I want to ultimately make the moving parts out of plexi but I made a prototype of one iris structure out of wood (because plexi is expensive!) and tried to hook it up to a servo. While the mechanism works by hand, albeit roughly, it does not work so well with the servo because of several reasons. 1. Material has a lot of friction. 2. The tolerances of the track on which it rotates needs to be tightened up a bit to decrease side to side movement. 3. The screws may be adding some extra friction from the threading.