SMoLBot-VS: A Soft Modular Robot Capable of Modulating Backbone Stiffness

Handling complex terrains is often problematic for miniature mobile robots due to their small size and low weight. Soft robots can utilize their compliance to overcome obstacles in the terrain, but their performances decline for tasks that require load-bearing capabilities. In this study, we present a miniature modular robot with tendon-driven variable stiffness backbones and investigate the effectiveness of the rigid and soft configurations for climbing obstacles and crossing gaps. The mechanism utilizes the design of a 3D-printed soft backbone with a layered structure that becomes rigid under compression applied by the linear actuator in the modules. In rigid mode, the robot can climb a 20mm step obstacle and cross a 105mm gap. In contrast, the soft mode obstacle height threshold jumps to 30mm, and the length of the gap that the robot can cross decreases to 55mm, showing that backbone stiffness modulation allows better adaptability for complex terrains.