The field of Biomechanics has been strong at FHL for decades, with research and classes exploring the links between biology and engineering in algae, invertebrates, and fishes.  This essay explores a different organism than the usual suspects: a remarkable marine bird, the gannet.  While we don’t have gannets in our nearby ocean, we can attract a diverse group of collaborators with expertise to study their unique body plan using sophisticated scanners and modeling tools.

Best,
Dr. Megan Dethier, FHL Director
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The rise of transformer robots is at FHL

by Ed Habtour

Ed Habtour is an assistant professor in the UW Aeronautics and Astronautics Department and founder of the Illimited Lab. The Illimited Lab focuses on revealing, understanding, and emulating the intrinsic functions of irregular geometric patterns found in nature, responsible for their remarkable maneuvers, sensing, control, and repair. The research was supported by the National Science Foundation CAREER award and grants from the PIs’ home institutions.   

Headlines reporting on the latest jaw-dropping feats of robots are almost unavoidable — machines that swim like fish, slither like snakes, or dance with humans.  Yet engineering nature-inspired transformer robots remain elusive — e.g., machines that can seamlessly shift from flying to diving.  Why does bio-inspired engineering fall short here?

Bio-inspired design emphasizes either structural simplification or optimization of regular patterns, i.e. precise, symmetric and repeated geometries, but overlooks opportunities presented by the specialized (and ‘deliberate’) geometric irregularities found in living systems.  Irregularity is defined as repeated periodic lattice structures but with distortions in their geometries, such as those commonly seen in living organisms.  Typically, three geometric variants define the construction of an irregular pattern: rigidity (size and shape) of a segment, interface between adjacent segments (via short muscles and/or cartilage), and trajectory (emerging global shape via connections with nonadjacent neighbors via large/long muscles).  The theory is that distortions of these geometric variants are intentional for gaining specialized functions.  For example, spiders distort the radius and angle of rotation of each turn of the spirals on their webs to tune the threads like a guitar.  When prey impacts the web (guitar), it produces a vibration signal with a specific tone that helps the spider identify prey size and location.

An international team of engineers and biologists, instigated by FHL’s collaborative culture, is changing the way we approach irregularities.  Starting with the diving seabird gannet, one of nature’s remarkable transformers, we are revealing distinctive and self-controlled dynamics of neck musculoskeletal irregularities.

From an engineering perspective, gannet necks defy well-established buckling theory.  Gannets are known for their dangerous plunge dives, striking the ocean surface at speeds exceeding 70 mph to hunt fish (Figure 1).  According to buckling theory, to survive such a brutal impact, a gannet’s beam-like neck must be straight, rigid, free of imperfections, and sufficiently damped, e.g. cushioned with shock absorbing materials.  However, CT scans and dissections of postmortem birds conducted at FHL revealed the exact opposite.  Their necks are highly curved, segmented, and undamped (Figure 2).  Today, designing a robot like this would result in the engineer’s immediate dismissal.  Through mathematical modeling and experiments of 3D printed prototypes, the FHL team also showed that breaking a structure into segments and tuning their stiffness can significantly mitigate impact forces without using any damping.  Avoiding damping might be an evolutionary advantage.  The neck irregularities ingeniously split the impact energy into many smaller energies with different time delays (Figure 3).  This is known as energy modulation, which may explain how gannets slow impact energy loss while retaining the required momentum to safely maximize their diving depth and catch prey.

These transformative findings were made possible in large part by FHL’s unique resources and location, nurturing cross-pollination between engineers and biologists.  Engineers learn that groundbreaking physics can be realized in the imprecise world of biology, while biologists realize that the seemingly rigid precision and symmetry of engineering are merely abstract tools for explaining the messy natural world.  The next endeavor is to design a full gannet robot and to study more complex systems such as batoids (stingrays).  Partners include Prof. Todd Trustcott at King Abdullah University of Science & Technology (KSA), Prof. Jovana Jovanova of TU Delft (NL), Dr. Thijs Masmeijer at U of Twente (NL), Prof. Frank Fish at West Chester University, and Profs Adam Summers and Ed Habtour at UW, along with FHL postdoc Dr. Bart Boom and graduate students Meg Vandenberg and John Michael Racy.

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