Free chiral self-propelled robots compared to active Brownian circle swimmers

TL;DR

This study compares the motion of free chiral robots to active Brownian circle swimmer models, validating the models' effectiveness in describing macroscopic active matter dynamics.

Contribution

It demonstrates the good agreement between experimental hexbug data and overdamped Langevin models, highlighting their robustness and limitations.

Findings

Good match in mean-squared displacement and ISF between experiments and models.

Deviations mainly occur in short-time propagator behavior due to translational noise.

Supports using overdamped Langevin models for macroscopic active matter when noise is minimal.

Abstract

Macroscopic active matter systems, such as bristle bots, provide a compelling platform for investigating nonequilibrium dynamics at highly visible scales. To fully leverage their accessibility, accurate mathematical models are needed to corroborate experiments. In this work, we study the motion of a free chiral hexbug (Nano-Newton Series) via video tracking and compare the results to theoretical predictions from overdamped Langevin equations for active Brownian circle swimmers (ABCs). We find good agreement between the hexbug's dynamics and ABC model predictions, particularly for the mean-squared displacement and the intermediate scattering function (ISF). Deviations between the hexbug data and the ABC model arise primarily in the short-time behavior of the real-space propagator, where translational noise is most evident. Our results generally support the use of models based on overdamped Langevin equations as a robust framework for describing hexbug motion when the influence of translational noise is negligible. Moreover, they demonstrate the sensitivity of ISF- and propagator-based analyses in characterizing active systems. Our approach opens new avenues toward refining coarse-grained models and advancing the theoretical understanding of macroscopic active systems.