Bed_Hoist_for_a_3D_Printer_ (D-Bot, Core_XY)

Edit (11-08-19): today published Bed Hoist for a 3D Printer - Final Version,
https://www.thingiverse.com/thing:3732450
Edit (14-02-19): today published Bed_Hoist_for_a_3D_Printer_ (D-Bot, Core_XY)_-_Version_2, www.thingiverse.com/thing:3427719.
That version 2 supersedes this one, because it is simpler: 1 belt, simpler parts.
No solution for the 2 mm-wave-error yet, though.
For a time I worked with one hoist and belt in this first version and that went ok, even somewhat better than with 2