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  • Open Access

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

Thomas Kiechl1, Amy Altshuler2, Anton Lüders1,*, Yael Roichman2,3,†, and Thomas Franosch1,‡

  • 1Institut für Theoretische Physik, Universität Innsbruck, Technikerstraße, 21A, A-6020 Innsbruck, Austria
  • 2The Raymond and Beverly Sackler School of Chemistry, Tel Aviv University, Tel Aviv 6997801, Israel
  • 3The Raymond and Beverly Sackler School of Physics & Astronomy, Tel Aviv University, Tel Aviv 6997801, Israel

  • *Contact author: anton.lueders@uibk.ac.at
  • †Contact author: roichman@tauex.tau.ac.il
  • ‡Contact author: thomas.franosch@uibk.ac.at
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Phys. Rev. E 113, 045409 – Published 6 April, 2026

DOI: https://doi.org/10.1103/274x-4vgn

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.

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Phys. Rev. E 113, 045409– Published 6 April, 2026
  • Received 10 October 2025
  • Accepted 4 March 2026
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