Servo - December 2016

the project. At 10. 25 pounds per foot, our two foot long/three inch diameter barrel would clock in at 20. 5 pounds. That’s as much as a pug dog. Or, way more than enough LEGO kits to completely fill up the bottom of a Christmas tree.

McMaster, unfortunately, doesn’t stock large diameter high pressure steel pipe. We would have to find another source. Googling around led us to Southern California based Totten Tubes. Totten has a wide selection of tubes, including the schedule 80 steel pipe we needed. Totten was able to cut the pipes to the length we required, and cut threads onto the outer edge of the tubes so that they would play nicely with our fittings. They even delivered right to our door.

On that day of Bot-mas, we were delighted to see that the threads on the tubes were beautifully cut, and as we hauled the tubes onto our work bench we were amused to think that the weight of the tubes far exceeded the weight of some of our other entire robots (like our Featherweight, Twibill Trouble).

High Pressure Parts are Coming to Town

In addition to the pipes and fittings, our high pressure cannon would need a variety of special parts to operate safely and effectively. The heart of the cannon, of course, would be the high pressure valve. Just like one of our PVC models, we wanted to use a large diameter ball valve to avoid pressure drop over the valve. This one required a lot of research. After the fact, it’s easy for us to write down that we found a great valve from DynaQuip: a two inch VAJ2.AR series forged steel body ball valve. However, that doesn’t capture the hours of research that went into the search — sifting through lots of valves that looked promising but then ended up having the wrong specs, or were prohibitively heavy or expensive.

At times, it seemed as hopeless of an errand as tracking down a Turbo Man action figure on Christmas Eve. Finding the right valve was a real team effort, but we ended up with a valve that we were really happy with. The DynaQuip valve was rated for 6,000 PSI and was one of the lightest weight high pressure valves we looked at, clocking in at only 13. 5 pounds. It was a bit pricey, but safety is priceless.

Why 6,000 PSI when we only want to pressurize the chunker to 3,000 PSI? We wanted to go with higher pressure parts in some areas that were really vital to the functioning of the device to ensure that the safety of it was beyond reproach. It would always be the best way to stay on the Nice List.

Another critical safety feature was to ensure that we had a way to purge the tanks in case something happened that prevented us from opening up the main valve and firing it off like normal. This was another challenging search, and we eventually decided on a solenoid valve from Clark Cooper. The solenoid valve — an EH30 series — was