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Completed cannon, but does not work as expected ?

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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Completed cannon, but does not work as expected ?

Unread postAuthor: Hidendra » Sat May 19, 2012 11:08 am

Hi lads

I built a cannon using 2" sch40 pipe ( 2.5'ish barrel, 2' tank ), and a 1" sprinkler valve w/ solenoid which is hooked up to 27V (3 9-volt batteries).

When I pump it up to 60 PSI the golf ball inside only goes maybe a quarter of the way up the barrel, even if it is not angled there is not a huge difference (except rolling slowly out of it). Any idea why this is?

Few pictures (sorry for the low quality, didn't realize until I got home)
http://i.imgur.com/WUWS9.jpg
http://i.imgur.com/Crgpt.jpg
http://i.imgur.com/FLcTJ.jpg

It does make a loud "woo" sound when the valve is opened and there is some air leaks but I don't think that would cause a huge problem during release (around 10 PSI / minute?)

Of note there is a Tee connecting the Valve and the barrel. Most of the other end of the tee is blocked off from the plug but would that cause the problem?

Thanks in advance
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Unread postAuthor: jackssmirkingrevenge » Sat May 19, 2012 11:16 am

Your valve is probably "honking" (rapidly opening and closing), you should think about modding the sprinkler valve for a more efficient manual piloting.
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Unread postAuthor: Hidendra » Sat May 19, 2012 11:29 am

jackssmirkingrevenge wrote:Your valve is probably "honking" (rapidly opening and closing), you should think about modding the sprinkler valve for a more efficient manual piloting.


according to the wiki, it should only decrease the muzzle velocity by 10% -- would that really account for it not working at all for me?
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Unread postAuthor: Crna Legija » Sat May 19, 2012 11:39 am

How well do the balls fit, 2 1/2'' barrel for 1.6'' projectiles big difference.
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Unread postAuthor: Hidendra » Sat May 19, 2012 11:43 am

Crna Legija wrote:How well do the balls fit, 2 1/2'' barrel for 1.6'' projectiles big difference.

it's a 2" barrel, around 2.5' long. it fits fairly well but is of course not snug, may try sleeving sdr 21 inside of it to see if it helps if I can find it
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Unread postAuthor: jackssmirkingrevenge » Sat May 19, 2012 12:03 pm

I hadn't realisted the barrel-projectile width disparity.

Yes, that's definitely your problem. Even a 1/8" gap would be far too much.
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Unread postAuthor: jsefcik » Sat May 19, 2012 12:15 pm

Mod the sprinkler valve!!!
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Unread postAuthor: mattyzip77 » Sat May 19, 2012 12:16 pm

The ball isnt even leaving the barrel though?? At 60 psi, it should at least make it out of the barrel I would think. Make sure all of your connections are tight. Is the valve going in the right direction?? Sounds to me like your valve is backwards. The arrow should be pointing in the direction your barrel is exhausting.
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Unread postAuthor: jimmy101 » Sat May 19, 2012 12:51 pm

Wad the golf ball up in paper towels (or a rag) so it fits pretty snug in the barrel and give it a try. If the gun then behaves more or less as expected than the loose ammo is the problem. If it still sucks then there is some other problem.

Or, go old school and use a big-ass spud. :D
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Unread postAuthor: Hidendra » Sun May 20, 2012 12:30 pm

jackssmirkingrevenge wrote:I hadn't realisted the barrel-projectile width disparity.

Yes, that's definitely your problem. Even a 1/8" gap would be far too much.

thanks! experimented a bit with padding it to make it slightly loose in the barrel (but not so it rolls down it on its own) and it flew out about 3 meters. made it even tighter and it kept going further.

The only store that sells sdr 21 piping close to me closed at Noon yesterday so I'll see about getting that on Tuesday (most likely closed tomorrow, victoria day)
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Unread postAuthor: Technician1002 » Sun May 20, 2012 7:16 pm

Some sprinkler valves have a flow control adjustment. Check your valve.
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