Body-Size Effects on Ω-Shaped Locomotion Performance of Cable-Driven Soft Robots

Inchworm-inspired soft robots generate Ω-shaped crawling through alternating end anchoring and whole-body bending, providing a simple locomotion strategy based on coordinated body deformation. Since the entire body deforms during each cycle, crawling performance may vary with robot size. This study investigates the influence of body size on the Ω-shaped locomotion of cable-driven soft robots through a comparison of two approximately geometrically similar prototypes. Two prototypes with body lengths of 145 and 235 mm were built, each with a slotted silicone body, three motor-driven cables sequentially bending the head, abdominal, and tail sections, nano-adhesive pads at both ends, and programmable control boards activating the motors in a preset sequence. At matched nominal motor-and-drum settings, both robots achieved an absolute crawling speed of approximately 1.43 mm/s, whereas the body-length-normalized speed of the smaller robot was about 1.63 times that of the larger one. The measured relative strides were 0.105 and 0.112. A conditional kinematic analysis relates preset timing and measured stride to crawling speed; across five nominal settings, the finite-difference gain ratios ranged from 1.41 to 1.98, with a mean of 1.67. The smaller tested robot attained a higher body-relative speed under the tested nominal settings; body and adhesive-pad scaling remain coupled in this two-specimen comparison.