Multi-robot connection towards collective obstacle field traversal

Environments with large terrain height variations present great challenges for legged robot locomotion. Drawing inspiration from fire ants' collective assembly behavior, we study strategies that can enable two "connectable" robots to collectively navigate over bumpy terrains with large obstacles. Locomotion experiments across an obstacle field filled with uniformly-distributed semi-spherical ``boulders'' shown that the connection length between the robots has a significant effect on collective mobility: connection length within 0.86 to 0.9 robot unit body length were able to produce sustainable movements across the obstacle field, whereas larger or smaller connection length resulted in low traversability. An energy landscape based model revealed the underlying mechanism of how connection length modulated collective mobility through the system's potential energy landscape, and informed adaptation strategies for the two-robot system to adapt their connection length for traversing obstacle fields with varying spatial frequencies. Our results demonstrated that by varying the connection configuration between the robots, multi-robot systems could leverage mechanical intelligence to better utilize obstacle interaction forces and produce improved locomotion.