Traditional robots are characterized by rigid structures, which restrict their range of motion and their application in environments where complex movements and safe human-robot interactions are required. Soft robots inspired by nature and characterized by soft compliant materials have emerged as an exciting alternative in unstructured environments. However, the use of multicomponent actuators with low power/weight ratios has prevented the development of truly bioinspired soft robots. Octopodes' limbs contain layers of muscular hydrostats, which provide them with a nearly limitless range of motions. In this work, we propose octopus-inspired muscular hydrostats powered by an emerging class of artificial muscles called twisted and coiled artificial muscles (TCAMs). TCAMs are fabricated by twisting and coiling inexpensive fibers, can sustain stresses up to 60 MPa, and provide tensile strokes of nearly 50% with <0.2 V/cm of input voltage. These artificial muscles overcome the limitations of other actuators in terms of cost, power, and portability. We developed four different configurations of muscular hydrostats with TCAMs arranged in different orientations to reproduce the main motions of octopodes' arms: shortening, torsion, bending, and extension. We also assembled an untethered waterproof device with on-board control, sensing, actuation, and a power source for driving our hydrostats underwater. The proposed TCAM-powered muscular hydrostats will pave the way for the development of compliant bioinspired robots that can be used to explore the underwater world and perform complex tasks in harsh and dangerous environments.
Keywords: bioinspired; control systems; muscular hydrostats; octopodes; twisted and coiled artificial muscles.