What are some good purist rotacaster / omni wheel designs? In robotics, rotacasters or omni wheels are often very useful.

It's possible to buy LEGO-compatible ones from some third parties, here's one random example:



Unfortunately, LEGO has yet to make any themselves, which means if you are looking for a purist solution (because of robotics competition rules for example) you are out of luck.

Or are you? It might be tough to make a small one, but surely it's possible to build one.

What are some good rotacaster / omni wheel designs?
Here's a design I've been using, based on this model by Lambert Varias:



It's not a perfect circle, but it is relatively small all things considered:



It's pretty simple, but here's a partial disassembled version to better show what goes into it:



Parts shown:


1x 55013
2x 4265c
2x 57585
6x 32013
6x 32556
12x 42610
12x 50945