holding steady. No apparent leaks. Just to be sure, we left
the 60 or so psi in the cannon overnight.
The next morning the pressure had dropped slightly,
but only by about 3 psi. We figured that was actually
because of the chilly temperatures overnight — the air in the
tank would have compressed in response to the nighttime
temperature drop. We deemed the first pressure test a
success — there were no leaks.
We couldn’t resist the opportunity to shoot something,
even though we didn’t yet have our high pressure nitrogen.
We took Protobot and the shop compressor to the
backyard, set up our trusty plywood target, and loaded the
cannon with a baseball. We filled the cannon to about 70
psi, guided by the readout on the panel meter. We used a
wrench to manually open the valve since we hadn’t yet
figured out the trigger mechanism for the steel cannon.
The valve opened easily, and the baseball careened into
the target with an audible thwack. It was a solid hit and
close to a bullseye — but it was also quite like the testing
we had previously done with the PVC prototypes. The
whole point of making the steel cannon was to crank
things up to 11 and fire a way heavier projectile at way
higher pressure, precipitating in (we hoped) way more
destruction. To do that, we would need to get our hands
on high pressure nitrogen.
Parts of Glory
As amply demonstrated during the Twelve Days of Bot-mas, acquiring robot parts is most often simply a matter of
placing an order online and waiting for the box from
McMaster-Carr to show up at your doorstep mere hours
later. Sometimes, though, you need to visit specialty
suppliers, and sometimes you need to bring a big truck.
A 6,000 psi tank of nitrogen is one such specialized
part. Even though the max pressure of the cannon would
only be 3,000 psi, we wanted a 6,000 psi tank to give us
more fills for testing. After lots of research, we found a
promising supplier: Action Gas, a welding supply store
based in Lake Elsinore, CA. They even had a store in
Temecula — Robot Central’s home base. We applied for an
account as Team Double Trouble Robotics, and we hoped
that we could pick up the canister from the Temecula
location. On the weekend we planned to pick up some of
our last materials needed for testing, we called Action Gas
and discovered that unfortunately the Temecula store didn’t
have a 6,000 psi canister in-store. However, the Lake
Elsinore location did. We took the truck.
The Lake Elsinore store was impressive — a bright and
open warehouse with welding equipment galore. The back
of the warehouse contained plenty of compressed gas
canisters, dutifully lined up and ready to ship out to help
weld some metal. We had other plans for our canister.
We were instructed to bring the truck to the back of the
store, and by the time we finished paying the very
reasonable rental fee, the canister was standing behind the
truck, daring us to load it in. The canister was about four
feet tall, and wide enough to promise a difficult time getting
it into the truck bed. The Action Gas guy that guided the
canister over to the truck looked at the canister, and then to
us, and asked if we had ever loaded one of these before. We
admitted that we had not. He gave us the scoop on tipping
the canister to lean in on the tailgate, and then lifting the
canister and sliding it in. He warned us that the 3,000 psi
canisters tip the scales at about 100 lbs. This was a 6,000 psi
canister. He wished us luck getting it loaded.
We eventually did. As we were strapping down the
canister in the bed of the truck, the Action Gas guy
wandered back and looked with approval at our efforts to
strap down the canister. He said we would want to be sure
to secure it really well — if something goes terribly awry and
a 3,000 psi canister blows, it’s like a bomb going off. But a
6,000 psi canister ... he speculated that would be more like
a ballistic missile. We added an extra strap.
Twin brothers hack whatever’s put in front of them, then tell you about it.
SERVO 04.2017 55
TAKING AIM AT
STRAPPING IN THE 6,000 PSI NITROGEN TANK.
POTENTIAL STEEL SLUGS: 6” LONG 4140, AND
3” LONG 1018, 4140, 1045, AND 8620.