58.4 Thursday, Jan. 5 Disturbed ground leads to failure in a sea turtle inspired robot MAZOUCHOVA, Nicole*; GOLDMAN, Daniel; Georgia Institute of Technology; Georgia Institute of Technology firstname.lastname@example.org
Animals like sea turtles that must locomote at the water-land interface use flippers for swimming in water and crawling on a sandy beach environment. To reveal locomotor principles of flipper-based interaction with granular media, we study the detailed mechanics behind the success and failure of a hatchling sea turtle-inspired robot (19 cm, 775 g) during quasi-static movement on a granular medium of poppy seeds. The device propels itself with a symmetric gait using two servo-motor driven limbs consisting of flat-plate flippers with passively flexible or rigid wrists. For a wide range of conditions a flexible flipper achieves a greater distance traveled per step than a rigid flipper. For the flexible flipper, at each step the limb penetrates vertically into the medium; once weight balances penetration force, the body lifts. The flipper remains in place, and as the limb retracts the robot is geometrically translated forward. During the step the belly remains lifted off the ground minimizing drag. In contrast, during rigid flipper locomotion, the penetration phase is similar, but the material begins to yield during retraction of the flipper as it slips through the material. Associated with the yielding, the body drops immediately during the step, and drag force increases. The rigid flipper creates a larger region of disturbed material than the flexible flipper. If subsequent steps interact with the previously disturbed ground, forward progress per step is decreased resulting in failure within a few steps. Measurements of intrusion force on a flat plate (3 cm wide) reveal that the penetration resistance (and thus lift) on a second intrusion decreases as the intrusion site approaches the site of first intrusion.