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.
In June, the journal Bioinspiration & Biomimetics published an open-access special edition focused on drone research. Fourteen research teams showcased their latest experimental efforts and the nature inspiration behind the technology.
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.
In a preface to the edition, 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.
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.”
Finally, 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.
See the open-access special edition of Bioinspiration & Biomimetics with multiple articles and papers on bioinspired drone technology.