John Ferrell wrote:
On Mon, 30 Nov 2009 10:31:12 -0800, Jim Lux
wrote:


3 9V batteries in series makes a fine source to actuate a sprinkler
valve. Put a 0.1 uf (or thereabouts, non critical) capacitor across the
pushbutton contacts to make it last a bit longer.

Got a little further today. It takes too many hands to twist the
valve, fiddle with the reel and aim the device. I black vinyl taped a
micro switch to the valve assembly with ONE 9 volt battery so that I
can thumb it to launch. I also moved the open face reel back to the
valve end of the barrel and fabricated (more black tape & paperclip)
an eye to pass the line through so that line retrieval with the reel
is less awkward. Today's final test was conducted in the dark so I was
unable to see much. I launched nearly 90 degrees and it was gone for
several seconds so I expect it did well.

I've found that a single 9V will open a valve if there's not much
pressure, the coil is cool, etc. Run the pressure up, grab the thing
out of the back of the car where it's been cooking in the sun, etc. and
a bit more current through the coil is handy. (Oh yeah, and with 3
alkaline 9Vs, they'll last basically forever, because it will still fire
when they're almost dead... use the ones you pulled out of your smoke
alarms at home)


VK2KC emailed me with some advice. He pointed out that it is usually
better to launch from the woods to an open space. I expect that will
be the case.

It seems to me that this device consists of three components: Barrel,
Valve and accumulator. It seems that to change to launching tennis
balls would be a matter of fitting a 2-1/2" barrel. I doubt that I am
going to find that in my area but I will keep my eyes open.

Don't neglect the possibility of using a slightly large barrel with a
liner (take a bigger diameter piece of plastic pipe, use a circular saw
to rip a slot down the length, and then squeeze it down to fit inside
the outer tube.

Or a sabot/piston made of closed cell foam (e.g. cut a disc of styrofoam
that fits snugly.. or I like polyethylene foam.. it's a bit springier)

Or, use one of those squishy fairly dense foam rubber balls (you see
them as "stress relievers" as a giveaway at trade show booths, for
instance) that are available in a variety of sizes and make a snug fit
with the ID of whatever barrel you use.



Tomorrow is another day!

John Ferrell W8CCW