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hybrid cartridge protoype without burst disk

Post questions and info about hybrid (compressed gas with fuel) powered cannons here. This includes discussion about fuels, ratios, ignition systems, build types, safety, and anything else relevant.
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Unread postAuthor: SpudFarm » Tue Aug 03, 2010 7:44 pm

jor2daje wrote: because you wouldnt want to store it at high mixes in large volumes.


My tip is still to have a "large" chamber that is premixed at 10x.
After you connect it to the chamber you pump oil in the bottom of the premixed chamber to displace the mix into the gun. Then just drain the oil to drop the pressure.

Or just use a premixed chamber able to contain the combustion of the stored mix.
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Unread postAuthor: JDP12 » Tue Aug 03, 2010 8:10 pm

Help me out here to make sure I'm understanding-- the basic idea is that you insert a bb into the cartridge, then insert the syringe from the front, push mix in, and that forces the bb back into the seal? Not sure why I'm not comprehending this all the way but SPG's diagram just wasn't working itself out in my head.

Thanks
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Unread postAuthor: POLAND_SPUD » Tue Aug 03, 2010 9:02 pm

Unfortunately, not enough pressure was generated to pop the BB out of the seal
damn I was expecting it. Now you can either use higher mixes or build a new one with an adjustable detent.

The first option sounds a lot more promising :D

I definitely want to go with a bigger cartridge body, like for example the 3/8" tubing

well wouldn't it be a better idea to use higher mixes ?? lol who said you can not use 6X or more ??
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Unread postAuthor: jackssmirkingrevenge » Tue Aug 03, 2010 11:04 pm

jor2daje wrote:I dont think going down in calibre would be a very good idea, because the surface area and force go down exponentially, so you would need very high mixes, and a pretty finicky detent/seal. I would find a easily and cheaply available material, maybe 1/2" copper pipe, and base cartridges on that. Although ofcourse as you get bigger cartridges you need bigger "syringes" or suitable replacement.


Fair points, but the appeal of a smaller calibre is that I get to keep the cartridges "firearm sized", indeed at the moment there's a 7.62 NATO cartridge on my desk which I had drilled out as a coaxial body that's looking quite tempting ;)

Perhaps you could devise a sort of 2 stage pump for pressurizing premixed fuel, because you wouldnt want to store it at high mixes in large volumes.


The beauty of the syringe method is that you're only storing the mix in the cartridge - while it's in the syringe it's only a 1x mix and only gets pressurised when you fill the cartridge, I see no current need for a pre-pressurised chamber.

SpudFarm wrote:My tip is still to have a "large" chamber that is premixed at 10x.
After you connect it to the chamber you pump oil in the bottom of the premixed chamber to displace the mix into the gun. Then just drain the oil to drop the pressure.


I fear something like that would be liable to blow up, it seems to make more sense to me to have something like the alternative filler presented in this diagram, where a pneumatic piston compresses a 1x mix while filling the cartridge - slowly of course, we don't want a single use diesel engine :roll:

JDP12 wrote:Help me out here to make sure I'm understanding-- the basic idea is that you insert a bb into the cartridge, then insert the syringe from the front, push mix in, and that forces the bb back into the seal? Not sure why I'm not comprehending this all the way but SPG's diagram just wasn't working itself out in my head.


Pretty much, once you pull out the syringe the pressurised mix tries to flow out but this forces the BB into the seal and plugs the hole.

POLAND[size=42]ialwaysknoweverythinginretrospect[/size]SPUD wrote:damn I was expecting it.


Typical :P :D

Now you can either use higher mixes or build a new one with an adjustable detent.


Forget the latter option, as to the first I need to modify a 50 (actually 60 :D) mL syringe as the nozzle doesn't match the seal.

well wouldn't it be a better idea to use higher mixes ?? lol who said you can not use 6X or more ??


