Unmanned aerial vehicle technology is advancing rapidly, and drones are getting smaller by the day. Militaries are now employing Micro, Mini & Nano UAVs into their operations. They provide situational awareness to a small group of soldiers by flying several stories above them for 10-20 minutes at a time before placed back into a pocket to recharge. These will be used to carry out tasks in urban environments, such as deliveries, surveillance, and search and rescue. Small drones are considered better because they are more agile, are harder to detect, and are easier for pilots to control.
Animals from bees to bats are inspiring the new generation of drones or flying robots, and large military strike drones aside, the robots themselves are getting smaller, with microdrones the size of a bug on a flower to eagle-inspired quadcopters with the ability to snatch up objects at speed.
Nature has found some elegant solutions to complicated problems and engineers have long been inspired by its designs. Long before aircraft took flight, birds, bats and insects conquered the skies.Drawing inspiration from what evolution has achieved to allow animals to fly allows us to create the drones that are closest to the flight of a bird or a dragonfly. Now scientists are designing drones that draw inspiration from biology for advanced new capabilities.
During millions of years of evolution, nature has developed processes, objects, materials, and functions to increase efficiency. Sometimes, looking at nature provides us with the best answers for the development and optimization of different types of systems, including aerospace systems. Nature always has effective solutions for many complex tasks in aerospace industries, such as drag reduction techniques, locomotion, navigation, control, sensing, and aircraft design.
The field of biomimicry, also known as biomimetics, seeks to emulate nature with technology. Such research is driving novel strategies to improve the safety, efficiency, dexterity and versatility of drones. It may also lead robotics to uncover biological secrets otherwise beyond the reach of scientists.
The applications of the drones, inspired variously by flight aspects of flies, bees, moths, pigeons, eagles, bats and even, slightly disturbingly, flying snakes, seem limitless, from those designed to fly in swarms for search and rescue missions to yet others with inner-city courier applications in mind. Yet others are designed to perch as a bird or bug and provide mobile surveillance or to carry sensors for environmental monitoring, such as pollution monitoring.
Professor David Lentink, from the Department of Mechanical Engineering at Stanford University, explains that nature has solved the problems of take-off, obstacle avoidance, swarming effectively, grabbing objects in flight and, in the case of the fruit fly, landing on the rim of a wine glass that the drones are still clumsily fumbling with.
The fluttering flight patterns of butterflies have long inspired poets but baffled scientists. The problem for these creatures is that they have unusually large wings relative to their body size, which are aerodynamically inefficient for flight. Back in the 1970s, researchers developed a theory that their big wings allowed the butterfly to clap them together on the upstroke to power their take off. Now, a new study reported in Jan 2021 shows at Lund University in Sweden that butterflies evolved an effective way of cupping and clapping their wings to generate thrust. The scientists say that this ability helps them avoid dangerous predators.
As well as recording slow-motion video of the butterflies in flight, the researchers constructed two simple pairs of mechanical clappers to test their ideas. One was rigid, the other flexible and more akin to the butterfly wings observed in the wind tunnel tests. The team found that the flexible wings dramatically increased the force created by the clap. It also improved the efficiency by 28%, which the authors describe as a huge amount for a flying animal. This leads them to conclude that the large wings and cupped, clapping action were an evolutionary advantage for butterflies when faced with predators. “If you are a butterfly that is able to take off quicker than the others, that gives you an obvious advantage,” said Per Henningsson.
Some drone devices and underwater vehicles already use propulsion systems based on wing clapping motion, but with limitations. The incorporation of the approach used by butterflies might bring major improvements, the scientists say. When the researchers recreated this using mechanical wings, they found that those with butterfly-like flexibility that form this pocket at the moment of impact were 22% more effective in the amount of force created and 28% more efficient in the amount of energy used compared with rigid wings. “We’re suggesting that the people that are working on these designs, they should look into this cup-shape behaviour, since there are lots of efficiency and effectiveness to be gained from it,” said Per Henningsson.
One of the research teams, from the University of Washington, took inspiration from the common house fly – a master of controlled flight. Using a scaled-up robotic model (with two acrylic wings some 230 mm in length), the team was able to demonstrate how flies adjust their wings and pitch for stabilised forward flight at different speeds.
The seeming simplicity of a fly’s flight belies the complexity of the animal’s neuromuscular architecture of the wing hinge that enables a fly to call on different stroke patterns during flight. Making the robotic wings required each to have three independently actuated degrees of freedom: stroke angle, deviation angle and rotation angle.
