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Most efficient combustion?

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: pat123 » Tue Mar 25, 2008 6:04 pm

I would recommened a electric bbq lighter they are 5 dollars more than a piezo and a lot better.

there is no age limit on propane and you can get a 14 oz can for 3 dollars
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Unread postAuthor: SpudBlaster15 » Tue Mar 25, 2008 6:50 pm

DYI wrote:Q: What is the ideal reduction from chamber to barrel?

A: None. The reducer increases surface area and therefore heat loss, and decreases the amount of force that can act on a projectile.


Larger barrels have greater surface area, so given a 1:1 diameter ratio and a fixed barrel length variable, I would expect the heat loss to the walls of this launcher to be greater than that of a cannon with a C:B reduction.

But, my analysis of the pressure curves I derived from the 3/4" and 2.5" Latke data shows otherwise, that this difference in surface area has a very minimal effect on the rate of heat loss in the cannon.
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Unread postAuthor: ROCK SOLID » Tue Mar 25, 2008 8:54 pm

Well the cannons me and bubba05 have is a two cap screw system where the igniter is under the combustion chamber but i the middle and the barrel is 38 in long with a 60mm inner diameter or ID for short and the combustion is 100mm in dia.

The ratio 0.85.1 is that a good ratio
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Unread postAuthor: jimmy101 » Wed Mar 26, 2008 2:50 am

rcman50166 said:
That doesn't conform with the assumption that the builders are age restricted kids.

Hmm, I don't see that restriction anywhere in the original post.

A syringe doesn't require any plumbing to speak of. The short length of hose can be had from a piece of insulated wire.

Starman's injector is a darn nice setup but it'll cost at least $30 if you start from scratch. A $2 syringe (available at a farm supply store) and a 99 cent butane lighter and you've got everything you need to meter fuel as accurately as a full-on meter system with pipes, regulator etc.
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Unread postAuthor: BigGrib » Wed Mar 26, 2008 3:59 am

Q What is the best spark gap placement?
A Centered in a 1:1 L: D barrel. To overcome this I would use multiple spark gaps. If you had a 4" barrel that was 24 " long i would place the first spark gap 2" in and then every 4 inches til you get to the end which will be 2" from the end. you would end up with 6 spark gaps. this is of course you have a powerful enough ignition system.

Q What is the best reduction from chamber to barrel (best reduction method and best reduction ratio)
A The best reduction method is a coupler with a bushing. I think the best reduction ratio would be 2:1 (ie 4 inch chamber 2 inch barrel, or at least 2" cam lock)

Q What is the best fuel system.
A Metered Propane Injection. Although mapp gas does have acetelyne in it, I have yet to see chronographical evidence that Mapp Gas provides any extra umpf. I do really really like starman's 2 stage metering system. I think i might steal it actually cause that is a really great idea. Save me some weight with my 9 1/2'

Q What is the most efficient design setup
A Every answer I have seen so far has said inline, which I would tend to agree with, but what about a co-axial setup? I would like to see some data dealing with 2 chambers the exact same volume and same spark setup how they compare cronographically. something to ponder over.

i'm done
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Yea, that's definitely going to get you at least a tazer.

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Unread postAuthor: rcman50166 » Wed Mar 26, 2008 1:12 pm

The idea is to make a cannon that is really cheap that still has performance behind it. When I mean cheap I mean kids on allowance can affort to built it. More than $50 would be expensive in this case. You also have to keep in mind that kids don't typically hve credit/debit cards. So finding items on the internet is out. (I'll add that under assumptions) Such items that would be only available on the internet are things like syringes and tasers. Tools used to build need to be common house hold tools. (power drill, saws, etc.) You can't really hope for everyone to have a milling machine, lathe, welder, plasma cutters or, in the case of spuddin, a homemade foundry in their backyard. In fact I don't have an of those things. :x Make those assumptions before you recommend things like propane meters and multiple gaps. You'd be surprised how many people consider a simple soldering iron a luxury.

