Robots have traditionally been purpose-built to perform a single, very specific task, but researchers at Beihang University are taking a very different approach with a new robotic drone which can work underwater just as easily as it does in the air, and it features a clever nature-inspired tip to maximize its range.
When you think of robots, one of two versions probably comes to mind: the highly capable humanoids that science fiction promised us, or the dumb articulated arms performing repetitive tasks in factories. This latter approach is more or less where we’ve been for decades, but as technology slowly catches up with the imaginations of science fiction writers, robot designers are beginning to develop automatons capable of performing greater variety of actions. Boston Dynamics Squarefor example, uses four dog-like legs to navigate varied terrain and perform many different missions, including protecting the ruins of Pompeii at night and generating detailed 3D maps of areas too dangerous for humans to visit.
The adaptable approach makes it easier for companies or research organizations to justify the high cost of a robot, but what Beihang University’s Biomechanics and Soft Robotics Lab has created is truly unique. Even with highly articulated legs, the Boston Dynamics Spot is still limited to ground missions. This new drone can perform tasks underwater, in the air, or both, without requiring intermediate modifications.
For most quadcopter drones, a water landing means the pilot will have to wade out to rescue it (and then replace most of its electronics). This drone is different. It is completely waterproof and has a set of self-folding propellers that collapse when used at lower speeds underwater to effectively maneuver the drone while submerged. They then extend automatically when the drone comes out of the water and takes flight. The researchers optimized the drone’s performance so that the water-to-air transition takes about a third of a second, and, like a pod of dolphins jumping out of the water, the drone is able to make repeated water-to-air transitions, performing seven of consecutively during the tests in about 20 seconds.
As with any electronic device, a robot’s autonomous capabilities are often limited by the capacity of its batteries, and that’s especially the case for flying drones that rely on four electric motors constantly spinning to stay aloft. In laboratory settings, you’ll often see advanced robots attached to cable tethers that provide a non-stop source of power, but that’s not a great option for bots designed to explore the ocean depths or collect aerial data—or both, in this case.
To dramatically increase the range of this drone, and to help conserve battery power while traveling to and from a mission site, the researchers gave it an additional upgrade inspired by the remora fish, better known as the suckerfish, which uses an adhesive disc on top of its head to temporarily attach itself to other underwater creatures in order to hitch a ride and conserve energy.
Drones that can land in order to carry out targeted observations while preserving battery life are not a new idea, but like robots in a factory, they typically use mechanisms tailored for specific surfaces, like articulated claws that grab a branch or gecko-inspired sticky feet that stick to walls. For a robotic drone designed with flexibility in mind, researchers wanted a more versatile way to attach itself to a variety of surfaces: wet, dry, smooth, rough, curved, or even those moving underwater, where the forces of water shear require extra strong adhesion.
The remora fish’s sticky disc was the perfect solution, as it includes built-in redundancies that allow it to stick to surfaces even in partial contact. Two years ago, Li Wen, one of the researchers and authors of the article published today, was part of another research project at Beihang University that reverse engineered the actual operation of the disc of the remora fish.
This research revealed that the remora fish adheres to surfaces similar to a suction cup, with a flexible oval ridge of soft tissue that creates a tight seal. As water is forced out of the space between the remora and its host, the suction holds it in place. The surface of the remora fish disc is also covered with ridges aligned in columns and rows called lamellae (similar to the ridges you can feel on the roof of your mouth) that can be extended by muscle contractions to engage tiny spinules that s cling more to hosting. These sipe ridges also help create smaller suction compartments that maintain their seal even if the larger lip of the disc does not. Unlike a suction cup, which releases its grip on a smooth surface when a small part of its edge is lifted, a remora fish will always hold.
The team was able to create an artificial version of the remora fish suction disk through a four-layer approach. They paired an ultra-flexible layer on top with stiffer structures underneath, as well as a layer with a network of small channels that can be inflated when filled with fluid, replacing living muscle tissue as the means to engage lamellar structures to further increase suction. .
Installed on top of the submersible drone, the suction mechanism allows it to stick to a variety of surfaces, even if they have a rough texture, are not perfectly flat, or have a smaller surface area than the suction mechanism. Like a remora fish, the drone could, at least in theory, find itself an underwater host (which isn’t immediately spooked by its spinning propellers) and attach itself for a free spin, requiring only power. of the suction mechanism, which is a minimum consumption of its on-board batteries. The same could be done in the air, although the challenges of successfully attaching the drone to another aircraft would be monumental, as even something as slow as a glider has a minimum speed of 40 mph: a moving target difficult.
A more plausible use of the vacuum mechanism is to temporarily perch the drone somewhere with an ideal vantage point for long-term observations. Instead of relying on its four motors to maintain a specific position underwater while fighting moving currents, the drone could stick to a rock or log and turn off its motors, while powering sensors and cameras. . The same could be done above the waterline, with the drone flying and sticking to the side of a tall building or below the nacelle of a wind turbine, and performing measurements and other data collection. data without the use of its battery-draining motors. It is a solution to battery technology that is still incredibly limited and obviates the need to repair the batteries themselves.
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