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This is what happens when your piston is too heavy!!!

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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This is what happens when your piston is too heavy!!!

Unread postAuthor: hyperspaz » Tue Apr 19, 2011 10:52 am

So here's a video of my golf ball cannon firing at 100 psi with a solid epoxy piston:


[youtube]http://www.youtube.com/watch?v=carYeOI4OQk[/youtube]
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Unread postAuthor: jackssmirkingrevenge » Tue Apr 19, 2011 10:58 am

Clucking bell!

What were you using as a bumper, and what was the piston travel?

A solid piston that big is a bad idea, there's plenty of advice inmy how-to on making lighter built-up pistons.
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Unread postAuthor: hyperspaz » Tue Apr 19, 2011 11:01 am

Bumper was a tennis ball and the piston travel was just under an inch.
Any ideas on how I can fix it? Is there any pipe that fits perfectly around a 2" coupler?
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Last edited by hyperspaz on Tue Apr 19, 2011 11:14 am, edited 1 time in total.

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Unread postAuthor: warhead052 » Tue Apr 19, 2011 11:14 am

Holy crap.... OW! Did you get hit by it?
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Unread postAuthor: Technician1002 » Tue Apr 19, 2011 12:20 pm

I had that happen once with my ABS cannon. The female breech was PVC. It shattered and the piston hit my foot. I was wearing heavy leather shoes at the time. I replaced the PVC with higher impact resistant ABS and made my bumper 4 X as long. Since then, I've used lighter pistons, shorter strokes, non brittle parts (except the original Marshmallow cannon which did finally break the cap) and longer bumpers.

Edit, Made you an avatar photo.. :D

Marshmallow Cannon with broken pipe cap. It is now replaced with Iron.
Image

Only fair to show the fix.
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Repaired cannon. Better than new.
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Unread postAuthor: SpudBlaster15 » Tue Apr 19, 2011 3:13 pm

Looks more like an issue of insufficient energy absorption by the bumper.

Given that the net force on the piston is fixed, and the valve is a captured system, the piston's impact energy will not vary significantly when the mass is changed. This may seem counterintuitive to many, but a little calculation shows it to be true.

Increase the amount of shock absorbing material in the back of the valve to an adequate level, and you should solve this problem.
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Unread postAuthor: Insomniac » Tue Apr 19, 2011 5:45 pm

Ah, I hadn't thought of that before SpudBlaster... You have a good point.
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Unread postAuthor: Gun Freak » Tue Apr 19, 2011 6:27 pm

Thank god you were remote firing it...
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Unread postAuthor: mark.f » Tue Apr 19, 2011 6:32 pm

Who was the guy saying "It broke..."? He earns my Captain Obvious award for the whole year. :roll:
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Unread postAuthor: jackssmirkingrevenge » Wed Apr 20, 2011 12:14 am

mark.f wrote:Who was the guy saying "It broke..."? He earns my Captain Obvious award for the whole year. :roll:


Perhaps he was harbouring the misapprehension that it operated on the "countershot" recoilless rifle principle, and that was meant to happen...

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Unread postAuthor: shiny455 » Sun Apr 24, 2011 6:03 am

you may have inspired me to test stuff with a string for the first time
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Unread postAuthor: jrrdw » Sun Apr 24, 2011 7:10 am

[youtube]http://www.youtube.com/watch?v=R5zpoJSFjmM[/youtube]

You earned it.
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Unread postAuthor: Technician1002 » Sun Apr 24, 2011 8:10 am

Absolutely amazing. A cannonball that can take 90 degree bends at velocity.

:D On a more serious note, a mod promoting a prohibited magic powder launcher? Will the shame never end?? :D :D
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Unread postAuthor: jrrdw » Sun Apr 24, 2011 8:18 am

Gotta love Wile E. Given my self this one over and over through out life... :P

So hyperspaz, rebuild plans?
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Unread postAuthor: hyperspaz » Mon Apr 25, 2011 2:13 pm

Well, I'm not quite sure how i am going to rebuild this one.

Image

It broke once before at the threaded female piece from over-tightening. You can see where I added a coupler and rebuilt the top part. but now if i try to do that again, there will only be an inch for the coupler to grasp, so I'm worried that it wont make a strong enough bond. I guess my best bet would be an inside pipe splicer like this: http://flexpvc.com/cart/agora.cgi?product=PVC-Couples-InsidePipe . then i could rebuild the top.
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