Long-term studies at the Cutkosky Lab and the Lentink Lab focused on bird-inspired aerial robots, which culminated in a new perching robot, outlined in a report published December 1 in Science Robotics. The researchers hope to use their knowledge from these projects to future projects. Quadcopter drones can be fitted with “stereotyped nature-inspired aerial grasper,” (SNAG) attachments that allow them to fly about, pick up and transport objects while perching on diverse surfaces. The researchers utilized this study to evaluate different sorts of bird toe configurations and to assess microclimates in a remote Oregon forest, demonstrating its potential adaptability.

The researchers previously studied parrotlets, the second smallest parrot species, by flying the birds back and forth between specific perches while five high-speed cameras captured their movements. They included sensors that measured the forces exerted by the birds when they came to a halt, sat down, and took off from the various types of perches.

Roderick, the paper’s primary author, said, “What surprised us was that they did the same aerial maneuvers, no matter what surfaces they were landing on,” It is as if they just let the feet deal with the wide range of surface texture variations and complexity alone. SNAG stands for “stereotyped” because of this formulaic behavior that is present in every bird landing.

SNAG approaches each landing in the same manner as the parrotlets. SNAG, on the other hand, is built on the legs of a peregrine falcon to accommodate for the quadcopter’s size. An intricate 3-D-printed structure replaces the bones, while motors and fishing line serve as the robot’s muscles and tendons.

In order to move back and forth and grip, each leg has its own motor. A similar device in the robot’s leg absorbs landing impact energy and passively turns it into grasping force based on how tendons travel around the ankle in birds. As a result, the robot’s clutch may close in as little as 20 milliseconds, making it exceptionally strong and quick. SNAG’s ankles lock once it is been wrapped around a branch, and an accelerometer on the right foot detects when the robot has landed, triggering a stabilization mechanism.

When Roderick transported his equipment from Stanford to rural Oregon for controlled testing during COVID-19, he brought with him a 3D printer from Lentink’s Stanford laboratory. His goal was to test the robot’s capabilities in diverse environments by sending it along a rail system that launched it at predetermined speeds and angles on various surfaces. It was also demonstrated by Roderick that SNAG is capable of picking up objects from the ground by hand, such as prey dolls and corn hole bean bags. Finally, Roderick and SNAG went for a walk in the adjacent woodland to test out their new inventions.

Next phases in SNAG development will likely focus on enhancing the robot’s situational awareness and flight control prior to landing.

Robots such as this one can be used in a variety of ways, including search and rescue and monitoring wildfires. They can also be used in conjunction with other technologies that are not drones. Snag’s proximity to birds provides unique insights about the biology of birds, as well. Anisodactyl, for example, has three toes in the front and one in the back, like a parrotlet, whereas zygodactyl has two toes in the front and two in the back, like a parrotlet. They were surprised to see that there was minimal variation in performance.

To a biologist like Roderick, SNAG’s potential use in environmental studies is one of the most enticing possibilities. A temperature and humidity sensor was also mounted to the robot, so Roderick could record microclimates in Oregon.

At its core, this research was aimed at helping scientists better understand nature, says Roderick. “If we could have a robot that could act like a bird, that could unlock completely new ways of studying the environment.”

When Roderick persevered through a project that lasted several years, Lentink, the paper’s senior author, applauded him. Research into perching aerial robots for environmental monitoring had its start six years ago when Will Lentink met with many ecologists at Berkeley and wrote his NSF Fellowship proposal. There is currently a 10 million dollar XPRIZE challenge to monitor biodiversity in rainforests thanks to Will’s study.

Stanford’s Fletcher Jones Professor of Engineering and member of Stanford Bio-X and the Wu Tsai Neurosciences Institute, Mark Cutkosky, is one of the paper’s co-authors. David Lentink is an associate professor of science and engineering at the University of Groningen in the Netherlands and a co-chair of the Biomimetics group.

The Air Force Office of Scientific Research and the National Science Foundation provided funding for this study.