Enhancing wet surface adhesion in walking robots: finite element-based analysis and morphology-changeable soft pads

In recent studies concerning walking robots, there has been a notable emphasis on investigating tribological phenomena and elucidating the role of capillary forces in tangential resistance. However, majority of these investigations have been restricted to specific geometric shapes, primarily spherical domes. In this research, we propose a novel approach based on the finite element method to address broader challenge of wet adhesion applicable to objects of various shapes. Additionally, we investigate the role of distributed domes on a soft foot in quantifying the tangential capillary force, which plays a crucial role in enhancing the performance of walking robots on wet surfaces. Through the optimization application, we identify that our designed foot (measuring 20 mm × 14 mm, comprising 78 domes with a radius of 0.5 mm and a distance of 1.5 mm between the two nearest domes) maximizes the value of the tangential capillary force. Moreover, we develop a finite element method using the Simulation Open Framework Architecture (SOFA) to model the interaction between wet liquid on a solid object's curved surface, enabling the calculation of wet adhesion force and capillary forces. Finally, to demonstrate the effectiveness of our proposed morphology-changeable soft pads foot, we conduct a presented a demonstration of a hexapod robot walking on different dry/wet condition of the surface. The obtained results are expected to pave a way to morphological design of soft pads for facilitating locomotion in various conditions. Supplementary video URL: https://youtu.be/yVteC95eqbo