The genius of those rockers consists in using both gravity and momentum. The
marbles fall on the rocker and are deflected such that in the beginning they
roll *upwards*, the rocker tips after that. The falling height of the marble is
critical, too little and it won't climb, too much and it might bounce back.
There is an inverted V slope behind the little rectangular 'guard' on top of
each rocker. That 'guard' is a side-plate which prevents the marbles from
falling off of the inverted V behind it.

Peter


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