This is my take on: http://www.thingiverse.com/thing:53451 which had no holes in the planets, as it was intended for use as a bearing.
However, I needed to actually use it as a gear set, so needed axile holes in the planets.
Also hex motor shafts are unusual, more common are the round shafts with a flat. So I added a choice for shaft type.
This is my first ever attempt at SCAD, it seems to work.
This design is fully parametric and should be adjustable in the Customizer app: http://www.thingiverse.com/apps/customizer/run?thing_id=138222