Bumblebees are not the most graceful flyers. They tend to bump into flowers about once per second, which causes damage to their wings. However, despite these damages, bumblebees are still able to fly.
Aerial robots, on the other hand, are not as resilient. If you poke holes in a robot’s wing motors or cut off part of its propeller, it will most likely be unable to fly.
Inspired by the toughness of bumblebees, researchers at MIT have developed repair techniques that allow a bug-sized aerial robot to withstand severe damage to its artificial muscles, which power its wings, without compromising its flying abilities.
Optimizing Artificial Muscles for Resilience
The researchers have optimized the artificial muscles in the robot to better identify defects and overcome minor damages, such as tiny holes. Additionally, they have developed a new laser repair method that can help the robot recover from more severe damages, such as fire damage.
Using these techniques, a damaged robot can still perform at a high level even after being jabbed with 10 needles or having a large hole burnt into its actuator. The robot can even continue flying after 20 percent of its wing tip is cut off. This resilience could make swarms of tiny robots more capable of performing tasks in challenging environments, such as searching through collapsing buildings or dense forests.
“We have invested a significant amount of time studying the dynamics of soft, artificial muscles, and with our new fabrication method and understanding, we have achieved a level of resilience comparable to insects. This is an exciting development, although insects still have the advantage since they can lose up to 40 percent of their wing and still fly. We still have some work to catch up,” explains Kevin Chen, the D. Reid Weedon, Jr. Assistant Professor in the Department of Electrical Engineering and Computer Science (EECS) at MIT and the senior author of the study.
Robot Repair Techniques
The robot being developed in Chen’s lab is about the same size and shape as a microcassette tape, with each corner equipped with wings powered by dielectric elastomer actuators (DEAs). These DEAs are soft artificial muscles made from layers of elastomer sandwiched between thin electrodes. When voltage is applied, the electrodes squeeze the elastomer, causing the wings to flap.
However, these artificial muscles can fail due to microscopic imperfections that cause the elastomer to burn. To overcome this, the researchers have employed a self-clearing process that isolates the failure and allows the artificial muscles to continue functioning. They have optimized the concentration of carbon nanotubes in the electrodes for improved self-clearing, striking a balance between preventing failures and maintaining the actuator’s power density.
For more severe damages, such as large holes, the team uses a laser to perform surgery on the muscles. By carefully cutting along the outer contours of the defect, minor damage is caused around the perimeter. Self-clearing is then used to burn off the slightly damaged electrode, isolating the larger defect. Electroluminescent particles in the actuator allow the researchers to observe the areas that have been successfully isolated.
Success in Flight Tests
After perfecting their repair techniques, the researchers conducted flight tests with damaged actuators. The robot maintained its flight performance, with only minimal deviations in altitude, position, and attitude as compared to an undamaged robot. Through laser surgery, a DEA that would have been irreparably broken managed to recover 87 percent of its performance.
With these improved repairs, the tiny robots become much more robust. The team is now focusing on teaching the robots new functions, such as landing on flowers and flying in swarms. They are also developing new control algorithms to enhance flight capabilities and enable the robots to carry their own power source.
This research is partially funded by the National Science Foundation (NSF) and a MathWorks Fellowship.