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Open Source Auto Hybrid .177 Calibre

A place to ask general spud cannon related questions.
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Open Source Auto Hybrid .177 Calibre

Unread postAuthor: SPG » Mon Nov 26, 2007 1:38 pm

Ever since I first saw a hybrid I've been trying to work out my personal Holy Grail - the 177 auto-hybrid. In fact it was what got me into spudgunning in the first place, the quest to make my own air rifle. I think I've finally cracked it.

The downside is, I know it'll probably involving machining and a level of work I'm not equipped to carry out, so I thought I'd throw it out there, make it open source and see what people think, work on refining it together, and maybe someone will actually build one. So, for now, here's a schematic I've left a couple of bits out but I think it's clear.

Firstly the ignition group. I'd imagined a small coil set up with a microswitch to trigger it. It allows for instant recharging, and should give a good spark.

Secondly the fuel tank. Because it's a small calibre high pressure hybrid it should be perfectly possible to use a pre-mix fuel/air set up running through an adjustable regulator into the 3-position ball valve shown. Obviously care should be taken to avoid this ignition, but I imagine building it strong and giving it a burst disc in case of ignition within.

Thirdly, various springs and levers. It's only a schematic, not a working diagram so for ease I left out the spring behind the piston, and also any levers going from a trigger group to the valve, and ignition switch.

I imagine building the whole thing into a rifle set up. An under barrel fuel tank would work well in this case (burst disc at barrel end). I also imagine some kind of helical pressurised magazine as discussed in another post on here, but a straight underbarrel would be fine and a hopper at a push.

So the firing sequence.

1. Empty - trigger is forward, three way valve is venting chamber to air.
2. Fueling - trigger is half way back, valve is open to fuel tank and chamber is filling.
3. Ignition - trigger is fully back, valve is closed chamber is sealed, microswitch opens and ignition fires.
4. Chambering/Firing - pressure builds, piston rushes forward, bb is chambered and magazine is sealed.
5. Purging - trigger is half way back, valve is open to fuel, fuel enters chamber alongside combusted gases, chambers is pressurised.
6.. Exhaust - trigger is fully forward, valve is open to air, chamber is venting exhaust gases.

Repeat.
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Unread postAuthor: Fnord » Mon Nov 26, 2007 1:48 pm

Alright, I was keeping this to myself, but for the sake of open source I guess I'll share it, since I don't think I'll be able to put it together any time soon.

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It's a "turbojet" stuck to a steel BBMG, nothing more. I know Cptn law has a jet already built, but I don't think he posts here anymore.
This design is also open to suggestions and improvments.

This could probably be portable when running from a HPA tank.
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Unread postAuthor: thespeedycicada » Mon Nov 26, 2007 4:46 pm

Fnord you dont need a rosscojector (or at least the one i know of as i dought there is another) they are built for pulsejets to suck air into the intakes to make a normally non running jet run.Besides rossco is a guy who will poke fun at you for using one in a bb gun.Another thing is that it is hard to get a good amount of energy out of these jets like the one you have in the pic.usually to get them to be even slightly efficient you need to get a conical shape akin to two funnels with the small ends put together.But you cc would be so tiny that the amount of airflow coming in would probaly make it work great.
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Unread postAuthor: Fnord » Mon Nov 26, 2007 4:55 pm

From what I understand, a rosscojector spreads gas out by forcing it through a thin slit, much the same way a spray bottle atomizes water. It's just there to ensure the gas is mixed the best it can in a small area.

And, if Rossco has a problem with it, whatever. I came up with the idea before I knew what it was called or that people were using them in PJs (yes, before I joined the pulsejets site).
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Unread postAuthor: SPG » Mon Nov 26, 2007 4:58 pm

Erm, excuse me, go start your own thread, blinking jetboys :wink:
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Unread postAuthor: thespeedycicada » Mon Nov 26, 2007 5:48 pm

_Fnord wrote:From what I understand, a rosscojector spreads gas out by forcing it through a thin slit, much the same way a spray bottle atomizes water. It's just there to ensure the gas is mixed the best it can in a small area.

And, if Rossco has a problem with it, whatever. I came up with the idea before I knew what it was called or that people were using them in PJs (yes, before I joined the pulsejets site).
Yes that is one reason but it also pulls in some air as usually the only way to get your jet to self start is to use a rosscojector and i didn't say he would have a problem with just that he would poke fun at you in a joking sort of way hes a nice guy really and im sure would like to hear that someone else thought of the idea before him.

Sorry spg :) i think the idea would work as it is pretty much a fancified piston hybrid.What sort of rof are you planning on and what sort of mixes?
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Unread postAuthor: Hubb » Mon Nov 26, 2007 6:10 pm

I think there is a lot of potential for this design (referring to the original), although, it will need some work.

You know, it's amazing what can be accomplished when one sets his mind to it. Keep it up, SPG, and let's see where this goes.

Edit: I know in the original post, your were looking for a hybrid design, but don't you think it may be easier to experiment with a pneumatic at first? Looking at the design, it looks like a pneumatic configured like this would have full-auto potential.
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Unread postAuthor: Fnord » Mon Nov 26, 2007 7:51 pm

Lol sorry for the thread hijacking SPG. :)

Depending on your ROF, you're going to have to get rid of heat quickly, or you'll start to damage the non-metal parts (o-rings/valve)
You may need heatsinks or a waterjacket for reliable operation.

For example, with higher mixes my hybrid chamber walls gain ~30 degrees (F) per shot. It isn't a problem, as after a few shots they will start to cool down quicker than I can put heat into them, but I can still get it hot enough to burn myself. This will be amplified if you are shooting aut, of course.


The reason I was throwing my diagram ot there is because it's basically what you're trying to achieve, but with no moving parts (And, because I want to see someone build it).
An advantage that it has is you could run it until the whole thing is glowing red and it won't be damaged, so long as the barrel is supported to keep it from deforming.

Speedy: I probably didn't think of it before him, as I imagine he's been doing things like this for longer than I have. In my case I just took an idea from a household item (sprayer) and used it for what I needed to do.
For example, my design wasn't cut at an angle, so the flow is slightly less.
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Last edited by Fnord on Thu Oct 07, 2010 4:26 pm, edited 1 time in total.
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Unread postAuthor: Ragnarok » Mon Nov 26, 2007 10:52 pm

The heat issue is one I'm going to have real difficulty handling for my 6mm auto combustion.

The all mechanical valves will easily be able to cycle faster than I can possibly supply it with gas and sparks.
A full firing and reload cycle will be measured in the tens of milliseconds, not tens of seconds like most combustions are now.

It'll never hit vortex strafer ROFs, but it could reach 25 RPS if I can supply that, and that's going to create heat like nobody's business.
I'm going to need to find one awesome cooling system, or the micro chamber fan(s) will be reduced to slag.

Obviously, I could dial the ROF down, but what's the fun in that?
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Does that thing kinda look like a big cat to you?
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Unread postAuthor: SPG » Tue Nov 27, 2007 6:02 am

Fnord, don't worry, I'm only joking with you.

I'd thought of this only as semi-auto, so heat build up wouldn't be such an issue, a decent heatsink would work fine.

For selective fire, I can see a stepper motor controlling the fuelling valve would work, and it'd even be possible to have 3 round burst-fire with some simple circuitry (beyond me though).

I've been looking at using components from RC combustion engines. You can now get Capacitive Discharge Ignition systems for these, which are nice and small, and will give repeated sparks. There's also no reason why the pistons, piston rings and cylinder heads used in these tiny engines couldn't be used, all it would mean is replacing the engine block with a machined chamber block. This cuts down on non-metallic parts and reduces the chance of heat damage.

Overnight I came up with this revised version, which reduces deadspace, reduces piston size (less power loss) and seems to me to be much simpler.

Now, who's capable of drawing this up in 3D?
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Unread postAuthor: Hubb » Tue Nov 27, 2007 6:15 pm

I would think the piston or bolt or whatever you call it, would begin to move due to the chamber pressure before it is ready to fire.
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Unread postAuthor: FeLeX » Tue Nov 27, 2007 8:20 pm

Actually I dont know about it being auto but that seems like a REALLY good idea for a non burst disk hybrid. All it need is some sort of a spring to retain the bolt from sliding forward when pressurized.
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Unread postAuthor: jackssmirkingrevenge » Tue Nov 27, 2007 11:27 pm

hubb017 wrote:I would think the piston or bolt or whatever you call it, would begin to move due to the chamber pressure before it is ready to fire.


You could have a blow-forward valve instead and adjust spring strength so it resists the mix pressure but moves when the mix is ignited.

edit: if anyone makes a prototype, I hope for their sake it doesn't explode, lest they be forced to endure "open sores hybrid" jokes :roll:

I still believe that the best solution here would be a hybrid cartridge. I drew up a design that might work - basically the rear end is a non-return valve which also provides a spark gap. The fuel would be metered in through the back with a syringe, then to add the compressed air the 6mm tube fits nicely into the cam-locking style seal like the one on this foot pump - you could also build a chamber with a premixed concoction of fuel and air and just fill once, but it would probably be tricky to get a homogenous mix - not mention the dangers of having a large quantity of premixed fuel.
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Unread postAuthor: SPG » Wed Nov 28, 2007 7:27 am

Are you thinking something along the lines of this...

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...when you say blow forward breech? (yes I know it's your design).

The problem I saw with that, was the cluttered chamber, don't forget you've also got to get a ignition source in there as well. Also there's the problems of sealing things when the seals are exposed to heat.

The reason, I've taken the "blow-forward piston" out of the chamber is to cut down on the need for seals (your's needs two sets - outer piston to chamber and inner piston to rod) whereas mine needs fewer seals which would hopefully be easier to put in place.

Hybrid carts sound fun, and I'd love to see them in action, but there's several issues I personally have with them.

1. Fiddly fuelling - having to load each one individually just would spoil all my fun.
2. Repeated manufacture - I'd get bored making fifty cartridges.
3. Power loss, in cycling the action.

That's not to say I don't think it's a great idea, it's just not my tasse du thé :wink:

And Hubb and Felix, the piston/bolt doesn't move forwards as it would be held back by a spring, I just didn't put them in (like I said in the OP) because drawing springs is fiddly.
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Unread postAuthor: jackssmirkingrevenge » Wed Nov 28, 2007 7:46 am

You're right, that is a little complex, maybe you can adapt the second version I made - blow forward bolt version 2 than involved a lot less precision casting.

You couldn't need to have the ignition etc within the mechanism, the idea is that the exploding mix vents through a port that feeds the breech.

As the the cartridges:

1. Fiddly fuelling - having to load each one individually just would spoil all my fun.


Not much that you can do about that unfortunately

2. Repeated manufacture - I'd get bored making fifty cartridges.


Fair enough but it's a one-time job

3. Power loss, in cycling the action.


Yes, but the trade off would be the immense COOL! factor of spent brass flying around :D

I'm going to give the electric drive pneumatic a go, if that flops I think some toying around with hybrids is long overdue :)
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