I don't know how to word it other than that. Perhaps try to design an efficient cannon that everyone can make.
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Unread postAuthor: starman » Wed Mar 26, 2008 1:41 pm

BigGrib wrote:I do really really like starman's 2 stage metering system. I think i might steal it actually cause that is a really great idea. Save me some weight with my 9 1/2'


While I did conceive of this concept on my own, I later saw this almost exact setup, on one of the older "random cannon" pages. I decided it was too good not to just replicate. I was going to use socket weld parts to build them up. These are all quick screw together parts.

You can build each injector for about $6-7, with the ball valve being the big ticket item. Female quick-connects are $3 or so each, the regulator at Home Depot is $20, the propane adapter is $8 and the little on-off valve is $6. So getting the propane tank setup going is a little pricey, but once you do it once, you're done with it and you have a portable system between cannons. All this is still 1/2 the cost of typical inline meter system.
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Unread postAuthor: Jared Haehnel » Wed Mar 26, 2008 2:23 pm

I would say that just you standard beginner spud gun is pretty efficient given that the person just pays attention to C:B ratio. Some people might be able to build one for under 25 dollars...

If I wanted to have a "fun" time I wouldn't want to fuss over fuel measurements or spark placements...I would say that any such advantage that those type of considerations would be minimal unless you were making a large cannon.... but thats my opinion 8)
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Unread postAuthor: chisox21 » Wed Mar 26, 2008 2:58 pm

Sorry if i dont have pictures to give, because i dont have a camera and my parents dont know that i have a cannon. (I cant really have pictures of my cannon layin in their camera)
Its a very simple design, a 1 inch PVC barrel, about a foot long, thrown onto a 1-3 i think reducer then with a combustion chamber. I used a bbq grill igniter from the hardware store (about 15$) and put it into a hole i cut into the barrel. from there i just spray in whatever im using (usually static guard-comparable in greatness to static guard) and fire away. A very simple, easy to make cannon that costed me about 35$.

Its basically the graphic at the top of the screen next to the word spudfiles, which is all you really need if you arent an avid spudder who has capability to construct such things under the radar.
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Unread postAuthor: DYI » Wed Mar 26, 2008 4:36 pm

So Spudblaster, what would you say the ideal size reduction was?
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Unread postAuthor: BigGrib » Wed Mar 26, 2008 8:57 pm

Make those assumptions before you recommend things like propane meters and multiple gaps.


So you dont have a mill or a lathe or a welder or a freakin foundry in your backyard. Neither do it. I'll tell you exactly whats in my "shop". I have a work bench that has a cordless drill on it, with a drill bit index and a couple other odds and ends. at the other end of my "shop" I have an old fridge that is tipped on it's side and used as a cutting area. Hanging from the ceiling is a power strip with a 4" angle grinder equipped with a skinny wheel and a grinding disk. I also have a tool box with some end wrenches and a some sockets from itty bitty ti 1 1/4" Really other than that I dont have a whole lot. Your assumption that you need all those fancy tools to make a chamber that has multiple spark gaps and a freakin metering system is just plain stupid. Very stupid.

For me to make a chamber with multiple gaps i use 4 #8 x 2" bolts and nuts for em. i use a drill <holy cow really expensive, but not quite as much as a mill or lathe) and then thread the bolts into the holes...holy cow it's rocket science. i can then use the nuts to tighten down the bolts in their positions and to adjust the gap width. geez i dont know if you guys with out all these tools can handle this.

