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Need Help/Advice On my First Cannon Build for School Please!

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Need Help/Advice On my First Cannon Build for School Please!

Unread postAuthor: bruno6491 » Sat Oct 13, 2007 9:48 pm

Hello, I am 16 and building a potato cannon that is air powered so i can use it in a competition to launch pumpkins at school. I want it to go at least 250+ yards.

My idea after all my research has been this.
A simple straight design, just one long piece. (Any advantage with a straight vs a U turn?

Using a 3" diameter barrel that is about 6 feet long, sch 40 pipe, could i use the cell-core stuff or should i just use the sch 40 for the barrel?

Using a 6" diameter chamber that is about 5.5 feet long, sch 40 pipe.

That gives me a chamber to barrel ratio of 3.67:1

Is that too high of a ratio, is it just a waist of material? Any experience and ideas much appreciated, any estimate to how far and what psi?

For my valve, i was deciding weather or not to go with a 1" sprinkler valve or a 2" ball valve with a red handle type of deal? Any opinions on which is best?

How would i go from a 6" chamber, to either the 2" ball valve or the 1" sprinkler valve, back to a 3" barrel, and how could i make the barrels interchangeable?

For inflating the chamber, i would use an old bike tire with a schrader valve and put it on the 6" end cap and fill it up that way, any ideas on this?

I think that is everything, any ideas/help is very helpful and hopefully i will win this year!!

Thank you for the help and sorry for a long post, just don't want to spend the money and have it not work

Bruno
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Unread postAuthor: LikimysCrotchus5 » Sat Oct 13, 2007 10:01 pm

Im pretty sure that cell core is bad look for pressure rated which is usually pvc and definately look for pressure rated fittings, make sure of that. A ball valve i guess would be okay, it would have a high flow rate but a slow opening rate. But look for some kind of configurations to make the valve open faster which will help alot. The faster and bigger air flow you have on your valve, the better. Im not so sure about CB ratio, that is usually more for combustions. Umm you can fill it with a schrader valave thats fine. Make barrels intercahngable by using threads. And i gues thats pretty much it :)
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Unread postAuthor: cwazy1 » Sat Oct 13, 2007 10:03 pm

Hello and Welcome

a u-turn is just more compact, it really doesnt matter.

i am not too sure about C:b ratios but i know that when you're making a pneumatic, only use pressure rated pvc, not abc or pvc drainage pipe.

as for the valve, definitly go with a sprinkler valve. a modded one ould be best, a ball valve would be sh1t slow and not as good.

a 6" chamber is huge, what i would do is change it to 2-4" chamber s or seomthing. plus a 6" pvc sch40 is only rated safe up to 150psi or so. but to tell you how to reduce, you get a coupling for what ever size pipe you have, then take many many many reducing bushings and take it down to what ever size you want. then do vice versa for going back up to 3" barrel.

yes a scherader valve is what you would use. if you just cut the valve off an innertube, then you will need to drill a hole in the end cap and epoxy it in, if you go to ace or HD or any hardware store, you might be able to get a schrader valve with a npt male threading on it. if you find the threaded one (MUCH BETTER/safer) you can either tap a hole into ur pvc using a tap and bit, orr, you can buy a t fitting with a female npt threading in the top hole, that way, you can take bushings and reduce to what ever size your schrader valve is, (same for your psi gauge)

good luck!
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Unread postAuthor: thespeedycicada » Sat Oct 13, 2007 10:08 pm

Wow you have alot of things that you need help with.No do not use cell core unless you want to kill yourself a ball vale of that size (3 inches right?) will give absolutely dreadful performance a 1 inch sprinkler valve will be far to restrictive of flow.So you're options are either a big piston,a combustion or a burst disc.As for the psi 85 psi should get you good range at least 350 yards and thats a conservative guess.As for the shape i would go with a u bend so you can get more chamber volume with less length.Im very glad you asked here first or you would be wasting ALOT of money.PS do they even make 6 inch to 3 inch reducers do they even make the pressure rated 6 inch pipe he needs i don't think i have seen it.
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Unread postAuthor: DYI » Sat Oct 13, 2007 10:13 pm

For increased power and decreased cost:
Cut the chamber volume in half
Double the barrel length
Use a 2" ball valve, and spring load it. Much higher flow than the sprinkler

With a 3" barrel, you should be shooting rutabagas, not potatos, if you really want to use vegetables.

