R5-b1 Framework: Port bow, above, isometric

ATR3-b1′s framework corner angles are imperfect. Welding the corners into permanent angles is one obvious solution, but welding is a complex art and the initial equipment expenses are high: $700 – $1300 for a MIG welder and necessary supplies.  Though a weldless build is realistically limited in strength and size, bolt-based designs only require a drill press and a pile of bolts/washers/nuts. But how to build a 3-dimensional right angle with only bolts, which allow rotation about their axes? Overtightening the bolt helps, but will not hold up against time and vibration.

Gridbeam is a “reusable structural system”. They solve the 3D right angle problem with tri-joints. ATR5′s new framework is built from the the same basis material as ATR3′s — 1/2″ square aluminum tube, 1/16″ wall. Unlike ATR3-b1, however, tri-joints force ATR5′s framework into a regular cube.  As the tips of all three rods can extend beyond the joint, tri-joints allow for rods to be cut generously and trimmed down to size after the joint is drilled [see image, right]. The cube is secured to the chassis in four corners and two additional points near the center.

Where only a 2-dimensional right angle is desired, a 1″ piece of material in place of the third rod forces alignment. [See image, below left.] This technique allows for 2D regular rectangles, squares, and right triangles.

R5-b1 Framework: Stern port lower tri-joint

R5-b1 Framework: Stern starboard upper tri-joint