Ok, I see! What do you want to put on the planes? The upper box, during its rotation, could go into collision with the object that you'll put on the second floor (second box). The same problem is even for the second box that collides with the objects in the first floor. Have you studied the trajectories of the boxes during their rotational movement? Have you considered a sort of envelop space? Once you have this space you have to be careful not to put objects in it. I hope you understand me...i'm so sorry for my english.