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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: jimmy101 » Thu Mar 27, 2008 11:25 am

rcman50166 wrote: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?

Yes. Whatever you spend on everything else for the gun, add $4 for a meter and container of fuel.

The $4 gives you fuel + meter that can be used on many cannons, it isn't dedicated to a single gun.

rcman50166 wrote:Don't think so.

Then you think wrong.

It aint rocket science, it's being creative and doing a bit of f'ing searching to find out how to do it on the cheap.
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Unread postAuthor: rcman50166 » Thu Mar 27, 2008 11:30 am

Well mentioning the price is probably something you chould have done in the first post. This changes a lot of things. Exactly how do you total $4 for a metering system? If it's easy enough I'll change the best fuel to propane.

I'm sorry by the way for my response to your post. I responded when I was angry.

Also does anyone have anything against a reduciton of 2:1 other than there isn't enough testing done? And how about the body weight to cannon weight ratio. Anyone have problems with that? The same question goes with the CB volume ratio. They all seem ideal to me. A new question is up for propane ratios.

If you guys are wondering why I keep asking all these noob questions is because I want the opinions of members. Opinions change over time and it's always nice to have reassurance by checking.
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Unread postAuthor: jimmy101 » Thu Mar 27, 2008 1:04 pm

rcman50166 wrote:Well mentioning the price is probably something you chould have done in the first post. This changes a lot of things. Exactly how do you total $4 for a metering system? If it's easy enough I'll change the best fuel to propane.

Disposable 60cc plastic syringe = $2 (from farm supply store)
Disposable syringe needle = ~$1 (from farm supply store)
Disposable butane lighter = $1
Short length of insulated wire = free
=======================================
TOTAL METER COST = $4

rcman50166 wrote:Also does anyone have anything against a reduciton of 2:1 other than there isn't enough testing done? And how about the body weight to cannon weight ratio. Anyone have problems with that? The same question goes with the CB volume ratio. They all seem ideal to me. A new question is up for propane ratios.


I don't think there is any such thing as an "ideal" reduction.
1. The barrel ID is really choosen based on the ammo.
2. The chamber ID should be the largest OD that your local hardware store has in pressure rated pipe and fittings.
These two factors control the "ideal" reduction, at least when "ideal" is being strongly affected by practicality. For spuds, the "ideal" barrel diameter is probably 1.5". 2" is also good but it takes big-ass spuds to seal the barrel. 1.5" is probably less powerfull but the ammo is cheaper, more available and less critical.

For cannon weight, a more important question is probably the total length of the cannon. The length of the cannon depends on how it is held when it is fired.
1. If it is shoulder fired it probably should be less than about 4' long.
2. Hip fired, perhaps as long as 6'.
3. From a mount it can be much longer.
The actual weight of the cannon is pretty irrelevant, PVC is light enough that weight is unlikely to be a problem. If you can handle the length of the gun, the weight won't be a problem. So, you design the gun to a total length based on how it will be fired.

So, the desired ammo, availability of PVC componets and how you will support the gun during firing pretty much completely defines the gun. The total length is partitioned between the barrel length and chamber lengths taking into account the two diameters and the desired CB.
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Unread postAuthor: starman » Thu Mar 27, 2008 2:21 pm

Rcman, please indulge me a moment. I want to challenge the premise of your goals here.

Anyone who is so young as to have available only "allowance funds" and hasn't engaged the assistance of a responsible parent or adult and their associated potential $ resources, has no business playing around with devices described on these pages....period.

Your fetish regarding the cost of things also is not valid. Spud-gunning is a hobby. Like hundreds of other hobbies, it will cost you X amount to properly participate. Just because some aspect of a hobby (ie. "expensive" metered fuel system) doesn't fit your personal budget, doesn't make it something you can ignore or circumvent. You can't expect to do very well on the golf course if you don't invest in some golf clubs, golf lessons, and many many hours on the course. If you can't afford golf, you don't play. If you can't afford spudding, you don't spud.

Your goals (inexpensive entry level spudder) are all solved with a basic hairspray spray and pray model. 4" X 1' chamber, 3' to 4' 1.5" barrel, associated cleanout connectors/cap, coupler and reducer bushing, and a BBQ ignitor.... That's it. There's no performance mods, no optimizations, no metering...it is what it is...something to shoot a tater 100 to 200 yards and go BOOM. Anything beyond this model and you have officially stepped into hobby world. You'll be expected to have access to tools and some money. How much depends on your dedication to the hobby.

Biggrib's sarcastic comments were funny and over the top but right on. I would much rather see you working on perfecting your carbureted gasoline fueling system/cannon. Your fertile mind is going to waste on this penny-annie endeavor.
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Unread postAuthor: BigGrib » Thu Mar 27, 2008 2:48 pm

rcman, i must apologize, like you when you responded I too was irritated when i responded. here is the good news though. I used starman's 2 stage meter idea with a total cost of 10 bucks to make the actual meter itself and another 5 bucks for the quick couplers. I will post pictures when i get home from work and I also have a new topic that will be coming up about refilling 14 oz propane tanks.
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Yea, that's definitely going to get you at least a tazer.

