Octopods, also known as octopuses or squid, are considered to be the most intelligent invertebrates. While they generally move along the ocean floor with their eight arms, they flee by swimming head-first, in line with the principles of propulsion.
When the mollusk does this, water is taken into its mantle, which is then closed by contracting sphincter muscles. The water is then squirted back out at a high pressure through a funnel. The resulting propulsion pushes the octopus forward in the opposite direction. By changing the position of the funnel, the octopus can precisely steer its direction of travel.
For researchers at the Fraunhofer Institute for Manufacturing Engineering and Automation IPA, this intelligent propulsion principle served as a role model for the development of an underwater propulsion system. The propulsion principle was integrated into the underwater actuators: four elastomer balls with mechanical inner workings create propulsion by pumping water.
Water is sucked into each actuator or elastomer ball through an opening; a recirculation valve prevents reflux. A hydraulic piston contracts the integrated cable structure like a muscle. In this way, it pushes the water out of the 20 x 6 cm ball. In turn, a motor pump moves the hydraulic piston. The actuator is well-suited for maneuvering small boats. It can also be used as a floating aid for jet skis, surfboards, or scooters that pull divers into deep water. In contrast to ship propellers, it is quiet, and fish cannot get caught in it.
The best part: the experts can produce the system in a single step with a 3D printer. In order to produce its complex geometry amorphously with soft plastic, the researchers opted for the fused deposition modeling generative production process, or FDM for short. With this approach, the plastics to be processed are heated and liquefied in an extrusion head and are transformed into a thin filament in the pressure nozzle. This filament is then applied in layers, from bottom to top, to produce a complex 3D component. The final product of this process is an underwater propulsion system that can stand extreme levels of pressure without breaking. Even in situations of very high stress, it always returns to its original shape.