As far as lifting or dropping the bridge goes, pnumatic cylinders much like the automotive hatch shocks could be used. It doesn't take much air to use them and they can lift a lot. A small compressor from a car with airbags likely wouldn't even need a tank. The fine reaction speed is as simple as an adjustable valve similar to that on fish tanks air lines. (try looking at Bimba cylinders. Try a Parker Store too. Get rebuildable ones if you can). Low volt control solinoids for pnumatics can be had too. (Mac was my fav, rebuilable) Pnumatics, various pressure valves, and flow limiting are what gives the better animatronics the lifelike movement characteristics, but with soft stops, etc. (when tuned right anyhow)
I like pnumatics because they are strong, yet not as destructive as a geared motor might be "worst case". Same limit switches, etc would apply. I'd only really consider a stepper motor in place of air.
Very nice depot.
