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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: Insomniac » Mon Jul 11, 2011 5:29 pm

Um, it looks like that one won't seal... Gas can get from behind the burst disk to the gap between the projectile and cartridge, then on to the atmosphere provided that the projectile doesn't seal perfectly.

Of course, with a 'rubbery' burst disk it will seal, but as-is gas can escape without ever encountering an O ring...
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I wonder how much deeper the ocean would be without sponges.
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Unread postAuthor: LeMaudit » Mon Jul 11, 2011 6:18 pm

argh you're right... damn... I need more coffee :shock:
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Unread postAuthor: jackssmirkingrevenge » Mon Jul 11, 2011 10:34 pm

LeMaudit wrote:argh you're right... damn... I need more coffee :shock:


It's not an easy solution to get to, but once we do... :D

We could replace the theaded section and o-ring with a length of silicone tubing forced in a cone, as was the original premise of this thread...
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Unread postAuthor: Gun Freak » Mon Jul 11, 2011 10:39 pm

I like that much better than the burst disk ones we've been discussing. Valveless is definitely the way to go. Loading it may be a pain though, especially if you want to use high mixes because the seal would be tighter.
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Unread postAuthor: jackssmirkingrevenge » Mon Jul 11, 2011 11:30 pm

Gun Freak wrote:I like that much better than the burst disk ones we've been discussing. Valveless is definitely the way to go.


For cartridges that need to be manufactured and reloaded in quantity, definitely.

Loading it may be a pain though, especially if you want to use high mixes because the seal would be tighter.


A threaded plug at the back is still an option.

A very important point as I've mentioned before is the fill rig pressure dump. Without the benefit of a spring to hold the valve shut or projectile in place, you need to dump pressure quickly in order to ensure a seal with minimal loss. I think the filling schrader is sufficient provided that there isn't much in the way of dead volume, ie the fill rig inner volume matches the cartridge outer volume.
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Unread postAuthor: Mr.Tallahassee » Tue Jul 12, 2011 12:18 am

I thought through a possible design, quite similar to a regular firearm round. I'm not sure how it would work as the reloading of the individual shells might be an issue. If you manufactured several of these shells and varied the thickness of the cone tip on the end, you could fill them up to pressure and possibly store them "loaded." Just thread in the cartridge and fire. You'd probably have to make a reloading jig from a vise and a steel block with a conical hole though.

As to the fuel and air mix, the syringe idea, except with a sort of pump. Make a large volume mix and use the pump to pressurize the cartridge with that mix.
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The light gray around the projectile is the seal. It's rather difficult to see sadly.
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Unread postAuthor: Insomniac » Tue Jul 12, 2011 12:50 am

That is essentially what JSR has already constructed. The problem is in creating a cartridge that seals reliably, releases the projectile at the right pressure, and doesn't rapidly degrade when used.
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Unread postAuthor: Insomniac » Tue Jul 12, 2011 12:57 am

jackssmirkingrevenge wrote:A very important point as I've mentioned before is the fill rig pressure dump. Without the benefit of a spring to hold the valve shut or projectile in place, you need to dump pressure quickly in order to ensure a seal with minimal loss. I think the filling schrader is sufficient provided that there isn't much in the way of dead volume, ie the fill rig inner volume matches the cartridge outer volume.


I'd purchase a Presta valve if I were you. They're very narrow (narrower than schraders), yet they can be easily actuated by hand and appear to vent MUCH more quickly than schrader valves can. I made a coaxial once that simply wouldn't fire with a schrader, but had no problems with a presta.

The downside is that the adapters I've seen for using presta valves on schrader pumps rely on an O-ring to seal, which scrapes past some of the thread when the adapter is removed. Great for attaching to a valve permanently, but continual removal (to allow uninhibited venting of the presta) will tear the O-ring quite quickly.

Of course, you could always use a seperate valve for filling, or lathe yourself a better design :wink:

Hell, now that I think of it, you could create your own high-flow valve to dump the fill rig pretty easily.


