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The Spudinator

Built a pneumatic cannon? Then post it here! This section is for completed, finished cannons that you have built. Please include pictures and information.
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Unread postAuthor: Ragnarok » Fri Nov 14, 2008 3:31 pm

jitup wrote:Also how do I get my youtube video to work on this site!!!!!!

Use the following forum code like this:
Code: Select all
[youtube]Insert full web-address of Youtube video here[/youtube]


... and that should work.
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Does that thing kinda look like a big cat to you?
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Unread postAuthor: jitup » Fri Nov 14, 2008 3:42 pm

Thank you, I tried that but for some reason it just won't work for me.
I posted a link to the vid. check it out and let me know what you think!!
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Unread postAuthor: Radiation » Fri Nov 14, 2008 4:21 pm

Ahhh particle board, the spudgunners arch nemisis. You blew it away quite handly!

You know perhaps you could use a modded sprinkler valve so you have a quicker release of air rather than the ball valve. Of course the priority should be the PVC chamber in place of the pop bottle. Any way it's a cool little gun with a lot of potential!
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Unread postAuthor: jackssmirkingrevenge » Fri Nov 14, 2008 4:26 pm

Ragnarok wrote:I've always see bottles fail well below 200 psi, even the ones for pressurized drinks.At much over 100 psi, a solid knock can cause them to break apart.


The bottles I tested were filled to the revelant level with water, then the headspace was pressurised with nitrogen. Logically this means less pressure is applied to the main body per unit area than if it was empty, perhaps therefore my pressure values are irrelevant in this case.
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Unread postAuthor: Ragnarok » Fri Nov 14, 2008 4:42 pm

Nice enough... although death metal for walking through the woods seems a little unnecessary. :P
To be honest, it's worth NOT going for that kind of music in spudgun videos, it's overdone, and seems too try-hard.

With a ball valve, no launcher is going to reach it's true potential (as valves go, a ball valve is very poor), so I can't honestly claim to be particularly amazed by it's power... but I'm sure with some practise and experience you can build launchers with better valves and more power.

Not bad going though - now use proper materials!!!

@JSR: That doesn't sound right, given water's incompressible nature, the pressure should be constant throughout the system - although I don't know your exact techniques. Were you supplying a constant pressure to it as it expanded, or just one fill, then leave it to expand?

But most likely we're using different styles of bottles. At the very least though, for a sensible margin, I personally, wouldn't want more than 50-60 psi at most in one myself, and wouldn't advise anyone else to.
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Unread postAuthor: Radiation » Fri Nov 14, 2008 4:43 pm

Also could the fact that you're talking about laboratory condition with Virgin Bottles that haven't been shipped in a freighter, put on the shelf, bought by the customer, cooled, heated, cooled, heated, emptied, thrown in the recycle bin after being drop kicked and then pulled back out... A lot can happen that laboratory conditions do not account for.

Aside from that lets face it, these manufacturers want to spend as little as possible on materials and will use anything that doesn't cause them to lose money on shipping and compromise the quality of their product. anything more is just not important to them, especially the conisderation that people might using them as potentially dangerous weapons. Just not part of the design consideration. :)
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Unread postAuthor: jackssmirkingrevenge » Fri Nov 14, 2008 4:51 pm

Ragnarok wrote:That doesn't sound right, given water's incompressible nature, the pressure should be constant throughout the system - although I don't know your exact techniques. Were you supplying a constant pressure to it as it expanded, or just one fill, then leave it to expand?


The bottles are given a constant pressure ramp until failure or reaching a pressure limit - yes, there were cases when the bottle did not fail.

Aside from that lets face it, these manufacturers want to spend as little as possible on materials and will use anything that doesn't cause them to lose money on shipping and compromise the quality of their product.


Indeed, just before I left the industry I was involved with a study to see if bottles could be made with lighter preforms (resulting in the bottle having thinner walls) and still comply with specifications. The only "real world"-ish structural tests I used to do were a 2 metre drop test - just dropping a filled bottle down a chute - and a vertical load test.
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Unread postAuthor: starman » Fri Nov 14, 2008 5:01 pm

jitup wrote:Can some one suggest a good length of pipe for the chamber of this gun ?

