How do you plan on using this system in real life? A tripod on each end? In case you leave the middle free all the time I would consider adding an upside down T profile to the camera. The horizontal part would prevent the camera from tipping over in case of an unfortunate encounter. (Even though I assume the entire construction has its center of gravity on top of one of the long beams.
Anyway, I'll come back tomorrow to watch it. Any plans on adding a motor in some way?