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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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Unread postAuthor: psycix » Tue Feb 03, 2009 10:43 am

I want it to be non-lethal. It hurts less when my friends inevitably "accidentally" shoot me with it.

Even a weak cannon can be lethal if it hits someone on the wrong spot. Limiting power of a cannon is NOT a safety measure.
1- NEVER fire in the direction of a human or animal.
2- Do not allow just anyone to fire your cannon, especially if they can't use it responsibly.
3- Always keep surveillance when people are shooting with your cannons.
4- When the operator of a cannon knows that the cannon is lethal, then he will operate it with caution. If he doesnt, he should not hold the gun.
5- When people think that the cannon is not very lethal, just like rag said "I didnt know that a paintball or potato could be so dangerous" make sure to tell/show them that before allowing them to fire it.

Realize that your friends are probably total spudgun noobs and you should not let them play with the cannons until they understand how dangerous a spudgun can be and why they should be careful with it.
Note that when your friends cause trouble with the cannon, and people will ask, who's cannon is that?, then you've also got some trouble. And on top of that, created a bad story for spudguns.
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Unread postAuthor: Ragnarok » Tue Feb 03, 2009 11:00 am

psycix wrote:5- When people think that the cannon is not very lethal, just like rag said "I didnt know that a paintball or potato could be so dangerous" make sure to tell/show them that before allowing them to fire it.

No - not tell. Show.

If you tell them, they'll probably think you're being over cautious and exaggerating.
If you show them, they'll have to believe it. My usual trick is putting a hole through 1mm steel with a paintball, which instantly commands respect. There is a big difference between a paintball at 300 fps, and at 1000 fps - 300 fps won't even dent the same steel.

Obviously in the case that the cannon is unable to make a sufficiently awe-inspiring demonstration, tell is regrettably necessary - but if you can, show is far better.

Put it this way. I told someone categorically that one of my cannons could be dangerous, and they still volunteered to be shot with it, so I said: "Let me show you what it can do first, just so you know." (although I had no plans to shoot them with it anyway)
Wouldn't you know it, after the demonstration, they were decidedly less keen to get shot. :roll:

That is the difference between telling and showing - showing is much more believable.
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Unread postAuthor: chenslee » Mon Feb 16, 2009 10:46 am

I stunk up my garage with propane last night doing some testing of the propane injection nozzle and ignition.

I was using my regulator assembly and a ball valve to dump a little fuel in.

With just the rear cylinder section, no bolt, and sparking to the nozzle, I got a satisfying blue fireball. Moving on I added the bolt which effectively lengthened the combustion chamber. For some reason, it seemed to run WAY rich even though I was dumping the same amount in. I think it might have something to do with the bolt choking down to 2" from the 2.5". Also my regulator was getting sweaty and the propane may have been getting denser. My next step is to finish building a spark rail and get some sort of metering.

I'm also thinking of ditching the nozzle I made and switching it out for a Bernzomatic head inside the combustion chamber to get better mixing.


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Unread postAuthor: Radiation » Mon Feb 16, 2009 11:33 am

You're kinda all over the place there. If you're going for metered propane, the only true way of precisely dumping propane into your chamber, then why put that nifty little bernzomatic torch head inside the chamber?
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Unread postAuthor: chenslee » Mon Feb 16, 2009 12:00 pm

This is what I've got right now:

Image

... which is just a pipe cap with a hole drilled in it. I want to replace this with just the tip and air hole section of the Bernzomatic. I don't need the knob and the propane tank fitting, I have all that upstream of the metering tank.

I'll still precisely meter the propane, because the air mixing holes from the torch will be inside the chamber. It will just mix the air that is already in there better than the crappy hole-in-a-cap I have now.

I still have a lot of testing to do with the cap design.
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Unread postAuthor: Radiation » Mon Feb 16, 2009 12:41 pm

Your mixture will be far from precise just because you put a propane air mixing torch head in the chamber.
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Unread postAuthor: chenslee » Mon Feb 16, 2009 2:01 pm

That is why I'm going to meter the propane.
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Unread postAuthor: Radiation » Mon Feb 16, 2009 2:25 pm

That still does not insure an even mixture, it insures a fixed amount of propane in the chamber.
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Unread postAuthor: chenslee » Mon Feb 16, 2009 2:56 pm

That is what the torch head is for.

Are you trolling me?

The discussion so far is:

"I'm also thinking of ditching the nozzle I made and switching it out for a Bernzomatic head inside the combustion chamber to get better mixing."


...and your reply:

"If you're going for metered propane, the only true way of precisely dumping propane into your chamber, then why put that nifty little bernzomatic torch head inside the chamber?"

Already you are asking a question whose answer is in the post that you are questioning.

