Trapped active toy robots: theory and experiment*

We characterise the diffusion, mean-square speed, mean-square angular displacement, radial and speed probability distributions of toy robots called ’hexbugs- nano’ that move on a dish antenna simulating a harmonic well. We notice that a semi- overdamped model suffices to describe the robots’ dynamics and that a self-aligned mechanism of their orientation vector toward their velocity does not reproduce the experiments. Instead, the inclusion of a constant external torque in the orientational dynamics provides a more appropriate description. Langevin dynamics simulation are also performed and a good agreement between theory, simulations and experiments is observed. Manufacturing differences between hexbugs-nano are also seen to affect the experimental measurements.