Resonance-regulated stick–slip locomotion in a dual-soft-legged vibratory robot

Inspired by the bristle-like anisotropic structures of foxtail grass, this Letter presents a dual-soft-legged vibratory robot that exploits frictional anisotropy to generate directed locomotion driven by a single eccentric motor. The interaction among structural deformation, eccentric inertial excitation, and tangential friction enables transitions among multiple locomotion states. A reduced dynamic model is then developed to couple forward translation, heave, and pitch rotation with Coulomb friction under unilateral contact. Numerical simulations identify different locomotion states governed by soft-leg stiffness and excitation frequency, including stationary, slow-forward, intermittent, transitional, and high-speed forward states. Experiments validate the results and show that the measured displacement arises from repeated stick–slip transitions. An implicit critical equation derived from the simplified dynamic model captures the onset boundary between stationary and moving states, while the resonance curves closely align with the characteristic regions in the numerical state map. This agreement reveals that locomotion emerges from the interaction among eccentric inertial forcing, dynamically modulated friction thresholds, and resonant structural response. This work establishes a physical framework for a friction-driven vibration mechanism and provides insight into the use of structural resonance for tunable stick–slip locomotion.