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The marine flatworm, the cuttlefish and the African knifefish have one thing in common: in order to propel themselves, they use their longitudinal fins to create a continuous wave which advances along their entire length. The BionicFinWave also uses this undulating fin movement to manoeuvre through a pipe system made of acrylic glass. At the same time, the autonomous underwater robot is able to communicate with the outside world wirelessly and transmit data – such as the recorded sensor values for temperature and pressure – to a tablet.
The longitudinal fins of the natural role models run from head to tail and are located either on the back, the belly or on both sides of the body. The fish use the wave-shaped movement of the fins to push the water behind them, thereby creating a forward thrust. Conversely, the creatures can also swim backwards in this way and, depending on the wave pattern, create uplift, downforce or even lateral thrust.
The BionicFinWave uses its two side fins to move along. They are completely cast from silicone and do not require any struts or other support elements. This makes them extremely pliable and thus able to faithfully replicate the fluid wave movements of their biological role models.
For this purpose, the two fins on the left and right are each fastened to nine small lever arms. These, in turn, are driven by two servo motors located in the body of the underwater robot. Two attached crankshafts transfer the force to the levers in such a way that the two fins can move individually. They can thus generate different wave patterns which are particularly suitable for a slow and precise movement and whirl up water less than a conventional screw propulsion system does, for example.
In order to swim in a curved line, for example, the outer fin moves faster than the inner one – in a similar way to the tracks on a digger. A third servo motor on the head of the BionicFinWave controls the bending of the body, enabling it to swim up and down. There is a cardan joint between each lever segment to ensure that the crankshafts are suitably flexible and supple. The crankshafts including the joints and the connecting rod were made out of a single piece of plastic with the 3D printing method.
The remaining elements in the BionicFinWave’s body are also 3D-printed. Their cavities enable them to act as flotation units. At the same time, the entire control and regulation technology system is installed safely in the smallest of spaces, coordinated and kept watertight. In addition to the PCB with processor and radio module, a pressure sensor and ultrasound sensors are located in the front of the body. They constantly measure the distances to the walls as well as the depth in the water, thus preventing collisions with the pipe system.
With cutting-edge bionic technology, our Bionic Learning Network is once again inspiring future work with autonomous robots and new drive technologies used in liquid media. It would be conceivable to further develop concepts such as the BionicFinWave for tasks such as inspections, measurement series or data collection – for example in water and wastewater engineering or other areas of the process industry. In addition, the knowledge gained during the project can be used for the manufacturing methods of soft-robotics components.