Meeting Abstract
41.1 Sunday, Jan. 5 10:15 Towards a terradynamics of heterogeneous granular media QIAN, F*; ZHANG, T; GOLDMAN, DI; Georgia Tech; Georgia Tech; Georgia Tech qianfeifei1114@gmail.com
Recently, we have made progress in understanding aspects of legged locomotion on flowable ground [Li et al, Science, 2013], proposing a “terradynamics” for movement on homogeneous granular media. However, many substrates are composed of particulates of varying size, from fine sand to pebbles and boulders. Locomotion on such heterogeneous substrates is complicated in part due to fluctuations introduced by heterogeneities. To systematically explore how heterogeneity affects locomotion, we study the movement of a legged robot (Xplorerbot, 15 cm, 150 g) in a trackway filled with ∼1 mm poppy seeds (the “sand”), with a single embedded 4 cm diameter plastic sphere (the “boulder”). We investigate how the presence of the boulder affects the robot’s trajectory under open-loop control, a minimal model for a rapidly running organism. We use an automated terrain creation system (including an air fluidized bed, tilting motors, and a universal jamming gripper) to set the initial condition of the substrate, including sand compaction and boulder location/burial depth. The kinematics of the robot are recorded and tracked by a high speed camera system. After each test, a universal jamming gripper retrieves and redistributes the boulder and robot, while the fluidized bed resets the compaction of the sand. We observe that before the interaction with the boulder the trajectory is straight; after the interaction the trajectory is angled relative to this line, and the angle depends sensitively on the leg-boulder contact position, leg phase at contact, and the boulder mobility within the sand. We view this as a scattering problem: analysis of the robot trajectory indicates that the interaction can be modeled using an attractive potential whose shape and magnitude depend on the parameters above. We expect that a terradynamics of locomotion on heterogeneous substrates can be informed by our scattering picture.
