Hyper-redundant manipulators offer high dexterity and manoeuvrability in constrained environments, yet their design must integrate structural efficiency with environmental adaptability. This study presents a co-design framework for lightweight, cable-driven hyper-redundant manipulators optimised for underwater applications, such as the usage in combination with a Remotely Operated Vehicle. Building on a modular architecture of an eight-degree-of-freedom cable-driven manipulator, the methodology integrates Gaussian process regression-based stress prediction and generative design to achieve mass and size reductions, as well as a hydrodynamically efficient shape while ensuring structural integrity under extreme static loads. A 3D-printed module fabricated from Onyx, a carbon fibre-reinforced nylon, achieved near-neutral buoyancy in seawater, validated through submerged testing of a two-module prototype. An external buoyant element design was then provided for manipulators with no inherent buoyancy, accounting for printability, density mismatch between actual and theoretical density, and joint range of motion. This work advances underwater hyper-redundant robot design by combining data-driven optimisation with modular buoyancy strategies and hydrodynamic efficiency, providing a scalable method for fluid environments.

In recent years, significant advancements have been made in robotics, especially with the introduction of continuum and hyper-redundant robots. These robots can be highly flexible and manoeuvrable, which makes them suitable for intricate underwater maintenance, exploration, and inspection tasks. Inspired by the motions of aquatic life, underwater snake-like robots offer a good way to accomplish subsea maintenance, exploration, and inspection activities. While many studies have been conducted on hyper-redundant, snake-like robotic arms for maintenance and inspection in land-based applications, not as much about robotics intended for marine or underwater applications has been studied. This review critically examines recent advancements in the design, actuation, and modelling of these robotic systems, categorising them into two primary families: untethered mobile robots and tethered robotic manipulators. Key insights include the identification of strengths and limitations associated with various designs and actuation strategies, such as the high manoeuvrability but limited speed of bioinspired swimming robots compared to thruster-driven designs, and the complexity versus precision trade-offs inherent in tendon-driven manipulator arms. Furthermore, the modelling techniques employed across categories are systematically analysed, as well as challenges such as the modelling of fluid–structure interactions and the need for improved real-time models for compliant and soft robots.

Compliant mechanisms (CMs), along with soft robotics devices formed therewith, may be defined as engineering systems achieving force and motion transmission via the deflection of flexible members. CMs have increasingly gained a strong foothold in the scientific arena owing to their hinge-less nature, shock resistance, potential single-piece manufacturability, safety in human–machine interaction, minimal maintenance requirements, and adaptability to work in unstructured environments. In parallel, current advances in the production of inherently compliant sensory-motor apparatus, as well as progresses in the development of robust control methods, are paving the way to practical CM adoption in a large variety of engineering fields, here including healthcare, manufacturing, inspection/maintenance, and agrifood.

Editorial - Since the official registration of the word “Mechatronics” as a trademark by Yaskawa Electric Corporation in 1971, explosive growth has been observed in mechatronics research and product development activities. Nowadays, mechatronics and mechatronic design methodologies play increasingly important roles in computer, communication, control, and consumer product (4C) technologies. As such, it is fair to agree that mechatronics technology has profoundly affected almost all aspects of human life, particularly, of engineering realities ranging from rehabilitation devices to ground and underwater robots, and from unmanned aerial vehicles to intelligent manufacturing facilities, constituting a rapidly progressing frontline.

In this paper, a novel design of a fully compliant locking device is presented, for possible application in robotic actuation systems. The synthesis method based on a rigid linkage mechanism is explained, a parametrization scheme is proposed, and an optimization procedure is conducted using kinetostatic flexible multi-body analysis in conjunction with global optimization techniques. The performance of the optimized locking device design is validated via numerical simulations.