Meeting Abstract
Analogous to fusiform shapes that reduce fluid-dynamic drag, terradynamically streamlined shape was recently discovered: cockroach’s ellipsoidal body shape facilitates body roll to slip through gaps between cluttered obstacles. Here, we hypothesize that there exists a broader range of terradynamic shapes that facilitate other modes of locomotion like turning and climbing in complex 3-D terrains. To test our hypothesis, we modified the body shape of the discoid cockroach (Blaberus discoidalis) by adding an oval and a rectangular shell to its back, and studied how it traversed vertical pillars. To efficiently obtain statistically meaningful data, we developed an automated system to motivate the animal to run through terrain modules and capture videos for 3-D kinematics analysis. Cockroaches with an oval shell traversed round and square pillars within 0.4 ± 0.2 s and 0.4 ± 0.2 s, significantly more quickly than those with a rectangular shell within 1.6 ± 0.7 s and 2.9 ± 0.7 s (P < 0.001, ANOVA). We discovered that an oval body shape facilitated body yawing while a rectangular body shape facilitated body pitching. Upon colliding with and pushing against the obstacle, animals with an oval shell always turned away from it (100% probability for both round and square pillars). By contrast, animals with a rectangular shell more often turned towards the obstacle (70 ± 17 % for round and 91 ± 7 % for square pillars). In addition, animals with a rectangular shell pitched up more often and (27 ± 14 % for round and 43 ± 16 % for square pillars) than those with an oval shell (18 ± 17% and 24 ± 19 %) (P < 0.001). We developed a locomotion energy landscape model to begin to explain our observations. Our study provides inspirations for robots to use morphing shapes to traverse obstacles in challenging terrains like building rubble.
