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Proposed piston housing design - please comment. Thanks!

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: limbeh » Mon Jan 21, 2008 6:24 am

LikimysCrotchus5 wrote:Man i really feel bad for you.

You guys know that gum is illegal there? Ya its crazy.
And if you wanna know why, well its because people kept putting gum on the subway door, and then that screwed it up and caused a major backup so then that had to be fixed and then it was decided that gum should be illegal.

That sucks though that there is no where for you to shoot.

The design looks fairly good to me just fix what JSR told you to.

Also what do you plan for as operating pressures and fill method?

Actually, my situation is probably very different from you guys.

As far as the law is concerned, a lot of things that you guys take for granted in the US / Australia / Europe / the West are stuff to dream of here. The law is pretty strict here, and bans firearms, including combustions. Here, possession of any kind of firearm or ammo (even spent bullet casings) is a severe crime here, with long (5-10 years+) jail sentences in a max security prison. And well, the chewing gum thing is true. In practice though, everyone brings in chewing gum in from Malaysia, just don't bring too many (consumption is allowed but retail is not allowed) and don't get caught. On the other hand, Singapore has very little crime.

Parts wise, information about parts isn't so easy to get - no Home Depot, Mcmasters or so on but instead a whole lot of small, family run hardware stores, so no websites or catalogues or stuff (a dream). Its a matter of going there and asking around. On the plus side, nobody knows what a spudgun is or cares what you're using it for, plus store owners are helpful so long as $$ flows in. PVC pipe is also easy to find, cheap, & pressure rated although not in Sch 40 dimensions. Schraders come easily, since lots of people ride bikes, and there are small, family run bike shops everywhere with lots of scrap schraders, so I can get them real cheap. No threaded ones though.

Waterbombs here are HDPE plastic bags. Any kind can be used (tie a knot to block the opening), though the ideal ones are those used for selling drinks (http://www.travelanja.de/wp-content/upl ... fe-016.jpg) - cheap (a few S$ for 100+). They are easily available, burst easily and do not need pressure (a tap) to fill up, so we can fill them from pails. This was something I took for granted till I read of people using heat sealed plastic bags and balloons and all kinds of sophisticated stuff just for a waterbomb.

Climate wise, the temperature is about 25-30C (all year round (ie summer) and always gets hotter every year (global warming), so no problems with winter, frozen guns and that sort.

However, as Singapore is an urban jungle (wiki Singapore), there is not much space to do shooting except in schools (which have fields / open spaces). Hardly anybody has a lawn / grass patch big enough for a sprinkler and so sprinkler valves are practically non existent. 90% of the population lives in a high rise apartment (me included) and so for me all shooting is done in school. Since my launcher is stored in school, its meant to be easily dismantled to prevent anyone from trying to gay kiang with my launcher.

Intended operating pressure of cannon = 110psi maximum. A disposable cup would probably be used as a sabot and also to prevent any waterbombs launched from bursting from the acceleration

Fill method - schrader valve from old bicycle attached by epoxy joint + bike pump.

I'll probably add equalisation holes + neoprene (old mousepads) into both the red & yellow ends of the intended piston.

Thanks for the all the help guys!
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Unread postAuthor: dongfang » Mon Jan 21, 2008 12:25 pm


Your construction techniques (if you can make the valve on your drawing) seem to be sufficient for making a DFTV (google for "DFTV Antenna Launcher" if you don't know what I'm talking about).

DFTVs kick ass. I have built 2 of them so I should know ;)

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Unread postAuthor: zeigs spud » Mon Jan 21, 2008 2:18 pm

Novacastrian wrote:It seems as though it would work, however why do you want to use this design and not a "solid" piston? It would seem that this design could constrict flow. Having said that i have never made a piston for a tee.

yea that is pretty much it, great that your thinking but, not really nessasary or completly practical.
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