I'm building a motion control platform with 3 DoF: 1 axis of rotation (theta) and 2 cartesian (x,y). In most applications, like wrist actuation, you have an X-Y stage with a rotating servo as the stage's payload. This configuration works well since little of the power and data wiring needs to transit to the non-linear moving portion of the platform.
For my inverted application, the stackup is reversed. The rotating axis comes first (from the mounting plane) with the stage connected as the rotating platform's payload. Now nearly all of the wiring (power, command, sensor, and otherwise) must be routed to the non-linearly moving section.
I can see two broad approaches:
The inside track, I route the cabling through the center of rotation.
The outside track, I route the cabling around outside the outer diameter of the rotating platform.
Mathematically, I can see that (1) results in minimum cable length, but maximum torsional loading, while (2) results in maximum cable length, but minimum torsional loading on the wires.
Having limited experience with cable routing (and the associated carriers, strategies, and products) in non-linear applications, my question is...
...which approach is better in practice?
Cost isn't really the issue here. I'm more interested in reliability, ease of construction, availability of commercial components (says something about the popularity of the technique), etc...
e.g. the generic concepts behind why you pick one over the other.
...of course, if you have some part numbers for me I wouldn't be upset <-- I know I'm not supposed ask that here ;-)