Elementary Slender Soft Robots Inspired by Skeleton Joint System of Animals.

In this article, we demonstrate elementary slender soft robots mimicking the skeleton joint system of animals with excellent locomotion performance and scalability. Inspired from bending characteristics of mammal joints, the soft joint, consisting of two Pneu-nets (PNs), one with three chambers and the other with two chambers, was developed. By using simple constraints and connections, the soft joint can be separately controlled by 180° bending and unbending, and exhibits large force output with limited volume and deformation. Then, a skeleton joint-like slender robot was proposed by including a different number of the soft joint and stiff skeleton for different functionalities. This robot exhibits excellent locomotion performance due to the skeleton joint design to achieve large deformation level and proper selection of gait to fully utilize the skeleton joint-like motion, that is, moving 0.5 body length per loading cycle and navigating both continuous terrains, such as a slope, and unprecedented terrains with "discrete" obstacles, such as a wall and stairs. Besides, the slender soft robot is scalable in joint and skeleton, and additional tuning joints can be introduced to achieve turning and spinning locomotion. The slender robot presented herein has not only the advantages of simple fabrication, light weight, good adaptability and scalability, and human-friendly interface but also provides insights for future development of mobile soft robots.