  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 legs being constrained to
contact with the ground to support the long body, which impedes
maneuverability. To improve the locomotion maneuverability of such robots, the
present study focuses on dynamic instability, which induces rapid and large
movement changes, and uses a 12-legged robot with a 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 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 way different from that in our previous work. In addition, the
pitchfork bifurcation induces a transition into a 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 that with the
previous controller. This study provides a novel design principle for
maneuverable locomotion of many-legged robots using intrinsic dynamic
properties.
