As of 8/1/2012
The way things are looking, there will be one real and two synthetic axis’ for the pan/tilt/roll of Wheatley’s face.
There is an inner gimbal that rides on a vertical post. This gimbal provides the pan motion of wheatley’s face. On this inner gimbal is a middle gimbal. It provides the roll axis of the face. Attached to this is the face assembly, a sort of yoke that rides on an axis that allows it to tilt. It also supports the eyelids.
By synthetic, I mean that there is not a direct correlation between a single servo, and the mechanical output. In this case, the servos will be anchored to the body, and to the “face tilt yoke” at positions to the left and right of a vertical plane that is perpendicular to the tilt axis. When both servos “push” the face will tilt down, when they both pull, the face will tilt up, and when they move in opposite directions, the face will rotate.
Because they are anchored to the body, and not the pan axis. the act of panning will also introduce some cross talk, but this should be minimal, and hopefully, correctable in software.
Presently, the pan and tilt are designed for +/- 20 degrees, and rotation is +/- 40 degrees.