This was one of my first creations. I intended to use this unit to move back and forth over several transmission driving rings (when the center axle is rotated left) and move a driving ring left/right (when the center axle is rotated right). The center axle could be motor operated using the mini-motor.
I never really used it though (it is not completely finished), only looked at it with a big smile.
Maybe there are some building tricks in here that you could use (see ldraw)