Tevo Tarantula Ultimate 3 carriages bed support

Why 3 carriages?

At the beginning of the month, as I wasn't pleased by the original Tevo design (4 wheels, 4 points leveling), I have developped and submitted a first bed support (https://www.thingiverse.com/thing:2810808)
Even though it improves leveling, it still has a major flaw : the huge ovehang of the arms from the wheels. I couldn't imagine any simple and cheap solution to overcome the fact, that the arms need to extend 210mm from each other in both direction, whereas the wheelbase is only about 100mm...

Therefore, I have thought a bit for a solution and have come to this conclusion : if you want a very stiff design, you need to get rid of the bed support itself and directly support your bed with 3 small carriages, independant from each other.
I think it will be a pretty stable design, without needing to buy an aluminum bed support.

You'll need to build the carriage components 3 times (main block, setting block, bull gear, thumb wheel) and the structure components 2 t