Hobson's Coupler

A Hobson's Coupler (or Hobson's Joint) is a mechanism that diverts rotational power around a corner. Unlike a universal joint, it can function at an angle of 90 degrees and is a true constant velocity joint, but the angle is fixed at construction..

I designed these parts so I'd have a simple model to play around with. Three or more angled rods (there are four in this design) connect a pair of rotating cylinders (which each resembles the cylinder in a revolver). Each arm of a rod is free to slide and rotate within its "chamber" in the cylinder. The rods force the cylinders to rotate in sync with one another. As a rod moves closer to the point where the cylinders are nearest, both arms of the rod slide into their respective chambers. As the rod moves further away, the arms slide back out.

The mechanism is used purely as a coupler in applications like the 90 degree Gearless Angle Drive (a ratchet/socket driver attachment by Cal-Van Tools), and in certain shaft-driven bicycle designs. It can also function as an engine in its own right (with the rods acting as the engine's pistons), such as in steam or compressed-air powered Elbow Engines, or in the 1970s Bricklin-Turner Rotary Vee concept engine (and similar designs ). It is also the basis for the fictional V-Engine used in the mecha setting Heavy Gear.