Uncrewed Systems Technology 049 - April/May 2023

8 Platformone April/May 2023 | Uncrewed Systems Technology A scalable, modular system for developing underwater autonomous robots is aiming to speed up their design process (writes Nick Flaherty). The system, developed by researchers at theMassachusetts Institute of Technology (MIT), builds deformable ‘aquabots’ using simple repeating substructures instead of unique components. The teamhas demonstrated the system in two example configurations, one like an eel and the other a wing-like hydrofoil. The principle allows virtually unlimited variations in formand scale. Existing approaches to soft robotics for marine applications are generally made on small scales, while many useful real-world applications require devices on scales of metres. Previous designs such as the RoboTuna used 3000 different parts and took about 2 years to design and build. The modular system consists of lattice-like pieces, called voxels, that are mostly hollow structures consisting of cast plastic pieces with narrow struts in complex shapes. The box-like shapes are load-bearing in one direction but soft in others, an unusual combination achieved by blending stiff and flexible components in different proportions. The soft elements allow the researchers to implement flow control to reduce drag and improve propulsive efficiency, resulting in substantial fuel savings. In one of the devices, the voxels are attached end to end in a long row to form a metre-long, eel-like structure. The body is made up of four segments, each consisting of five voxels, with an actuator in the centre that can pull a wire attached to each of the two voxels on either side, contracting them and causing the structure to bend. The whole device of 20 units is then covered with a rib-like supporting structure, and then a tight-fitting waterproof neoprene skin. The researchers deployed the structure in anMIT tow tank to show its efficiency in the water, and demonstrated that it was capable of generating enough thrust to propel itself forward using undulatingmotions. The voxel approach allows the designs to be scaled up to larger sizes without requiring the kind of retooling and redesign that would be needed to scale up current systems. “Scalability is a strong point for us,” said MIT researcher Parra Rubio. “Treating soft versus hard robotics is a false dichotomy. This is something in between, a new way to construct things.” There have beenmany eel-like robots before, for example for NASAmissions in space, but they are generally made from bespoke components as opposed to these simple and scalable building blocks. The other device they demonstrated has a wing-like shape, or hydrofoil, made up of an array of the same voxels. It can change its profile shape and so change the lift-to- drag ratio and other properties of the wing. Unlike the eel design, the wing is covered in an array of scale-like overlapping tiles, which are designed to press down on each other to maintain a waterproof seal even as the wing changes its curvature. One possible application might be as an addition to a ship’s hull to reduce the formation of drag-inducing eddies and thus improve the vessel’s overall efficiency. The system can also be applied to a submersible craft, using a morphable body shape to create propulsion. Underwater vehicles Simpleway tomakeAUVs The eel-like version generated enough thrust to propel itself forward Scalability is a strong point for us. Treating soft versus hard robotics is a false dichotomy. This is something in between, a new way to construct things