I have made a version of gearboxes for shoulder and elbow joints that feature thin wall bearings 61818 and 61816 respectively (sometimes denoted 6818 and 6816) instead of 3D-printed bearing with metal balls inserted between two grooves.

CAD sources available in gihub here: https://github.com/surynek/RR1/tree/main/rev.2

I expect smoother rotation from this update. However it means disassembling the current build of the robot and making the exchange.