Battery-Free Flying Robots Use Origami to Facilitate a Soft Landing

Small flying devices that can change how they move through the air using an origami folding technique pave the way for new battery-free designs in micro-sized flying robots, or microfliers, which can carry sensors to survey environmental conditions.

Researchers at the University of Washington (UW) have developed the robots, which snap into a folded position during their descent, dropping to the ground after tumbling through the air. The microfliers—which are dropped into the air from a drone—use a Miura-ori origami fold for the sudden switch, a technique that allowed the team to overcome previous design challenges for such devices, the researchers said.

The technique allows the flying robots to mimic the movements of different types of leaves in midair, noted Vikram Iyer, UW assistant professor in the Paul G. Allen School of Computer Science & Engineering. The robots tumble while unfolded in the wind like an elm leaf, but then switch "to the folded state [that] changes the airflow around it and enables a stable descent, similarly to how a maple leaf falls," he said in a post on UW News.

“Using origami opens up a new design space for microfliers,” he explained. “We combine the Miura-ori fold, which is inspired by geometric patterns found in leaves, with power harvesting and tiny actuators. This highly energy efficient method allows us to have battery-free control over microflier descent, which was not possible before.”

Small But Powerful Flying Robots

The microfliers are tiny, weighing about 400 milligrams—which is about half as heavy as a nail. However, they can travel the entire distance of a football field when dropped from 40 meters, or about 131 feet, in a light breeze, the researchers said.

"When unfolded and flat, the microfliers exhibit a tumbling behavior that increases lateral displacement in the wind," the researchers shared on a website about the technology. "When folded inward, their orientation is stabilized, resulting in a downward descent that is less influenced by wind."

And while they are light and small, they carry significant technology capable of engineering the mid-air shape change; specifically, each device has an onboard battery-free actuator, a solar power-harvesting circuit fabricated directly onto the folded origami structure, and programable microcontroller. The low-power electromagnetic actuator produces peak forces of up to 200 millinewtons within 25 milliseconds on solar power, according to the researchers.

In addition to this essential technology, the robots also can carry onboard sensors to survey environmental factors such as temperature, humidity, and other conditions while they fly.

Researchers published a paper on their work in the journal, Science Robotics. In tests, the microfliers demonstrated the ability to change their shape in midair—needing only about 25 milliseconds to initiate the folding movement—while traveling in a light breeze and wirelessly transmitting data via Bluetooth up to 60 meter away, the researchers reported.

While the current crop of microfliers can only transition in one direction—from the tumbling state to the falling state—future devices will be able to transition in both directions, the researchers noted. The former allows researchers to control the descent of multiple microfliers at the same time for dispersal in different directions on their way down; however, the latter will allow for more precise landings in turbulent wind conditions, they said.