This was a very nice engineering project - a rig to open up a small section of a huge 15 x 9m LED screen, allowing a 30W laser to be fired through.
After initially considering a curved rack and pinion, a cable-driven method seemed a better approach, as it would keep the mechanism out of the way of the laser as much as possible.
The control box has a motor with a 3000:1 reduction gearbox, which moves an arm connected to an ultra-flexible 133 strand 1.5mm diameter steel cable. The arm has a built in cam that activates a limit switch 19mm before decelerating to a stop. An electronic braking system could have been implemented, but the T-shaped cam seemed a much gentler method.
The control box responds to DMX, with the address set via DIP switches.
Big thanks to Toby, James, Nilkanth and Marcus.
This project was for the Chemical Brothers (not to be confused with the Bohman Brothers).