In similar research from Brown University and the University of Missouri, a team took inspiration from the membrane wings of the bat in building their robotic copy. They were able to demonstrate the wing’s remarkable uplift and glide ability. “Unlike flapping birds and insects, bats possess membrane wings that are more similar to many gliding mammals. The vast majority of the wing is composed of a thin compliant skin membrane stretched between the limbs, hand and body,” the researchers write in their published paper. Several other teams also focused on the bat, examining aspects such as how muscle arrays in the wing could change the rigidity of the membrane.
Yet another group, from the University of North Carolina, modelled the behaviour of hawkmoths and how they adapted their flight to turbulent air conditions. Professor Lentik writes that the insights gained “can guide the design of appropriate test facilities to assess the robustness of drones to environmental turbulence”.
A team from the California Institute of Technology, Pasadena, and the University of Washington also called on the fruit fly and the honey bee, but this time for vision to detect position, objects and avoid collisions. Big animals like humans use object recognition and stereo vision to estimate distances to things, for example, how far our hand has to reach to pick up a tea cup. However, small insects like the fly and the bee rely on calculations of optic flow, which can provide a measure of the ratio of velocity to distance using compound eyes, so that they know when to slow down and extend their legs for landing. To model the way an insect uses optic flow to estimate distances for efficient landings, the researchers developed an algorithm with which they were able to demonstrate the effectiveness of using images streamed with a translating camera. Professor Lentik writes that the research could “improve the visual guidance of drones through GPS-denied and complex environments”.
Inspired by the eagle, a team from the University of Pennsylvania and Carnegie Mellon University made and demonstrated a flying quadrotor drone capable of snatching up objects on the move, predator-avian style. The researchers write, “Dynamic grasping is relevant for fast pick-and-place operations, transportation and delivery of objects, and placing or retrieving sensors.”
Researchers from the Harvard Microrobotics Laboratory demonstrated drones that could fit on your finger tip with wings that flap like an insect. Although they can take off vertically and hover, apparently, there are still flight control issues to overcome.
Drones with Flapping Wings
Since at least the time of Leonardo da Vinci, scientists have sought to mimic the acrobatic way in which bats and birds maneuver the sky. Increasingly, researchers are designing biologically inspired aircraft known as ornithopters that fly by flapping their wings and may one day prove more versatile, safer and quieter than existing drones.
For example, Gih-Keong Lau at the National Chiao Tung University in Taiwan and his colleagues have developed an ornithopter drone that mimics the aerobatic maneuvers of the swift, one of the world’s fastest birds. The robot weighs just under an ounce (26 grams), the equivalent of two tablespoons of flour, and can glide, hover at very low power, and stop quickly from fast speeds, all things quadcopters cannot do.
The ornithopter is also incredibly agile, turning within a one-and-a-quarter inch (32 millimeter) radius, and could recover to a stable gliding motion without tumbling after a 90-degree body flip. In addition, it consumes 40 percent less electrical power for the same level of thrust as a comparable propeller-driven robot.
“With a weight of less than 30 grams, it can fly for eight minutes,” Lau said. “In comparison, a 30-gram quadcopter can only fly four minutes. So a flapping-wing robot can be more efficient than a quad-copter, at least at small scales.” The researchers noted their ornithopter’s light weight and slowly beating wings would make it safer for use around humans than multirotor drones. While the ornithopter could crash into humans or other obstacles in its environment and cause them little to no damage, multirotor drones spin their propeller blades at dangerously high speeds.
The scientists “are now sizing up the robot so it can carry more batteries and even a camera,” Lau said. Potential applications could then include monitoring crowds and traffic, or surveying forests and wildlife. Other uses “could be inside greenhouses for pollination or pest control,” he added. “Quadcopters with their propellers spinning at very high speeds could cut into vegetation if they fly too close.”
As an example, one of the interesting aspects of avian flight dynamics is how natural flyers, such as birds and insects, can deform their shape to optimize their flight in different flight modes. Therefore, the concept of morphing structures for aerial vehicles can be traced to the observation of birds as they fly. Birds are able to fly so efficiently because they can adjust the shape of their wings, down to individual feathers, depending on the task at hand. This has been closely studied by aerospace engineers with a view to developing shapeshifting wings for larger, low-energy aircraft, and now the Researchers has found it to be useful for drones too.
That versatility could prove useful in a variety of complex scenarios, such as search and rescue missions. For example, Floreano and his colleagues—who are developing several biomimetic projects—noted that pigeons can fold their wings to optimize their gliding efficiency over a broad range of speeds, and choose different shapes for their wings to negotiate gaps of different sizes.
