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Researchers at the University of Washington have developed robotic microfliers that can change how they move while in the air by snapping into a folding position during descent. The microfliers use a Miuri-ori origami fold when dropped from a drone to switch from tumbling and dispersing outward through the air to dropping straight to the ground. 

Each microflier weighs about 400 milligrams, or half as heavy as a nail, and can travel the distance of a football field when dropped from about 131 feet (40 meters) in a light breeze. To help spread out the fliers during testing, the research team controlled the timing of each device’s transition using a few methods: an onboard pressure sensor to estimate altitude, an onboard timer, or a Bluetooth signal. 

“Using origami opens up a new design space for microfliers,” co-senior author Vikram Iyer, UW assistant professor in the Paul G. Allen School of Computer Science & Engineering, said. “We combine the Miura-ori fold, which is inspired by geometric patterns found in leaves, with power harvesting and tiny actuators to allow our fliers to mimic the flight of different leaf types in mid-air. In its unfolded flat state, our origami structure tumbles chaotically in the wind, similar to an elm leaf. But switching to the folded state changes the airflow around it and enables a stable descent, similar to how a maple leaf falls. This highly energy efficient method allows us to have battery-free control over microflier descent, which was not possible before.”

On each microflier there is an onboard, battery-free actuator, a solar power-harvesting circuit, and a controller to trigger these shape changes mid-air. The microfliers also have the capacity to carry onboard sensors to survey temperature, humidity, and other conditions while in the air. 

UW’s microfliers are able to overcome several design challenges that plague other kinds of robots. They’re stiff enough to avoid accidentally transitioning to the folded state before the signal but are still able to transition between states rapidly. The device’s onboard actuators only need about 25 milliseconds to initiate folding. 

The robots are also able to change shape while untethered from a power source as the microfliers’ power-harvesting circuit uses sunlight to provide energy to the actuator. 

The devices do have some drawbacks that the researchers are hoping to address in the future. Right now, the microfliers can only transition in one direction, from the tumbling state to the falling state. This switch allows researchers to control the descent of multiple microfliers at once, so they disperse in different directions on the way down. 

In the future, however, the team wants to create fliers that can transition in both directions. This added functionality will allow for more precise landings in turbulent wind conditions. 

Along with Iyer, other co-authors on the paper include Kyle Johnson and Vicente Arroyos, both UW doctoral students in the Allen School; Amélie Ferran, a UW doctoral student in the mechanical engineering department; Raul Villanueva, Dennis Yin and Tilboon Elberier, who completed this work as UW undergraduate students studying electrical and computer engineering; Alberto Aliseda, UW professor of mechanical engineering; Sawyer Fuller, UW assistant professor of mechanical engineering; and Shyam Gollakota, UW professor in the Allen School.

This research was funded by a Moore Foundation fellowship, the National Science Foundation, the National GEM Consortium, the Google fellowship program, the Cadence fellowship program, the Washington NASA Space Grant Fellowship Program and the SPEEA ACE fellowship program.