Meeting Abstract

5-1  Saturday, Jan. 4 08:00 - 08:15  Animals and robots transition from more challenging to easier locomotor modes to traverse obstacles OTHAYOTH, R*; THOMS, G; LI, C; Johns Hopkins University

Animals transition between multiple locomotor modes when traversing obstacles in complex terrain. However, the physics of such locomotor transitions are not well understood. Previous studies in our group of grass-like beam obstacle traversal observed that the discoid cockroach often pitches up when initially interacting with the beams (pitch mode). To traverse, the animal then either continues pushing down the beams with sustained pitching, i.e., continue to use the pitch mode, or transitions to roll mode by rolling the body into the gap between the beams. Curiously, whether the animal continues to use the pitch mode or transitions to the roll mode depends strongly on the stiffness of the beam obstacles. Here, we tested a robophysical model traversing beam obstacles with different stiffness and developed a potential energy landscape to understand these animal observations. We found that the system states were always strongly attracted to local minima basins on the potential energy landscape. Regardless of beam stiffness, the system was always more likely to transition from more challenging (higher minima) to easier locomotor modes (lower minima) on the landscape. At lower beam stiffness, the pitch local minimum was lower than the roll local minimum, i.e., the pitch mode was easier. Thus, pitch-to-roll transition did not occur. As beam stiffness increased, the pitch local minimum became higher than the roll local minimum, making the roll mode easier. Thus, the system was more likely to transition to the roll mode. These results from robophysical experiments were consistent with our animal observations. Our study revealed the physical principles governing the direction of locomotor transitions in complex terrain and is a step in establishing energy landscapes for locomotor transitions.