As such, researchers have explored morphing drones that can change shape during flight to better suit a specific task or environment. For instance, at Purdue University Xiumin Diao and his colleagues are working on a drone that can use motors to move its arms. “We got our inspiration from bees,” Diao said. “Their rotatable wings have at least three degrees of freedom.”
Rotating the arms of a drone can alter its center of gravity, enabling more balanced thrust. In computer simulations, the researchers found such a balancing act could boost the energy efficiency of the UAV by up to 13 percent during a steady hover. Field experiments found such balancing could save even more energy—shifting the arms could help the drone keep steady in a more energy-efficient manner than constantly accelerating or decelerating the rotors to stabilize the drone. Diao worked with Purdue University to patent this drone design, and they are now looking for partners to license this technology.
Micro air vehicles (MAVs), have to navigate in close proximity to obstacles. These MAVs should be highly manoeuvrable in order to rapidly change course with a small turn radius: for a given weight of the aerial vehicle, a small turn radius is obtained by maximizing the wing surface and the lift coefficient of the wing. However, wings with a large surface are very sensitive to wind; while, wings with a small surface generate less frictional drag allowing an aerial vehicle to fly faster and keep a constant forward ground speed in comparatively stronger headwinds.
Several bird species solve this problem by changing the shape of their wings to adapt to the different aerodynamic requirements. Several flying animals use morphing wings to improve flight capabilities. For example, birds exploit surface morphing to actively control their attitude and to achieve high aerodynamic performance within a wide range of flying speeds.
Scientists are developing Morphing wings that change the shape and configuration of an aircraft taht can expand the flight capabilities of a flying vehicle to fulfil opposing requirements. A wing with a morphing surface could adapt its aerial surface to optimize aerodynamic performance to specific flight situations.
Bird wings are composed of flight feathers that can overlap connected to an articulated skeleton controlled by muscles. The outermost feathers, known as primary flight feathers, significantly reduce the surface of the wing when folded.(b) Shows prototype of the morphing wing drone described by M. Di Luca, S. Mintchev, reported in 2017. Similar to birds, the drone is equipped with a feathered wing that folds the outermost sections in order to modify the surface area and also control roll angle for turning.
Feathered drone uses morphing wings and tail to fly like a raptor
In 2016, Researchers fro Switzerland’s École Polytechnique Fédérale de Lausanne (EPFL), had taken inspiration from birds to produce a feathered drone with unique capabilities. The team has continued refining this design to introduce more moving parts, enabling the drone to now fly with “unparalleled agility.”
For their updated version, the EPFL researchers have paired these shapeshifting wings with a morphing tail, which ups the biomimicry even further. This is modeled on the flight behavior of the northern goshawk raptor, which is able to cut through forests and make in-flight adjustments to chase down its prey. “Goshawks move their wings and tails in tandem to carry out the desired motion, whether it is rapid changes of direction when hunting in forests, fast flight when chasing prey in the open terrain, or when efficiently gliding to save energy,” says Enrico Ajanic, the first author of the study.
The drone uses a propellor for forward thrust rather than its wings, which the researchers say is more energy efficient. Just as it adjusts its wings in flight, the drone can move its tail in tandem to change direction more rapidly, improve its aerodynamics when trying to fly fast, or even to help it slow down without falling to the ground.
“Our design extracts principles of avian agile flight to create a drone that can approximate the flight performance of raptors, but also tests the biological hypothesis that a morphing tail plays an important role in achieving faster turns, decelerations, and even slow flight,” says Dario Floreano, who led the research.
What winged drones like this one offer that quadcopter drones don’t is longer flight times, which makes them well-suited to certain applications such as delivering medical supplies over great distances or surveying farmlands. What they don’t offer, however, is the same hovering capabilities or agility in the air, but the researchers see their solution as something of a happy medium. “The drone we just developed is somewhere in the middle,” says Floreano. “It can fly for a long time yet is almost as agile as quadrotors. This combination of features is especially useful for flying in forests or in cities between buildings.”
Protective Cages reported in Oct 2020
Delivery drones are currently equipped with unshielded propellers, which may prove dangerous to bystanders and therefore limit the potential for in-hand parcel delivery. A possible solution is to enclose unmanned aerial vehicles (UAVs) in protective cages, but these structures face a number of tradeoffs when it comes to their designs. A cage with a dense grid of bars restricts airflow, while a sparse grid does little to protect hands from rotors. In addition, a large cage is heavy, while a small cage shortens the arms on which a drone’s propellers are placed, reducing its aerodynamic efficiency and stability.
