These photos show some of the details of stage 6 of the build. In particular lots of gears, including some differential gearing.
Stage 6 Sub-assembly
This is about one quarter of the way through this build stage.
Differential Gears
This is a closeup photo of the complicated gearing at the front end of the unit.
Gear Change Mechanism
The back end of the unit has a way of changing gears. The little red piece, circled, moves the grey clutch piece left or right from the central neutral position. Click the photo for a bigger image.