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First Spud-Gun

A place to ask general spud cannon related questions.
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First Spud-Gun

Unread postAuthor: Debaser » Wed May 17, 2006 9:38 pm

Hello all, I am making my first pneumatic spud-gun for a physics project, and I am in dire need of some advice. I have chosen a golf ball for my projectile.
As for the layout, i was planning on having a "over-under" setup, with a 3' long barrel overtop of a 3' resevoir. For valving, I have a modded 1'' Watermaster valve, which would be located right after the resevoir, but before the 2 90 degree elbows.
My plan was to have the 3' 1.5'' barrel, followed by a 1.5'' to 1'' reducer, then have a 90 degree 1'' elbow, followed by another 90 degree 1'' elbow, then the valve. After the valve, it would go from 1'' to 4'', then the 3' resevoir. As for materials, I could not find sdr 21 for the barrel, but managed to find sdr26. (May be because I live in Canada). Any who, I don't think I will have any problem getting any of the other parts. With all this planning I have done, I still have a few questions:
1). Will the sdr 26 barrel be a tight enough seal for the golfball? Should I use another size pipe for the barrel?
2). Should I sleeve the barrel, and if so, what size pipe should I use?
3). If all works as planned, at 100 psi, what kind of distance should I be looking at?
4) Any suggestions/tips?


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Unread postAuthor: ProfessorAmadeus » Wed May 17, 2006 9:49 pm

i dont know about sdr26 but if you need you can find sdr21 in the classifides from pimpman. if you buy it from him you can buy sleeved or unsleeved or you can do it yourself with Sch80. at 100 psi that golf ball should go very very far
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Unread postAuthor: Shrimphead » Wed May 17, 2006 9:50 pm

Pm Pimppmann about sdr-21. He sells it sleeved and unsleeved.

For distance, download the ggdt and put the numbers in for your gun.

A 1" sprinkler valve is really going to choke the flow from the 4" chamber. If you have 100 bucks to blow, you can get a suphah valve from http://www.spudtech.com. They are the fastest dumping valves and Joel makes them with excellent precision. But be prepared to wait a while because he is really backed up on orders. You could also make your own piston valve to use instead of the sprinkler or suphah. Go the the spud wiki to learn about how piston and diaphragm valves work if you don't already know. Pistons dominate sprinklers, but still aren't quite as good as suphahs.
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Unread postAuthor: sgort87 » Wed May 17, 2006 9:55 pm

1.) SDR-26 should work fine but 21 is a better fit.

2.) You should sleeve your SDR with 2" SCH 80 pipe. It fits over SDR like it was made to.

3.) Too lazy to calculate for you sorry. (Should be a nice distance but would be nicer with a longer barrel, say 5'.)

4a.) Put your sprinkler valve just after the 2 90s to reduce the dead space between the valve and golf ball.

4b.) A 4" chamber may be overkill.

4c.) Point gun at 35 degrees for the best distance. (Many say 45, but that is only true in a vacuum where there is no air resistance.)

Edit: I gotta respond faster next time. There were no responses when I started...
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Unread postAuthor: Debaser » Wed May 17, 2006 10:29 pm

I am on a very short deadline for this project, so I supose I am going to have to make due.
I only have a week to have this done, so I am going to have to use the sdr 26. I took a look at it today, and it has a relativly good fit, so I figure if I throw a few thick coats of paint onto the golf balls, it will tighten it right up.
As for the valve, I already have the 1'' valve, so I will have to make due with that.
Also, I should have enough material for a 5' barrel.
Last but not least, anyone have anymore tips to make this gun fire to it's full potential?
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Unread postAuthor: dgr-c » Thu May 18, 2006 10:38 am

Debaser wrote:Last but not least, anyone have anymore tips to make this gun fire to it's full potential?



If it is just for a grade on a project, I wouldn't worry too much about "full potential." I made every design mistake in the book building my first pneumatic -- unmodded sprinkler valve, too much dead space, wrong chamber:barrel ratio, slow pressure leak somewhere I can't find, ...


...and I can still chamber a spud round, charge it at 100psi, and launch out of sight/blow holes in stuff/dent 1/8" sheet steel/create a fine mist of moist starch.

Build it, write it up well, list the potential design improvements, take it to the school's athletic field and fire it in front of your class. Don't forget to wear safety glasses, it is, after all a science class.

BTW: If the teacher is thinking at all, a golf ball round will scare the bejeezus out of him/her. For school demo purposes, use a spud round. Most civilians, even those who should know better, don't take them seriously until after you've fired the first round through a cardboard box and into a wall. With any luck at all, you're teacher's response will be, "H0ly $h!t" and he'll have to give you A.

Just my 2¢ worth.
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Unread postAuthor: Benny » Sat May 20, 2006 2:57 am

that reminds me, we were doing a science thing when i was in grade six, and the teacher overheard me talking to my friends about it, so she asked me to bring it in, so in frount of the class i explained how it worked, then she asked if i could do a demonstration, so i loaded it with a paper ball because we were doing it inside, i charged it up with my portable compressor,[looks like a drill but it is a compressor] to 50 psi, aimed at the wall and fired, as i fired she yelled F**K at the top of her voice, also our class got like 5 phone calls from other classes asking what the bang was,rofl. :lol: neally everyone in the class jumped, like 2 inches in the air they got such a shock, ahh, good times.
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