Reconstructing self-righting behaviors in centipedes via robophysics

Centipedes locomote by propagating body undulation and limb-stepping waves, but little is known about how they self-right after tipping from obstacle interaction, an essential biological skill to avoid predation and exposure. Here, we used a comparative biological and robophysical approach to understand centipede self-righting schemes. We released S. polymorpha (N = 3; length = 11.3 ± 0.9 cm) upside down from a 10 cm height and captured their self-righting using top and side view high-speed cameras. Kinematic analysis revealed two primary strategies: the “one shot” (all body segments roll at once) and the “sequential” (the roll propagates from end to end) strategies. We hypothesize that these behaviors can be prescribed by two traveling waves superimposed in the body’s lateral and vertical planes, respectively. We successfully reconstructed both self-righting behaviors on an elongate robophysical model with non-actuated limbs, obtaining a phase diagram for how two key wave parameters affect self-righting effectiveness: the spatial frequency, which characterizes the sequence of body-rolling, and the wave amplitude, which characterizes body curvature. Our results suggest that body motion is critical to effective elongate self-righting and that legs increase the necessary body amplitude.