Thanks to all for comments on here. With help from here and other places I have managed to get my Cloudray wheeled rotary axis working on a Ruida RDC6445S controlled ebay White and Blue 100W laser. It’s running RDC-V26.01.17 firmware.
After unsuccessfully trying the Y axis option (my Y axis M415 stepper driver puts out a max of 1.6A and the Cloudray NEMA23 needs 3A) I enlisted the invaluable help from Matt at MW Laser. He gave me a link for a DM542 stepper driver which has the required current output.
Fitting the hardware was trivial with the help of Matt’s YouTube videos. The software setup was also fairly simple using the help from posts above. Firmware v.17 has the ‘rotating axis’ menu option in User Settings as mentioned by GregP, which I set to the U axis.
In Lightburn I selected ‘Enable Rotary’ set up my steps per rev and wheel diameter and ignored the Y axis section and the other greyed out options, which doesn’t include the U axis.
I followed the workflow that was suggested by @Lignumaqua on this thread:
[Ruida 6445 and Rotary - #18 by Lignumaqua]
and, after some fine tuning of the steps per rev was engraving on the rotary axis successfully with a 6445S.
As an aside, it is worth noting that the Cloudray wheeled axis is quite tall (around 130mm) which may limit the diameter of objects that can be engraved, depending on how low your Z axis will travel and/or the height of any honeycomb, etc.