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Biomimicry in action: octopus inspired propulsion

06 July 2013

Researchers turn to the octopus for inspiration when they set about devising a silent propulsion system for small boats and water sport devices.

Four elastomer balls pump water and provide the required propulsion in this laboratory rig (photo: Fraunhofer IPA)
Four elastomer balls pump water and provide the required propulsion in this laboratory rig (photo: Fraunhofer IPA)

When an octopus moves, 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 comprising four elastomer balls with internal mechanisms to create propulsion by pumping water.

Water is sucked into each 20x6cm elastomer ball (actuator) through an opening; a recirculation valve prevents reflux. A hydraulic piston contracts the integrated cable structure like a muscle, pushing the water out of the ball. In turn, a motorised pump moves the hydraulic piston.

The researchers believe the actuator is suitable for manoeuvring small boats. It can also be used as a floating aid for water sport devices such as jet skis, surf boards, or scooters that pull divers into deep water. Moreover, it is quiet, and harmless to marine fauna.

3D printing
Significantly, the system can be produced in a single step using a 3D printer. In order to produce its complex geometry amorphously with soft plastic, the researchers opted for the fused deposition modelling (FDM) generative production process.

The team used thermoplastics such as polyurethane because of their flexibility. 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.

Thanks to robot-assisted FDM, the actuators can be scaled up. In fact, components of up to 2m in size can be printed three-dimensionally. 

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