Meeting Abstract
76.5 Sunday, Jan. 6 Principles of flipper use during walking on flowing ground MAZOUCHOVA, N.; UMBANHOWAR, P.B.; GOLDMAN, D.I.*; Temple Univ.; Northwestern Univ.; Georgia Tech daniel.goldman@physics.gatech.edu
Animals, like lobe-finned fishes, likely first walked on wet sand and mud. In the evolutionary transition from aquatic to terrestrial locomotion, the rheology of limb (fin) interaction changed from slipping through fluid to pushing against materials that can be fluid or solid. Locomotor strategies thus changed as bodies and appendages shifted from generating thrust during swimming to generating both lift (to maintain posture and reduce ground contact) and thrust (to propel the body). However, as little is known of the biomechanics of walking/crawling on soft substrates, detailed hypotheses for how limbs and control strategies adapted to these substrates are lacking. To discover principles of flipper/fin based terrestrial locomotion, we study a sea turtle-inspired robot, FlipperBot (FBot), during quasi-static movement on dry granular media. FBot implements a symmetric gait using two, servo-motor driven front limbs with flat-plate flippers and either freely rotating or fixed wrist joints. For a range of gaits, FBot moves with constant step length. For gaits with sufficiently shallow flipper penetration or sufficiently large stroke, step length decreases with successive steps resulting in failure after a few steps. The biologically inspired free wrist is less prone to failure than the fixed wrist, largely because it does not yield material and can thus maintain FBot’s base above the surface. Failure occurs when FBot interacts with ground disturbed during previous steps; measurements reveal that flipper forces decrease as step length decreases. When step length is constant, models provide insight into how disturbed ground leads to locomotor failure. We hypothesize that the evolution of limb morphology (like a flexible wrist) and control strategies in terrestrial locomotors was influenced by flowing substrate rheology.
