Meeting Abstract

147.4  Monday, Jan. 7  Sensitivity of foot intrusion kinematics during walking on granular media KINGSBURY, M A*; GATESY, S; GOLDMAN, D I; Georgia Institute of Technology; Brown University; Georgia Institute of Technology mkingsbury3@gatech.edu

Many long-legged organisms walk across granular media (GM), substrates whose properties depend on compaction state and disturbance history. Previous studies of a short-legged hexapedal robot [Li et al, PNAS, 2009], revealed that mobility was sensitive to timing of limb kinematics. However, limbs were short, feet were not biologically realistic (compliant c-shapes) and spatial kinematics were fixed. To begin to understand the role of foot kinematics on locomotion performance of long-legged locomotors, and to simplify analysis, we study walking in a bipedal robot (39 cm tall, 1.6 kg) moving on a GM of poppy seeds. Each leg is composed of 4 motors connected by segments which mimic avian limb morphology. Its feet are flat disks (diameter 9.2 cm), and toe tip trajectories and foot angle can be varied. The robot uses an alternating striding gait in which toe tips trace rectangular trajectories in the body frame. The robot is constrained by bearings that allow horizontal and vertical motion, but do not allow body rotation. We used an air fluidized bed to create loosely packed GM with volume fraction (the ratio of solid to occupied volume) φ=0.58, and closely packed GM with φ=0.63. We examined the role of the foot angle θ (defined as the angle of the foot relative to horizontal throughout its gait) in a range of -8<θ<15°, with positive defined as the toe tip protruding from the GM. Despite its long limbs and large feet, robot performance was remarkably sensitive to θ and φ: forward speed in φ=0.58 was low (1.2 cm/sec) for θ<8° and increased by a factor of 2 as θ increased to 15°. For φ=0.63 speed was as low for θ<0, but increased by a factor of 3 as θ increased to 0°, after which speed was insensitive to θ.