Meeting Abstract
Mudskippers and salamanders can both swim and navigate outside of the water. We wish to understand how limbs and body morphology contribute to performance, particularly in the evolution of animals that use multiple modes of locomotion. Here we study a fire salamander (S. salamandra) to understand the coordinated movement between the flexible body and limbs. Experiments (10 adults, 5 trials each, varying inclines and presence/absence of sandy surface) revealed that salamanders propelled themselves using diagonal leg pairs and body undulation. To investigate mechanisms governing effective locomotion, we built a robophysical model and tested its performance on hard ground (HG) and yielding granular media (GM) of poppy seeds of different inclinations. Our servo-driven robot (430 g, 38 cm long) has four limbs, a flexible trunk, and an active tail. Each limb has two motors to control vertical position and step size of limb. A joint in the middle of the body controls horizontal bending. We assessed performance of the robot by measuring body displacement over a few limb cycles. On HG at 0o and 10o slopes, the robot performed well; feet did not slip and body bending increased step length (SL) by ~50% (on level) and ~1% (on 10o slopes ). On GM, the robot’s SL decreased by ~40% (on level) and ~80% (on 10o slopes) relative to that on HG due to limb slip. Back bending restored performance on GM, leading to SLs only ~20% (on level) and ~25% (on inclined) less than those on HG. A geometric mechanics model revealed that on level GM media body bending was most beneficial when phase offset 180 degrees from leg movements.
