Well, I decided to do it, I have made a mockup of how I think the gearbox for 42070 could work. 42070 gearbox by Saberwing007, on Flickr In this image, we have the basic gearbox, with control levers.The brown lever switches between drive and crane modes, and the purple levers switches between crane functions. 42070 gearbox2 by Saberwing007, on Flickr In this image, I have hidden the some structural parts, so you can better see what is going on. For each motor, there is a two position splitter, linked to a common shift lever. When the lever is in the down position, the motors are linked to the drive mechanism, and allow the model to drive. However, the two driving rings can also go the other way, which connects each motor to another splitter. Then, each of those splitters have two positions, and are slaved together so that they shift together. the parts are color coded, as follows: The blue driving ring and red driving rings are run by each motor, and controlled by the brown lever. The dark blue and dark red gears would connect to the drive and steering. The orange and lime green gears take the power from the other output of the red and blue driving rings, and take that to two more driving rings. The black and dark green gears are the two outputs of the XL motor in crane mode. The white and tan gears are the two outputs for the M motor in crane mode.