FORTH's OCTOBOT: Robotic swimmer with supple silicone web mimics octopus

Highlighting this month's news of developments in marine robotics: Researchers from the Computational Vision and Robotics Laboratory (CVRL) Foundation for Research and Technology-Hellas (FORTH) in Greece have worked out a way to mimic the movements of an octopus.

The robot, which swims and crawls, is inspired by the morphology and very able locomotor capabilities of the octopus.

The octopus of their creation, which is being described by various sites as the octobot or "robotic swimmer," among other terms, propels itself underwater either alone of interconnected via a passively compliant web, said the team.

Their study, "Multi-Arm Robotic Swimming with Octopus-Inspired Compliant Web," was prepared for this year's IEEE/RSJ International Conference on Intelligent Robots and Systems in Chicago.

They used flexible silicone webbing, which served them well. The authors said, "Speeds of 0.5 body lengths per second and propulsive forces of up to 10.5 N were achieved, with a cost of transport as low as 0.62."

Evan Ackerman reported Wednesday in IEEE Spectrum that the research reflects a success story where the team last year reported they were working on adding another physical feature in the version of the octopus: a web between tentacles, which they said might help swimming speed or efficiency.

"Now the researchers report that the addition of a soft and supple silicone web has nearly doubled the speed of the roboctopus, and not satisfied with that, the scientists have also taught it to crawl, carry objects, and swim free in the Aegean Sea," said Ackerman.

By contrast, reported Meghan Rosen in Science News, their webless version had shown it could propel itself at up to 100 millimeters per second, slowly opening stiff plastic arms, then snapping them together.

This year's robotic swimmer, with arms and a web made of soft silicone, swam at up to 180 millimeters per second.

"The web helps the octobot generate more force," wrote Rosen, "so it can push through water faster than using arms alone."

Credit: D. Tsakiris /Institute of Computer Science /FORTH

What benefits could result from this type of research?

Team member and computer scientist Dimitris Tsakiris said the creation may support biologists' attempts to observe marine ecosystems.

"We want to put a camera on it and see what we can do," he said in Science News.

Another bit of encouraging news about their work is that other sea creatures did not appear to be frightened off at the sight of the robot swimmer.

Tsakiris said the faux octopus was taken out for a swim in the Mediterranean and tiny fish tagged along.

Jupiter's Moon, Europa mimics Earth tectonics

False-colour image of Europa’s trailing northern hemisphere, where subduction zones are hypothesised (?) to exist. 

Credit: NASA /JPL /University of Arizona

Jupiter's icy moon Europa may have active tectonic plates similar to those that shape the Earth, which had long been thought unique in this respect, scientists said Sunday.

They used images captured by NASA's Galileo spacecraft, which orbited Jupiter and its moons from 1995 to 2003, to study the criss-cross of ridges and fractures on Europa's ice shell.

The moon, slightly smaller than the one orbitting Earth, has one of the youngest surfaces in the Solar System, implying "rapid recycling", said the team.

They found evidence that a piece of the surface had disappeared along a boundary between two ice plates, possibly when one sunk under the other.

They took this as evidence of surface material being recycled into the moon's interior, similar to parts of Earth's crust which sink into the underlying mantle at so-called subduction zones where tectonic plates converge.

This conceptual illustration of the subduction process (where one plate is forced under another) shows how a cold, brittle, outer portion of Europa’s 20-30 kilometer (roughly 10-20 mile) thick ice shell moved into the warmer shell interior and was ultimately subsumed. 

A low-relief subsumption band was created at the surface in the overriding plate, alongside which cryolavas may have erupted.

Image Credit: Noah Kroese, I.NK

The team studied an area of 134,000 square kilometres (51,700 square miles), using the images and a reconstruction of geological features.

They found that a 20,000 km2-portion of surface was missing.

"We propose that Europa's ice shell has a brittle, mobile, plate-like system above convecting warmer ice," they wrote in the journal Nature Geoscience.

"Hence, Europa may be the only Solar System body other than Earth to exhibit a system of plate tectonics."

Europa is one of the four largest moons of Jupiter, the fifth planet from the Sun and the largest in our Solar System.

Close-up view of a proposed zone of mid-ocean-ridge-like plate spreading on Europa (unrelated to the region studied in this work). 

This dilational band called Phaidra Linea, located in Europa’s trailing hemisphere near Argadnel Regio, shows internal striations related to spreading and bilateral symmetry about a central axis. Older geological features can be matched perfectly to either side of the spreading zone. 

The black strip in the center of the image is a narrow region where the images overlap and there is no image coverage. 

Credit: NASA/JPL

More information: Nature Geoscience, dx.doi.org/10.1038/ngeo2245

Fish-like sensors mimics lateral line

A PRESSURE sensor that mimics the way a fish's lateral line works could help submersible craft navigate.

The technology could improve underwater robots' ability to detect hazards, such as deep sea vents and shipwrecks, when the water is too murky for a camera to work effectively, or the object is too close for sonar, says Douglas Jones at the University of Illinois at Urbana-Champaign.

The lateral line is a sense organ that runs along the sides of most fish and enables them to detect changes in water pressure. This allows fish to sense depth and the direction of the current, and also means they can swim in synchronised schools even in darkness.

The line is peppered with hair cells called neuromasts that fire in response to pressure waves. The pattern of signals generated along the line allows the fish to pick out the tiniest flick of a nearby tail.

Jones, alongside Chang Liu at Northwestern University in Evanston, Illinois, made an artificial neuromast by adding boron to a 500-micrometre-long silicon hair to create a stress-sensitive resistor. As the hair bends in response to water motion, its resistance changes, allowing the force of the water's movement to be calculated.

The researchers tested the sensor by fixing an array around a plastic pipe and measuring the response to various objects placed in the water, including a live crayfish. The animal's wiggling legs generated a pattern of pressure signals that enabled the team to calculate its precise location in relation to the pipe. Because the hairs in the array are oriented at right angles to each other, the direction of the water motion can be easily determined (see diagram).

Finally, the distance to the object can be worked out in the same way a fish would, by moving water in the direction of the object and timing how long it takes to receive an echo (Bioinspiration and Biomimetics, DOI: 10.1088/1748-3182/5/1/016001). "We're hopeful it will be useful for making sure any underwater vehicle doesn't get trapped by unseen obstacles," says Jones.

"Anything that fortifies an undersea robot's sense of its environment, and its ability to avoid obstacles, is to be welcomed," says Andy Bowen of Woods Hole Oceanographic Institution in Massachusetts. Bowen designed Jason Junior, the remote-controlled robot sub that famously imaged the wreck of the Titanic in 1986. "In the search for new deep sea vents, I can imagine this artificial lateral line autonomously sensing a hydrothermal plume and using an on-board algorithm to home in on the source of it. It's a fascinating technology," he says.