Leveraging fluid resistance in soft robots

A key advantage to Fluidic Elastomer Actuators (FEA) is that they permit easy fabrication of robots capable of sophisticated manipulation and mobility. This advantage arises primarily from the continuous stretching and relaxation of elastomeric material that defines an active degree of freedom (DOF), prescribed during the manufacturing process. While the low elastic moduli of the soft material allows for infinite passive DOFs, each active DOF typically requires a valve and/or pump. On-board valving adds weight and size to the robots, and off-board valving requires tubing that imparts resistance to flow and requires higher pressure differentials for reasonable actuation velocities. In contrast to these methods, the work presented here exploits fluidic resistance in poroelastic foam actuators to create a traveling wave using only a single valve and pressure inlet. This concept is evaluated with respect to foam volume and fluid viscosity, and further demonstrated in a three-legged robot capable of millipede-inspired locomotion. The robot is capable of traveling at ∼1.1 mm/s, with individual legs (closest to the inlet) extending 41.28, 27.36, and 12.95 mm. These results represents an important step towards increasingly complex behavior in soft robots that remain simple to fabricate and control.