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Pumpkin Cannon Complete Success

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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Pumpkin Cannon Complete Success

Unread postAuthor: SDdan » Wed Oct 28, 2009 4:27 pm

3 test shots today from a 6" pumpkin gun.

Shot 1 25 psi 110 Yd
Shot 2 30 Psi 130 yd
Shot 3 40 Psi 225 yards! I was not expecting that Very happy

The wadding used was a foam dodge ball 6.25" Works very very well.

Video to follow.

Thanks for all the help!

Dan
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Unread postAuthor: psycix » Wed Oct 28, 2009 5:40 pm

40 psi is kinda low... how high can you go?
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Unread postAuthor: SDdan » Wed Oct 28, 2009 5:50 pm

I do not know. Gun is 6" foam core sch 40 pipe with all sch 40 fittings. In line 10 ft long. This is my first one so I am unsure on how high I can safely go. Any ideas.

I am using a plastic ball valve rated to 150 psi.


Thanks Dan
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Unread postAuthor: Moonbogg » Wed Oct 28, 2009 8:00 pm

How about a picture or something? Sounds cool!
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Unread postAuthor: Technician1002 » Wed Oct 28, 2009 8:16 pm

Checking his other posts reveals the launcher. I would critique it for the tiny plumbing between the chamber and barrel and the use of foam core. I would bolt it to a 2X4 for rigidity and only run low pressure. That would be real awesome with a 3 inch valve and pressure rated pipe. The length of the skinny part can also be shortened for better flow.

An uneven launched projectile causing barrel whip will pop this into two.

http://www.spudfiles.com/forums/viewtopic,p,265381.html#265381
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Unread postAuthor: jackssmirkingrevenge » Wed Oct 28, 2009 10:16 pm

Horribly inefficient design there but it makes up for it with sheer size so good work :) Is the pipe rated? "foam core" and "psi" don't look like the should be together...
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Unread postAuthor: suburban spudgunner » Thu Oct 29, 2009 7:10 am

Much as I hate to ask the typical question...could we have a video?
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Unread postAuthor: psycix » Thu Oct 29, 2009 10:24 am

That gun SCREAMS for a larger diameter valve, and pressure rated pipe.
Looks like a monster though!
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Unread postAuthor: jackssmirkingrevenge » Thu Oct 29, 2009 11:14 am

psycix wrote:That gun SCREAMS for a larger diameter valve


Or simply being made as a combustion.
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Unread postAuthor: psycix » Thu Oct 29, 2009 1:44 pm

If he ever wants to show off this cannon on a pumpkin' chunkin' event, it'll probably need to be pneumatic.
Combustion makes people whine about explosions.
Of course, we know better, but "normal people" don't.
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Unread postAuthor: jeepkahn » Thu Oct 29, 2009 2:17 pm

Chunkin won't allow pvc parts, rated or not...
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Unread postAuthor: SDdan » Fri Oct 30, 2009 9:04 am

The pipe is rated and sch 40. As far as valves this is what I could find for cheap and quickly. What type of valve would work better. 2" was the largest I could find in town as the contest is tomorrow.

Is the inefficiency from the valve type and size. Length?

I am very happy with how it works. I pull the valve with a pully so it snaps open pretty quickly. We have video and will post some soon.

for less that $100 and 1 hour it is very fun.


Thanks Dan
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Unread postAuthor: jackssmirkingrevenge » Fri Oct 30, 2009 9:37 am

SDdan wrote:Is the inefficiency from the valve type and size.


A good valve has high flow and low opening time.

In this case, at full opening a 2" valve has just 11% of the flow a 6" valve would have. Even upgrading to a 3" valve will give you more than double what you have now.

While I'm sure your valve opens "pretty quickly", there's no way it can match a pneumatically actuated valve. On this scale it would get expensive though, a cheaper idea would have been to have a large threaded coupling between the barrel and the chamber, with a frangible disk (aluminium foil or similar) sandwiched in between. Then you could have simply pressurised the chamber until the disk burst, giving you instantaneous opening and full flow.

Another thing, the equally sized barrel and chamber are inefficient in this case, you probably would have had better performance using 75% of the total pipe for the barrel and the remaining 25% for the chamber. I'll punch some numbers in GGDT when I get home and give you a better idea.

For the next competition perhaps ;)
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Unread postAuthor: Technician1002 » Fri Oct 30, 2009 10:24 am

jeepkahn wrote:Chunkin won't allow pvc parts, rated or not...


That's news to me.. Is this a new rule? Many of the chucking events I've seen use 10in PVC barrels. One of the videos online show a barrel whip snapping one.

Edit; found the 2009 rules. This year no PVC barrels..
http://www.punkinchunkin.com/punkinchunkinrulesv10.pdf

Sorry I can't seem to find the vid at the moment.

@JSR in regards to the "oversize" chamber to barrel ratio. At lower pressure the best ratio shifts toward a larger chamber. Plug in the numbers in GGDT at several pressures. With the restrictive valve and it's loss, a 1:1 is about right for 25-35 PSI.
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Unread postAuthor: SDdan » Fri Oct 30, 2009 10:57 am

The Barrel is 4 Ft and the chamber is 6 Ft. Not quite 2 to 1 but the best I could do. The tinfoil idea in neat but I will be in a church parking lot and need all the control I can have. Can you point me to a 3" valve that might work?

Thanks for the help Dan
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