Fired at the correct angle, the design mentioned above will fire a 1 pound rutabaga over 300 yards at 100 psi, with a muzzle velocity of 300 fps. Good luck.
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Unread postAuthor: cwazy1 » Sat Oct 13, 2007 10:13 pm

i dont think they make 6-3" reducers, maybe in abs or drainage pvc, wouldnt a coupling and multiple bushings work??
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Unread postAuthor: thespeedycicada » Sat Oct 13, 2007 10:15 pm

he said he was launching pumpkins i just realized i dont know if pumpkins will fit in a three inch barrel will they? EDIT:multiple bushings and junk will look bad and be cumbersome/haphazard.
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Unread postAuthor: bruno6491 » Sun Oct 14, 2007 8:45 am

they are very little pumpkins with almost exact size of 3" diameter

How would i make a ball valve into a spring operated one?? Would using a chamber of 4" in diameter and about the same length of my barrel be a good size, how would i make a U turn and where to place a ball vlave, before or after the U turn

Going to Home Depot now to check what they have

Any opinions are very much appreciated, i am also glad i asked ere as well

Thanks again, Bruno

Are these air powered cannons considered weapons??
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Unread postAuthor: LikimysCrotchus5 » Sun Oct 14, 2007 10:10 am

Umm if you look around on this website you are sure to find a way to make a ball valve spring loaded. I cant help you on that because i have never made one. I would put the ball valve right before the barrel of the cannon. I would want to have the barrel somewhat bigger than the chamber. You can use the same size for the barrel and the chamber in diameter but for the size make the barrel bigger. You can always mount this onto a tripod if it gets too heavy. Depending on where you live, this can be considered illegal because different cities and counties have different laws about this stuff. Ask a police officer and they can tell you :D And also to say, i have a ball valve pneumatic and i used to have a modded sprinkler valve on it and the ball valve and the spinkler valve are both 3/4. I found that my ball valve gave me a greater velocity and distance because of the flow rate. But it has a slow opening rate which is a disadvantage. Thats why we recommended the ball valve to be spring acutated because it will give you greater opening speed and therefore greater power. Modded sprinkler valves are good it just depends on the size of it.

FYI: when making other cannons i recommend you go from bigger to smaller meaning that the chamber is big, then the valve the same size if you can, and then a smaller barrel and you will have more force into the barrel because there is more air needed to be pushed into it and you will then have a greater force. But this also depends on how good the valve is. There are many factors that can make a cannon good or bad :D

For more information....Search the Website :D
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Unread postAuthor: bruno6491 » Sun Oct 14, 2007 3:02 pm

i made the cannon today with my dad

I went with a 4" chamber, 6 feet long of sch40 pvc, then a 4" 90 degree elbow, another short 4" piece, another 4" 90 degree elbow to a 4" to 3" reducer, to a 3" to 2" into a 2" ball valve. Then just a straight barrel with 2" about 7 feet long.

I loaded it up with an apple about 3 hours after making it, used about 20 psi for a test shot, had no leaks and it went about 70 yards. I am happy with the ball valve but searched and can't find how to make a spring ball valve, any links??

Thanks for the recommendations, will take pics and post to show my first cannon, overall, very pleased.

Bruno
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Unread postAuthor: DYI » Sun Oct 14, 2007 3:18 pm

Make the barrel 12 or 16 feet long and you will notice a significant increase in power.

For spring loading the ball valve, attach a cable to the handle of the valve, and attach the other end to tension spring. Hold the spring tensioned with some sort of pin. Then release the pin, and the spring will yank the wire attached to the valve. With a big enough spring, this can achieve some crazy fast actuation times, probably under 25ms. Can't compete with sprinkler valve opening times, but the high flow makes up for it.

Also, I thought you were using a 3" barrel. You can get higher performance with a 3" barrel of the same length as the existing 2" one.
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Unread postAuthor: sandman » Sun Oct 14, 2007 3:24 pm

firing 3 hrs after making it is very hazardous, u should wait at least 1 day
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Unread postAuthor: Gepard » Sun Oct 14, 2007 3:25 pm

4" pipe at HD? Isn't that cell core?......
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Unread postAuthor: veginator » Sun Oct 14, 2007 3:28 pm

sandman wrote:firing 3 hrs after making it is very hazardous, u should wait at least 1 day

I did that once and it blew apart in my hands. It scared the sh1t out of me. :lol: Btw the 4 inch pvc at HD is pressure rated if you buy the smaller sections.
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Unread postAuthor: bruno6491 » Sun Oct 14, 2007 3:41 pm

My HD had 4" pressure rated in 10' lengths

I decided that a 2" barrel will be much smaller and allow for a smaller chamber since HD or Lowes did not sell 6" pvc

I was happy with just a test run and wanted to make sure it works, i will wait till tomorrow to shoot some more.

I thought that if i made the 2" barrel that long i would loose velocity and went with the 7' which gave me a perfect 4:1 ratio

I will try to use a spring, but i you can give more details on it i would be much appreciated

Thanks once again

Bruno
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