Sunday, March 06, 2011

I had a busy Saturday. Jason G, who has a big workshop in his basement & garage, wanted to try building pumpkin-throwing devices for Jessica's little event in the fall, and his girlfriend was out of town for the weekend. So we spent the morning with Dan W, digging through piles of scrap at a junkyard in the ruins of a quarry facility outside of Pleasant Gap. We ended buying about fifty pounds of aluminum and iron bars, springs and the like, then hit a tractor supply shop and Triangle Lumber over near Jason's house. We met a couple of university folk back at Jason's place - Antonios whom I know from Otto's Tuesdays, and a guy named Jim who I think was at Jason's Superbowl party this year.

I was going for a simple spring-pull ballista, while Jason had this idea for a torsion-axle trebuchet design. I really just banged about without much estimation, calculation, or design, building a wooden frame around a nicely-formed piece of aluminum scrap. The frame and shuttle was mostly done by yesterday evening, although there's a lot of work & thought required in figuring out the exact nature and details of the pull and latch mechanism. I'm thinking a simple latch hanging off of the shuttle, and a cross-bar just before the full extent of the spring, so that the latch can simply "drop" onto the bar when pulled back across the locking cross-bar during cocking. When the device is inverted and placed into firing position, the latch can easily be yanked down by cord, triggering the device.

Dan W and I *tried* to assemble the device so that the formed-aluminum slot at the core was properly aligned so that the latch would be placed at the rear of the aluminum core, but I'm not sure if it'll do so or no. If not, we can always set up a bar across the top of the device instead, although that'll be yet another failure point. At least we went with a cheap and new heavy-duty door spring instead of the ancient and far-too-strong car-shock-absorber springs which we bought at the scrapyard. To be honest, this device doesn't feel like it'll throw a pumpkin all that far, if it works at all. But what the hey.

Jason's device is much more elaborate, and looking kind of steampunkish. He and Antonios and Jim were working all afternoon and evening on a lot of grinding, metal-cutting, and welding tasks, modifying one of the shock-absorber springs and building a delicate, cross-supported throwing arm out of little strips of steel. The in-process result I looked at at the end of the evening was about five-six pounds, I guess. Most of the mass of the device will be in the fulcrum cross-arm and the base of the device, I guess. My machine has most of its mass already - the only thing to be added is the latching mechanism, a detachable pull-stirrup, and another cross-bar.

Antonios is some sort of chemistry PhD, a professor I think, and he spent much of the afternoon filabustering, trying to come up with rules-lawyering ways around the "mechanical advantage only" design requirements. Talking about water-pressure rockets, gunpowder, dynamite, air-pressure - but mostly going on about a preposterous Mentos and Diet Pepsi driven device. I told him about the dry-ice and water in a two-liter toy we had made back at the Witch House which destroyed a garbage can.

But anyrate, yesterday, we tinkered, and made a heck of a mess in Jason's garage and workshop.

No comments: