a moter for raising bridges and drawbridges.(winds cable in when boat is about to go lets cable out after boat is passed).
Hinges for drawbridges. and vertical tracks to keep raising bridges from swinging around once they are hoisted up.
and last. curcular tracks and turning motors for swinging bridges.(note: swinging bridges are bridges that turn to allow ships through rather than raising. this saves a lot of energy for the small bridges.)