FlipWalker: Jacob's Ladder toy-inspired robot for locomotion across diverse, complex terrain

This paper introduces FlipWalker, a novel underactuated robot locomotion system inspired by Jacob's Ladder illusion toy, designed to traverse challenging terrains where wheeled robots often struggle. Like the Jacob's Ladder toy, FlipWalker features two interconnected segments joined by flexible cables, enabling it to pivot and flip around singularities in a manner reminiscent of the toy's cascading motion. Actuation is provided by motor-driven legs within each segment that push off either the ground or the opposing segment, depending on the robot's current configuration. A physics-based model of the underactuated flipping dynamics is formulated to elucidate the critical design parameters governing forward motion and obstacle clearance or climbing. The untethered prototype weighs 0.78 kg, achieves a maximum flipping speed of 0.2 body lengths per second. Experimental trials on artificial grass, river rocks, and snow demonstrate that FlipWalker's flipping strategy, which relies on ground reaction forces applied normal to the surface, offers a promising alternative to traditional locomotion for navigating irregular outdoor terrain.