remotely like Carrie White.
We needed to craft a mechanism that would rapidly
open the ball valve. Since we could only load one projectile
at a time, we would only need to worry about opening the
valve. The most efficient solution for a rapid release
appeared to be a spring. A spring would be a compact way
to store plenty of energy to actuate the valve that would be
released very rapidly. We envisioned a torsion spring — the
mechanism would be cocked by twisting it closed, with
some sort of stop or latch holding it closed. All we would
need to worry about would be opening the latch, and the
spring would handle the rest.
We hadn’t worked much with torsion springs in the
past, but fortunately they are as plentiful in the McMaster-Carr catalog as unspeakable monsters in the Todash
darkness. We picked up a few springs with the highest
torque rating of 40 in-lbs and with a variety of leg
orientations. Standard torsion springs, fortunately, take
much less time to ship than custom high pressure ball
With our parts in hand, all that was left to do was
everything. The first task was to determine how best to
mount the trigger mechanism. Ideally, we wanted to mount
it to the cannon itself because that would keep everything
as self-contained as possible. To ensure that the spring
tensioned properly, we would need to mount in line with
the axis of rotation of the valve.
Many of the high pressure valves we were looking at
had a bolt coming out of the axis of the handle, and we
wondered if we could achieve a similar mounting solution
with our big plastic valve. We gingerly popped the big blue
handle from the valve using a flat head screwdriver and
plenty of finesse. We were very pleased to see a large
plastic shaft, roughly circular with various cutouts that
allowed the handle to catch. Best of all, there was a hole
running through the center of the shaft. It just so
happened that the hole was perfectly suited for tapping
with half inch threads.
Since the plastic valve didn’t have a bolt protruding
from the center axis, we would install our own. We very
carefully tapped the hole. Splitting the plastic would be as
disastrous as a mysterious pulse turning every cell phone
user into a raging lunatic. Since the PVC cannon was all
cemented together, we couldn’t simply swap out another
valve. We would need to start from scratch, like the
survivors of Captain Trips gathered in the Boulder Free
The tapping went as planned, and we installed a
length of half inch all thread without incident. We added
some nuts to the all thread which created a good sized
mount for the torsion spring that wouldn’t allow it to
bounce around willy-nilly, but would leave enough room for
the inner diameter to shrink as the spring was tensioned.
Now, we needed to affix one leg of the spring to a fixed
point and the other to the valve.
The easy one was the leg going to the valve. We lined
up the leg with one end of the blue handle, bent the end
of the leg with a large vice and steady hands, and drilled a
mounting hole through the top of the valve. We completed
the mount with a hose clamp that gripped the spring leg as
tightly as the cuffs gripped hapless Jessie Burlingame in
The Orange Mile
To properly mount the second leg of the spring, we
had to ensure that however we affixed it, the trigger would
have enough tension to spring open when released. To
ensure that we stored enough energy in the spring, we
opted for a 180 degree version instead of a 90 degree
spring, with the angle referring to the angle between the
legs. We were concerned that a 90 degree spring wouldn’t
have enough energy to push through the end of the
rotation and fully open the valve, and that’s not the kind of
part we wanted in our ka-tet.
We wanted to mount the 180 degree spring so that
when the valve was closed, it would put a high tension 180
degree rotation on the spring. Next, we needed to devise
what kind of fixed point we could mount the fixed leg to.
TAPPING THE BALL VALVE.
A CADRE OF TORSION SPRINGS.
56 SERVO 10.2016