From: brad@slammer.UUCP (Brad Isley)
Newsgroups: rec.pyrotechnics
Subject: Re: Tennis Ball Cannons
Date: 10 Oct 92 05:04:02 GMT
Organization: Just me & my computers

>In <BvpH1J.DJ2@acsu.buffalo.edu> v064myby@ubvmsb.cc.buffalo.edu (Christophe J Quaranta) writes:
>	Some friends of mine in Ohio made an excellent tennis ball cannon.
>It used a large coffee can as the c.c., and 5 or so soup cans as the barrel.
>About 1 inch from the back of the c.c. was a can lid cut to the shape of
>a turbine wheel. They affixed this in place and put some metal scraps between
>it and the back of the coffee can. This was so the fuel could be mixed well
>with air.


One more time...
If you pay attention to the details of loading and firing mentioned below,
you'll have a Most Excellent tennis ball cannon.

Barrel:

	Take a tall aerosol can of correct diameter.  Most paint cans are just
	right.  Make sure the can is EMPTY.  This means punch a hole in it in
	a location that is to be discarded.  With a dremel tool or other
	grinder, cut off the top completely.  This includes removing the crimp.
	Leave a smooth end.  Then take a can opener and remove the bottom.
	Leave the crimp ring on the bottom of the can.

Chamber:

	Smaller aerosol can of same diameter.  Large WD40, etc.  With same
	dremel tool or similar cut off the very top of the dome.  This will
	form a stop for the ball as it is loaded.  Punch a small hole in the
	side near the bottom.

Ignition source and handle:

	Get one of those trigger operated butane lighters that has a piezo
	electric trigger.  Zippo makes the one I use.  The lighters I use are
	red and white with a long chrome-plated steel extension for lighting
	fireplace starters.  Remove the coil thingie behind the trigger.
	Unfortunately the coil thingie will vary quite a bit.  Some are not
	useable - they have a brass cap on the end.  I was unable to solder a
	wire to the brass cap.  Solder a wire to each post on this piezo
	thingie and imsert it in a handle of sorts.  I made a postol-shaped
	handle attached to a flat board like so:

          -------------------------------=------------------
          |                             /|                 |
          |                    Dome -> | |                 |
barrel -> |                             \|                 |  <- chamber
          -------------------------------=------------------
                                Rings: -/ ==================  <- flat board
                                                    \    \
                                   piezo thingie -> [#\### \==  <- wires
                                                        \    \    <- handle
                                                          \    \
                                                            ----

Construction:

	Using duct tape, tape the ringed end of the barrel to the dome
	end of the chamber.  Be sure the fit is tight.  Drill a hole in the
	handle where you want the trigger.  Arrange for the wires to go in
	first and allow for an exit where you want it.  Attach the handle
	to the flat board with screws.  Duct tape the handle to the chamber.
	Run the wires around to the hole you punched.  Twist the ends of the
	wires together for about an inch so they will stay in close proximity.
	Strip the ends about 1/8" and make a gap about 1/8".  Test the spark
	by pulling the trigger.  Get as long a spark as the peizo will make.
	Insert the wires into the hole such that the gap is close to the center
	of the rear of the chamber.  Test spark with no fuel to make sure you
	get good ignition.

Use:
	Denatured alcohol is difficult to measure into a proper combustable
	mixture.  It is also much more powerful than naptha and caused the
	handle to be ripped off the chamber in our tests.  Two layers of duct
	tape solved this.  We have had excellent repeatability with the
	following fueling method with naptha.  If recently fired you should
	sling the gun around in large arcs to get a fresh charge of O2.
	Holding the barrel upright using a standard lighter filler squirt for
	1 second or a little less straight through the hole in the dome of the
	chamber.  Make sure that approximately 1 second's worth goes through
	the hole in the dome.  Fuel in the barrel is useless.  IMMEDIATELY
	insert a tennis ball into the barrel ALL THE WAY to the dome.  Wait
	about 5 seconds and pull the trigger.  Don't get in the way of the
	ball.  I have a hole in the ceiling of my garage from a shot.

More fun:

	Use aerosol caps for projectiles instead of tennis balls.  Makes a
	LOUD bang and moves like a bat out of hell.

Even more fun (use caution - wear safety glasses):

	Place a tennis ball can over the barrel for a projectile.
	Stay the hell out of it's way.

And no, I'm not responsible for your foolishness if you get hurt doing this.
-- 
emory!slammer!brad   (Brad Isley)
+1 404 841-4169 Work			 Nopottopeein: "Howzit Goink?"
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