July 22nd, 2010

An engineering problem

I'm building a gun-carriage for a water-balloon cannon. Ye basic truncated Necker pyramid; four struts screwed to the corners of a plywood-sheet base at the bottom and a set of conduit pipe-straps at the top that will hold the trunnions of the cannon. I have four 45" 2x2's for the struts; given that the base is to be 20" square, the pipe clamps are two and a quarter inches between the screw-holes, the trunnions are an inch and a quarter in diameter and the barrel is 8.5 inches thick, I need to figure out the angles at which to cut the ends of the 2x2's so that they're flat perpendicular to the floor at both top and bottom, and slope in from the corners of the 20" square to form a narrow rectangle 8.5" from side to side and 1.75" front to back.

Current best idea is outline a 20" square on the grass, set the pieces up, and draw lines on 'em freehand. I'd like to figure out how to do the elegant theoretical job, and also if there is one the easy approximation.

Anybody wanna water balloon?