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Semi-auto combustion concept

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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Semi-auto combustion concept

Unread postAuthor: Ragnarok » Wed Oct 22, 2008 6:54 pm

As promised a few days back, this is the basics of the semi-auto combustion concept I have sitting in my mind.
This is the solenoid operated one, the pressure operated one is probably more complex and harder to build than most of you would be interested in - it's a much more elegant design by a couple of orders of magnitude, but equally about the same amount more work to make, and I don't want to have to explain the maths required to design it.

Image

Most of the basics should be obvious, but the less obvious stuff:
- The propane feed will need regulation, and moderately precise regulation at that.
- There will need to be an air flow between Feed A & B - whether a vacuum on point B or a pressure feed on point A isn't that important.
- Figure out your own loaders - I suggest something powered off the same solenoid might be apt.

Of course, if anything isn't obvious, ask away. Equally, if you feel like ripping the idea to shreds... ;)
I know it's not perfect, but I'm throwing it out there to inspire others - I'm unlikely to build it myself, for some time at least, if not at all, so no point in wasting it.
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Unread postAuthor: SEAKING9006 » Wed Oct 22, 2008 7:01 pm

I remember a few years back there was some work done on cartridge based designs. There was one prototype made and a video taken, I see it around here from time to time.
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Unread postAuthor: starman » Wed Oct 22, 2008 7:12 pm

Depending on how large your spool valve and cylinder is, you might get by with the spool valve itself being your propane meter. You could conceivable make it much smaller, say with copper and incorporate an external meter tube. That way you could build the "valve stack" as a one size fits all component, sizing the "external" meter tube as necessary for the chamber size.

A tank of compressed air (or online compressor) I believe would be the easiest solution to provide air flow.
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Unread postAuthor: Velocity » Wed Oct 22, 2008 7:13 pm

Cartridge based designs are completely different field than this type of launcher. In my opinion, they are a bit less elegant.

Would it be too much trouble to post the pictures of the thing at various stages?
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Unread postAuthor: Ragnarok » Wed Oct 22, 2008 7:31 pm

starman wrote:You could conceivable make it much smaller, say with copper and incorporate an external meter tube.

An option I had considered, but I was too lazy to make two animations.

The different sizes of chamber can be compensated for within reason by varying the propane pressure. As each person will likely make their own valve stack, the adjustment with an external meter tube may not be necessary.

A tank of compressed air (or online compressor) I believe would be the easiest solution to provide air flow.

You could also expand the propane meter idea you mention above - a side tank of air for venting - filled when the valve is left, used to vent when it's right.
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Unread postAuthor: starman » Thu Oct 23, 2008 12:47 am

Ragnarok wrote:You could also expand the propane meter idea you mention above - a side tank of air for venting - filled when the valve is left, used to vent when it's right.


Shhhhh...you're giving away part of my super double secret probation plans for future cool cannonage.... :wink:
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Unread postAuthor: jackssmirkingrevenge » Thu Oct 23, 2008 12:58 am

Why not have just one feed from a premixed reservoir?
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Unread postAuthor: POLAND_SPUD » Thu Oct 23, 2008 1:23 am

@JSR uhmm it would be easier sure... but what if it explodes ?
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Unread postAuthor: starman » Thu Oct 23, 2008 1:38 am

POLAND_SPUD wrote:but what if it explodes ?


THAT would be a big bummer...would ruin your day for sure... :wink: ...although I would say odds are fairly low.
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Unread postAuthor: ALIHISGREAT » Thu Oct 23, 2008 2:11 am

a pre-mixed reservoir is a good idea, all you would need is two cut off valves between the chamber and the pre-mixed tank to ensure no explosions :wink:
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Unread postAuthor: F.E.A.R._Sniper » Thu Oct 23, 2008 8:53 am

venting here is gonna be the problem and if your gonna use a 'noid and try to use it to vent the chamber then the rof will be so slow as to make the semi-auto part negligible
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Unread postAuthor: ALIHISGREAT » Thu Oct 23, 2008 9:06 am

you wouldn't need to vent if you used pre-mixed fuel... but you would just inject fresh air from a HP resevoir if you want quick venting.
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Unread postAuthor: F.E.A.R._Sniper » Thu Oct 23, 2008 9:15 am

if he used premixed fuels then efficiency (sp?) may suffer because of the burnt gasses that ned to be pushed out of the chamber

and if he injects fresh air into the chamber then he will need to add another solenoid into the mix and timing for two noids is a pain in the ass, i know from experience

not saying that this isn't a bad idea, i have ideas for a semi-auto myself. just a difficult project to finish

and Ragnarok, in your drawing i don't know if you are gonna use an already made noid or if you are going to custom make one but the areas i circled in blue are areas that don't need to be turned down. they can remain the full diameter of the rod you use to make the spool

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edit: now i think i see that feed a is pushing fresh air through to vent it
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Unread postAuthor: Ragnarok » Thu Oct 23, 2008 9:32 am

jackssmirkingrevenge wrote:Why not have just one feed from a premixed reservoir?

Safety reasons.

Three simple rules I recall D_Hall reciting at one point:
- Don't have it around before you need it.
- Don't have more of it than you need at any one time
- Don't have workers around that don't need to be.

The last of the three doesn't really apply here, but that's the simple fact of the matter. It might not be dangerous having it, but I'm diligent about safety, and having a pre-mixed tank would break the first two rules.

Also, a premixed reservoir would require a lot of space. In theory, this design just needs the propane tank and an air flow - which could be some kind of fan which doesn't take much space.

~~~~~

@FEAR Sniper: Yes, that's why I said there needs to be an air flow. I know it won't vent fast naturally, you actually need to introduce that new air somehow.

The mechanical semi-combustion idea I have DOES provide it's own air flow, which boosts it's ROF to the extent I imagine some kind of cooling will be needed to stop it destroying itself.
However, that version needs a lot of maths to get it to work, as the range of certain variables needs to be fairly precise to get it to work, and I really don't want to have to go into explaining that. Partly because I fear I'll get it wrong somewhere (or equally, be misunderstood) then find some poor sod went off to get parts made which then won't work.

So to avoid that, until I'm completely finished with it, to avoid problems like that, I'm going to be quiet about it. (For another thing, the mechanical version requires much finer tolerances.)

Also, I'm not entirely sure whether I want to build it myself yet.

EDIT: No, those bits don't have to be turned down. You could do it for weight reasons if you wanted.

But it's like that in the animation because I couldn't be arsed to make it that way. The valve was just done with a grey rectangle to which I attached identical O-ring shape bits to save time and effort when I had to adjust things around to get it all working right.
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Unread postAuthor: jimmy101 » Thu Oct 23, 2008 11:16 am

Rag, that's a nice design. And I agree, having a cylinder with pre-mix around is a really bad idea.
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