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coaxial piston cannon, pump include! piston dont work! help

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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Unread postAuthor: jean » Sun Dec 16, 2007 8:49 am

@ALIHISGREAT
mh the chanber pressure i think is ~70psi
the port vent the pilot air is 7mm and piston travel is ~10mm
i can hold it with my finger when i pump the half pressure
@hubb017
sorry the pic is not scale
piston travel is ~10mm volume ~ 10cm3 bevore this the pilot volume was larger

i will explain but my english is bad..here a picture
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Unread postAuthor: VH_man » Sun Dec 16, 2007 9:08 am

it looks like your piston does not have much travel room..............

have you tried the 1/2 inch ball valve yet??? i am SURE it will work that way.
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Unread postAuthor: jean » Sun Dec 16, 2007 10:17 am

thanks for link this gun is cool! the rest of wrote i dont understand sorry :oops:

the piston travel is 10mm is this to little?
next day i will buy a ballvalve
i wonder the blowgun is to tiny
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Unread postAuthor: MaxuS » Sun Dec 16, 2007 10:28 am

Ive nevr seen that design in a coaxial before, its brilliant!
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Unread postAuthor: clide » Wed Dec 19, 2007 1:11 am

jackssmirkingrevenge wrote:Very interesting design, reminds me vaguely of clide's mini-pump, though this is more conventional. It must take quite a bit of effort to compress the air but kudos for thinking out of the box and coming up with something different :)


Yep, I actually recently built a variation on the minipump that is almost exactly like that except I used the minipump's no pilot-valve method of triggering. (see attached pic) I'll make a post about it eventually.

Nice work on the gun jean. 10 mm should be plenty of movement for the piston. Theoretically you only need 1/4 of the barrel's diameter, but I usually do a bit more than that for good measure.

Hopefully it will start working with a bigger exhaust valve.
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Unread postAuthor: jean » Wed Dec 19, 2007 10:36 am

hi

thx for comments :)

i buy a 1/2 ball valve and it will work very good! thanks for the tipp.
and i tune up my blowgun. the minibolt is now half in diameter and bore ist now 6 mm (bevore 4,5mm) and it will work good.
i go to my washingroom and scale said 40kg must press down to load the cannon. so i thimk the pressure is ~ 5bar.
yesterday i take some carrots and the max. range is 40m

@ clide

now i search all of your posts..... all what your make are amazing :shock: really cool stuff
i see on the pic you will use a Bayonet mount! good idea or not? my spring to lock the pump is broken now use a bolt (pic)



next i will make the same cannon but longer and more power
have 50cm of 34mm id barrel and 50cm of 32mm od barrel but i have no idea to make the oring groove to the barrel.
in encap that was easy but in barrel.....

here pics
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blow.JPG
piston.JPG

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Unread postAuthor: MrCrowley » Wed Dec 19, 2007 3:26 pm

jean wrote:i buy a 1/2 ball valve and it will work very good! thanks for the tipp.


No problem :P

I've probably helped 5 or 6 people with that tip.
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Unread postAuthor: clide » Wed Dec 19, 2007 10:21 pm

jean wrote:now i search all of your posts..... all what your make are amazing :shock: really cool stuff
i see on the pic you will use a Bayonet mount! good idea or not? my spring to lock the pump is broken now use a bolt (pic)

next i will make the same cannon but longer and more power
have 50cm of 34mm id barrel and 50cm of 32mm od barrel but i have no idea to make the oring groove to the barrel.
in encap that was easy but in barrel.....

Glad you got it working, and thanks for the compliments.

The lock I used on that one seems to work pretty well and it was simple to make, but it does seem to be wearing down, but that is mostly because my design has to also release the pump part while the gun is pressurized. With your setup I think it could work pretty well.

Someone also recently pointed out to me that threads could work as a locking mechanism too. A female thread on the front of the outside body of the gun and a male thread on the pump could secure it well.

You could always carefully cut the o-ring groove by hand with a knife or a file, but that usually takes a lot of work. Other methods I have seen involve hooking the part up to a drill as a makeshift lathe and using any sort of cutting tool to cut the grooves.

Make sure and post your next gun here when you build it, I'm looking forward to seeing more of these types of guns around.
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