.....if you take some excerpts from:
www.uark.edu/ua/pirelli/testing/Unit2/CMwBang!10.htm
...thinking about a "modified" trebuchet (self-moving...playing short-long arm...) , as a gravity motor !?
Al_ex
.....if you take into consideration the following animation , at :
http://en.m.wikipedia.org/wiki/Orbit#/image/File:Orbit2.gif
It's about two bodies , with different mass orbiting a common barycenter...let's say , two celestial bodies in a continuous ( "perpetuum" ) motion .
Now , how about "...two bodies , with different mass orbiting a common fulcrum , with the barycenter's trajectory on the same side (semi-space ) of the fulcrum "?!
If we play variable / oscillatory leverage...can we obtain a continuous unbalance in a gravity field ?!
The lever ( as a rotating "seesaw" ) can play with a single variable arm .
Al_ex
.....if we take into consideration , as a starting point , a simplified test ( with the mechanical part , only...! ) , you can see at : https://m.youtube.com/watch?v=O6lKItCBB_8 (https://m.youtube.com/watch?v=O6lKItCBB_8)
The idea is to play the variable/oscillatory leverage, of two masses ( only! ) , in such a manner , so to obtain self-motion due to a continuous gravity unbalance ( torque difference on the same side of the fulcrum ) .
Al_ex