Invited Speakers

Daniel Goldman digoldma@berkeley.edu Berkeley

Biologically-inspired mechanics Organisms like insects, lizards and crabs negotiate complex terrain in ways that no human-made robot can. While there has been progress made in the study of terrestrial locomotion on rigid, level, high friction substrates, understanding how organisms move over materials that present a complex foot interaction (like sand, bark, leaves, grass) is still a challenge. This talk will describe examples in which controlled laboratory experiments are used to investigate the mechanisms that organisms use to negotiate complex terrestrial environments. A fluidized bed, a collection of granular media forced by a flow of air, is used to vary the strength of sand to study the performance of rapidly running sand-dwelling lizards and crabs. Pulses of flow to the bed strengthen the material, while a constant flow below the onset of fluidization increases penetration depth and time of disks dropped into the medium. While crabs suffer a decrease in speed as the material weakens, surprisingly the lizards maintain high speed, even when the material is fully fluidized. Spiders and cockroaches maintain high speed across substrates with low foothold probability, like debris and sparse vegetation. Laboratory experiments on wire mesh (with over 90% of material removed) reveal that they achieve such performance by distributing contact along limbs. Spine and hair structures on the limbs increase effective contact. The spines and hairs share a unidirectional compliance: they resist deflection when pushed toward the body to aid in contact and they fold down the leg to prevent catching during swing phase. The addition of prosthetic spines to the limbs of ghost crabs with similar directional properties enhances performance on wire mesh. Foot adhesion to a substrate is critical during rapid climbing. Despite differences in adhesion mechanism and body morphology, cockroaches and geckos display similar dynamics during rapid (>5 body-lengths/sec) climbs. Mechanical models of climbing cockroaches capture the forces produced during vertical locomotion; simple changes to the motor pattern capture the forces produced in level locomotion. Through collaboration with a multidisciplinary group of engineers and biologists, these studies have influenced the design of RiSE, a robot capable of negotiating complex vertical and level terrain.