Hello all, please forgive the English.
I designed and built the Delta Tau controlled deltas found on YouTube.
http://www.youtube.com/watch?v=Gv5B63HeF1E
I have spent many years working on parallel kinematic mechanisms. Delta Robots and Hexapods.
http://www.youtube.com/watch?v=bQtT4EDyQVU

The hexapod joints are 12mm ball magnets, constrained with a simple four bar linkage on the base... or actually the top, as it is hung upside down.

The delta robot inverse kinematics can be calculated using simple trigonometry, projection of triangles, law of cosines.
Hexapod kinematics are a different matter. I encourage everyone to discover the benefits of parallel kinematic mechanisms. They are superior in rigidity, speed, cost.
My friend and colleague has a website on the subject http://www.parallemic.org/