The beaver ball: a chaotic rolling robot

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• Keith Moffatt (University of Cambridge)
• Thursday 30 November 2017, 09:30-10:10
• Seminar Room 1, Newton Institute.

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GFSW04 - Form in art, toys and games

Equations describing the rolling of a spherical ball on a horizontal surface are obtained, the motion being activated by an internal rotor driven by a battery mechanism. The rotor is modelled as a point mass mounted inside a spherical shell, and caused to move in a prescribed circular orbit relative to the shell. The system is described in terms of four independent dimensionless parameters. The equations governing the angular momentum of the ball relative to the point of contact with the plane constitute a six-dimensional, non-holonomic, non-autonomous dynamical system with cubic nonlinearity. This system is decoupled from a subsidiary system that describes the trajectories of the center of the ball. Numerical integration of these equations for prescribed values of the parameters and initial conditions reveals a tendency towards chaotic behaviour as the radius of the circular orbit of the point mass increases (other parameters being held constant). It is further shown that there is a range of values of the initial angular velocity of the shell for which chaotic trajectories are realised while contact between the shell and the plane is maintained. The predicted behaviour has been observed in our experiments.  

Work in collaboration with V.A.Vladimirov and K. Ilin

This talk is part of the Isaac Newton Institute Seminar Series series.

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