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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: jackssmirkingrevenge » Mon Aug 02, 2010 3:34 pm

Had a bit of a rethink here about addressing the mixture problem that is likely the failure of my efforts in this endeavor so far.

By having a 1x mix in a syringe and using that to pressurise a cartridge, any pressure you reach would technically be at the right ratio. Using it manually would naturally limit you to the pressures you can achieve through the pressure you can exert, so a possible solution to this would be modifying the syringe to enable the plunger to be pushed by air pressure - that or closing it in a vice ;)

Thoughts?
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cartridge fuelling concept
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hybridcartrethinkvalvedetail.GIF
detail of what a combined one-way valve and electrode might look like
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Unread postAuthor: JDP12 » Mon Aug 02, 2010 4:52 pm

Hm. Interesting idea JSR. Despite my limited knowledge I think it should work.
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Unread postAuthor: jor2daje » Mon Aug 02, 2010 5:05 pm

It seems like it could be a good idea, the only issue i see is getting a good seal between syringe and your homemade fill valve, perhaps stick with a shcrader with spring removed and just epoxy a good valve cap onto your syringe.

The other thing would be to do the initial fill without a projectile in so the unmixed air can simply flow on the barrel, if you dont do this you are adding to atmospheric air already in the chamber which could mess with your mix, especially in such small volumes.
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Unread postAuthor: SpudFarm » Mon Aug 02, 2010 7:30 pm

Looks good, you have a good ability to make things much simpler then I thought was possible! A syringe is genious!

As to the "problem" with the additional atmosphere of air already in the chamber, just add one additional mix of propane to your premix chamber. It worked to fuel a 3/8" tee fitting.

I haven't followed your cartrige project to much as I thought you where going to make some complex setup that was impossible to make reasonably cheaply.

This certainly is a project in my future to!
Keep on giving this one hard thought, I like your results!
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Unread postAuthor: jackssmirkingrevenge » Mon Aug 02, 2010 8:56 pm

jor2daje wrote:the only issue I see is getting a good seal between syringe and your homemade fill valve, perhaps stick with a schrader with spring removed and just epoxy a good valve cap onto your syringe.


It's actually in my interest to eliminate the schrader, it will help with the arcing problems I was having for small diameter cartridges. As to getting a good seal, the push-fit between the syringe nozzle and the cut down needle will be very good.

Ever tried that old trick of sticking a syringe needle (we're talking the ones with a removable needle like these) in soap or wax in order to block it, then pushing the plunger until the needle segment pops off? Many times, the needle won't come off even if you take the plunger to the end because it's such a tight fit. So not worried there ;)

The other thing would be to do the initial fill without a projectile in so the unmixed air can simply flow on the barrel, if you dont do this you are adding to atmospheric air already in the chamber which could mess with your mix, especially in such small volumes.


As SpudFarm pointed out, this can easily be compensated for by adding the cartridge volume to the syringe volume when calculating the amount of fuel to be added.

I haven't followed your cartrige project to much as I thought you where going to make some complex setup that was impossible to make reasonably cheaply.


With cartridges, it's either cheap and simple or not worth doing, hence the focus on developing the right design instead of just saying "feck it" and making the effort to produce a complex design.

I'll keep thinking about any potential improvements throughout the day, if I can't think of any improvements the prototype will probably look something like the diagram above.

If this works, the hybrid pengun might actually be feasible ;)
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Unread postAuthor: Gun Freak » Mon Aug 02, 2010 9:03 pm

jackssmirkingrevenge wrote:If this works, the hybrid pengun might actually be feasible ;)

Ah, yes, but how about 300x? :wink:
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Unread postAuthor: SpudFarm » Mon Aug 02, 2010 9:13 pm

When looking at your design I might see a problem.
If the seal between the projectile and the chamber is a rubber tube attached in that fachion it might just invert and completely chocke flow.