One new biomimetic cage design is loosely inspired by the box turtle. When the quadcopter dubbed the GearQuad flies close to people, its arms and propellers retract to stay fully confined within the cage, but when flying at cruising altitudes high above people and other obstacles, its arms and propellers extend outward, increasing its aerodynamic efficiency by more than 20 percent. “Another advantage of this design is that when the drone is not in use, you can store it in a small space,” said researcher Dario Floreano, director of the Laboratory of Intelligent Systems at the Swiss Federal Institute of Technology Lausanne. “The cage becomes the wrapping material, the box for the drone.”
To keep the cage light while still protecting bystanders, Floreano and his colleagues made GearQuad’s frame from carbon fiber beams, with the “bars” of the cage constructed of grids of plastic wires, much like the strings of a tennis racket. These wires are densely packed enough to keep out even a child’s fingers, making GearQuad safe enough to hold in one’s hand during operation, the scientists noted. In this scenario, the parcel is located on top of the drone, and the cage replaces the need for landing gear.
All in all, the components that help GearQuad extend and retract its arms from the cage weigh 169 grams, about 6 percent of the drone’s total mass, which is more than offset by the boost in lift the UAV gets from not keeping its propellers confined with the cage, the researchers said. The cage itself weighs just under six ounces (377 grams), about 15 percent of GearQuad’s total mass, a weight penalty the researchers suggested was reasonable given the added safety for people.
Another creature inspiring techniques to improve drone safety is the pufferfish, which blows up like a balloon to scare away predators. Scientists at the Atlas Institute at the University of Colorado at Boulder have developed a quadcopter drone they’ve dubbed PufferBot. Based on a DJI Flame Wheel F450 frame, the robot carries a shield of plastic hoops on top of itself that can expand in size from roughly 20 inches to 33 inches in diameter in about six seconds, acting like an airbag to prevent dangerous collisions. The shield and the motor used to drive it together weigh about 3.5 pounds. “When the frame is not needed, it can contract so the drone can go into a tight and narrow space,” researcher Hooman Hedayati said. The PufferBot team is working on making the structure as light and stiff as possible, and to boost the speed at which it expands and collapses.
Instead of just modifying the arms of multirotor drones to make them more versatile, Floreano and his colleagues have also explored altering the entire frames of a UAV to make it more changeable. “This flexible design was inspired by the wings of wasps, which can hit obstacles like grass or sticks thousands of times without breaking,” Floreano said.
When drones collide with obstacles, the encounter can often prove catastrophic for the drones and dangerous for whatever they hit, limiting their use around people and in confined spaces, such as in buildings or forests. Instead of relying on protective cages, which add weight, Floreano and his colleagues have devised drones with flexible frames that can absorb the shock of impact and minimize damage.
The researchers developed a small quadcopter UAV with a frame made of an elastic membrane sandwiched between rigid plates. The frame is stiff enough to carry the drone’s weight and withstand the thrust of its propellers, but it softens during collisions to avoid permanent damage, snapping back into shape once past the obstacle.
The inspiration from way falcon kills it’s prey may lead to counterdrone systems reported in Jan 2018
Falcons are among the fastest and most agile predators in the sky. They’re also highly adaptable – capable of thriving in nearly every habitat on Earth – thanks to their ability to capture prey under almost any conditions. The US military wants to be just as effective at capturing enemy drones: The Air Force had funded an Oxford University study designed to understand the “method of attack” of the peregrine falcon, one of nature’s fiercest hunters.
The researchers used miniature GPS receivers and onboard video cameras to track peregrines attacking dummy targets that were either thrown in the air by a trained “falconer,” or towed by an aerial drone. After studying 55 “attack flights” in total, the researchers found that falcons behave more like guided missiles than they had previously realized, with some exceptions. When modeled in a mathematical simulation, the birds’ hunting behavior exhibited similar patterns to the rules of “proportional navigation,” which is a system commonly used to direct combat missiles in flight.
However, the falcons showed a greater ability to adjust the angle of their attack than is commonly seen in proportional navigation. According to the researchers, they make these adjustments to compensate for their slower speeds than certain prey in the sky. By creating navigation algorithms that allow military aircraft to behave even more like falcons, the research initiative may ultimately help protect US lands and people from airborne enemy combatants.
“Our next step is to apply this research to designing a new kind of visually guided drone, able to remove rogue drones safely from the vicinity of airports, prisons and other no-fly zones,” says Professor Graham Taylor of Oxford University’s Oxford Flight Group.