Also how do I get my youtube video to work on this site!!!!!!


8" of 3" PVC + end cap or 12" of 2" PVC + end cap would be more than enough for this gun. Your back piping before the ball valve should also be considered a part of your chamber.
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Unread postAuthor: mark.f » Fri Nov 14, 2008 6:52 pm

[youtube]http://www.youtube.com/watch?v=JXceET3-awc[/youtube]

Video related. :P

But yeah, it's a pretty good gun. The only thing I would change would be to either use a different material for the chamber or use lower pressures (<90 PSIG), and to replace the ball valve with something a little faster. Oh, and to also make the barrel longer.
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Unread postAuthor: Radiation » Sat Nov 15, 2008 1:13 pm

markfh11q wrote:But yeah, it's a pretty good gun. The only thing I would change would be to either use a different material for the chamber or use lower pressures (<90 PSIG), and to replace the ball valve with something a little faster. Oh, and to also make the barrel longer.


Sooo that leaves what, the pressure gauge? :P
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Unread postAuthor: Biopyro » Sat Nov 15, 2008 4:48 pm

I have to agree with JSR here, I have tested these bottles, and they really are a lot more robust than what you give them credit for. An unrated drinks bottle, easily took up to 100psi, and then ruptured after I gave it a sharp whack. While it was extremely loud, the explosion would have done little more than slight cuts and some bruising. I have used rated bottles past 100psi, and they do not rupture, even after sharp shocks. Held onto 22mm pipe by friction alone, when give a sharp shock, they fire like a loud, empty water rocket.

I spoke to an engineer at http://somex.ie/ and they said
a typical pressure requiremnet for a PET bottle would be 135 psi, hold for 13 seconds, the pressure is then increased to 200psi, the volum eof the bottle will increase by 30-50% of its original volume during thid test.

Typically for users of PET bottles the same test will apply regardless of bottle volume,however the designers may have different standards - I am not aware.


Perhaps you were a bit quick to give this guy a shaming, after all, he has clearly done his research, it's not his fault that the person on the other end go it wrong. A nice clean cannon give the knowledge and materials he had.

people have been killed

Really? Injured, yes but I've never heard of anyone who has been killed in a spudgun related accident.
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Unread postAuthor: Lentamentalisk » Sat Nov 15, 2008 5:26 pm

well I am not sure that anyone has been killed in a true spudgun accident, but there have been people who put solid propellants in pipes (read: pipe bombs,) and then call them spudguns, who blow themselves to pieces, but that doesn't count.
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Unread postAuthor: starman » Sat Nov 15, 2008 5:28 pm

Biopyro wrote:I have to agree with JSR here, I have tested these bottles, and they really are a lot more robust than what you give them credit for. An unrated drinks bottle, easily took up to 100psi, and then ruptured after I gave it a sharp whack. While it was extremely loud, the explosion would have done little more than slight cuts and some bruising. I have used rated bottles past 100psi, and they do not rupture, even after sharp shocks. Held onto 22mm pipe by friction alone, when give a sharp shock, they fire like a loud, empty water rocket.


Even so, compared to PVC, soda bottles are NOT robust and a lame choice for a chamber structure. PVC is just too cheap not to just use.
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Unread postAuthor: Biopyro » Sat Nov 15, 2008 6:37 pm

Can't say I disagree with you there starman. Something I forgot to add is that while it probably won't explode, it seems kinda pointlees to keep using it. PVC is cheaper and safer. Perhaps it PET bottles were 3mm thick then they'd be perfect, but they aren't.
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Unread postAuthor: jitup » Sat Nov 15, 2008 7:07 pm

If I change out the bottle for 3inch pipe that is 8 inches long, what do you guys think the maximum safe pressure is?

Also I am currently designing a spring loaded trigger mechanism to activate the ball joint, I am sure some one has seen something like this so please give me your thoughts about the Idea.
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