Servo - December 2016

explosives, the big boom is really what it’s all about.

Of course, our paramount concern with this project is safety. We wanted to ensure that every component was properly pressure rated. With respect to the steel pipe fittings, that meant we would be using schedule 80. Given the challenges we faced in tracking down pressure-rated PVC for our previous efforts, we undertook the search for the fittings with some trepidation. Would we be hamstrung by the lead times for specialty parts right from the get-go? The anticipation would be torturous, like having to wait to open the present under the Christmas tree that was clearly in the distinctive shape of that Razor scooter that you had been waiting patiently for all year.

However, we were as pleasantly surprised as a shopper emerging from Black Friday without getting trampled at the entrance to Best Buy in the wee hours of the morning. All of the schedule 80 fittings we could ever want were available at good prices through the McMaster-Carr catalog, and they arrived at our door mere days later. We picked up all of the elbows, tees, nipples, and end caps we needed, in addition to a few other smaller fittings.

We would need a new setup for the input valve — a Schrader valve like on a bike tire wouldn’t work for something we wanted to pressurize up to 3,000 PSI. We opted for a Foster straight-through quick disconnect fitting that would allow input through a manual ball valve. The ball valve would allow us to reliably open and close the tank, and McMaster even had a great selection of small high pressure ball valves. We placed our orders and eagerly awaited our presents.

Making a Parts List, Checking it Twice

Thankfully, the wait wasn’t long because we didn’t even have advent calendar chocolates to count down the days. The heavy duty boxes arrived at our doorstep, and we must say that it was a different experience than with smaller scale projects. Don’t get us wrong — we like a bright red SparkFun box just as much as the next roboticist, With the fittings in hand, we could begin to lay out the cannon and get a sense of the scale. Given the smaller diameter pipe than our PVC versions, we were concerned at first that the cannon might look too small and thus lose some valuable cool factor. Fortunately, laying the fittings out like a really heavy jigsaw puzzle didn’t disappoint us at all. It was a lot more like putting the first ornaments on a freshly cut and fragrant Christmas tree — an exciting preview of even more exciting things to come.