Multi-Functional Granular Propulsion: Bio-Inspired Orientation Control and Local Fluidization for Crawl-To-Dig Transitions

Abstract

Existing robots designed for locomotion in granular media typically excel at a single purpose—either surface travel or subsurface digging—while lacking the ability to perform both within the same platform. In contrast, nature offers various examples of burrowing organisms that exhibit multi-functional digging behaviors by separating their body into two essential parts: a digger for substrate intrusion and rest of the body as anchor for stabilization and controlling digger orientation. Inspired by these biological strategies, we present an extension to an existing Screw Propelled Vehicle (SPV) that incorporates an adjustable body anchor to reduce drag and enable orientation control. This integration allows the robot to transition between horizontal crawling and vertical digging. We also investigate the effect of local fluidization (LF), a bio-inspired technique that temporarily reduces the resistive forces in granular media. Experimental results show that integrating LF improves surface propulsion performance in terms of speed and depth with increment of over 5x compared to the baseline configuration. These findings support the hypothesis that bio-inspired design principles—specifically body–anchor separation and local fluidization—significantly enhance both the functionality and efficiency of granular locomotion robots, providing a pathway toward more versatile, autonomous, and high-performance subsurface exploration.