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SET AND REST A SPELL

FLYING CREATURES conserve energy by occasionally perching. And, as reported in Science, published weekly by the American Association for the Advancement of Science, engineers are applying nature’s techniques to make aerial robots of all sizes more efficient.

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“Learning From Nature How to Land Aerial Robots” by Mirko Kovac is in the Insights portion of Science, May 20, 2016. It summarizes a more technical paper in the same issue, “Perching and Takeoff of a Robotic Insect on Overhangs Using Switchable Electrostatic Adhesion” by M.A. Graule et al.

Here I share the high points that stuck in mind (sorry for the pun).

Flight, natural or manmade, is a high-energy activity. Thus, to enhance duration of this activity, an occasional perch is beneficial. In general, the larger the creature, or robot, the more complex its perching maneuver.

Examples at one extreme include large birds and, come to think of it, the recent soft returns of space hardware accomplished by Space X and Amazon. Crucial to such maneuvers are complex sensing, planning and control of flight dynamics.

A perching eagle, for instance, uses visual feedback to maintain a constant expansion pattern of the landing area on the retina. A smooth deceleration is achieved to reach zero velocity just before touchdown. The bird senses the nuances of air flow and reshapes its wings to bring about an aerodynamic deep-stall. At the same time, the eagle extends its legs. Its talons attach to the landing surface through a passive grasping that researchers call a “digital tendon locking mechanism.”

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Different approaches of perching for creatures—and robots—of different scale. Image from Science, May 20, 2016.

Science author Mirko Kovac observes that “smaller animals have a different perching strategy that relies more on mechanical intelligence of their body morphology.” Houseflies, for instance, touch down (or upon a ceiling!) with no reduction of velocity. Instead, their legs extend and provide passive damping upon impact.

The ballooning spider spins a silk-thread parachute that allows it to be propelled by the breeze. The thread also permits perching.

Even some plant seeds exhibit a form of ultra lightweight perching: Their bristles interlink with bird feathers for long-distance hitchhiking.

What with the increased use of robots for observation (some of it clandestine), the duration of their operation at high vantage points becomes more crucial. Engineers have transformed several of nature’s perching tricks into similar robotic rest stops.

Research details in Science are from M.A. Graule, Department of Mechanical Engineering, M.I.T., working with colleagues at Harvard; City University of Hong Kong; the University of Washington, Seattle; Illinois Institute of Technology; and SRI International. Their robotic insect can fly around, stabilize itself beneath a target, attach itself through electrostatic adhesion, then switch off the adhesion to resume flight.

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Robot design and principle of operation. This and the following image from Science, May 20, 2016.

Researchers call these devices MAVs, micro aerial vehicles. The one shown has a wingspan of little more than 1 inch. Applications aren’t only spy stuff; MAVs can provide bird’s-eye view of disaster areas, detect hazardous chemical or biological matter, or enable ad hoc communication networks.

A MAV’s ability to perch on trees, buildings or power lines extends its on-board battery life. What’s more, an overhang perch gives the device protection from weather, yet with a clear view of the area below.

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The robot attaches itself to (B) a leaf, (C) a glass and (D) unfinished plywood.

The researchers note that previous MAV perching depended upon specific surface irregularities, whereas their electrostatic approach works on a variety of surfaces. Its energy demands in perching are three orders of magnitude less than that required for sustained flight.

Set a spell and rest up for the intended mission. ds

© Dennis Simanaitis, SimanaitisSays.com, 2016

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