Omni Wheel for Servos

UPDATE 2016-09-26:
I've decided to switch to off-the-shelf omni wheels, since I was unhappy with the traction from ninjaflex tires. I've uploaded the DesignSpark Mechanical drawings for these if anyone wants to continue iterating on this design.

This omni wheel is a design I'm working on for a BB8 build. It mounts directly to a servo horn (I'm using these nice metal ones: http://www.robotshop.com/en/hitec-spline-metal-servo-tapped.html) and is designed to be assembled with 4-40 hex socket head machine screws. The axles are LEGO Technic axles, 4 pegs long. Each roller is 2 parts with a hub and ninjaflex tires.

First test print of the hard parts came back pretty good, but I've adjusted the position of some of the screw holes to ease printing and assembly, and adjusted tolerances so that the ends of the rollers don't need to be sanded for smooth rolling. Rollers had to be drilled out with a 13/64" bit (as intended) so that they have nice smooth bearing surfaces.

Tire test is mos