Multi-robot connection towards collective obstacle field traversal

Environments filled with large rocks and boulders can be challenging for legged locomotion. Inspired by ants collectively traversing obstacles through physical connections with each other, we study the locomotion performance of a group of "connectable'' robots over an obstacle field filled with half-cylindrical "boulders''. Each robot is extremely simple, with a cuboid body and one rotary motor actuating four vertical peg legs that move in pairs. The robots could connect to one another through the side of their cuboid bodies. Simulation results suggested that individual robots could not advance well within the obstacle field on their own (less than 0.75 body length (BL) over 15 stride cycles). However, by connecting to a neighboring robot, the two-robot system could begin to produce continuous displacement (up to 1.5 BL per stride cycle) across the obstacle field. Using an "obstacle disturbance selection'' framework, we modeled obstacle disturbances exerted on each individual robot leg as a function of obstacle inclination at the contact positions. The model suggested that by connecting to different neighbors, the two-robot system could produce collective translational or rotational movements through the utilization of obstacle disturbances.