One easy possibility for eliminating the sag is to use rotating arms. A long horizontal arm that rotates in the xy plane will have the same droop/sag no matter where it rotates to (being the same distance to the end of the arm no matter how you rotate it). The software would then have to adjust for a curvature in movement for the other axial directions, but you'd eliminate the effects of differby merlz - General
There was some discussion a while back about something similar to this. There are some printable mechanical stepper motor designs and a small investigation into using water for logic circuits. Should be somewhere on http://www.3dreplicators.com/cgi-bin/cblog/index.php I think "art of illusion" is the free CAD-like tool of choice around here. I'd love to see your designs too. Not that I'd wanby merlz - Plastic Extruder Working Group