The design of robots able to locomote effectively over a diversity of terrain requires detailed ground interaction
models; unfortunately such models are lacking due to the complicated response of real world substrates which can
yield and flow in response to loading. To advance our understanding of the relevant modeling and design issues,
we conduct a comparative study of the performance of DASH and RoACH, two small, biologically inspired,
six legged, lightweight (~10 cm, ~20 g) robots fabricated using the smart composite microstructure (SCM)
process. We systematically examine performance of both robots on rigid and flowing substrates. Varying both
ground properties and limb stride frequency, we investigate average speed, mean mechanical power and cost
of transport, and stability. We find that robot performance and stability is sensitive to the physics of ground
interaction: on hard ground kinetic energy must be managed to prevent yaw, pitch, and roll instability to
maintain high performance, while on sand the fluidizing interaction leads to increased cost of transport and
lower running speeds. We also observe that the characteristic limb morphology and kinematics of each robot
result in distinct differences in their abilities to traverse different terrains. Our systematic studies are the first
step toward developing models of interaction of limbs with complex terrain as well as developing improved limb
morphologies and control strategies.
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