Four things required for any gravity power device to work

[brian334]

1. On the down side the object must be heavier than the same object on the up side.
2. At the bottom the object must change from being heavier on the down side to being lighter on the up side.
3. On the up side the object must be lighter than the same object was the down side.
4. At the top the object must change back from being lighter on the up side to heavier on the down side.

[TinselKoala]

You're forgetting about moment arms. Even if the object on one side is heavier than on the other side, if the moments about the center of rotation are not correct the device still won't rotate.

http://www.lhup.edu/~dsimanek/museum/physgal.htm

[brian334]

Cola,
That is daum.

[Digjam]

yep it's amazing how that little thing called "equilibrium" tends to get in the way

[pequaide]

It is a function of time. If the same mass (upon which gravity applies a force) takes longer to fall than it does to rise then you have an energy producing machine.