I would clamp a small steel ring around the rubber tube to make it tighter in one spot. Calculate the surface area of the bb and find out how much weight will act on it when the mix is ignited.
Then you use a ramrod and a scale to push a bb through frequently while clamping the ring a tiny bit tighter after each time.
When the scale tells you that you are at about 60% the weight that will act upon the bb at peak combustion pressure you just cast it into the epoxy.
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Unread postAuthor: jackssmirkingrevenge » Tue Aug 03, 2010 12:51 am

The diagram isn't quite accurate, it would be more like the attached. In that configuration, it should happily hold the BB to 200 psi or so ;)
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Unread postAuthor: POLAND_SPUD » Tue Aug 03, 2010 2:45 am

it looks pretty good...
But you can probably simplify it a bit by turning o-ring detent and the fuelling port into one
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Unread postAuthor: jackssmirkingrevenge » Tue Aug 03, 2010 4:15 am

POLAND_SPUD wrote:But you can probably simplify it a bit by turning o-ring detent and the fuelling port into one


You might have a point there, the only problem I can see is actually generating enough pressure to relaibly jam the BB in place once you pull the syringe out, though chamfering the seal might help.
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Unread postAuthor: POLAND_SPUD » Tue Aug 03, 2010 5:15 am

yeah that's exactly what I meant... though I'd use a rubber washer not an o-ring...

I think this will help to sped up loading and fuelling process

also If I were you I'd try to find some standard fittings that can be used for an o-ring/rubber washer detent holder.... something as simple as a 1/4" (or 3/8") coupler with a lip + nipple.... or threaded copper pipes adapters
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Unread postAuthor: jackssmirkingrevenge » Tue Aug 03, 2010 6:20 am

It will certainly make cartridges easier to make.

Why bother with o-rings, washers and standard fittings? I have 6mm O/D 4mm I/D silicone tubing that is perfect for holding 4.4mm BBs up to 150 psi or so and will fit nicely in 6mm I/D brass tubing I will use for the cartridge body, bit of epoxy and Robert's your mother's brother. If the seal wears out, just drill it out and replace it, if not throw the whole thing away and make a new one. I reckon I could make a batch of 25 of these in less time than it takes for epoxy to cure.

with a lip + nipple...


Backup, are we still talking about cartridges?

:D :D :D

By the way, worth pointing out (for the second time in this thread) that this is turning into almost exactly what SPG had suggested back in April 2006 on Spudtech, this is the diagram he had made:
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Unread postAuthor: SpudFarm » Tue Aug 03, 2010 9:01 am

Looks good! Any chance to get a pointer where you get your brass tubes and those rubber seals/1mm rods?
I guess a hobby shop or something?

Your design should also work in bigger calibers like a marble cartrige. This might just be a better option then a piston valve..
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Unread postAuthor: POLAND_SPUD » Tue Aug 03, 2010 9:20 am

Robert's your mother's brother
lol... is it cockney or something ??

Why bother with o-rings, washers and standard fittings
because it is easier to build and is adjustable

this is turning into almost exactly what SPG had suggested back in April 2006 on Spudtech
well it isn't surprising, this happens to be the simplest method
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Unread postAuthor: jackssmirkingrevenge » Tue Aug 03, 2010 10:04 am

SpudFarm wrote:Looks good! Any chance to get a pointer where you get your brass tubes and those rubber seals/1mm rods?
I guess a hobby shop or something?


All my tubing/rods are from a hobby shop, and most of the flexible tubing I scrounge from the lab. In this case however, the seal tubing which I'm going to use was purchased from a pet shop, I presume it's intended for use in an aquarium.

lol... is it cockney or something?


It's "Bob's your uncle" in a more complete form ;)

because it is easier to build and is adjustable


Adjustable, perhaps, but cheaper and easier than epoxying a tube into another one?

Anyways, prototyping time :)

edit: I made 2 cartridges, one with a separate fill valve and one that is filled through the breech. These are the internals of the former one, I'm not sure if it will seal with this system so I may have to try with a pin/nail and small o-rings of the sort one would find in lighter mechanisms:
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