The structure will be mostly in aluminium, with square profiles, i studied the capabilities of this kind of structure and it can work fine. i solve the problem with the horizontal movement with a set of cilindrical aluminium profiles, exactly with 7 of 20 mm of diameter and 6 of 10 mm, i choosed this solution because it is cheaper than a large cilindrical profile and has much more strenght, this set will be joined with 3d printed part and holded by 3 bearings, 2 lazy susan with an 80mm diameter and 1 to support the vertical force, in those 3 images you can see the system.
The first one, is a 2d sketch, the possition of the profiles. The blue circle marks the limit of the 3d cover.
second one, you can see the cover, with 7 circular profiles of 20 mm
and 6 of 10 mm, all the profiles will be empty so i will pass alt he
cables to the rest of the arm by the central one.
this image you can see the central column with a bearing, i choose a
lazy susan with 80 mm of diameter, and it will be holded to the
structure by a 3d piece(the red one) and some square profiles of 16 mm.
is the motor of the horizontal movement, with 3d printed gears, under
the central column there is an encoder so i can know the position.