Meet NeRemo, the robotic mouse with a flexible spine

A flexible spine

The robot's spine, comprised of eight ball-and-socket joints, is driven by a tendon-pulley system that emulates muscle contraction. The robot also has compliant knee and elbow joints that provide a realistic replication of rodents' musculoskeletal anatomy.

They showed that NeRemo could increase its static stability by adjusting its posture using the lateral flexion of the spine. They also showed that the spine could effectively extend the stride length of a gait and, therefore, improve NeRemo's walking speeds. 

Lastly, they showed that NeRemo could perform agile maneuvers that require both a small turning radius and fast walking speed with the help of the spine.

The researchers said their work advances the understanding of spine-based quadruped locomotion skills and highlights promising design concepts to develop more agile-legged robots. They also said that their robot could be used as a platform to study the neural control of spine-based locomotion in animals. 

Flexible spine system replicating the biological counterpart

The researchers also explained why a flexible spine system replicating the biological counterpart's features has excellent potential to push the physical performance limit of legged robots.

They said that although various excellent-legged robots have been developed in the past, they mainly concentrate on leg-based motor skills that lead to stable walking performances on diverse terrains, such as stairs, tunnels, or wild lands. Because of their powerful actuation systems, they can already perform limited dynamic behaviors relying only on their legs. 

However, using a functional spine will further improve motion capabilities, especially for small quadruped robots underpowered by size limitations.

They said few detailed investigations of legged robots equipped with flexible spines have been conducted. A few examples explore the spine's functionalities in simulation or implementing somewhat simplified spine systems with one or two revolute joints. 

They mentioned several robots that have utilized the spine to enhance their movement, including Boston Dynamics' Cheetah robot, EPFL's Bobcat robot, the Waseda rat robot and its successors, the Kitty robot, the Gecko robot, the Slalom robot, and the Salamander robot.

However, they also acknowledged the drawbacks of these robots, such as the absence of leg actuation, the use of wheels instead of legs, the intricacy of the spine mechanism, or the challenge of regulating spine flexion.

To overcome these challenges, they developed NeRmo, a biomimetic mouse robot that harnesses a flexible spine for agile motion skills.

As an underactuated quadruped robot, NeRmo aims to mimic the structural and functional principles of the mouse and, therefore, the features of its flexible spine, musculoskeletal actuation systems, and fully functioning body.  

They said their robot could be further improved by adding more degrees of freedom to the spine and the tail and implementing more complex neural controllers to generate adaptive and robust motion patterns. They also said their robot could inspire new applications in search and rescue, exploration, entertainment, and education.

The study was published in the journal Science Roboticson December 6.