The dynamics of an elongate multisegmented C-leg robot

Multi-legged elongate robots coordinate horizontal and vertical body waves with leg stepping to traverse diverse environments. Previous work [Chong et al 2023] demonstrated that a robophysical model with point-contact legs self-propelled via horizontal undulation and controlled leg slipping. Introducing a retrograde vertical wave further enhanced this frictional-swimming robustness on rugged terrain. Here we introduce SCUTTLE, a multisegmented robot with a new leg morphology, C-shaped legs that rotate in the sagittal plane. This platform displays in open loop significantly enhanced locomotion capability in challenging terrain. We study a five-segment robophysical model of SCUTTLE (BL = 80 cm) and characterize its dynamics on flat and rugose terrains, the latter defined by a flipped Gaussian height distribution (mean = 6 cm, SD = 2 cm). The C-shaped robot exhibits similar dynamics when replicating point-contact conditions by cyclic limb tapping. In rotary mode, rotation dynamics can modulate the number of legs in ground contact, enabling rapid transit of one BL per cycle, three times faster than point-leg swimming. While this contact modulation has little effect on locomotion over rugose terrain, introducing a horizontal body wave with appropriate phasing further enhances performance. Experiments also reveal that a direct vertical body wave benefits the system—speed increasing from 0.12 to 0.20 BL per cycle for leg-only gait—in contrast to the retrograde wave observed in the point-leg robot.