i prototyped this using two windshield motors (powerful worm gears for cheap) and two slip rings to transfer power / position data between the arms

it looks awesome but I need to work on making it easier to produce by figuring out a better way to sense where the connecting arm is (hall effect?), and do more work to account for backlash in the relatively inexpensive / tolerant worm drives

i built one that rotates about the hour hand and another the rotates about the minute hand to try both ways out; it's pretty cool to see the whole thing swing around once an hour but probably not something you want in a home...