Delays caused by other work have held up construction. The control box and stepper motors have been tested and work well. The overhead bars (the original plan) do not. There is too much bounce, and the plan to use threaded rod was not a good idea. 10mm threaded rod moves 1.5mm per turn, which would make for a very slow dolly. It also has problems with backlash. Instead, the bars will be shortened to 2m and mounted on a base. A 1500mm ballscrew (16mm dia x 5mm lead) will control the dolly. This modification will also enable the whole rig to be moved and positioned, a definite advantage over the ceiling mounting.