An usual design...

[iacob alex]

.....starting as a general idea (relative motion between two points,bodies ) , you can see at :
     www.youtube.com/watch?v=tqUWUxjMaqU
A motion collector is a machine connected between a fulcrum/support (fixed point) and a process of change of position (mobile point ).
The up-down motion (fall) in gravity ,as a wave (on a sea-shore...)/fluid state of matter ,can express a suggestion for a gravity power collector as a pendular "wave motor"...if we consider a free falling inverted pendulum ,equivalent to a solid state gravity wave.
It can be the first "image" of a possible next to be "movie"...
     Al_ex