ideal solution for a robotic punkin chunker would be a
solenoid valve that we would simply need to put power and
control to; like a large scale version of the electric sprinkler
valve we used on the mini tank and the first incarnation of
the chunker. We were looking for a ball valve that would
ideally be about the same diameter as the pipe to avoid
excessive pressure drop over the valve, so about 2. 5” or so.
The problem is that large diameter/high pressure
solenoid valves are as prohibitively large, heavy, and
expensive as is an entire set of signed first edition Stephen
Kings. Some of the solenoid valves we researched tipped
the scales at over 50 lbs. If we wanted to make a large
scale/high pressure punkin chunker, we would have to find
Another way would be to pick up a high pressure ball
valve and come up with our own way to actuate it. Finding
a high pressure ball valve that was reasonably priced was a
chore, but eventually we discovered a 2” Dynaquip ball
valve that fit the bill. We opted for a 2” valve instead of a
2. 5” version to control costs (the price difference was
significant), and to ensure that any projectile wouldn’t fall
back into the valve. There were other benefits too.
Since we were looking at a manual ball valve, the high
pressure chunker would need some sort of actuation
mechanism. An important parameter to consider when
designing the actuation mechanism is the actuation torque
of the valve — how much torque it takes to open and close
it. Many of the catalogs for the valves included helpful plots
of actuation torque, and they revealed an interesting
relationship. The pressure and actuation torque had a
proportional relationship: the higher the system pressure,
the higher the actuation torque.
We saw that for high pressure valves, the pressure drop
over the valve was lower for larger diameter valves, and
that a valve of at least a 2” diameter had significantly less
pressure drop than smaller valves. So, a 2” valve looked like
a safe bet. We opted for a 6,000 psi rated valve for safety
We were actually hoping to have everything we needed
to build the high pressure chunker by the time this article
deadline rolled around. Instead, we learned the hard way
that parts for extreme conditions (like high pressure ball
valves rated to 6,000 psi) are sometimes custom parts with
long lead times. We’ll have to be patient like Pennywise the
Dancing Clown, but fortunately we won’t have to wait 28
years to resume our wave of pumpkin terror. The part
would be ready in a couple weeks, but unfortunately that
would be a little too late for us.
Cycle of the Punkin Chunker
In any event, we’ll be able to test out some trigger
designs as we wait for the rest of the high pressure parts to
arrive. Refining a trigger design would be important
because opening the valve by hand next to a vessel
pressured to 3,000 psi struck us as risky as taking a winter
caretaker job at a remote Colorado hotel.
Our second PVC prototype uses a large diameter ball
valve, and we used it to verify that pressure drop does
indeed play a huge role in the effectiveness of an air
cannon. The ball valve is manual, and comes with a large
blue handle that turns 90 degrees to open or close. Last
time, we never fully robotified the cannon, so we essentially
wreaked pumpkin havoc by hand like Normal Daniels. With
an automatic trigger, we could wreak pumpkin havoc
Twin brothers hack whatever’s put in front of them, then tell you about it.
SERVO 10.2016 55
A BALL VALVE IN NEED OF ACTUATION.
SNORLAX FOR SCALE.
GETTING A HANDLE ON THE HANDLE.