The main design goal for this gearbox was to have a reliable and comprehensive gearbox with more than 2 gears. One thing that was very important was that the gearbox had to be able to handle a lot of torque. It had to be able to drive large Lego Technic models. Another aspect was that switching gears had to be very easy. First, the transmission itself is a double serial 2-way transmission, where one has a different gear ration compared to the other. Then I develloped a kind of switching-logic, where 1 M-motor would be able to switch 2 driving rings, each in either direction. For this I used differentials, 24z clutch gears and an inverter-mechanism which uses a sliding worm-wheel.
The instructions for the gearbox can be downloaded for free.n You’ll find them here.