PWM-controlled hobby servo (1-2mS pulse evert 20mS or so) is the one-directional control I had in mind. When you are under $100 range a surprising number of servos use the same simple 1-wire protocol, even large-ish 150 kg-cm / 100W units.
Dynamixels are two-way, and they are an exact thing I'd wanted to see in search results.