Antenna rotator is working fine, using USB-UIRT plugin, no Girder required.
Hardest part was that it took several tries before the USB-UIRT learned correctly.
The rotator controller is a ChannelMaster 9521, a programmable electronic controller. I was able to teach it the locations of all my stations, so that when the USB-UIRT sends the channel number being tuned in, the rotator turns to the correct direction for that channel.
Now the picture is always clear when recording, instead of sometimes recording snow when the antenna is pointing the wrong way.