… after that title… I think the mechanic or engineer should be a class by itself.
here you can se a drawbridge
which would have a limited lenght and would requiere a power source to function, the best way to keep invaders out, a water wheel, which would be connected to a universal engine, which could recieve power from wind and water mechanical pieces and power machinery.
and lastly the pump.
the pump would be used to set traps as oil,magma or water traps as to move these resources arrounds with ease. for instance bring water up from a fixed source to be used in whatever is requiered.