Advanced turning maneuver of a multi-legged robot using pitchfork bifurcation

Legged robots have excellent terrestrial mobility for traversing diverse environments and thus have the potential to be deployed in a wide variety of scenarios. However, they are susceptible to falling and leg malfunction during locomotion. Although the use of a large number of legs can overcome these problems, it makes the body long and leads to many contact legs being constrained on the ground to support the long body, which impedes maneuverability. To improve the locomotion maneuverability of the robots, the present study focuses on dynamic instability, which induces rapid and large movement changes, and uses a 12-legged robot with flexible body axis. Our previous work found that the straight walk of the robot becomes unstable through Hopf bifurcation when the body axis flexibility is changed, which induces body undulations. Furthermore, we developed a simple controller based on the Hopf bifurcation and showed that the straight walk instability facilitates the turning of the robot. In this study, we newly found that the straight walk becomes unstable through pitchfork bifurcation when the body-axis flexibility is changed in a different way from that in our previous work. The pitchfork bifurcation not only induces the straight walk instability but also the transition into the curved walk, whose curvature can be controlled by the body-axis flexibility. We developed a simple controller based on the pitchfork-bifurcation characteristics and demonstrated that the robot can perform a turning maneuver superior to the previous controller based on the Hopf bifurcation. This study provides a novel design principle for maneuverable locomotion of many-legged robots using intrinsic dynamic properties.