Here are some pictures of the next steps:
For the second version I changed the traction, straightforward: it works good, the motors were powerful enough to level the plate form.
In the meantime I have made the third version of the base:
I relifted the plate form itself:
and used a different traction method with Technic Worm Screw:
but between the 'Technic Gearbox 2 x 4 x 3 & 1/3' and the 'Technic Gear' the tension was to high and it didn't worked: the gear jumped, this was not rigid enough and it didn't leveled the plate form. I will go back to a solution between version 2 and 3.
For more pictures see http://www.flickr.com/photos/51449863@N ... 841285633/
To be continued...