Keeping the cartridge volume small and upping the mix would certainly also be an option, let's imagine you have 1mL cartridge volume 0.5mL of dead space and a 60mL syringe. You could technically reach a 40x mix or so, though the force needed to push down the syringe would be around 590 lbs :roll:

Say with a 5mL syringe, this works out to about 12x mix (but with 5 times the volume) and a more reasonable 170 or so lbs on the syringe...
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Unread postAuthor: JDP12 » Tue Aug 03, 2010 11:09 pm

THat's what I thought. Just a word of advice here-- have you thought about reinforcing the syringe somehow? That's going to create some tremendous pressure inside the syringe itself... and if your syringes are anything like what mine are, they aren't exactly super pressure rated. Wouldn't want one blowin up in your face.
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Unread postAuthor: POLAND_SPUD » Wed Aug 04, 2010 12:27 am

alwaysknoweverythinginretrospect
I did test some tubing as a detent so I know that even if they are just a little bit compressed they require very high pressures to release the bb

I think it might be a good idea to build a sort of stirrup meter... basically something that will let you first achieve the right mix and then compress it easily (and safely) to 10-15X....
it would be cool if you could find a way to use standard filling adapters for shrader valves
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Unread postAuthor: jackssmirkingrevenge » Wed Aug 04, 2010 12:43 am

POLAND_SPUD wrote:I think it might be a good idea to build a sort of stirrup meter... basically something that will let you first achieve the right mix and then compress it easily (and safely) to 10-15X....
it would be cool if you could find a way to use standard filling adapters for shrader valves


That's pretty much what I was sketching while you posted that :D

This is what I was thinking of, a slightly more sophisticated approach that uses schrader valves for filling and a reinforced syringe to compress and inject the mix, allowing high mixes to be reached easily. I drew it with pneumatic compression but a manual stirrup handle as you suggested will work just as well.
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Unread postAuthor: Insomniac » Wed Aug 04, 2010 1:13 am

Would I be correct in thinking that you're unlikely to have issues with air leaking from behind the plunger to the front, and ruining the mix, as there will be (almost) equal pressure on each side at any one time?

I get the feeling that using air will be more effective than compressing it mechanically with a stirrup for that reason...
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Unread postAuthor: POLAND_SPUD » Wed Aug 04, 2010 1:15 am

with a good seal that shouldn't be a problem...
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Unread postAuthor: jackssmirkingrevenge » Wed Aug 04, 2010 1:24 am

POLAND_SPUD wrote:with a good seal that shouldn't be a problem...


Agreed, however for the sake of practicality I'm more inclined to the stirrup system. We'll see, I'll be off on vacation soon so it might be a while before you see the complete system come to fruition.
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Unread postAuthor: SpudFarm » Thu Aug 05, 2010 5:16 pm

Any progress?
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Unread postAuthor: jackssmirkingrevenge » Fri Aug 06, 2010 12:15 am

Nothing actual, and I'll be away from my workshop for a week as of tomorrow. In the meantime however I've been reshuffling configurations in my head, I like the simplicity of using the projectile as the valve but at the same time the screw attachment system of the schrader to the syringe makes sense, so I was pondering making a... well, hybrid :) something like this:
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Unread postAuthor: JDP12 » Fri Aug 13, 2010 10:17 pm

seems like that could make filling a bit easier. Good luck!

JSR: have you ever considered purchasing small unions and epoxying them into tubes to make burst disc holders? Would be alot more reliable and easier than a rubber seal. I know around here I can get ones for 1/8" NPT thread, and are at biggest .93" across.

I know thats too big to make some realistic cartridges, but it would allow to make some shells the size of an anti-tank cartridge pretty well, or a shotgun shell.

I know this is a cartridge w/o BD thread but thought I'd mention it nonetheless
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Unread postAuthor: SpudFarm » Sat Aug 14, 2010 2:52 am

JDP12 wrote: have you ever considered purchasing small unions and epoxying them into tubes to make burst disc holders?


IMO that is just another hybrid. I think that JSR want's a system that can be used easily and have the rate of fire of a bolt action rifle.

I really like the idea about his cartriges.. If you can chamber them in a gun you could use relatively thin walled and small cartriges with a very high mix. Perhaps even continue working on it untill you can make a cartrige that can be chambered in a real rifle?

I guess you could make a spud gun with the performance of a hunting rifle this way..
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Unread postAuthor: jackssmirkingrevenge » Sat Aug 14, 2010 3:27 am

I had flirted with the idea of union based burst disks but as Spudfarm said, that beats the point of making a simple and easy system, for example the last design I posted wouldn't work as you'd need a separate filling valve.

I'll be back in Epoxyland tomorrow, so expect some prototypes soon :) but first, off to Bovington woo!

Perhaps even continue working on it untill you can make a cartrige that can be chambered in a real rifle?


It's conceivable, but probably with the projectile epoxied in place as there wouldn't be much room for a seal.
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