Regarding the tradeoffs between field-oriented vs robot-oriented...
It's really simple to set up the controls so that the driver can use whichever one works best for a given situation or maneuver. Set up one stick to operate robot-oriented and another field-oriented. Whichever one is non-zero takes control. Have a precedence rule in case both get grabbed, but in practice that won't happen if the same driver moves the same hand from one to the other.
2077 has used this arrangement with holonomic drive for the past two years. Our driver uses the field-oriented motion stick when looking directly at the field (3rd person viewpoint, 3rd person control) and the robot-oriented stick when looking through the camera (1st person orientation). We prefer rotation on a separate stick, common to both modes, but using twist on the motion sticks would work too.
Try that with your 6wd and let us know how it goes
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