As for the propane metering, which get's really complicated now and i doubt anyone without a doctorate in physics is gonna be able to build one, i use 1/4 npt fittings, which if you have a lowes or a home depot or even a harbor frieght near by your house, will have ever single part you will ever need, including this stuff called teflon tape, i dont know if you've heard of it, but NASA uses it a lot. throw in a couple ball valves and a, hang on let me spell this out so you get the whole effect of me being sarcastic, p-r-e-s-s-u-r-e- g-a-u-g-e, and you're set. assemble it in whatever manner your little heart desires. now if it is gonna be permanently mounted on the chamber you will need a 1/2 inch drillbit to drill your hole in the double wall of a chamber and thread a male end into it. epoxy it in and attach the rest of the meter accordingly.

now nowhere in there did i need a mill a lathe a welder a plasma cutter or a freaking foundry to make a chamber with dual gaps and a metered propane system

diclaimer. if you have been offended by any of this sarcasm too bad and as chopper say harden the f*ck up[/quote]
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Yea, that's definitely going to get you at least a tazer.

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Unread postAuthor: DYI » Wed Mar 26, 2008 9:16 pm

now nowhere in there did i need a mill a lathe a welder a plasma cutter or a freaking foundry to make a chamber with dual gaps and a metered propane system


Damn right. The redneck engineer will always find a way. If you can't figure it out, you aren't being creative enough.

The people with the least resources often end up having the most creativity, because they've been forced to use it. Look at what JSR builds, and you'll get the idea.
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Unread postAuthor: ROCK SOLID » Thu Mar 27, 2008 3:02 am

that is right my friend im one of those people with out much resources too. :wink:
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Unread postAuthor: Hubb » Thu Mar 27, 2008 3:33 am

^^Sometimes, that is your greatest resource. Creativity
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Unread postAuthor: rcman50166 » Thu Mar 27, 2008 5:47 am

BigGrib wrote:
Make those assumptions before you recommend things like propane meters and multiple gaps.


So you dont have a mill or a lathe or a welder or a freakin foundry in your backyard. Neither do it. I'll tell you exactly whats in my "shop". I have a work bench that has a cordless drill on it, with a drill bit index and a couple other odds and ends. at the other end of my "shop" I have an old fridge that is tipped on it's side and used as a cutting area. Hanging from the ceiling is a power strip with a 4" angle grinder equipped with a skinny wheel and a grinding disk. I also have a tool box with some end wrenches and a some sockets from itty bitty ti 1 1/4" Really other than that I dont have a whole lot. Your assumption that you need all those fancy tools to make a chamber that has multiple spark gaps and a freakin metering system is just plain stupid. Very stupid.

For me to make a chamber with multiple gaps i use 4 #8 x 2" bolts and nuts for em. i use a drill <holy cow really expensive, but not quite as much as a mill or lathe) and then thread the bolts into the holes...holy cow it's rocket science. i can then use the nuts to tighten down the bolts in their positions and to adjust the gap width. geez i dont know if you guys with out all these tools can handle this.

As for the propane metering, which get's really complicated now and i doubt anyone without a doctorate in physics is gonna be able to build one, i use 1/4 npt fittings, which if you have a lowes or a home depot or even a harbor frieght near by your house, will have ever single part you will ever need, including this stuff called teflon tape, i dont know if you've heard of it, but NASA uses it a lot. throw in a couple ball valves and a, hang on let me spell this out so you get the whole effect of me being sarcastic, p-r-e-s-s-u-r-e- g-a-u-g-e, and you're set. assemble it in whatever manner your little heart desires. now if it is gonna be permanently mounted on the chamber you will need a 1/2 inch drillbit to drill your hole in the double wall of a chamber and thread a male end into it. epoxy it in and attach the rest of the meter accordingly.

now nowhere in there did i need a mill a lathe a welder a plasma cutter or a freaking foundry to make a chamber with dual gaps and a metered propane system

diclaimer. if you have been offended by any of this sarcasm too bad and as chopper say harden the f*ck up
[/quote]

Feel Better? Now, I said that $50 would be relativley expensive for anyone who gets money of an allowance. Can you build a cannon with propane metering for under $50? Don't think so. So the equipment used to build one isn't even my primary concern.
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