completed it. First, we hooked up the pressure transducer
to the panel meter, ensured the cannon valve was closed,
and loaded the projectile. We wrapped the baseball in a
single sheet of newspaper for wadding and loaded the ball
with a long rod of all-thread topped with a tennis ball (our
own custom ramrod). Once the cannon was loaded, we
would go nowhere near the business end of the barrel until
the projectile was evacuated.
Next, we connected the high pressure hose from the
nitrogen canister to the cannon input valve using our
locking Foster connector. We then opened the cannon
input valve. We closed the regulator bleed valve and then
opened the nitrogen canister, calling out and confirming
every step along the way. Finally, to fill the tank, we opened
the regulator valve. The knob on the regulator valve gave us
fairly fine control over the fill rate, and one of us would call
out the rising pressure as reflected on the panel meter. We
quickly surpassed 90 psi — the highest pressure we ever
tested the PVC prototypes at ... 100 psi, 200 psi, 300, 400,
500 ... eventually, we closed the regulator valve at 616 psi.
We called out every step of disconnecting the nitrogen
canister too. We closed the nitrogen canister valve, closed
the cannon fill valve, and then slowly opened the regulator
bleed valve to let the pressure out of the high pressure
hose. We opened the bleed valve slowly because it was
actually pretty loud (though we were wearing hearing
protection, which would be even more essential just a few
moments later). We disconnected the locking Foster
connector from the high pressure hose to the cannon input
valve, and we were finally ready for testing.
Since we hadn’t yet figured out our remote trigger
mechanism, we had to do with the low-tech solution of a
cable attached to a wrench so that we could open the valve
manually. We fired.
The baseball was a complete blur as it crashed into the
straw bales. The ball bounced off, but the bales worked as
intended and absorbed most of the force. Now it was time
for the chromoly slug.
2001 PSI: A Bot Odyssey
The chromoly slug was a snug fit with just one sheet of
newspaper for wadding. We pressed it in with our ramrod
and wondered what pressure we would be comfortable
shooting it at for the first time. We settled on 1,000 psi,
and went through the same call and response step-by-step
to pressurize the cannon. Equipped with our hearing
protection and safety glasses, we let it rip.
It sounded like a bomb going off, and the chromoly
slug ripped straight through the straw bales and it was out
of sight before the cloud of nitrogen at the mouth of the
barrel dissipated. The recoil from the cannon blast was
impressive. The entire assembly — with the 120 lb cannon,
the extra 100 lbs of gravel, Protobot, the particle board
platform, and various cinderblocks for wheel stops — must
have weighed easily over 300 lbs. Yet, a shot at 1,000 psi
caused the entire thing to buck noticeably — particle board
and gravel and all.
We dashed up the hill, hoping that we wouldn’t have
to hop the fence to the neighbor’s yard to retrieve the slug.
We found the slug at the very top of the hill — well over
100 feet away from the cannon. Would we dare to increase
the pressure even more?
Of course we would. We pressurized the cannon to
2,000 psi, following our same step-by-step routine. This
time, the slug obliterated one of the straw bales, but it
didn’t seem that much stronger than the 1,000 psi shot.
That’s because the actuation torque on the cannon valve
had increased significantly with the higher pressure. We
couldn’t get a nice smooth release on the valve, and the
cannon wasn’t putting the full might of the 2,000 psi
behind the slug. We tried again at 2,000 psi and had the
We dropped back to around 1,000 psi for our final
tests — we wanted a nice clean release, and we wanted to
see what the 10 lb slug would do to our plywood target at
an estimated muzzle speed of about 180 miles per hour.
We again followed the same step-by-step firing procedure,
and the slug blasted right through the target as if it was
58 SERVO 04.2017
OUR TARGET IS WORSE FOR WEAR.
BULLSEYE (ALMOST) AT 1,000 PSI.