I try to clarify:

"I want to replace this with just the tip and air hole section of the Bernzomatic. I don't need the knob and the propane tank fitting, I have all that upstream of the metering tank. "

And then I reiterate taking a different angle:

"I'll still precisely meter the propane, because the air mixing holes from the torch will be inside the chamber. It will just mix the air that is already in there better than the crappy hole-in-a-cap I have now. "

To which you reply:

"Your mixture will be far from precise just because you put a propane air mixing torch head in the chamber."


I'm pretty sure I said I was metering, but just to make sure:

"That is why I'm going to meter the propane."


And now you come full circle, back to your original question, that was answered before you asked it, and explained two different ways:

"That still does not insure an even mixture, it insures a fixed amount of propane in the chamber."


Am I missing something here? I came to this forum for intelligent discussion about projects similar to mine and so far I've had my ONE thread hijacked, and then turn into a circular discussion.

For the record:

YES. I understand the safety issues of, and I plan to treat my ballgun as if it were a real gun.

YES. I know how to be safe with a real gun.

YES. I understand the concept and importance of fuel metering.

YES. I understand the concept and importance of fuel/air ratios.

YES. I understand the concept and importance of fuel/air mixing.
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Unread postAuthor: Radiation » Mon Feb 16, 2009 3:11 pm

Wow sorry I irritated you so much. I was just stating that neither a metered setup or your propane air nozzle will do anything to actually insure an even mixture once the fuel is injected into the chamber. I'm not sure I understand your method and perhaps you don't understand what I'm trying to convey to you. Basically the only thing that will insure an even mixture is a fan or some sort of ACTIVE air aggitator. Simple as that. No harm meant.
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Unread postAuthor: psycix » Tue Feb 17, 2009 1:57 pm

I think there is a misunderstanding here.

METERING - Making sure you inject EXACTLY the right amount of propane into the chamber.
MIXING - Making sure that the fuel is dispersed evenly through the chamber.

chenslee, as far as I can understand, you are stating that by putting the torch head inside the chamber, you achieve better metering and mixing.
For the mixing part, you NEED a fan to mix best, direct injection does not much have to do with it.
For the metering part, well, it does not have anything to do with the amount of fuel injected.


For metering you need a fuel meter and you seem to tell us that you are simply sticking the torch head directly in the chamber and hook it up to the tank.
Maybe you didn't state it clear enough that you are using a fuel meter between the tank and the in-chamber torch head (Just a wild guess at the misunderstanding. Was this what you were trying to say?)
I hope this clears things up.
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Unread postAuthor: chenslee » Wed Feb 18, 2009 12:07 am

I once made a cannon by just sticking a blowtorch in. It worked; I moved on.

What I'm working on now has metering, a nozzle, and air purge. It does not use a blowtorch. It does not use a fan.

Here are some pictures:

This is the nozzle. It's a cap with a hole. Both propane and air pass through here, but not at the same time. Please note that this is an older picture and the fittings shown are no longer in this configuration.

Image

This is my entire set up right now.

Image

This the purge cylinder. It's an air actuator that pumps air. It pumps air on both strokes. The stainless steel fittings are check valves.

Image

This is the second valve of the meter. It's a pin actuated poppet valve. The hose itself is the metering tank. Also note the stainless check valves. They keep propane out of the air purge lines, and air out of the propane lines. All together there are 6 check valves.

Image

Here is another picture. The first valve of the meter is just a ball valve. Also there is a pressure gauge and a regulator. The amount of propane used is adjusted by changing the meter pressure.

Image

Also, as soon as Youtube is finished with maintenece, I'll upload the video of 3 consecutive shots.
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Unread postAuthor: Lentamentalisk » Wed Feb 18, 2009 12:27 am

Ok, I must admit, this is going to be one sweet looking tennis ball cannon...
Plumbers wet-dream, yes, but none the less, it is looking incredibly well made, and I love your whole fueling system.
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Unread postAuthor: chenslee » Wed Feb 18, 2009 1:46 am

Yeah, there are a lot of fittings. Now I have to figure out how to fit them all on the gun!

Here's the video. I just uploaded it, so it might not be fully cooked yet.

Stuff, purge, fill, empty, ignite.

[youtube]http://www.youtube.com/watch?v=tkY414upxRQ[/youtube]
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Unread postAuthor: Lentamentalisk » Wed Feb 18, 2009 2:51 am

Beautiful.
The purge pump won't empty the entire chamber, but it will do a decent job, and when you fire it, there is fair amount of air sucked back in, and when you open the breach to load the ball, you will get a little more exchange too. I wouldn't worry about it. Besides, the combustibility limits of propane are so wide that it is hard to over fuel, especially if you intentionally run the mix a little on the lean side.
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