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Perching Bird-Like Robot Developed

When attached to a quadcopter drone, the Stereotyped Nature-Inspired Aerial Grasper (SNAG) forms a robot that can fly around, catch and carry objects and perch on various surfaces.

The SNAG robot. Image credit: William Roderick.

The SNAG robot. Image credit: William Roderick.

“It’s not easy to mimic how birds fly and perch. After millions of years of evolution, they make takeoff and landing look so easy, even among all of the complexity and variability of the tree branches you would find in a forest,” said Dr. William Roderick, a researcher in the Department of Mechanical Engineering at Stanford University.

In the previous studies of parrotlets, the birds flew back and forth between special perches while being recorded by five high-speed cameras.

The perches contained sensors that captured the physical forces associated with the birds’ landings, perching and takeoff.

“What surprised us was that they did the same aerial maneuvers, no matter what surfaces they were landing on,” Dr. Roderick said.

“They let the feet handle the variability and complexity of the surface texture itself. This formulaic behavior seen in every bird landing is why the ‘S’ in SNAG stands for stereotyped.”

Just like the parrotlets, SNAG approaches every landing in the same way. But, in order to account for the size of the quadcopter, the aerial robot is based on the legs of a peregrine falcon.

In place of bones, it has a 3D-printed structure and motors and fishing line stand-in for muscles and tendons.

Each leg has its own motor for moving back and forth and another to handle grasping.

Inspired by the way tendons route around the ankle in birds, a similar mechanism in the robot’s leg absorbs landing impact energy and passively converts it into grasping force.

The result is that the robot has an especially strong and high-speed clutch that can be triggered to close in 20 milliseconds.

Once wrapped around a branch, SNAG’s ankles lock and an accelerometer on the right foot reports that the robot has landed and triggers a balancing algorithm to stabilize it.

There are countless possible applications for this robot, including search and rescue and wildfire monitoring; it can also be attached to technologies other than drones.

SNAG’s proximity to birds also allows for unique insights into avian biology.

“Part of the underlying motivation of this work was to create tools that we can use to study the natural world,” Dr. Roderick said.

“If we could have a robot that could act like a bird, that could unlock completely new ways of studying the environment.”

The work appears in the journal Science Robotics.


W.R.T. Roderick et al. 2021. Bird-inspired dynamic grasping and perching in arboreal environments. Science Robotics 6 (61); doi: 10.1126/scirobotics.abj7562

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