Industrial Electronics

Video: Soft robot reacts to changes in bodies of water

26 March 2021

Researchers at Duke University have developed an electronics-free soft robot shaped like a dragonfly that skims across water, reacting to varying environmental conditions.

The robot is a demonstration of what could be the future of autonomous, long-range environmental sentinels for monitoring pH, temperature or the presence of oil.

The team started development of the soft robot based on a fly but settled on the shape of a dragonfly engineered with a network of interior micro-channels that allow it to be controlled with air pressure. The body is about 2.25 in long with a 1.4 in wingspan and was made by pouring silicon into an aluminum mold and baking it. Soft lithography was then used to create interior channels connected with flexible silicon tubing.

Called DraBot, the soft robot works by controlling the air pressure coming into its wings and the micro-channels carry the air into the front wings, where it escapes through a series of holes in its back wings. If the wings are down, the airflow is blocked and the robot does not move but if both wings are up, DraBot moves forward.

For control, Duke University designed balloon actuators under each of the back wings close to DraBot’s body. When inflated, the balloons cause the wings to curl upward and the direction can change whether the wings are up or down.

“We were happy when we were able to control DraBot, but it’s based on living things,” said Vardhman Kumar, a PhD student working on the project at Duke. “And living things don’t just move around on their own, they react to their environment.”

Researchers painted one set of wings with a self-healing hydrogel, which made DraBot more responsive to changes in the surrounding water’s pH. When the water became acidic, one wing fused with the back wing, and, instead of traveling in a straight line as instructed, the imbalance caused the robot to spin in a circle. Once the pH returns to a normal level, the hydrogel “unheals” and the fused wings separate.

Additionally, the team leveraged sponges under the wings and doped the wings with temperature-responsive materials so when the robot skims over water with oil floating on the surface, it soaks it up and changes color according to the corresponding color of oil.

These types of robots could play an important part in an environmental robotic sensor in the future and its ability to soak up oils could make it a candidate for the detection of oil spills or environmental cleanup, Duke said.

The next steps could be to improve on the concept of the soft robot by adding wireless cameras or solid-state sensors. Another possibility would be to create a form of onboard propellant to help the bots break free of their tubing.

“Instead of using air pressure to control the wings, I could envision using some sort of synthetic biology that generates energy,” said Shyni Varghese, professor of biomedical engineering at Duke. “That’s a totally different field than I work in, so we’ll have to have a conversation with some potential collaborators to see what’s possible. But that’s part of the fun of working on an interdisciplinary project like this.”

The full research can be found in the journal Advanced Intelligent Systems.

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