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So I built a couple of basic combustion cannons over the summer with my friend, shot a few potatoes 200 yards, and had some good times watching potatoes turn to potato dust. Of course, a basic cannon is a basic cannon and I think it's time to move on to better things (since most of the time you end up spraying in the wrong amount of fuel and get a bad shot anyway).
I'm looking to do something a little more advanced (maybe what someone would call in intermediate-level cannon if they had difficulty ratings). I'm starting to lean towards a pneumatic because it simply seems a little safer than messing with a cannister of pressurized explosive gas (correct me if i'm wrong). However, there seems to be many different pneumatic configurations and few tutorials. I'm basically looking for a general design suggestion that will outperform a basic combustion as far as distance and constancy. I'll probably end up using a shock pump for fueling for portability reasons. Also, how much money does a pneu generally cost?
i would say go with some sort of coaxial device, do a search on spudfiles and you'll get a ton of info. they are pretty easy to build and are powerful. my coaxial cannon can outperform my combustion at 60psi, and the combustion cannon has metered propane injection, a chamber fan, etc. so thats my suggestion. if you want a small diameter barrel then go with something that uses a sprinkler valve, but they constrict the flow, i don't like using them on barrels larger than one inch diameter. so i would say go for a coaxial design, do some research, there's a ton of stuff on spudfiles about them, ive built a number of coaxial devices of all different shapes and sizes and i still find out new stuff just by browsing around.
the cost would be anywhere from probably $25 to $75 plus, depending on what systems you use. like for the pilot valve, do you use a blow gun, or a ball valve which is more expensive but MUCH higher flow, a blow gun doesn't work well on full sized coaxials, or do you go for a sprinkler valve or qev for the pilot? (each of these is progressively more expensive). just be sure all parts are pressure rated, and familiarize yourself fully with the concept of the design before you begin. have fun
Well your pneumatics are normally classed by valve types, there are 3 types:
1. Ball valve - Just your simple ball valve
2. Sprinkler Valve - Just a basic sprinkler valve, normally modded
3. Piston valve - Visual explanation of the,
3.(1) Coaxial - See ^^
3.(2) Barrel Sealer - See ^^
3.(3) Chamber Sealer - See ^^
The configuration can be broken into 3 types
1. Over under
3. Coaxial (only specific to coaxial piston valves)
If i missed anything or there are errors. just say
I hope this helped
Failure to plan is planning to fail.
The 7 P's - Proper Prior Preparation Prevents Piss Poor Performance
Heres a really simple one but has some decent power.
3/4 Ball valve
2L coke bottle
A pipe to use as a barrel
And a Bike tire valve.
Thread and epoxy them all together and you got yourself a basic inline pneumatic that out-performs a combustion.
Raise your horns if you love metal.
I would say the pneumatics are a little more dangerous than a basic combustion. Mostly because combustions peak out at around 60 PSIG but pneumaitcs are generally run at whatever the gunner's compressor peaks out at, typicall ~120 PSIG. Tha's a heck of a lot more stress on the PVC, joints etc.
Before you move on to a new gun have you installed a chamber fan in your first gun? A chamber fan is pretty easy to retrofit on a gun and it will usually boost the perfromance by a fiar amount.
Or, tried fuel metering? You can get a 60cc syringe for a buck, a cheapo butane lighter for a buck and have a pretty precise fueling system. Consitent fueling will boost the performance of the gun, or at least make it perform more consitently.
Put the two together and you'll be getting about the maximum performance possible for the chamber and barrel size.
Where do you get syringes? Whenever I ask where they are, people think I'm a heroin addict.
I've heard combustions are more dangerous, just because they have a really sharp pressure spike, but I could be wrong. I'd recommend doing a simple over under sprinkler valve pneumatic first, just since they're easy. Make sure not to use DWV though, since that does make pneumatics much more dangerous.
Also, I've heard shock pumps are really slow. It takes a bijillion pumps to get anywhere with a regular sized chamber, so unless you're doing a pistol or something small like that with a small chamber, I'd use a regular bike pump (unless you can afford a compressor or CO2 system)
EDIT: If you're worried about failing cement joints, I'd recomend using galvanised steel, which needs no cement, is a lot stronger, and is easier to service and such. However, it's a bit harder on the wallet if you know what I mean. Also, it comes in 1/4" sizes, unlike PVC which only goes down to 1/2."
You can usually get plastic syringes up to about 60cc at farm supply stores, or any store that carries medicines, feed etc. for horses, cows, pigs. In the midwest, try Tractor Supply Hardware (TSH) stores. A 60cc syringe is about $1. Also get a couple blunt needles, IIRC they are 2 for $1.
The pressure spike in a combustion gun really isn't all that sharp. It takes ~50mSec for a typical combustion spud gun to fire. The fastest part of the pressure rises occurs over 10 or 20 milliseconds which really is not all that fast. Besides, the movement of the spud really dampens how sharp the pressure peak is and what the maximum pressure is.
In my closed chamber tests (3"ID x 14"L chamber) the pressure peaks at ~120 PSIG and the PVC doesn't appear to have problem with that pressure. Normally, a spud gun peaks out at around 60 PSIG.
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