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auto piston v3.0

A place to ask general spud cannon related questions.
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Unread postAuthor: SPG » Sun Dec 30, 2007 11:50 am

I think you'll have to do a fair amount of research into springs but it could work.

As constant rate springs are difficult to get hold of I'd suggest a long rising rate spring, and only use a very short bit of its compression either by getting a stiff spring or pre-loading a weaker one using the "lips" you've omitted here for clarity.

I think this might be why in the past valve like this have sat half open. The force applied by the spring decreases as it extends, and you come to a point where the pressure in the chamber can build up through a partially open vent such that the forces equal each other.

Does that make any sense?
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Unread postAuthor: SPG » Sun Dec 30, 2007 12:51 pm

Looking at it closer I think this is how it works. I've dropped the spring completely and that little port into the barrel and am using air as a spring.

Blue is high pressure air, green is lower pressure air and if it's white it's at normal atmospheric pressure.

1 high pressure air enters the system
2 piston pushed across, opening valve
3 high pressure air is free to flow down barrel
4 pressure decreases and system resets

Well I think that's how it works.
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Unread postAuthor: POLAND_SPUD » Sun Dec 30, 2007 1:24 pm

JSR that drawing sucks so don't bother looking at it, you know it was late at night and it was a wrong interpretation of that diagram that I've found in the documentation of that valves.....

this is much better and it would work for sure.... you could also use a free floting idea for that brown piston in these pictures.. i think it would improve the whole thing.... the real problem is that it would waste some air.....
    and I suppose it is still not the same as the mechanism used in those pulse valves
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    XZ.jpg
    first phase... air is slowly moving the piston to the open position
    XZ.jpg (18.71 KiB) Viewed 729 times
    XZ1.JPG
    second phase... air is let to the barrel the piston is still moving to the left
    XZ1.JPG (19.31 KiB) Viewed 729 times
    XZ2.JPG
    third phase... air is let throught that opening (brown piston) and the spring moves the whole valve to the right blocking the flow to the chamber... possibly wthe brown piston could be free fpoating to give more time before the valve opens... or the realesed air could be used to power an air cylinder that would help the spring to close the valve and would give more delay before it opens again.... but this makes everything more complex and it is needed to realese air from the aircylinder afterwards...
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    Unread postAuthor: jackssmirkingrevenge » Sun Dec 30, 2007 3:59 pm

    Interesting thoughts guys, thanks for the input. Needs more study though, it will be a while before I build something again - it will have to be a design radically different from what I've been doing for me to go from drawing board to workbench.
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    Unread postAuthor: F.E.A.R._Sniper » Sun Dec 30, 2007 5:20 pm

    jackssmirkingrevenge wrote:Interesting variation there, animated it for clarity.

    My third prototype is ready and curing, expect the usual results in around 24 hours. I'm not expecting it to work to be honest, it's just a design I wanted to get out of the way, so I can safely say I've explored this possibility to death and can move on to something different.


    jsr, wouldn't your third version cause it to have a super high ROF? one shot one when the piston moves forward and one shot when it returns to the original position?
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    Unread postAuthor: POLAND_SPUD » Sun Dec 30, 2007 5:29 pm

    I think that you are very close to making this work...

    on the other hand, I am wondering from the very begining... do you really need a fullauto ? you see there are some fullauto BBMG but most 'normal' spudguns are single shot (there are few exeptions). Not to mention that a fullauto spudgun that is using marbles or ball bearings as ammo would consume a lot of air ( and ammo)

    for me a semiauto with a magazine holding 20 ammo would be more impressive... something that is powerful (200 - 300 psi) but yet capable of firing 2 rounds per second....
    I am still waiting for my 1/2" QEV to arive I ve got to try building semi someday.....

    BTW It would be nice to have here some thread devoted to automatic and semiauto schematics or ideas even if only 1% of ideas there would actually work :wink:
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    Unread postAuthor: tansit234 » Sun Dec 30, 2007 8:21 pm

    JSR if you have the air supply to make this work you'll prolly be tied to a shop, and thus power right? Unless you have bulk nitro, HPA, or Co2. You could always go with electric control couldn't you? and then adjust the cycle times or even a "no ammo" disable so it won't dry fire. I know electrics look ugly but its easy as pie, just use an electric sprinky as a piston pilot.

