have already held a
suitable key. The
that we originally
installed for our
sandbag filling lever
arm (in the February
2015 issue) was set
up as a winch for
reeling in a synthetic rope. We envisioned re-routing the
pulleys so that the Fisher-Price motor could pull a pin to
release the valve. Not unlike pulling the pin on a grenade.
For the pin, we cut the threads off of a long eye bolt.
The smooth shoulder should slide better than threads for an
easy release. We tied the end of the synthetic rope to the
eye bolt, and routed the pulley so that the motor would
pull downwards on the pin. We drilled a hole in one of the
U-bolt mounts to accommodate the pin, and it was snugly
held in place by the tension in the valve spring.
We added a small amount of pressure to the cannon
and did not load a projectile for some initial testing. We
were able to auditorially confirm that the sluggish start on
the valve opening did, in fact, lead to an initial slow release
of pressure. With that in mind, we set about our fully
robotic chunking with some
For the testing itself, we wanted
to do something a little different.
Using the cannon, we had already
chunked softballs, pumpkins, and
Christmas ornaments at our trusty
plywood target (and a Christmas
tree). The pumpkins splattered nicely
with our large valve PVC cannon, but
how could we ensure maximum gore
while doing something festive and
To ensure maximum carnage, we
picked up a Styrofoam craft store
jack-o-lantern and gave it a quick
orange paint job that Edgar
The valve opened slowly, with a high pitched whine like
the Mangler getting ready to steam and fold another
hapless victim. Unlike the Mangler, however, the newly
robotified PVC cannon was anything but deadly. Enough
pressure escaped the slowly opening valve so that once the
spring popped it open, it only had enough oomph to barely
push the softball projectile out of the barrel, where it fell
like Humpty Dumpty.
We needed to open the valve much more
instantaneously. We tossed around some solutions using
traditional springs to add a little more tension, but the
easiest solution to implement was to add some bungee
cords. Swift thinking was a high priority — on the day we
happened to test the cannon, it was over 100 degrees and
feeling decidedly un-Halloween-like. We felt like Robinson
executing his revenge against Dolan’s Cadillac under the
harsh sun of the Nevada desert, so we went with what was
expedient. It also happened to be effective.
The newly bungee equipped trigger opened with the
TRICK OR TREAT.
IT’S A DUD.
READY TO PULL THE PIN.
58 SERVO 10.2016