Nicholas did a post on the RR forums with error from an earlier design:
http://forums.reprap.org/read.php?178,233674,253348#msg-253348
Looks like that one has been fixed. I was curious about positioning accuracy, though, and wanted to do a back-of-the-envelope calc to get a sense.
Assumptions/rough measurements:
50mm gear radius
6.25mm spool radius
~69 mm bolt separation
~70 mm dist from center of arm 608 to pulley center
-assume 16x micro stepping actually yields 16 position steps
-200 steps/rev motor
6.25mm * 2 * pi/rev / 3200 steps/rev = 0.0039 mm string positioning accuracy.
Accuracy at tip of the arm when arm bars are parallel: 0.0039 * (70mm / 34.5mm) = 0.0079 mm, a best-case.
That seems entirely good enough. What do you think?
Does this look correct?