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valveless marble machinegun

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valveless marble machinegun

Unread postAuthor: jackssmirkingrevenge » Fri Nov 30, 2007 12:32 am

This is a combination of my ideas for a "valveless" design for hard spherical projectiles with my interpretation of this design by pvcmaster.

The operation is fairly obvious but I've included an animation for clarity, basically as the relief valve pops off, the piston is forced down by the return spring allowing a marble to be released. As the chamber re-pressurises the piston is forced back up, blocking the barrel and holding the next marble in place, and the cycle is continued.

The advantage of this design is that it has the performance of a burst disk valve, with instant "opening time" and no dead space, so the individual marbe energy should be quite impressive. The rate of fire could be tuned by adjusting the rate of flow to the piston chamber or the pop off valve release pressure.

No plans to build this is as yet as my plate is already quite full at the moment but it's potentially on my "to do" list :)
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valvelessmg.gif (11.55 KiB) Viewed 2032 times
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Unread postAuthor: Zen/// » Fri Nov 30, 2007 12:53 am

"the piston is forced back up, blocking the barrel and holding the next marble in place, and the cycle is continued."



Im not sure the tiny thing holding the ammo back is enough, what pressures do you expect to use?
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Unread postAuthor: jackssmirkingrevenge » Fri Nov 30, 2007 12:57 am

Look at my valvess prototype, you only need a small protrusion inside the barrel to block it off (assuming your marble is a tight fit in the barrel) - it's the ammo that provides the strength to hold the pressure, all the piston has to do is stop it from rolling forward.

This would be hooked up to a compressor so around 100 psi.
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Unread postAuthor: Novacastrian » Fri Nov 30, 2007 1:30 am

JSR that is quite simply beautiful, no dead space, no burst disc (power like one though). You don't need me to tell you your a f*&^%n gem!

I could imagine much trouble with the seals and spring (finding the right one)
but this design has so much potential it's not funny! You would have to make the "holding pin" out of some tough stuff too.To sum up i love this idea, it makes me smile inside :P

Rock on MR JSR :D

Edit: Just thought, why not have the holding pin contact the outside of the ammo seal, it would be a smoother action i think.
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Unread postAuthor: MrCrowley » Fri Nov 30, 2007 1:42 am

Bloody genius!

A few questions.

Are the marbles just going to be loose in the 'chamber' like a cloud?

You could possibly get some hop-up with the seals, yes?

If you extend the top seal further into the barrel then the bottom one, I don't see why not, considering how marbles aren't exactly the most accurate ammo, giving it some spin should sort that out.

Oh and what stops the pop-off valve from remaining open? I know on my 90psi one, even after it's below 90psi sometimes it can stay open for a bit longer.
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Unread postAuthor: Novacastrian » Fri Nov 30, 2007 1:58 am

I have the same question in regards to the ammo as MrC, I think a tube as such filled with ammo and using a piston to push the ammo down would work.
Maybe a line from the "pilot" air line to pressurise the ammo "magazine".
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Unread postAuthor: jackssmirkingrevenge » Fri Nov 30, 2007 2:08 am

this design has so much potential it's not funny!


true, the piston could even power a reciprocating breech mechanism like this one:

Image

why not have the holding pin contact the outside of the ammo seal, it would be a smoother action i think.


Interesting thought, though the trade off would be that you'd get increased wear through fatigue stress.

Are the marbles just going to be loose in the 'chamber' like a cloud?


That's the idea

If you extend the top seal further into the barrel then the bottom one, I don't see why not, considering how marbles aren't exactly the most accurate ammo, giving it some spin should sort that out.


easily done

Oh and what stops the pop-off valve from remaining open?


I was thinking of having some kind of flow adjustment to the piston, in practice the flow would have to be minimal given the small size of the piston chamber.
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Unread postAuthor: MrCrowley » Fri Nov 30, 2007 2:19 am

Well seems like you have it all sorted, I'm really looking forward to this one.
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Unread postAuthor: Novacastrian » Fri Nov 30, 2007 2:20 am

A simple way to achieve "flow adjustment" would be to plumb a schrader valve into the side of your piston housing, you very well know that if you adjust the screw valve inside said valve you can basically use it as a regulator.
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Unread postAuthor: jackssmirkingrevenge » Fri Nov 30, 2007 2:47 am

It would be easier to make this on BB scale but it would be less powerful than my ball valve strafer so not worth the effort. You can also potentially use the piston to actuate a Girandoni style reloading mechanism like the one BrianTheBrain had built, meaning you wouldn't be limited to spherical projectiles. There would be leaks, of course, especially with a homemade system, but I think it would still be viable.
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Unread postAuthor: rna_duelers » Fri Nov 30, 2007 2:49 am

I spot a valve! :D
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Unread postAuthor: jackssmirkingrevenge » Fri Nov 30, 2007 2:57 am

Well ok, if you're going to be pedantic, it's a "valveless" MMG with a relief valve and check valve :P :D
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Unread postAuthor: Novacastrian » Fri Nov 30, 2007 2:59 am

jackssmirkingrevenge wrote:It would be easier to make this on BB scale but it would be less powerful than my ball valve strafer so not worth the effort. You can also potentially use the piston to actuate a Girandoni style reloading mechanism like the one BrianTheBrain had built, meaning you wouldn't be limited to spherical projectiles. There would be leaks, of course, especially with a homemade system, but I think it would still be viable.


I think in this case actual power is non-important. Seriously, look at early rifles compared to their modern day "counterparts".
You are in my opinion Jack, a modern day revolutionary.And no i'm not saying this to appease
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Unread postAuthor: jackssmirkingrevenge » Fri Nov 30, 2007 3:10 am

Why thank you, I do my best :) I dion't think I have better ideas than others, but the difference is that the type of construction I use (epoxy, epoxy, epoxy...) is much more versatile that what most others use and therefore I'm in a better position to flesh out my ideas.

Power would be an issue for me, even if a project is of mechanical interest i will tend to give up on it early unless it promises to do some serious damage.

Right now there's the blowback prototype on my workbench, but I might give this some consideration later. Depending on the performance of the blowback, I might even combine the two ideas and use the reciprocating piston to drive the blowback bolt :D
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Unread postAuthor: rna_duelers » Fri Nov 30, 2007 3:35 am

I've ha d a few ales and I feel like replying at this moment.

I agree wiht jack if there isnt any power to start wiht then why bother...It'll end up on a junk heap..power and power and more power!All man eveyr needs and some food,beer,women etc but mainly power or atleast the false feeling of power.
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