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Questions about "spudguns"

A place to ask general spud cannon related questions.
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Questions about "spudguns"

Unread postAuthor: Maethor » Fri Nov 10, 2006 2:41 am

I am currently planning on building a pneumatic projectile launching device. However, first, I have a few questions for some of the more experienced people. First, on the idea of interchangeable barrels, does having screw on barrels effect the power of ability of the gun. I plan on using a 3 or 4 inch chamber with being able to change the barrel size from about half an inch in diameter to about 3 inches.

The reason behind this is that I want to be able to fire smaller projectiles as tests but ultimately I want to design larger gliding projectiles similar to missiles as well as a separate idea I have in my head to design. My other idea is basically a glider that will launch from the barrel and eventually release wings so that it can glide. Eventually I want to have the ability to have controls and a camera attached so that I can control the glider on its way down, maybe a fan so it can stay airborne longer. I might have the initial projectile be a projectile that serves as a capsule releasing the actual glider. That whole rant was largely irreverent to the design though.

2. What is the safest material to make the gun as while it will largely be designed for power and altitude I don't want it blowing up in my face, although largely I do plan on being a good distance away from it.

I would guess that copper piping is the safest but I am guessing that copper piping at the 3inch and 4 inch diameter size is expensive and I am a college student who lives on ramen to save money so cheap is good.

3. What kind of valve would you recommend I was planning on going with a 1inch sprinkler valve because I can get one for under 20$ and it has much better performance than a ball valve but would a 1inch valve be quick enough to unleash that much pressure.

4. Am i possible overkilling on the chamber size and barrel size. I am an aerospace engineering student so I know about how projectiles fly and everything but as for the cannon itself is over my head.
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Last edited by Maethor on Fri Nov 10, 2006 5:00 am, edited 1 time in total.

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Unread postAuthor: Tyro » Fri Nov 10, 2006 2:53 am

1. I'm Not Cool enough to know that one....

2. I would make it out of Pressure rated PVC You could use Copper, I'm not sure about the Price Dif though.
Do Not Pick Any Stuff Of the Shelf Go ask for the Stuff!

3. You Could Have a 1" sprinkler valve, But a Home Made Piston Valve Would be better. Yes A Sprinkler valve is Better then a ball valve but If you use a sprinkler valve. Please Mod it http://www.spudfiles.com/forums/viewtop ... 5&start=0&

4. No Have W/E Size you want But I would Make It Bigger Or as big as Your Largest barrel.
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Unread postAuthor: Maethor » Fri Nov 10, 2006 4:09 am

How hard is a piston valve to make I am pretty short on tools as I live in a studio near campus so all my tools were left at home. Mainly I have my pc repair kit with my soldering/electronics tools on me which most of is designed for finesse work not large scale. I might be able to get access to some one of the shops at the college and they have every tinkerers wet dream in tools you could want in the engineering shop and I mean name a machine and its there.
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Unread postAuthor: CS » Fri Nov 10, 2006 4:12 am

1) Does the use of a Male/Female threaded connection effect a given launchers performance?

These are the possible problems that Id think could result from the given instance.
-Possible obstructions within the connection could disrupt and create turbulence.
[Wont discuss since the effects would probably be rather minimal. Not to mention beyond that I wouldn’t know what the hell im talking about.]
-Dead space
-Air loss via threaded connection joint

Id suspect the difference to be minimal. The largest factor Id expect to be the dead space created by the span of the two fittings. Not to worry this will no where near effect your launcher in any noticeable terms of 'power'.

'Dead Space' - Volume between that of the valve and the projectile.

Good luck on the whole plane/ glider bit, but there is better ways to spend your resources to accomplish the same thing.

2) What material will suit my intentions safely?

PVC will suit your intentions. Unless your projectiles create significant weight/ friction.

3) What valve will suit my intentions?

This obviously depends on the size specifications of your launcher. If your going to be spending all this money on Buzz Lightyear pop-out winged projectiles to take photos, Id suggest a piston valve of some sort. Purchased or constructed on your own.

4) Are my specifications overkill?

