Swarm Robotics

Lateral contact yields longitudinal cohesion in active undulatory systems

Overview: This project investigates how undulatory swimmers, such as three-link robots in experiments and multilink swimmers in simulations, interact through contact to achieve stable collective behavior. By varying the phase offset between neighboring swimmers, the study examines how contact forces and spatial configurations emerge. Results show that undulatory motion naturally drives swimmers into stable planar arrangements, leading to the development of a “gait compatibility condition” that predicts collision-free configurations. Simulations further reveal attractive interaction forces that guide swimmers toward compatible states. These findings highlight the role of undulatory phase coherence in forming cohesive and stable active-matter swarms.

Link: Video

Proprioceptive feedback design for gait synchronization in collective undulatory robots

Overview: This project explores how undulatory robots achieve collective gait phase synchronization through contact interactions, inspired by the collective movement of animals. In high-density environments where visual and auditory sensing are limited, mechanical contact becomes a key interaction mechanism. The study demonstrates that synchronization emerges without direct communication, relying instead on a proprioceptive feedback control system. A simplified toy model validates the control approach, while simulations and experiments with three-link robots further illustrate controlled phase synchronization. Finally, experiments show that synchronization enhances locomotion efficiency in confined spaces, highlighting its potential benefits for swarm robotics applications.

Link: Video

Collective synchronization of undulatory movement through contact

Overview: This project investigates how undulatory swimming robots synchronize their movement through physical contact interactions. While biological systems often synchronize through fluid interactions, increasing density leads to direct contact, which can influence collective motion. Through experiments and simulations with simple undulatory robots, we demonstrate that contact-based interactions drive phase synchronization, with in-phase and antiphase oscillations emerging in pairs. Larger robot collectives also exhibit synchronization, but antiphase modes disappear when positional adjustments are allowed. Synchronization significantly reduces interaction forces within confined groups, highlighting potential energetic and safety benefits. This work provides insights into how contact interactions shape collective motion in undulatory active matter systems.

Link: Video

References

• Zhou, W., Peralta, J.D., Hao, Z. and Gravish, N., 2022. Lateral contact yields longitudinal cohesion in active undulatory systems. Physical Review E, 105(5), p.054604. (Article link)
• Hao, Z., Zhou, W. and Gravish, N., 2022. Proprioceptive feedback design for gait synchronization in collective undulatory robots. Advanced Robotics, 36(13), pp.654-669. (Article link)
• Hao, Z., 2021. Design principles for locomotion synchronization in undulatory robot groups. University of California, San Diego. (Article link)
• Zhou, W., Hao, Z. and Gravish, N., 2021. Collective synchronization of undulatory movement through contact. Physical Review X, 11(3), p.031051. (Article link)
• Hao, Z., Zhou, W., & Gravish, N., 2021. Synchronized swimming: adaptive gait synchronization through mechanical interactions instead of communication. In The 9.5 th International Symposium on Adaptive Motion of Animals and Machines (AMAM2021) (p. 55). (Article link)