:I can't determine exactly why there are two peaks for firing, but it may either be a minor echo off a nearby object, mechanical noise from the valve, or an artefact of the muzzle brake.
I'm betting on echo or mechanical noise from the valve. I think what we're seeing is the sound of the piston hitting the bumper/stop first, then the sound of the compressed gas expanding out the muzzle... but that's quite an amateur opinion.
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Unread postAuthor: Hotwired » Fri Dec 17, 2010 10:01 pm

Now that it has been mentioned I do notice the pause filled with a hiss before the double "plop" of the piston triggering and impact.

Whether its an issue or not depends on your point of view. Can't say it's occurred to me to take note of such delays in videos previously.

The piston isn't moving until the pilot has significantly vented so the only thing happening in that pause is air escaping.

As long as aim is held in the short time between trigger press and piston tripping it's going to hit the target.
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Unread postAuthor: jackssmirkingrevenge » Sat Dec 18, 2010 6:38 am

The design is sound and clearly performs very well. If I recall correctly, the pilot flow isn't brilliant but as the piston is airtight this isn't an issue. A better pilot valve would would improve performance, but as it is and considering what it's made for I would say it's more than adequate.

Could easily be made over-under, two shots is better than one :)

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Unread postAuthor: USGF » Sat Dec 18, 2010 10:07 pm

The valve / cartridge assembly in question here must have gone through 5 or 6 iterations before it was thought it might be presentable. Cost rears its ugly head again. Yes, Rag, we could go tweak it further more. Maybe do some CFD calcs. How about some artic testing or other Mil spec tests?

We are early in the design stages. Indeed, we don't know how much market acceptance we can expect. I suppose we could pour another few tens of thousands of dollars into it. We certainly now know of one more slight issue we may have to address on the next iteration. Like Velocity mentioned though, if the clients so far have not objected, it must not be a major issue. JSR brings up another point, the intention of the VARGAS is to gage interest in developing such a cartridge, with the eventual development of a multishot weapon.

Imagine how much time and effort it would take you guys to build such a weapon. Even if you choose a small mill and lathe, it costs a lot. When Mike builds something to the level he has in the VARGAS, you are talking about months of 60 hour weeks.

You guys don't mean any harm, indeed you probably mean to be helpful. Just make sure you word it such that a guy who has spent essentially 6 months full time on it won't be poked in the ribs.

Merry Christmas guys

USGF
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Unread postAuthor: MrCrowley » Sat Dec 18, 2010 10:44 pm

Hmm so does this compete with the Eclipse launcher posted by Solar on this forum? That'd make things interesting.
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Unread postAuthor: Hotwired » Sat Dec 18, 2010 10:51 pm

Battle of the 40mm launchers? :P

I'd call one a "light" launcher and the other a "medium" launcher from the current versions.

The eclipse would seem to have better features for prolonged firing but it is a lot heavier for example.

Never know how it'll go though.
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