Not that I can specifically determine that because the only notation you gave to any dimensions was a 3" or 4" chamber diameter rambling. Well thanks to a Aerospace Engineer by the name of Dave Hall, you have a program that you can gracefully conduct this issue if your specifications are 'overkill'. It is called 'Gas Gun Design Tool'. This can be found via a Google search, or visiting the 'Spud Wiki' located at the top of this page.
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Last edited by CS on Fri Nov 10, 2006 4:15 am, edited 1 time in total.
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Unread postAuthor: MrCrowley » Fri Nov 10, 2006 4:13 am

first don't call it a "weapon"
1.interchangeable barrels shouldn't make a big difference just make up for it if your worried about it in chamber size.
2.Pressure PVC pipe,don't worry about it blowing up in your face if you use the right stuff,prefably(sp?) sch80 pressure pipe.
3.sprinkler valve would be fine but use a piston valve for performance and it would cost you roughly the same.
4.in pneumatics you get to a stage before you "over-kill" and that stage is when you need a 'deuce and a half' to transport the gun. :lol: just make it to your standards though at some point upgrading the chamber length/diameter will make little difference in distance/speed.

goodluck on making the gliders though,a fan,camera and controls will make it very heavy how big will it be?

didn't see pimp's post,kind of renders mine useless.. :roll:
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Unread postAuthor: Tyro » Fri Nov 10, 2006 4:33 am

Piston valve should be quite easy to make, you just need a lot of pieces!
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Unread postAuthor: Maethor » Fri Nov 10, 2006 4:43 am

The design in my head is a 3 inch, at wide end, oval with fold out wings so the actual glider wont be that big and I could probably get all the circuitry in a design less than 2inches wide. But thats my project for next semester this semester I want to stick with simpler designs. Sorry about calling it a weapon as technically thats what I want to work on for a living is military jets and UAV's and watch the military channel a lot, so I tend to think in those terms a lot and technically a pneumatic cannon/gun is considered a weapon even if it is only used for recreational and educational purposes.

EDIT
Actually you would be surprised how light you can get a projectile and still include a camera, servos for control and a fan. Honestly it wouldnt add that much weight to the entire plane. The hardest part is the fold out wings because i cant put the servos/wingflaps on them so I would have to actually make entire wings move and I don't know how well that will work.
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Last edited by Maethor on Fri Nov 10, 2006 4:54 am, edited 1 time in total.

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Unread postAuthor: joannaardway » Fri Nov 10, 2006 4:54 am

first don't call it a "weapon"


As you've said that, I'll say that it annoys me people going around saying "this is my gun", or "nice gun there" - you know the stuff.

To me, both "gun" and "weapon" are equally bad - they both bring up negative images. I try not to use either.
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Unread postAuthor: Maethor » Fri Nov 10, 2006 4:56 am

I understand its just the terminology I am used to using. I changed the wording so as not to make anyone angry.

Edit to clarify my plans for Pimpmann22. The current plans I have are 3 or 4 inch diameter chamber at 2 or 3 feet long depending on the prices with about a 5 or 6 foot barrel. I eventually plan on making a stand for it. Part of the reason for the removable barrel is actually to make transportation easier.
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Unread postAuthor: POS » Fri Nov 10, 2006 6:08 pm

joannaardway wrote:To me, both "gun" and "weapon" are equally bad - they both bring up negative images. I try not to use either.


How can a "thing" be bad. If you look at it, it just lies there, doing nothing but lying down. the "thing" could be a rock, an orange or a gun. It's the person who picks it up that does bad things with them. You can do bad things with a barbie doll to.

Call it as you want, spudguns are guns, weapons, rifles, whatever. Pneumatics can be made so they have deadly force. Figure out what a golfball or marble would do to your head, when it can fly trough a 1 inch wood board. According to Belgian law, they are weapons. If you use combustion, these are considdered firearms, also hybrids.
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Unread postAuthor: POS » Fri Nov 10, 2006 6:12 pm

Maethor wrote:I understand its just the terminology I am used to using. I changed the wording so as not to make anyone angry.

Edit to clarify my plans for Pimpmann22. The current plans I have are 3 or 4 inch diameter chamber at 2 or 3 feet long depending on the prices with about a 5 or 6 foot barrel. I eventually plan on making a stand for it. Part of the reason for the removable barrel is actually to make transportation easier.


May I suggest you put this plans in a drawer for a while, and first make (test) a small version of a pneumatic.

My first pneumatic costed me over a 100 euro. It was realy crappy. But... I learned a lot of building it, especialy how it is not done. My second pneumatic is a beast. If you are low on budget, try to make a small piston valved pneumatic. See what it does, and learn of your mistakes. It would be a shame to spend all your money on parts of a big gun, when it cant even blow a hole in a sheet of newspaper at ten feet. Start small and learn. Take that from someone who made mistakes in the beginning. And please, do research on this site and others.
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Unread postAuthor: Maethor » Fri Nov 10, 2006 7:31 pm

That sounds like sound advice so I am going to start small and build something more reasonable first and then work on a bigger one next semester, since it will be easier to compute the chamber size and barrel length needed once I know how much my glider will weigh.
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