    Course it depends on what you really want, a fast firing GB/BB/marble gun or to be able to say it only needs ammo and air as well. I think you want that pure mechanical beauty to it all.
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    Unread postAuthor: punkin » Sun Dec 30, 2007 11:39 pm

    I've found some off the shelf parts that are used to provide pulsed air.... it generates 5 Hz pulses of air (so a pulse every 0.2 second) (sorry but expressing this is very difficult if your not a native speaker of english )
    It is interesting becasue you can also regulate how many times per second pulses are generated
    some pics and a diagram that I think might be very useful for you



    The pics and diagram are intriguing, but a brand and part number and source would excite me much more! Do tell!
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    Unread postAuthor: jackssmirkingrevenge » Mon Dec 31, 2007 1:26 am

    on the other hand, I am wondering from the very begining... do you really need a fullauto ? you see there are some fullauto BBMG but most 'normal' spudguns are single shot (there are few exeptions). Not to mention that a fullauto spudgun that is using marbles or ball bearings as ammo would consume a lot of air ( and ammo)


    What I'm trying to create is something that's a middle ground between powerful single shot spudguns and cloud/vortex BBMGs - I want a greatly reduced rate of fire, in the order of 2-3 rounds per second maximum, and greatly increased power for individual projectiles - say 6 ft/lbs from a 1 gram 0.22 lead pellet. The idea is that you could obliterate a target with a 5-10 second burst without filling your shooting area with BBs, and each shot on the target would have a clear hole, not the collection of dents and tears that BBMGs tend to leave.

    The reason I want full auto is that I'll soon be the proud owner of one of
    these, fully self contained semi-auto at more power than I could hope to achieve with my 110 psi compressor - so naturally, if i'm going to make the effort with something homebuilt, I'd want a different sort of effect on target.

    Course it depends on what you really want, a fast firing GB/BB/marble gun or to be able to say it only needs ammo and air as well. I think you want that pure mechanical beauty to it all.


    I've come up with several electric designs, one of which is being trialled by punkin here, but personally I'm trying to stick to the air-only approach for the time being.

    The pics and diagram are intriguing, but a brand and part number and source would excite me much more! Do tell!


    Agreed, but I doubt such a valve would have sufficient flow for our applications.
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    Unread postAuthor: Hotwired » Mon Dec 31, 2007 6:28 am

    Measure twice cut once.

    Or in the case of spudguns, we measure bugger-all except lengths so better make sure the design is guaranteed to work the first time.

    With this modification it will work irregardless of the force of the spring, the flow coming in and the flow going out:

    Image

    However with a stronger spring, higher pressures will be built up before the shot goes and the incoming flow can change the ROF.

    Ion paintball guns use a bolt which acts in a similar manner but uses air pressure instead of a return spring.
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    Unread postAuthor: SPG » Mon Dec 31, 2007 6:35 am

    Errr

    OK, maybe I'm being stupid, but how would that work? Surely because you have an equal but opposed pressure acting on both pistons, and both pistons are connected by a rod they'll just sit there doing nothing?

    Or is there a bit missing?
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    Unread postAuthor: Hotwired » Mon Dec 31, 2007 6:37 am

    No, it might be hard to see but the bottom piston has been slimmed down so a positive pressure is still upwards (after the pressure overcomes the spring anyway).
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    Unread postAuthor: jackssmirkingrevenge » Mon Dec 31, 2007 6:41 am

    Interesting, basically my design, but incoming flow is blocked off to ensure that the chamber empties and there is sufficient pressure drop to allow the spring to reset the piston. There is however the difficult of lining up two concetric pistons for a friction free setup in the absence of a machine shop, but still, food for thought, thanks :)

    edit: how about this
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    Unread postAuthor: Hotwired » Mon Dec 31, 2007 7:28 am

    I'm not too keen on the idea of a dead stop - to do that you either have a very small outlet port or you get incoming and outgoing flow at the same time which you've gathered has a tendancy to fix the piston at that point.

    The sliding seal means that you guarantee only one port is open at a time, dumping the floating chamber of air between the pistons and leaving the spring to reset the pistons without any issues with air pressure opposing it.
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    Unread postAuthor: jackssmirkingrevenge » Mon Dec 31, 2007 7:40 am

    All I've done is reconfigured the design you proposed, I don't see what the difference is in terms of functionality?
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