Underwater robot with unique fin propulsion

The turbellaria, the cuttlefish and the African knifefish have one thing in common: in order to move, they use their longitudinal fins to create a continuous wave which advances along their entire length. With this so-called undulating fin movement, the BionicFinWave also maneuvers through a pipe system made of acrylic glass. The autonomous underwater robot can communicate with the outside world via radio and transfer 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. With the wave-shaped movement of the fins, the fish push the water backwards, resulting in a forward thrust. Conversely, the animals can also swim backwards and, depending on the wave pattern, provide lift, downforce or even sideways thrust.

Flexible silicone fins for lifelike swimming maneuvers

The BionicFinWave uses its two fins for locomotion. They are completely molded from silicone and do not require any struts or other support elements. This makes them extremely flexible and enables them to implement the fluid wave movements of the biological role models in a lifelike manner.

The two fins on the left and right are each attached to nine small lever arms. These in turn are driven by two servo motors located in the body of the underwater robot. Two crankshafts in contact transmit the force to the levers so that the two fins can be moved individually. This allows them to generate different wave patterns that are particularly suitable for slow and precise movement and create fewer eddies in the water than, for example, a conventional propeller drive.

To swim in a curve, for example, the outer fin moves faster than the inner fin – comparable to the tracks of an excavator. A third servo motor at the head of the BionicFinWave controls the bending of the body, enabling it to swim up and down. A cardan joint is located between each lever segment to ensure that the crankshafts are correspondingly flexible and can bend. For this purpose, the crankshafts, including the joints and the connecting rod, were manufactured from plastic in one piece using the 3D printing process.

Intelligent interplay between all kinds of components

The remaining body elements of BionicFinWave are also printed in 3D. With their cavities they provide buoyancy. At the same time, the entire control and regulation technology is watertight; its various components are matched to one another and safely installed in the tightest of spaces. In addition to the circuit board with processor and radio module, a pressure sensor and ultrasonic sensors are located in the front of the body. They permanently measure the distances from the walls and the depth position in the water, thus avoiding collisions with the pipe system.

New impulses and approaches for the process industry

With this bionic technology test bed, our Bionic Learning Network is once again signaling the approach to future work with autonomous robots and new propulsion technologies 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 in the project can be used for the production processes of soft robotic components.