I'm working on a motorized focuser for the SpaceCat / RedCat. I saw that K-Astec is using a timing belt flipped inside out--brilliant. I've also seen DeepSkyDad's version, with the 3D-printed gear ring--very cool. I just ordered a couple test belts with a 2.5 mm pitch to see if that will work with the Cat's focus ring.
Right now I'm using my AF1--dismantled a bit--to test the belt tension and torque.
UPDATE: I was just emailing with Pavle at DeepSkyDad.com, and I ordered their latest AF3s motor/controller combination with the Cat timing belt ring, belt, custom pulley and L bracket. After a few days trying to get the 2.5mm pitch timing belt to work with the Cat's focus ring--with a lot of slipping and different configurations, different step sizes, speeds, etc., I went ahead and got the DSD working set. I'm pretty sure part of the problem is the softness of the Cat's focus ring, so that even with a timing belt with matching pitch it wasn't going to behave like a pulley, just not rigid enough--made for human hands to grip and adjust. I was going to have to go with supplemental gearing, either a reversed timing belt glued-down like K-Astec, or with the 3D printed rigid ring developed by Pavle. https://deepskydad.com/autofocuser/redcat. I went with the standard enclosure instead of the RedCat mount so this should work well with the camera rail.