Hitchhiker-like suckerfish: soft robot clings to underwater surfaces

The ray-finned fish can hold on tight to anything from boat hulls to jumping dolphins, even human divers. Researchers found that remora fish do this with a specially adapted fin on their undersides called a suction disc, which consists of a soft, circular “lip” and linear rows of tissue called lamellae. The lamellae sport tiny, needle-like spinules. The remora fish can use tiny muscles around the disc to change its shape to attach itself to the host; the spinules then provide major gripping power by adding friction to the equation.

Researchers from the Bio-Inspired Soft Robotics Lab of Beihang University used microcomputed tomography (microCT) to scan, segment, and reconstruct a preserved remora, turning to an environmental scanning electron microscope (ESEM) to measure the geometries of over 30 spinule samples. Then, they created a CAD model to help fabricate a multi-material 3D printed prototype with composite lamellae, which were lined with roughly 1,000 laser machined, at-scale carbon fiber spinules. In order to allow the disc to move just like a real remora disc, the researchers embedded six pneumatic actuators — basically little air pockets — that could inflate and deflate on cue.




Fig 1. Side-by-side comparison of the remora’s dorsal fin and the artificial suction disc (Image credit: Science AAAS magazine)


Like the fish’s specialized sucker, the “biomimetic remora disc” can make a tight seal using the same circular pattern as the fish. And its rows of flaps, dotted with tiny spikes, allow it to raise and lower how close it is to the surface.

To test this fishy bot, researchers attached it underwater to a variety of surfaces, some rough, some smooth, some rigid and some flexible. These included real mako shark skin, plexiglass, epoxy resin and silicone elastomer. The robot clung quite nicely to all the surfaces, the researchers found.

The force needed to pull the remora robot off the smooth plexiglass was about 436 newtons, which translates to 340 times the weight of the robot itself. On rougher surfaces, the bot clung a little less tightly. It took about 167 newtons of force to pull the bot off real sharkskin, for instance.

Finally, researchers attached it to a remote-controlled submarine (ROV). When the researchers directed the robot to attach to a submerged material, like plexiglass or sharkskin, the sucker grabbed onto both in less than 4 seconds on average, holding fast until researchers pulled it off. Once stuck, it took 45 kilograms of force to remove it. The disk worked just as well on dry land as it did in water, without any noticeable loss of suction. The researchers said such systems could one day greatly extend the range of robotic undersea explorers.

The development of this unique soft robot could mark a major step forward in several studies, and researches are being conducted to study the ocean bed and the soft-skin creatures living in there. It could easily attach to the skin of sharks and dolphins to study their habits, no matter how fast they’re swimming or deep they’re underwater.

Moving ahead, the team plans to attach their bot to swimming sharks or dolphins to see its real-world applicability.




Fig 2. Attachment of an underwater vehicle using the biorobotic remora disc



Li Wen, associate professor, school of mechanical engineering and automation, Beihang University, E-mail: liwen@buaa.edu.cn



Yueping WangXingbang YangYufeng ChenWainwright, Dylan K.Kenaley, Christopher P.Zheyuan GongZemin LiuHuan LiuJuan GuanTianmiao WangWeaver, James C.Wood, Robert J.Li Wen; A biorobotic adhesive disc for underwater hitchhiking inspired by the remora suckerfish, Science Robotics, 2, 10 (2017).

Related Links

Science Robotics paper link: http://robotics.sciencemag.org/content/2/10/eaan8072?ijkey=NjTiSHjkePTLk&keytype=ref&siteid=robotics

Science/AAAS magazine: http://www.sciencemag.org/news/2017/09/robotic-remora-can-cling-objects-force-340-times-its-own-weight

MIT Technology Review: https://www.technologyreview.com/the-download/608916/scientists-have-built-a-shark-sucking-robot-that-is-hideous-and-cool/