Stanford University Researchers Create Biohybrid Morphing Wing for "PigeonBot" Feathered Drone

Researchers at Stanford University's Department of Mechanical Engineering have published a paper detailing a new flying robot, PigeonBot, constructed from real feathers in an attempt to better understand how living birds control their flight.

"Since the Wright Flyer, engineers have strived to develop flying machines with morphing wings that can control flight as deftly as birds," Stanford University's Eric Chang, Laura Y. Matloff, Amanda K. Stowers, and David Lentink write in the abstract to their paper on what they have dubbed PigeonBot. "Birds morph their wing planform parameters simultaneously — including sweep, span, and area — in a way that has proven to be particularly challenging to embody robotically. Previous solutions have primarily centred around the classical aerospace paradigm of controlling every degree of freedom to ensure predictable performance, but underperform compared with birds.

"To understand how birds accomplish wing morphing, we measured the kinematics of wing flexion and extension in common pigeons, Columba livia. The skeletal and feather kinematics show that the 20 primary and 20 secondary feathers are coordinated via approximately linear transfer functions controlled by wrist and finger motion. To replicate this control principle in a robot, we developed a biohybrid morphing wing with real feathers to understand the underlying design principles."

The result is PigeonBot, a feather-wearing robot with 42 degrees of freedom (DOF) controlling 40 elastically-connected features through four servo-actuated wrist and finger joints. "Our flight tests demonstrate that the soft feathered wings morph rapidly and robustly under aerodynamic loading," the researchers claim. "They not only enable wing morphing but also make robot interactions safer, the wing more robust to crashing, and the wing repairable via 'preening.'"

The team's experiments began with the measurement of pigeon wings in motion, then the creation of a biohybrid wing 3D printed in nylon onto a fixed wing root aerofoil created from balsa ribs and card stock - plus Teflon sheeting to minimise friction in the pin joints that connect the feathers to the structure. The result is a robot weighing around 280g, roughly half the weight of a real pigeon, which was tested in a wind tunnel, aerodynamic simulations, and finally outdoor free-flight experiments.

"In flight tests," the team writes, "we found that both asymmetric wrist and finger motion can initiate turn maneuvers — evidence that birds may use their fingers to steer in flight."

The full paper is available under open access terms in the journal Science Robotics, while interviews with the team behind PigeonBot can be found on IEEE Spectrum and NPR.