OctoBot
Octopus-inspired compliant-body aquatic robot

Computational models: Octopus arm muscles exhibit nearly incompressible hyperelastic behavior. They are simulated by a detailed elastodynamic model based on a three-dimensional non-linear implicit finite element (FEM) numerical procedure. The model uses appropriate activation functions for the generation of primitive octopus arm behaviors involving large deformations, such as bending, reaching, fetching and grasping, and is used to enhance the design of robotic arms and control strategies.

An accurate evaluation of the hydrodynamic forces acting by the surrounding fluid on octopus-like robotic arms is performed, in the three-dimensional space, by utilizing a high-fidelity CFD finite-volume numerical scheme to solve the governing equations of fluid flow. The hydrodynamic studies indicate the complexity of the vortical flow structure around the arm. They are also employed to assess the validity of the fluid drag model, used in our work, and to specify the associated normal/tangential force coefficients.

A lumped-parameter dynamical model of a 3D 8-arm robotic swimmer was developed using the Simulink/SIMUUN simulation environment. The model, which considers body and arm compliance, as well as forces from the aquatic environment, was used to study the effect of various kinematic parameters on swimming by arm sculling movements and arm undulations, for both straight-line and turning gaits. The simulations have demonstrated that forward propulsion for such gaits can be successfully generated by sculling arm movements.

Experimental investigation: An 8-arm octopus-inspired compliant-body robotic swimmer has been developed to experimentally demonstrate and investigate underwater propulsion by arm sculling movements, for straight-line and turning gaits. The robotic swimmer is energetically autonomous (powered by batteries), and fully untethered. Eight compliant arms were used, fabricated by polyurethane or soft silicone rubber, and controlled by individual waterproof micro-servomotors. An additional set of compliant arms interconnected with an octopus-like web has been fabricated from soft silicone rubber, in order to better approximate the characteristics of the biological counterpart. The experiments successfully demonstrate propulsion with arm sculling movements, reaching speeds of up to 0.5 body lengths per second, in the configuration with the web, and propulsive forces of up to 10.5 N, with a cost of transport as low as 0.62. This range of velocities is comparable to that exhibited by the real animal.