.....or a rotating pendulum with a pulsatory hub,can be an elementary "self-device" that is possible to work due to gravity fall.
A well known pendulum (pivot-rod-bob ),free to fall from the top/vertical line/ position ,can turn around the pivot ,no more than 330* (due to friction).
The first idea that comes into mind :with a little "help" (incipient velocity or something else...),it can make as real a full turn (360*).
So,to be a self-turning pendulum ,it needs every period ,this small "help"...nothing more.
This "little help" can be introduced by a pulsating hub,that plays recurring at regular intervals,a centric-eccentric game.
Then,the proposal is:
-bob
-rod
-pulsating hub,that performs as a whole as an additional,90* shifted pendulum/eccenter for a 180* sequence,only. For the next 180* sequence,the hub is simply a rotating centered mass,with stored inertial potential...
All the best for the 2010 New Year ! / Alex