Meeting Abstract
Epimorphic centipedes running at high speed display a characteristic body undulation. Elucidating the interplay between body and limb waves and the resulting running performance is difficult because of the many degrees of freedom in the flexible body and numerous limbs. We characterized the body undulation and the limb stepping wave using amplitude and wavenumber, and captured the coordination by the relative phasing between the two waves. We used geometric mechanics (e.g. Hatton et al., PRL, 2013), in which inertial effects were assumed negligible, to model and predict the locomotion performance of a centipede with 19 leg pairs and body joints. Our theory predicted that the body-lengths traveled per cycle (BLC) was maximized when the body undulation (with 1.6 waves, maximum body curvature = 0.42 BL^(-1)) had a phase 2.51 rad ahead of the leg wave (with 2 waves, maximum leg joint angle 0.65 rad ). At this phase offset, the theoretical prediction of centipede speed was 0.40 BLC, compared to 0.25 BLC with no body undulation and 0.10 BLC with worst body undulation. Using high-speed video, we captured the motion of five trials of centipede (Scolopendra polymorpha , 19 leg pairs) running on a treadmill and tracked the position of each leg and body. The centipedes ran at 0.41±0.05 BLC with a leg-body phase offset of 2.51±0.71 rad, in good agreement with our best-performing theoretical prediction. The good agreement indicated that our geometric approach can capture the kinematics of centipede locomotion without including inertial effects. Further, our results revealed that body undulations enhanced running performance, but only if the body and limbs were properly coordinated.