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Unread postAuthor: SpudBlaster15 » Thu Mar 27, 2008 2:52 pm

starman wrote:Anyone who is so young as to have available only "allowance funds" and hasn't engaged the assistance of a responsible parent or adult and their associated potential $ resources, has no business playing around with devices described on these pages....period.


Hey... I'm 16, and as it is almost impossible to obtain employment in my (soon to be ghost) town, my only source of steady income over the past 5 years has been my $40/month allowance, and a few hours that I worked landscaping last summer. In the past year and a half, I've built 4 advanced combustion launchers, 5 pneumatic launchers, 2 hybrid launchers (one of which created an entirely new concept that enabled more precise fueling), a high pressure pump, and have probably wasted several hundred dollars on air pumps that broke, launchers that initially didn't work the way I intended them to, paint finishes I have had to sand off and replace, and concepts that failed entirely. Yet, I still have enough money in the bank/in my wallet to fund almost any launcher existing on this site if I had such desires. You don't have to have a high level of income to build advanced launchers, you simply have to use your available funds intelligently, and use some creativity to obtain funds from other sources when in times of need.
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Unread postAuthor: starman » Thu Mar 27, 2008 2:57 pm

BigGrib wrote:rcman, i must apologize, like you when you responded I too was irritated when i responded. here is the good news though. I used starman's 2 stage meter idea with a total cost of 10 bucks to make the actual meter itself and another 5 bucks for the quick couplers. I will post pictures when i get home from work and I also have a new topic that will be coming up about refilling 14 oz propane tanks.


Cool. What did you use for the propane regulator? That was a $20 "big ticket" item in my setup.

@SpudBlaster15:
Way to go SB15, you have the right idea about this stuff. You want it bad enough, you find a way. Your resourcefulness proves your maturity.
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Unread postAuthor: BigGrib » Thu Mar 27, 2008 11:59 pm

No regulator, I went from the meter body which is a sch 80 sprinkler riser with endcaps one of which is drilled out and fitted with a 1/4 npt male coupler to a t out to a 1/4 ball valve and a male quick connector. the other side of the t has a 160 psi gauge on it. i just open the ball valve slowly til i hit the pressure i want and then close the valve. the regulator i had is a harbor freight special wich sucks but that was only like 5 bucks.
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Yea, that's definitely going to get you at least a tazer.

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Unread postAuthor: boilingleadbath » Fri Mar 28, 2008 6:00 pm

I fired up EVBEC and figured out the performance, performance/cost, and performance/weight of launchers with a fixed overall length, but variable chamber length and chamber diameter.

What I found is that (in my rather simplistic modeling of combustion) vastly oversized chambers are cost and mass effective.

Cost effective because whatever the builder does, they still have to buy 10' of large pipe, fittings, and 10' of small pipe... and bigger chambers get more performance from a fixed overall length.

By vastly oversized, think a 4" chamber at least 2' long on a 50"x2" barrel. Smaller chamber diameters are even more exagarated.

Mass effective too. It's not as clear why, perhaps my math calculations are off, but... again, really big chambers are a good thing.

In both mass and cost feilds, smaller diameter (4" vs 3"... vs 2", even) chambers are more effective. This of course ignores the reality of fuel mixing in such a long, narrow chamber.

**********************

Essentially, I determined that optimizing the economy spudgun is kindof silly... I conclude that, if the point is to get someone excited about spudding, the gun should be:

1) Really cheap.
2) Leave leftover material that can be used in later guns

I propose the following:
* 2" chamber, 6" long - easy mixing, venting, easy to acquire pressure rated pipe and fittings in this diameter, leaves 9' 6" of potential barrel for other guns
* 1.5" barrel, 12" long - leaves an ultraportable 18" over-all-length, good barrel material, cheap and available.

Yeah, muzzle velocity stinks: perhaps 140 fps with a 50 gram potato (32 foot-pounds energy), but it's still enough energy to be interesting. Range will be a good deal farther than just about anyone can throw something.

Furthermore, it's cheap and easy to assemble:
Cost is perhaps 14$ of PVC, most of which isn't used (plus 4$ meter?)
2" fittings are easy to glue

**********

A slightly larger (3" chamber, 2" barrel) model could be built... but 3" pressure fittings are moderately hard to find locally, harder to glue, and the performance still ain't that great.

I think that if one is going to spend the money on a 3 or 4" chamber, one should include a fan... otherwise you can't make it big enough to justify ordering the expensive 4" fittings.
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Unread postAuthor: BigGrib » Sat Mar 29, 2008 5:50 am

Biggrib's sarcastic comments were funny and over the top but right on. I would much rather see you working on perfecting your carbureted gasoline fueling system/cannon. Your fertile mind is going to waste on this penny-annie endeavor.


Dude Starman, I didn't even read that post of yours when I apologized to rcman. I just read it and laughed my ass off.
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Yea, that's definitely going to get you at least a tazer.

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Unread postAuthor: starman » Sat Mar 29, 2008 8:46 am

BigGrib wrote:
Biggrib's sarcastic comments were funny and over the top but right on. I would much rather see you working on perfecting your carbureted gasoline fueling system/cannon. Your fertile mind is going to waste on this penny-annie endeavor.


Dude Starman, I didn't even read that post of yours when I apologized to rcman. I just read it and laughed my ass off.


Your stuff was funny too. I just hope rcman moves on to something more worthy of his ingenuity.
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