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PigeonBot Uses Real Feathers to Explore How Birds Fly

Airplanes have a lot to learn from birds, and PigeonBot is teaching us about the magic of feathered flight

4 min read
PigeonBot
Image: Lentink Lab/Stanford University

Birds have been doing their flying thing with flexible and feathery wings for about a hundred million years, give or take. And about a hundred years ago, give or take, humans decided that, although birds may be the flying experts, we’re just going to go off in our own direction with mostly rigid wings and propellers and stuff, because it’s easier or whatever. The few attempts at making artificial feathers that we’ve seen in the past have been sufficient for a few specific purposes but haven’t really come close to emulating the capabilities that real feathers bestow on the wings of birds. So a century later, we’re still doing the rigid wings with discrete flappy bits, while birds (one has to assume) continue to judge us for our poor choices.

In a paper published today in Science Robotics, researchers at Stanford University have presented some new work on understanding exactly how birds maintain control by morphing the shape of their wings. They put together a flying robot called PigeonBot with a pair of “biohybrid morphing wings” to test out new control principles, and instead of trying to develop some kind of fancy new artificial feather system, they did something that makes a lot more sense: They cheated, by just using real feathers instead. 

The reason why robots are an important part of this research (which otherwise seems like it would be avian biology) is because there’s no good way to use a real bird as a test platform. As far as I know, you can’t exactly ask a pigeon to try and turn just using some specific wing muscles, but you can definitely program a biohybrid robot to do that. However, most of the other bioinspired flying robots that we’ve seen have been some flavor of ornithopter (rigid flapping wings), or they’ve used stretchy membrane wings, like bats.

Stanford PigeonBotBy examining real feathers, the Stanford researchers discovered that adjacent feathers stick to each other to resist sliding in one direction only using micron-scale features that researchers describe as “directional Velcro.”Image: Lentink Lab/Stanford University

Feathers aren’t just more complicated to manufacture, but you have to find some way of replicating and managing all of the complex feather-on-feather interactions that govern wing morphing in real birds. For example, by examining real feathers, the researchers discovered that adjacent feathers stick to each other to resist sliding in one direction only using micron-scale features that researchers describe as “directional Velcro,” something “new to science and technology.” Real feathers can slide to allow the wing to morph, but past a certain point, the directional Velcro engages to keep gaps from developing in the wing surface. There are additional practical advantages, too: “they are softer, lighter, more robust, and easier to get back into shape after a crash by simply preening ruffled feathers between one’s fingers.”

With the real feathers elastically connected to a pair of robotic bird wings with wrist and finger joints that can be actuated individually, PigeonBot relies on its biohybrid systems for maneuvering, while thrust and a bit of additional stabilizing control comes from a propeller and a conventional tail. The researchers found that PigeonBot’s roll could be controlled with just the movement of the finger joint on the wing, and that this technique is inherently much more stable than the aileron roll used by conventional aircraft, as corresponding author David Lentink, head of Stanford's Bio-Inspired Research & Design (BIRD) Lab, describes:

The other cool thing we found is that the morphing wing asymmetry results automatically in a steady roll angle. In contrast aircraft aileron left-right asymmetry results in a roll rate, which the pilot or autopilot then has to stop to achieve a steady roll angle. Controlling a banked turn via roll angle is much simpler than via roll rate. We think it may enable birds to fly more stably in turbulence, because wing asymmetry corresponds to an equilibrium angle that the wings automatically converge to. If you are flying in turbulence and have to control the robot or airplane attitude via roll rate in response to many stochastic perturbations, roll angle has to be actively adjusted continuously without any helpful passive dynamics of the wing. Although this finding requires more research and testing, it shows how aerospace engineers can find inspiration to think outside of the box by studying how birds fly. 

The researchers suggest that the directional Velcro technology is one of the more important results of this study, and while they’re not pursuing any of the numerous potential applications, they’ve “decided to not patent this finding to help proliferate our discovery to the benefit of society at large” in the hopes that anyone who makes a huge pile of money off of it will (among other things) invest in bird conservation in gratitude.

Stanford PigeonBotWith the real feathers elastically connected to a pair of robotic bird wings with wrist and finger joints that can be actuated individually, PigeonBot relies on its biohybrid systems for maneuvering.Image: Lentink Lab/Stanford University

As for PigeonBot itself, Lentink says he’d like to add a biohybrid morphing tail, as well as legs with grasping feet, and additional actuators for wing folding and twisting and flapping. And maybe make it fly autonomously, too. Sound good to me—that kind of robot would be great at data transfer.

[Science Robotics ]

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The Bionic-Hand Arms Race

The prosthetics industry is too focused on high-tech limbs that are complicated, costly, and often impractical

12 min read
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A photograph of a young woman with brown eyes and neck length hair dyed rose gold sits at a white table. In one hand she holds a carbon fiber robotic arm and hand. Her other arm ends near her elbow. Her short sleeve shirt has a pattern on it of illustrated hands.

The author, Britt Young, holding her Ottobock bebionic bionic arm.

Gabriela Hasbun. Makeup: Maria Nguyen for MAC cosmetics; Hair: Joan Laqui for Living Proof
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In Jules Verne’s 1865 novel From the Earth to the Moon, members of the fictitious Baltimore Gun Club, all disabled Civil War veterans, restlessly search for a new enemy to conquer. They had spent the war innovating new, deadlier weaponry. By the war’s end, with “not quite one arm between four persons, and exactly two legs between six,” these self-taught amputee-weaponsmiths decide to repurpose their skills toward a new projectile: a rocket ship.

The story of the Baltimore Gun Club propelling themselves to the moon is about the extraordinary masculine power of the veteran, who doesn’t simply “overcome” his disability; he derives power and ambition from it. Their “crutches, wooden legs, artificial arms, steel hooks, caoutchouc [rubber] jaws, silver craniums [and] platinum noses” don’t play leading roles in their personalities—they are merely tools on their bodies. These piecemeal men are unlikely crusaders of invention with an even more unlikely mission. And yet who better to design the next great leap in technology than men remade by technology themselves?

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