It's just a diagram, but it looks like it might be promising. I'm not a
mathematician or physics expert, so I haven't been able to do any
calculations to see why it won't work.
One thing that might need to be done is put air vents in the side of the
cylinders closest to the rotation axis for the air to enter and escape
freely; otherwise, their might be an air pressure problem. Of course, then
the space between the cylinders weights would need to be water tight.
If no one can figure out why it wouldn't work from the diagram, I'll try
building it. The design is pretty simple, so materials won't cost much.
I don't know about how efficient it would be to run a generator off of it.
It wouldn't rotate at a consistent rate (at first glance anyway). But some
kind of perpetual motion using gravity would be pretty interesting, anyway.
Adios.
-pb