Investigation of efficient creeping locomotion for snake-like robots with compliant passive joints

Snake-like robots leverage their slender bodies to navigate confined spaces by coordinating the multiple actuated joints, which enable effective movement through constrained pathways. However, their high degrees of freedom in fully actuated systems engender significant challenges in reducing energy consumption. To address these challenges, this paper derives insights from the muscle functions of biological snakes and investigates the integration of compliance passive joints into snake-like robots, with the aim of enhancing locomotion efficiency. Passive joints, equipped with torsional springs, facilitate indirect actuation through energy storage and release. Under such background, we propose a dynamic model to investigate the influence of passive joints on locomotion performance. Simulations are utilized to analyze the effects of varying spring stiffness beyond experimental constraints. To facilitate systematic validation, a modular snake-like robot is designed. It allows flexible joint configurations, reassembly, and adjustable joint placements. Additionally, passive joint mechanism is refined to eliminate the requirements for motor gear reconfiguration, thereby improving experimental adaptability. The proposed model is evaluated through simulations and experiments to investigate the effects of joint stiffness on locomotion speed, while energy efficiency is analyzed experimentally. The results reveal that appropriate stiffness parameters significantly enhance motion efficiency. Moreover, the placement of passive joints plays a key role in the robot’s motion performance. Among all configurations, a compliant passive tail joint with an appropriate spring setup achieves the best performance. It increases motion speed by 26.8% and reduces energy consumption by 52.2%. These findings provide insights into the role of passive joints in snake-like robots, potentially contributing to future design improvements in locomotion efficiency and adaptability.