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New JSR semi-auto prototype (split topic)

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: JDP12 » Wed Jan 06, 2010 4:19 pm

Well becauseeven though you would think the piston would slide back and seal it up, which I assume your banking on, you have to remember that the volume of the air in front of the piston will actially be LESS than that behind it it because of the reservoir. So I'd be willing to bet that the piston won't even unseat, and the reservoir will just dump through the schrader.

Just my thoughts

EDIT: saw BTBS post so maybe it will work
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Unread postAuthor: jackssmirkingrevenge » Wed Jan 06, 2010 4:23 pm

The logic is that air is coming out of the pilot schrader quicker than it can come in from the thin line from the main chamber, pressure in the pilot chamber will drop compared to that in the firing chamber et voila, just like any piston valve.
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Unread postAuthor: JDP12 » Wed Jan 06, 2010 4:26 pm

Yea that kinds what I figured..

Idk your most likely right as that flow will be restricted a lot. So yea I Spose
:D
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Unread postAuthor: POLAND_SPUD » Wed Jan 06, 2010 4:31 pm

It works...so..
lol I draw exactly the same conclusion... cool attempt but don't you think that you are reinventing the wheel here?

just get a small QEV and buy a pop-off valve rated to high pressures and you are all set
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Unread postAuthor: JDP12 » Wed Jan 06, 2010 4:34 pm

Popoffs don't vent very well though.

Look up BTBs marble cannons, he found that a QEV plus popoff isn't that powerful. I think it's because they only release a small amount of air for a split second, not allowing it to vent as well
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Unread postAuthor: jackssmirkingrevenge » Thu Jan 07, 2010 1:36 am

POLAND_SPUD wrote:cool attempt but don't you think that you are reinventing the wheel here?

just get a small QEV and buy a pop-off valve rated to high pressures and you are all set


What happened to the spudding "build your own" philosophy :P ;)

I think I'll give the pilot-feeding design a go, here at work I have fine stainless HPLC tubing rated for at least 5000 psi that should do the job nicely of pressurising the pilot chamber.
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Unread postAuthor: POLAND_SPUD » Thu Jan 07, 2010 12:23 pm

What happened to the spudding "build your own" philosophy
it died when one of its epoxied parts exploded :D

Look up BTBs marble cannons, he found that a QEV plus popoff isn't that powerful
but technically it's the same design
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Unread postAuthor: Brian the brain » Thu Jan 07, 2010 3:59 pm

but technically it's the same design


No it's not.I used a modified QEV, the air came in from the chamber side.
Wich is the more like the first design JSR made...in this topic.

Look up BTBs marble cannons

EDIT: saw BTBS post so maybe it will work

Since when am I considered to be the expert on this?!?!?!

I have often needed JSR's advice on my builds.You make it sound like he doesn't know what he's doing, but I somehow do..often it's the other way around...
:D
he found that a QEV plus popoff isn't that powerful.

Not true.I used a small chamber so I could feed it off a small bottle.My combo wasn't powerful enough for me.

My " Old Shatterhand" gun is very powerful, wich also works by piloting a split second.But with a larger QEV, larger chamber and longer barrel than my modded QEV-snapvalve combo with .177 bbgun barrel.The latter did manage to swell my thumb up to twice it's size after hitting it at 3 bar.
At 20 it was probably quite powerful to most..

Psycix' combo ( wich I have played around with) is very powerful, for a 6 mm launcher.
A lot depends on the pressure setting of the pop-off and chamber size.
His is upgraded to 19 bar now.I shot it at 11.

Oh and Jack, to answer your question earlier...It's a single action trigger.
And please don't try to explain basics like that to me.. :D
I studied the difference at the age of 11.
All because I wanted to know what Colt SAA stood for and what it meant..
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Unread postAuthor: JDP12 » Thu Jan 07, 2010 5:15 pm

Alright sorry, I just recalled you vein disappointed in it because it wasn't powerful enough and that's why you tried building a snap valve..

I stand corrected. Sorry
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Unread postAuthor: POLAND_SPUD » Thu Jan 07, 2010 6:39 pm

I used a modified QEV, the air came in from the chamber side


yes you used.... but I was referring to psycix's experiment -> linky
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Unread postAuthor: jackssmirkingrevenge » Fri Jan 08, 2010 12:23 am

modesty incarnate wrote:Since when am I considered to be the expert on this?!


