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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: JDP12 » Wed Mar 16, 2011 1:22 am

good idea... thin metal tubing + presure + rubber = bad things...
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Unread postAuthor: Crna Legija » Wed Mar 16, 2011 3:57 am

unless you need the mix pressure behind the. piston why not fill from the barrel? could make it a bit smaller.
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Unread postAuthor: jackssmirkingrevenge » Wed Mar 16, 2011 5:28 am

-_- wrote:unless you need the mix pressure behind the. piston why not fill from the barrel? could make it a bit smaller.


This is just a prototype but if I were to use it as a cartridge I'd probably make it like this and use the fill rig to charge it:
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Unread postAuthor: mark.f » Wed Mar 16, 2011 8:31 am

Agh, I think it's about time I built some of these. :) Although I think I'd stick with burst disks instead of fiddling around with detents and pistons.

One thing I can see is that power might be a little lower for these piston prototypes compared to a similar sized burst disk or detent. Since the only thing adding to the force sealing the piston is that spring, the cracking pressure will be relatively low (again, compared to a burst disk or detent), allowing combustion gases to escape at lower pressures. Not going off firsthand experience here, just did some playing around in HGDT.

But don't get me wrong, they'll still pack a good punch. The spark gap placement is also more ideal than the earlier prototypes.
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Unread postAuthor: jackssmirkingrevenge » Wed Mar 16, 2011 1:44 pm

mark.f wrote:Agh, I think it's about time I built some of these. :)


It's spreading :D

Although I think I'd stick with burst disks instead of fiddling around with detents and pistons.


I don't blame you, it's the route daccel and ilovefire pursued with success.

One thing I can see is that power might be a little lower for these piston prototypes compared to a similar sized burst disk or detent. Since the only thing adding to the force sealing the piston is that spring, the cracking pressure will be relatively low (again, compared to a burst disk or detent), allowing combustion gases to escape at lower pressures. Not going off firsthand experience here, just did some playing around in HGDT.


True, depending on the strength of your spring. I like th idea of the piston shutting off the flow in terms of noise suppression though.

As to the prototype (illustrated below), it worked as a coaxial pneumatic at 150 psi but when I was going to try it out as a hybrid it started to leak, typical. Sleeved it in 3/4" PVC and added moar epoxy, testing tomorrow.

In the meantime I'm making a bigger full rig that will allow me to fill cartidges up to 1" O/D.
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Unread postAuthor: Labtecpower » Wed Mar 16, 2011 2:09 pm

BOOOOOOOOOOO!!!!

Now I have to wait another day to see the results!

Where does it leak?
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Unread postAuthor: jackssmirkingrevenge » Wed Mar 16, 2011 2:53 pm

Labtecpower wrote:BOOOOOOOOOOO!!!!

Now I have to wait another day to see the results!


Damn, my turn now :D

Have a whip round, start a "buy JSR a CNC lathe" fund and your wait will be greatly reduced :)

Where does it leak?


Where they usually do - the back end ;)

Usual story, not enough depth of adhesive.
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Unread postAuthor: Labtecpower » Wed Mar 16, 2011 3:13 pm

BOOOOOOOOOOOOO!!!!!


is a standard lathe not good enough for you? :D

and I dont know where you live, but I doubt your floor would hold the weight :roll:

but it would be cool if you had the ability to mass-produce stuff :D
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Unread postAuthor: Crna Legija » Wed Mar 16, 2011 9:59 pm

lol if you get him a free cnc lathe i think he would reinforced his floor if need be :lol: id give up my bed room for the lathe, my house is built on a slab, it should hold a few tonne.

man can dream
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Unread postAuthor: JDP12 » Wed Mar 16, 2011 11:15 pm

if JSR had a CNC machine.... I believe the world may well be under his control... Because then he wouldn't have to wait 24 hours for every single project to even start testing.....
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Unread postAuthor: jackssmirkingrevenge » Thu Mar 17, 2011 1:01 am

JDP12 wrote:Because then he wouldn't have to wait 24 hours for every single project to even start testing.....


