...can be made,after you watch carefully a short movie on youtube.com ,more exactly at:
http://www.youtube.com/watch?v=hl8dM2wQBk&feature=related
It's a classic design in the old manner of the "old PM folklore"...
Now let's simplify it,so to use the "essence idea" :
-take only one simple hinged arm (spoke)
-move the rotating axle of the hub...not having,this time the axis placed centrally,so to get a "self pulsatory lever" equivalent (fixed arm/eccentric hub vs. pulsatory arm/simple hinged mass).
If you like ,take this as a "flapping fish" in two "surroundings"(gravity flow and rotational inertia).
It can be a simple mobile "toy" ...or maybe more...
All the best! / Alex
...sorry about the wrong address...
So,try again at: http://www.youtube.com/watch?v=hl8dM2wQB4k&feature=related
All the best ! /Alex