Development of Bio-inspired Underwater Robot with Adaptive Morphology Capable of Multiple Swimming Modes

Bio-inspired underwater robots have several benefits compared to traditional underwater vehicles such as agility, efficiency, and an environmentally friendly body. However, the bio-inspired underwater robots developed so far have a single swimming mode, which may limit their capability to perform different tasks. This paper presents a re-configurable bio-inspired underwater robot that changes morphology to enable multiple swimming modes: octopus-mode and fish-mode. The robot is 60 cm long and 50 cm wide, weighing 2.1 kg, and consists of a re-configurable body and 8 compliant arms that are actuated independently by waterproof servomotors. In the robot, the octopus-mode is expected to perform unique tasks such as object manipulation and ground locomotion as demonstrated in literature, while the fish-mode is promising to swim faster and efficiently to travel long distance. With this platform, we investigate effectiveness of adaptive morphology in bio-inspired underwater robots. For this purpose, we evaluate the robot in terms of the cost of transport and the swimming efficiency of both the morphologies. The fish-mode exhibited a lower cost of transport of 2.2 and higher efficiency of 1.2 % compared to the octopus-mode, illustrating the effect of the multiple swimming modes by adaptive morphology.

Inverse kinematics and reflex based controller for body-limb coordination of a salamander-like robot walking on uneven terrain

Laura Deanne Fleury, Tomislav Horvat, Auke Ijspeert, Konstantinos Karakasiliotis, Kamilo Andres Melo Becerra, Robin Thandiackal

Search and rescue (SAR) missions are being carried out by several types of robots. They include ground, marine and air vehicles depending on the terrain and mission to be tackled. A particular niche for SAR activities are shallow waters. They present high difficultly for conventional ground or marine robots because of the mix of water and ground. Such an environment is difficult to be accessed for a robot without some built-in amphibious capabilities. Our lab has experience in the design of amphibious salamander-like robots. In order to consider whether these robots would be suited for SAR missions in shallow waters, a key requirement is the ability to tackle rough terrains. In this paper we present a control framework for a highly redundant salamander-like robot. It involves bio-inspired spine control, inverse kinematics-based limb control, proper limb-spine coordination, reflex mechanisms and attitude control. The framework is validated in a simulation and on the real robot. In both cases, the robot is used in two different configurations: with and without its tail, in order to investigate how the tail (which is necessary for swimming) affects ground locomotion. With this exploration, we aim to set the precedent for improving the problem of dynamic locomotion of salamander-like robots over unperceived rough terrain. Our results confirm that the design of reflexes like stumbling and extension, combined with an attitude controller, allows for the improving of the performance of the robot in a generic rough terrain which includes stairs, holes and bumps with several levels of complexity adjusted according to the robot dimensions.

IEEE2015

Variable-Stiffness Tensegrity Modular Robots

Davide Zappetti

The need for a new generation of robots able to safely locomote and manipulate beside or cooperatively with humans or in un-constructed environments has recently emerged as a priority of the robotics community. ln the past two decades, this challenge has been tackled by the growing field of soft robotics mostly focusing on developing completely deformable soft robotic bodies that can freely deform along any direction and comply with any unexpected or excessive external force. However, intrinsic softness can be a limitation in situations that require exerting substantial forces, to withstand bodyweights or to modulate forces applied to the environment. Inspiration for a novel mechanically hybrid approach in robotics can come from a novel model for biological structures based on the concept of tensegrity. This model rejects the idea of the vertebrate musculoskeletal system as beams, columns, and levers, and acknowledges the bones as stiff under compression elements held and stabilized in their positions by the pull of tensile components such as muscles, tendons, ligaments, and fascia. Therefore, rather than a frame supporting an amorphous soft tissue mass, the whole vertebrate body is divided into several modules stabilized by these tension components and its stiffness can vary depending on the pre-stress (i.e. tone) and stiffness of its muscles. This structural organization allows biological organisms to be more mechanically adaptive, robust, and lightweight at the same time. They can exhibit high physical compliance, apply efficient forces to the environment when needed, and, at the same time, withstand their bodyweight at different scales. In the same way, modular tensegrity structures used in robotic applications can provide a lightweight and robust framework where integrating stiff under compression struts for bodyweight support; variable stiffness cables for applying directionally larger forces when required, and soft cables to absorb energy and allow compliance. ln this thesis, tensegrity modular structures are investigated as a new approach to develop soft robots with variable stiffness capabilities. This investigation led to a set of design strategies to manufacture and actuate tensegrity modules with programmable stiffness and deformation; to mechanically and electrically connect tensegrity modules to develop untethered applications, and to implement variable-stiffness capabilities in the modules for active and passive stiffness change. Finally, preliminary results and insights are presented on using heuristic algorithms as a design method to find task-optimal morphologies, stiffness, and control of modular tensegrity robots. In this thesis modular tensegrity robots have been developed for performing locomotion and grasping tasks, however, the design methods presented can provide a guideline for designing robots for diverse applications where being lightweight, robust, and having variable-stiffness capabilities are of primary importance. We believe that the work presented and discussed in this thesis answered a gap in the current literature and most importantly, will pave the way to future research on tensegrity robots for a great variety of tasks and robotic applications.

EPFL2021

Benchmarking Agility For Multilegged Terrestrial Robots

Peter Eckert, Auke Ijspeert

In this paper, we present a novel and practical approach for benchmarking agility. We focus on terrestrial, multilegged locomotion in the field of bio-inspired robotics. We define agility as the ability to perform a set of different but specific tasks executed in a fast and efficient manner. This definition is inspired by the analysis of natural role models, such as dogs and horses as well as robotic systems. An evaluation of existing benchmarks in robotics is done and taken into account in our proposed benchmark. After the general definition, the actual normalized benchmarking values are defined, and measuring methods, as well as an online database for agility score collection and distribution, are presented. To provide a baseline for agile locomotion, various videos of dog-agility competitions were analyzed and agility scores calculated wherever applicable. Finally, validation and implementation of the benchmark are done with different robots directly available to the authors. In conclusion, our benchmark will enable researchers not only to compare existing robots and find out strengths and weaknesses in different design approaches, but also give a tool to define new fitness functions for optimization, learning processes, and future robots developments, intensifying the links between biology and technology even further.

2019

Variable-Stiffness Tensegrity Modular Robots

Davide Zappetti

EPFL2021