All,
Some exciting ideas of the range of possibilities open up by applying four bar linkages (both planar and spherical) to recumbent design (mostly applicable to FWD lowracer recumbents)!
First, two tutorials with good basics, the first on basic four bar linkage terminology and math, the second focused on "principles of geometrical construction of a four-bar linkage which traces an exact symmetrical circular arc for a finite portion of its coupler curve". Both have a few good nuggets to help orient your brain to the basics, but neither are too in-depth.
http://www.mines.edu/fs_home/dgolson/mce302-1.html
http://www.mines.edu/fs_home/dgolson/mce302-2.html
Using a four bar linkage for steering, it might be possible to take advantage of having varying steering characteristics, like a twitchy, sensitive center range and gentle dampened extremes, similar to rear suspension VPP designs. Or try to figure out how to compensate for pedal-induced steering movement the way Santa Cruz/Intense VPP compensates for pedal-induced suspension movement!
Spherical Four Bar Mechanisms:
http://www.vrac.iastate.edu/~jmvance/SPHERE/SPHERE.htm
Spherical four bar mechanisms can do really cool things! You could design one that would pivot like a Python (or pivot around a different point) and raise the front wheel as the turning radius increased (mimicking the hanging pendulum seat raising trick).
Or one that would steer the front wheel CCW or CW when you tried to lean the BB left or right, rotating the BB around the horizontal axis parallel to the boom (also perpendicular to the horizontal axis around which the BB allows the cranks to rotate), like having your feet attached (by clips or cleats) to the 10 o'clock and 4 o'clock positions on a tiny steering wheel (equivalent to left pedal high/right pedal low).
Michael