Well you are one of the leading authorities of high pressure pneumatics on this forum, there aren't many launchers here made on the level of Ol' Shatterhand ;)

Brian the brain wrote:I have often needed JSR's advice on my builds.You make it sound like he doesn't know what he's doing, but I somehow do..often it's the other way around...


But many times, it isn't :D

Oh and Jack, to answer your question earlier...It's a single action trigger.
And please don't try to explain basics like that to me.. :D
I studied the difference at the age of 11.
All because I wanted to know what Colt SAA stood for and what it meant..


Sorry if that sounded patronising, it was more for the sake of any more clueless members who might be reading. I would like to go for double action personally, it doesn't make sense to have an autoloader that still has to have its hammer manually cocked for every shot.

I started building the pilot-feeding design I drew up earlier but I'm not comfortable of feeding into the pilot because it smacks of the inefficiency I abhor. I was thinking of giving the original design another go, this time with a sort of "integrated valve unit" that fits into a single ported tube. This will allow a tiny pilot chamber that will reset quicker and a smaller diameter piston that will be much better supported. The only issue is the rather tiny 3mm porting, which is only 44% of the flow through a 0.177" barrel and just 30% of the flow through a 0.22" barrel.

I'll give it a go over the weekend, if it doesn't work it's cartridges FTW! :D
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Unread postAuthor: psycix » Fri Jan 08, 2010 2:11 pm

BTB wrote:His is upgraded to 19 bar now.I shot it at 11.

Wasn't that with the default 8 bar popoff? (Somewhere like 8.1 to 8.5 bar)

I plan to machine two popoffs next week. One for you, one for me.
However, I might look into using an air spring because of the force needed to hold it at pressures greater then 30 bar...

---

Well jack, how's your prototyping going?
Any pictures of the progress?
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Unread postAuthor: JDP12 » Fri Jan 08, 2010 2:47 pm

JSR- here is what I PMed you about.

Basically this is what I have come up with to make a full auto or semi auto gun.

It's a coaxial type design, only the pilot area is always full, acting as an air bumper. The idea is thus:

The reservoir is connected to the chamber, not the pilot. The piston seals against the barrel due to the PERMANENT air reservoir (bumper) behind the piston, and then the piston is held in place with a lever, which would go to a trigger mechanism.

The reservoir then fills the main chamber, and when I want to fire it, i simply pull the trigger, which releases the piston and is forced backward by the air in the chamber. It then automatically reseats due to the air behind it, which is not vented. The chamber then fills slowly enough to ensure that the piston reseats.

I put a little hole in the drawing of the piston, and i think it may have to not only seal on the face but an airtight seal around the barrel as well- just may make it easier for the lever to grab the groove and not have to worry about it sealing.

I'm not sure of exact numbers right now, but I'm in the midst of calculations to figure out how much air at what pressure needs to be behind the piston, what pressure will force it back, all those things.

So those will come in a couple days, but thats the basic design. It'll basically be pulsing, controlled by me.

I know someone is going to say that i could just use a QEV and popoff and get almost the exact same effect, but that really only gives auto.

The advantages of this, as I see it are:

1) Semi and possibly Full-auto
2) Has the potential to be very compact
3) A mechanical release of the piston

Some disadvantages:

The biggest I see is the valve not staying open for very long, resulting in a small amount of the chamber getting dumped into the barrel, very inefficient.
However, as i said, I am doing a lot of calculations to figure all of this out and make it as efficient as possible. those will be up in a couple of days


What do you guys think? I won't be building this for a while as I'm pretty much dried up of money, but if I do get it to work I plan on incorporating it into a Tec-9 or MP9 design, with the magazine being a reservoir/ammo storage combined.

Of course if this doesn't work, I may say screw it and just work on a pneumatic cartridge like JSR
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Unread postAuthor: POLAND_SPUD » Fri Jan 08, 2010 3:12 pm

this is basically his design :wink: the one that could be built by modding a QEV

the only difference is that yours uses a mechanical way of actuation while his relied on a valve between the tank and the valve
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Unread postAuthor: JDP12 » Fri Jan 08, 2010 3:15 pm

I never claimed this was some new and revolutionary idea. its basically a basic piston design, only using a mechanical actuation.

i know that. That's kind of the point. This allows for semi auto and full auto I believe. And is smaller than a QEV

The mechanical actuation makes it better I think.

As efficient? Probably not. But I still think its going to work.'


I'll clear something up- the schrader is to fill the air bumper and control how much air is in it.
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