The first one, a two speed gearbox by Sariel, based on a 3 speed design by Misha van Beek
Another automatic design by Misha van Beek
Click Here to see it working
This gearbox by Zblj using 2 differentials switches between 1:1 and 1:5 gear ratios:
Sariel make a more compact version of this and published this two shots at facebook
From the same builder is this 3-speed "simple, yet effective gearbox, using a very unique design to change gears"
YotamPoleg show us in the first part of this video a real CVT gearbox:
Another interesting concept, this one is controlled by a centrifugal device:
And finally my own first prototype of automatic gearbox, mixing Misha and Zblj concepts, two differentials to switch between 1:1 and 1:5 gear ratios, and a third differential to unlock the 1:5 gears when more torque is need and lock it when less torque and more speed is wanted, also the 1:1 gears got anti-return device in order to prevent the stop of the entire gearbox.