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-----Original Message-----
From: Steven Bixby <[EMAIL PROTECTED]>
To: Warren Wu <[EMAIL PROTECTED]>
Date: Tuesday, April 10, 2001 5:56 PM
Subject: Re: Fwd: [RCSE] Jet-X (and Tennis Ball Cannons)
>Have you experimented with the chamber size? Bigger is better, smaller is
>better, just-right is best?
I've not really experimented with chamber size.. I've just been using the same pipe as
the barrel, 3". On potato guns (yes; I do those, too), I follow the same technique.
>Just from random thinking (I'm 'just' a
>software engineer), I would suspect a bigger chamber can feed a larger
>quantity of air into the barrel for the same pressures, so it would be a
>safer way to get suitable 'oomph'.
I would suppose so, but you'd be hard pressed to find any pipe bigger than 3 inches.
Heck, I have a lot of trouble finding 3" in the first place. BTW, don't use electrical
conduit (plastic or metal). Electrical conduit doesn't have a reliable pressure rating.
>How about the length of the barrel? Or the relationship between the two?
Length of the barrel.. hmmm.. I've just used lengths that make a gun that is
convenient for me to carry. Most of my guns come out to around... 30-35" long.
Sprinkler valve excluded.
>And, while I'm at it - any suggested part maker/model-#'s for the sprinkler
>valve?
I've had good luck with Rainbird valves.... 12 volts.. 1 inch. Some of my more
adventurous [reckless] friends have used brass valves. They say they have longer valve
life, but I think it's safer to avoid metal on a device that could *potentially*
explode. Also; it's difficult to make a good bond with metal and plastic.
>Seems like it could also be fun to mount the whole contraption on a cutesy
>old-fashioned wheeled cannon mount; partly because I admit to having some
>concerns about the smaller joints being susceptible to stress fractures from
>independent movement of the compression chamber and barrel.
I think the cannon mount idea is great. I've constructed an altitude-azimuth mount so
that I can keep aim at "enemy positions" and fire the cannon at distance. About the
stress concerns; with the 1" valves, stress is reduced to the point where I would
almost call it negligible.
I have cannons that have fired ~400 balls that show no signs of stress, though for
safety reasons, I throw out guns that have fired over 600 rounds. (I also destroy the
compression chamber, lest a neighborhood kid come digging in my garbage). The 600
rounds lifetime is of course, purely arbitrary, but I think it represents a good
compromise between safety and economy. But... to further reduce stress (and provide
for a more stable aiming platform) I have a center wooden brace between the chamber
and barrel so that joint stress is kept to an absolute minimum in the first place.
I should note that the sprinkler valves often have threaded outputs and inputs. Try to
use threaded PVC components for strength, when possible; though certain components are
not available in threaded form (the PVC piping, for instance)
Again, I can't be held responsible for accidents; however improbable they may be.
Good luck and have fun,
Warren | KC0HAK
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