The bouncing dynamics of inertial self-propelled particles reveals directional asymmetry

TL;DR

This paper investigates the bouncing dynamics of inertial self-propelled particles, specifically a hexbug robot, revealing how directional asymmetry arises from leg bending and can be modeled using a Brownian active particle framework.

Contribution

It introduces a combined experimental and theoretical analysis of active particle bouncing, highlighting the role of leg bending in directional asymmetry and employing a pulsed Langevin model for simulation.

Findings

Experimental validation of hexbug bouncing behavior

Successful simulation of motion using a pulsed Langevin equation

Identification of leg bending as a key factor in asymmetry

Abstract

This study aims to examine experimental conditions in which active particles are forced by their surroundings to move forward and backward in a continuous oscillatory manner. The experimental design is based on using a vibrating self-propelled toy-robot called hexbug, which is placed inside a narrow channel closed on one end by a rigid moving wall. Using the end-wall velocity as a controlling factor, the main forward mode of the hexbug movement can be turned to mostly rearward mode. We investigate the bouncing hexbug motion on both experimental and theoretical grounds. The Brownian model of active particles with inertia is employed in the theoretical framework. The model itself uses a pulsed Langevin equation in order to simulate abrupt changes in velocity that mimic hexbug propulsion in the moments when its legs make contact with the base plate. Significant directional asymmetry is caused by the legs bending backward. We demonstrate that the simulation successfully reproduces the experimental characteristics of hexbug motion after regressing the spatial and temporal statistical characteristics, especially when directional asymmetry is under consideration.