Lattice transport via mechanical intelligence in undulatory locomotors

Limbless locomotion emerges across length scales and within complex environments. Theoretical and robotic models have emphasized body kinematics and neuro/electronic control, but these approaches are far from reproducing the performance of even seemingly simple limbless organisms like tiny nematode worms. Our observations of nematode locomotion in obstacle lattices suggest that many collision-instigated behaviors occur passively, thus we hypothesize that the bilateral muscle actuation mechanism provides favorable passive mechanics for heterogeneity navigation. To test the hypothesis, we implemented the bilateral actuation morphology in a limbless robophysical model (L=86cm, W=7cm), and the limbless robot demonstrated unprecedented open-loop mobility (high speed, low energy cost) in lattices (40cm, 20cm, and random spacing) that approaches nematodes. The limbless robot also displayed analogous passive behaviors as we observed in nematodes. The highly damped nature of the locomotion allows the meter-scale robot model to reveal the importance of mechanical intelligence in C. elegans in complex environments. We further implemented a nematode mechanosensation-inspired closed-loop strategy that reinforces the robot's inherent mechanical intelligence and augments locomotor performance. Our robophysical approach suggests a fruitful modeling approach to understanding the relative roles of mechanical intelligence and active control in limbless animal behavior and neurobiology.