Summary

Hollow universal joint, printable as a single unit & parametric with openscad.

The scad's got a decent amount of comments, I might clean it up and upload a better version later, but it's pretty straightforward.

Instructions

Print! The joint+ring stl should print well - there's a 1mm gap between the ring and the joint. Be sure to use Brim or some other method to get the part to adhere strongly.

Doesn't require any connectors, the pieces just snap together.

Idea came from http://www.thingiverse.com/thing:25872, also used http://www.thingiverse.com/thing:3140 to start the openscad bit, but I went through and parameterized everything.

To resize, all you should need to change are the outer_rad and wall parameters - the first is the overall radius (so the part will be twice as wide), the 2nd is the wall thickness.

As written, the inner diameter is outer_rad2-(wall2+1).
The part displayed is 20mm outer_rad and 3mm wall, so outside is 40mm around and inside hollow is 33mm.

hollow universal joint - printable & parametric