I actually got a job in order to have something to do while the epoxy cures :roll: :wink:

World domination aside, larger fill rig is curing as is the sleeved piston prototype. I would say testing tonight but in spite of my complete and utter lack of Irish ancestry, I'll probably be too fishmuzzled to care :)

edit: mini piston hybrid testing here.

Some questions JDP12 had about the fill rig which others might be wondering about:

JDP12 wrote:Do you inject fuel through this as well? if you do, I'm assuming you would do fuel calculations for the cartridge volume + the fill rig volume? Basing that on SB15's calculations with meters for hybrids, since the gas distributes evenly...


Yes, the calculation is as follows:

Fll rig volume + pump volume after check valve (1.75mL in the case of my Beto shock pump), and from this value I subtract the cartridge material volume (basically the outside volume of the cartridge minues the internal volume).

The result is then multiplied by 0.035 et voila, the correct volume of propane/butane gas to be injected for a 1x mix :D

And I'm assuming the ball projectile essentially acts as a one-way valve, to prevent air/fuel from escaping once its fueled?


Precisely.

How do you get the projectile into the cartridge? Especially with stronger tubing like I'm using, it seems like it would be a b!tch to get it through there- do you find you have to lube it at all? I feel like I may due to the larger diameter and "harder" tubing.


The simple reality is easy in -> easy out

If it's not a b!tch to force in, then the pressure will find it easy to pop out.

Let's take one of my 3/8" bearings, in order to hold back a 2x mix (chamber at 14.7psi) then it has to be able to hold 1.62lbs of force without popping out.

If I can push it in easily (say using only 5 lbs of force) that's great to load, but in practice I'm limited to 4x mixes, because any higher premix pressure will pop the projectile when you try and load.

In this regard, lube isn't a good idea either, because while it facilitates pushing in the projectile, it also makes it easier to pop out. One thing you might try is wiping the lube off the seal after pushing the projectile in.
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Unread postAuthor: dewey-1 » Thu Apr 14, 2011 1:25 pm

Where does it leak?
Where they usually do - the back end ;)

Usual story, not enough depth of adhesive.


I think the major reason for the leak on the back end is due to voids in your spark gap electrode.

If you get a chance, try an electrode like I mentioned in one of the pictorials I did for you. (page 21)

I am redoing the CAD drawing due to some possible flaws. The valve core may hit the electrode.
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Unread postAuthor: jackssmirkingrevenge » Fri Apr 15, 2011 3:06 am

dewey-1 wrote:I think the major reason for the leak on the back end is due to voids in your spark gap electrode.


To be honest I haven't seen a corelation between the electrode position and leak position, what happens is that the ignition stretches the chamber material and if the connection with the epoxy plug is not strong enough, the chamber detaches from the plug. This is imperceptible visually but as soon as you apply pressure it starts to leak. In extreme cases, the plug can detach completely and become a projectile...

The solution is to use a thick enough plug, and strong enough chamber material.
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Unread postAuthor: jackssmirkingrevenge » Wed Jul 06, 2011 6:16 pm

JDP12 wrote:if JSR had a CNC machine.... I believe the world may well be under his control... Because then he wouldn't have to wait 24 hours for every single project to even start testing.....


Well, not CNC yet, but we're getting there :)

I'm giving this valveless design a go:

Image

The o-ring is to be sandwiched between two threaded sections in order to make the pop-off pressure adjustable <sup>TM</sup>

There's still epoxy involved, curing as we speak :)

Here it is compared to a 7.62 NATO cartridge.
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Unread postAuthor: warhead052 » Wed Jul 06, 2011 6:39 pm

Oh wow, thats nice. Having fun waiting for the epoxy to cure? Or are you getting on edge?
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