Ratcheting and tumbling motion of Vibrots

Systems of granular rotors (Vibrots), that is, small devices that convert linear vibrational motion into rotation by frictional impact, are of scientific interest since they could reveal various types of collective behavior. Looking at an isolated Vibrot, we note at least two different dynamical modes, depending on the parameters of the vibrational driving. By means of finite element simulations, we reveal the driving mechanism for both cases which may be correspondingly identified as ratcheting and tumbling. The transition between both modes resembles period doubling in certain bouncing ball problems leading eventually to chaotic motion in such systems.