Print-in-place eccentric cycloid planetary gear

This is an example of an idea I've had floating in my mind for a few weeks now, having seen people make eccentric cycloid gears for robot joints on youtube.  I thought they might make quite effective printed bearings, because they only (*in theory*) have rolling contacts, and no sliding ones.

This one needs printing at 50% size otherwise the clearance between the parts is mahoosive.

When it comes off the build plate it feels like it's locked up and won't turn.  It's fibbing to you.  Get some grease onto the pins and rattle it around a bit and it'll loosen up.  I'm not quite sure what the problem is with the initial configuration: it's not a problem with the print, all the parts are separated cleanly off the print-bed, it's something geometrical.

This one doesn't spin too cleanly. If you print the top or bottom half alone, when you turn it the pins want to pop out.  That's why this one is herringbone-configuration.  I think what's going on to make it not spin well is that at the joint between the top and bottom half, the profile is sensitive to being even slightly out of alignment.  The reverse in direction of the spiral means that if the planet is even slightly out of position, the profile doesn't fit well.  This has 0.4mm clearance between the surfaces by design, which doubles up to 0.8mm if the planet is in direct contact with the opposing surface on the far side.  With a 5mm profile diameter (as here) that's significant.

The next experiment is to see if reducing the clearance makes things better or worse.  I suspect introducing a gap in the profile between the top and bottom halves will help too, but that's