After more tries on Tuesday, I found a way to flip the marbles vertically. I tried to use again the plastic part, without results. I make a huge comparison of all the configuration we tried before and at last, I shift a little the marbles from the coils, and with this, they flip in an easier way, even vertically, with a hole of 9.9mm. After finishing this, we can now concentrate on the PCB and the other problems of conception and programmation.
The shifted box is a box with the coils, a disk of metal, a 2mm plastic plank, a 3mm plastic plank (in green) with holes of 12mm of diameter, shifted of 5mm. This plank is at the level of the centre of the marbles. And at 7mm over the marbles, there is a plank of oak with holes of 9.9mm of 1.5mm of thickness.
I will publish a scheme of this on a next post.