EDIT: Damn, was just going to copy-paste this into my prevoius post, but forgot and hit submit. :roll:
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I wonder how much deeper the ocean would be without sponges.
Right now I'm having amnesia and deja vu at the same time. I think I've forgotten this before.

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Unread postAuthor: jackssmirkingrevenge » Tue Jul 12, 2011 4:56 am

Insomniac wrote:I'd purchase a Presta valve if I were you.


Interesting idea, the adapter would be a non-issue as it would likely be permanently attached.

Hell, now that I think of it, you could create your own high-flow valve to dump the fill rig pretty easily.


Aren't lathes wonderful :D really though I think sticking with the schrader and making a fill rig which is exactly the same size as the cartridge with negligible dead space is the easiest and simplest solution

EDIT: Damn, was just going to copy-paste this into my previous post, but forgot and hit submit. :roll:


Happens to the best of us ;)
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Unread postAuthor: Insomniac » Tue Jul 12, 2011 5:24 am

I figured that out when I saw my double post :D

The problem with the adapters are that when attached, you once again need to poke something in to reach the valve stem. Whereas it is exposed in a regular presta, making it extremely easy to quickly actuate by hand (I'm planning on making a small pen-gun using one, once I get some tubing).

The plus side of a somewhat larger fill rig is that you'll be able to try slightly larger cartridges... ableit at the expense of more pumping and more wasted gas.
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I wonder how much deeper the ocean would be without sponges.
Right now I'm having amnesia and deja vu at the same time. I think I've forgotten this before.

Add me on msn!!! insomniac-55@hotmail.com
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Unread postAuthor: LeMaudit » Tue Jul 12, 2011 6:31 am

We could replace the theaded section and o-ring with a length of silicone tubing forced in a cone

:shock: How weird... here's what I had in mind during the night :lol:

Using a length of copper tubing, a length of silcon tubing fitting inside, and some crimping to keep everything together.

In term of "mass" production it would be ideal.
The operation would be:
- Put the tubing in the lathe, ball side on the jaw
- crimp the lefter groove (a bit less deep than the other two)
- insert the ball
- crimp the other groove to keep the ball in place
- insert the plug (with a little groove in the middle)
- crimp at the groove position
- separate at exact length with the blade

You would need something like a knurling tool with a specific wheel shape:

Image
Knurling tool

But it is much much more fun to design and build the tool, than to machine the same piece a gazillion times :D
This one cost $28; You would have to mill down the shank to 1/4" (or buy the 3/8" Sherline holder :wink: ), and make yourself a wheel in steel with the positive shape of the groove.

And... you would have a shiny knurling tool to play with, for the same price :lol:
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Unread postAuthor: saefroch » Tue Jul 12, 2011 6:51 am

I have (had) a bike pump that had a presta attachment, since I own a bike that has presta tire valves. On the connection, there's one for schrader valves and one for presta. Does that design suffer from the adapter problem?

The bike pump I currently use has something like an adjustable detent that clamps onto either a presta or schrader valve, but it hasn't had any seal damage after being unattached and reattached a great many times.
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Unread postAuthor: LeMaudit » Tue Jul 12, 2011 6:59 am

In my excitement I forgot a place for the spark :lol:

Alright, here's with two pieces of tubing inside, and a little crimping at the end to be sure the plug stays in place
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Unread postAuthor: jackssmirkingrevenge » Wed Jul 13, 2011 10:45 am

:shock:

Copper? Crimping?!

What on earth has gotten into you?

:D

Interesting thoughts. I wouldn't recommend that setup for the base plug, I have a feeling it would blow out.

Also, given this is going to be compact, I think I will scale up to 3/8" from the 0.22" I had in mind. Some designs/prototyping in the works, but first, dimples.
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Unread postAuthor: LeMaudit » Wed Jul 13, 2011 11:06 am

What on earth has gotten into you?


I feel ghetto... or "Kurdish" as they say at Patator :lol:

too much shininess I guess... :?

Can I say duck tape?

And if I tell you I'm shopping for some green laser... :shock:
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