Concerning the big megawatt wind turbines, if there is such a big trouble with gearbox bearings failing much earlier than expected and costly maintanence or replacement of huge gearboxes, what is keeping people from placing the whole power unit(gearbox, generator, transformer, etc.) down on the ground, connecting the gearbox and turbine rotor with a chain-sprocket drive?
With a belt or chain ,a certain margin of flexibility would compansate for misalignment of axis and absorb shock loads. Apart form delivery time, replacement of damaged parts would take much less time and effort.
Continuously variable transmission systems are already being adapted to wind turbines so such a drive should not be an unrealistic option. Turbines with hydraulic drives are already being built with down tower power units.
I know this would have been done if it had more advantages but what is the big disadvantage here that overcomes such a saving of time and cost?