Ingenious Underwater Drone Can Take to the Air in Under a Second

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The drone, which was inspired by the suckerfish, can also attach itself to other moving objects and catch a ride.

Robots have generally been designed to do a single, very specialised task, but Beihang University researchers have developed a new robotic drone that can operate underwater as well as in the air, and it includes a clever, nature-inspired trick for extending its range.

When you think about robots, you typically see one of two types: highly capable humanoids from science fiction, or mindless articulated arms performing monotonous chores in factories. The latter technique has been the norm for decades, but as technology catches up to sci-fi writers’ fantasies, robot designers are beginning to construct automatons capable of performing a wider range of tasks. For example, Boston Dynamics’ Spot uses four dog-like legs to travel a variety of terrains and complete a variety of tasks, including nighttime protection of the ruins of Pompeii and the generation of detailed 3D maps of regions too dangerous for people to visit.

The customizable method makes it simpler for businesses or research institutions to justify the high cost of a robot, but the Biomechanics and Soft Robotics Lab at Beihang University has built something genuinely unique. Despite having highly articulated legs, Boston Dynamics’ Spot is limited to land missions. This innovative drone can carry out operations underwater, in the air, or both without requiring any adjustments.

A water landing for most quadcopter drones means the pilot will have to wade out to rescue it (and then replace most of its electronic components). This drone is unique. It’s entirely waterproof, and it comes with a set of self-folding propellers that compress when the drone is handled at lesser speeds underwater, making it easier to manoeuvre the drone. They then lengthen automatically as the drone exits the water and takes to the air. The researchers tuned the drone’s performance so that the water-to-air transition takes about a third of a second, and the drone can perform multiple water-to-air transitions in a row, like a pod of dolphins leaping out of the water. During testing, the drone performed seven water-to-air transitions in about 20 seconds.

A robot’s autonomous capabilities are sometimes restricted by the capacity of its batteries, as is the case with any electrical device. This is especially true for flying drones that rely on four electric motors constantly spinning to stay aloft. Advanced robots are frequently seen tied to cable tethers in laboratory settings, but this isn’t an ideal solution for bots designed to explore the ocean depths or collect airborne data—or both, in this case.

The researchers gave the drone an additional improvement inspired by the remora fish, sometimes known as the suckerfish, which utilises an adhesive disc on top of its head to temporarily attach itself to other underwater species in order to catch a ride and save energy.

Drones that can land to conduct targeted observations while preserving battery life are not a new concept, but they normally use mechanisms suited for certain surfaces, such as articulating claws that grasp a branch or sticky gecko-inspired feet that attach to walls, just like factory robots. The researchers needed a more versatile technique to connect to a range of surfaces for a robotic drone developed with flexibility in mind: wet, dry, smooth, rough, curved, or even those going underwater, where the shear forces of the water require an extra-strong grasp.

The sticky disc of the remora fish was the ideal option since it has built-in redundancies that allow it to stick to surfaces even when only partially touched. One of the researchers and authors of the report released today, Li Wen, was involved in another research endeavour at Beihang University two years ago that reverse-engineered how the remora fish’s disc worked.

Remora fish stick to surfaces in the same way that a suction cup does, with a flexible oval ridge of soft tissue that forms a tight seal. Suction holds the remora in place while water is forced out of the gap between it and its host. The remora fish’s disc is also coated in lamellae, which are ridges aligned in columns and rows (similar to the ridges on the roof of your mouth) that can be expanded through muscle contractions to engage tiny spinules that hold the host even tighter. Those lamellae ridges also aid in the formation of smaller suction compartments that retain their seal even if the disc’s bigger lip does not.A remora fish, unlike a suction cup, will maintain its grasp on a smooth surface even if a small part of its edge is lifted.

A fourlayer method was used to produce an artificial facsimile of the remora fish’s suction disc. They combined an ultraflexible layer on top with more rigid structures beneath, as well as a layer with a network of small channels that can be expanded when pumped full of fluids, replacing living muscle tissue as a mechanism to activate the lamellae structures and increase suction even further.

The suction mechanism, which is mounted on top of the submersible drone, allows it to attach to a range of surfaces, including those with a rough texture, aren’t completely flat, or have a smaller surface area than the suction mechanism. The drone, like a remora fish, might find an underwater host (one that isn’t driven away by its spinning propellers) and attach itself for a free ride, requiring only the suction mechanism to be powered, which is a minor drain on the drone’s onboard batteries. In the air, the same could be done, albeit the obstacles of the drone properly latching to another aircraft would be enormous, as even a sluggish sailplane has a minimum speed of 40 mph: a  challenging moving target.

The suction mechanism might also be used to temporarily rest the drone somewhere with a good vantage position for longterm observations. Rather than relying on its four motors to hold a specific position underwater while fighting shifting currents, the drone could attach itself to a rock or log and turn off its motors while keeping sensors and cameras powered. The drone could do the same thing above the water line, flying up and sticking itself to the side of a tall building or the underside of a wind turbine’s nacelle, and taking measurements and other data without using its batterydraining engines. It’s a workaround for  battery technology that’s still severely limited.

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