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Semi/Full-auto inline design, need feedback.

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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Semi/Full-auto inline design, need feedback.

Unread postAuthor: Leonard » Sat Jul 19, 2008 12:12 pm

Good day!
After too many hours trying to get the blow-forward bolt to work properly, i have only achieved my goal partially, as you can see in this post :

http://www.spudfiles.com/forums/6mm-sem ... 15353.html

I am afraid that the use of springs is the main problem in regular bolt designs and i'v been trying to find a way to make the piston and the bolt to move at the same time, as part of the same phase of shooting. I read about paintball mecanism and airsoft mecanism and finnaly i think i got the solution from this thread :

http://www.spudfiles.com/forums/wip-val ... 15097.html

If we could attach the bolt to the front of the piston in this kind of valve, exhaust of air would push the piston, open air flow AND close the breach at the same time. Then, by releasing the trigger, the flow of air would push the piston back in original position, opening the breach and another ammo would fall into barrel. We could easily reach "full"-auto by setting a solenoid valve as the pilot and attaching a chip that would open the valve a certain ammount of time each seconds, just like an electropneumatic PB marker.


Here's a diagram of the idea (the two port on the bottom are the air in and the exhaust) :

Image

So, would that work?
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Unread postAuthor: Leonard » Mon Jul 21, 2008 10:33 am

Woa, so that's it? No comment...? Is my diagram unclear or something?
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Unread postAuthor: MaxuS the 2nd » Mon Jul 21, 2008 11:24 am

It is a little unclear..

Do you have software to make an animation?
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Unread postAuthor: Leonard » Mon Jul 21, 2008 1:19 pm

Here, it should make everything much more clear.

Image
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Unread postAuthor: keep_it_real » Mon Jul 21, 2008 2:05 pm

I think the bolt would slide forward when the chamber is filled because there's nothing holding it back. then it would just start farting air. That's my guess. I have a similar design I posted a while ago that works similarly. I'll try and find it.

So this design stops the bolt from sliding forward because it has equal pressure on both sides. the red triangle is a check valve and the tube coming out the bottom is pilot/fill.
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semi valve.png
Here it is. Same general idea
semi valve.png (23.94 KiB) Viewed 1163 times

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Unread postAuthor: Leonard » Mon Jul 21, 2008 2:24 pm

Humn... I was thinking that the air would push the piston back when filling and seal itself in front as the area of the piston where air pressure is applied is larger than the sealing area in front (wich would basicly just be a o-ring squeezed on it's side). I could be wrong thou...
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Unread postAuthor: iknowmy3tables » Mon Jul 21, 2008 3:04 pm

I don't think that the bolt can be accomplished with use of a sealing face, a plug possibly but not a sealing face, there is too much distance between the valve opening and the bolt closing
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Unread postAuthor: Leonard » Mon Jul 21, 2008 3:48 pm

iknowmy3tables wrote:I don't think that the bolt can be accomplished with use of a sealing face, a plug possibly but not a sealing face, there is too much distance between the valve opening and the bolt closing


I dont quite understand what you mean. Are you talking about the o-ring between the piston shaft and the bolt that closes the breach (where the inner tube shrink slightly)?
If so, you're talking about replacing it with a plug, Do you mean that instead of a sealing face there should be a conical rubber piece that would "plug" into a tube to make a more efficient seal?

Sorry if im asking all those explanations, but im not that good in english, so it is sometimes hard for me to understand.
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Unread postAuthor: MaxuS the 2nd » Mon Jul 21, 2008 4:25 pm

That's much clearer thankyou.
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Unread postAuthor: SEAKING9006 » Mon Jul 21, 2008 8:22 pm

This is almost the same thing as mine, but without electronics. Might be difficult to fine-tune after building it if you get something wrong. That's why I chose sprinkler valves on my system.
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Unread postAuthor: keep_it_real » Mon Jul 21, 2008 11:16 pm

I agree that when you first fill it, the bolt will move backwards and create a seal. But when the pressure in front of and behind the piston has equalized, there's nothing to hold the bolt back. Anyone else agree?
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Unread postAuthor: jackssmirkingrevenge » Tue Jul 22, 2008 12:01 am

A little too complex for my liking in the sense that there are moving parts that need a perfect seal, and also you're still stucck with the need for a timed externally powered valve - if you're going to bother with the latter, might as well hook it up to your existing semi-auto blow forward design.

I've taken a break from such research, being away from my beloved workshop, however one idea I would definitely like to try is the direct blowback bolt. At compressor pressures, direct blowback doesn't look like it will work if fed from a blowgun type valve, as I discovered here.

Image

Basically, the above is not going to happen unless the bolt is externally powered. Such a system worked for my cartridge fed prototype but only because the air was coming from a mini-piston valve.

The theoretical solution I came up with was to increase the surface area available to blow the bolt back by attaching it to a larger piston as in the crude diagram below. I believe this would have a good chance of functioning correctly, though of course one would have to build it to find out.

Image
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Unread postAuthor: Leonard » Tue Jul 22, 2008 1:03 am

Your design are very inspiring JSR, it's exciting to see all these concepts that are just waiting to be built and tested.
But I have to admit, i'v had so much trouble getting the right spring for the semi-auto design i mentionned in my first post that i cant even look at a spring without being frustrated.
:o


So, as i feel there is a chance that my idea could work,

Let's talk about your quote Jack :

jackssmirkingrevenge wrote:A little too complex for my liking in the sense that there are moving parts that need a perfect seal.



I may be completely out of track, but as i was thinking about the concept, I imagined it without any o-rings or seal exept the one in front of the piston shaft (where the seal is created when compressed air fill the chamber).
When that part will be sealed, no air should leak out of the chamber side, as the shaft is fullfilled with epoxy (between chamber side and breach side) AND no air can leak around the piston shaft, as it will also be blocked by the same sealing face.

When air will be exhaust, the piston should travel frontward, letting the air travel through both set of hole in the shaft, into the barrel. Then, when pressure will be down to a certain ammount, the incomming air source (regged c02) will push the piston back, reseting the piston and getting the gun ready once again.

Let's just see it working as a semi-auto concept before thinking about going full-auto with the whole solenoid stuff. For now anyway.


So, do you see anywhere where the moving piston/bolt would need to seal perfecly?
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Unread postAuthor: jackssmirkingrevenge » Tue Jul 22, 2008 11:05 am

I may be completely out of track, but as i was thinking about the concept, I imagined it without any o-rings or seal exept the one in front of the piston shaft (where the seal is created when compressed air fill the chamber).


The way I tend to look at things, even this is a seal too many. Seals on moving parts for me equal more friction and greater wear and tear, so I tend to avoid them where possible. Again, this is just a personal view, if you're comfortable with it there's no reason why it shouldn't work.

I still don't think it will have a significant advantage over your existing project however.
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Unread postAuthor: SEAKING9006 » Tue Jul 22, 2008 11:15 am

How about my flow-thru piston design? With a larger surface area contacting the chamber sealing area, it should have less of a leakage problem.
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