MIT’s Tiny Robotic Lightning Bugs Take Flight



Lightning bugs use their luminosity for communication in order to attract a partner, fend off predators, or lure prey, lighting up dark backyards on warm summer evenings.

Researchers at MIT were similarly inspired by these shimmering fireflies. They created electroluminescent soft artificial muscles for flying, insect-scale robots, taking inspiration from nature. When the robots fly, the tiny artificial muscles that drive their wings generate a colored light.

The robots may be able to converse with one another because to this electroluminescence. For instance, a robot that finds survivors while on a search-and-rescue mission within a fallen building could use lights to alert others and request assistance.

These paper-clip-sized microscale robots are now one step closer to flying on their own outside of the lab thanks to their capacity to generate light. Since these robots are too light to carry sensors, researchers must track them using large infrared cameras that are ineffective in the outdoors. They've now demonstrated that with just three smartphone cameras and the light the flying robots emit, they can be tracked precisely.

Robotic Lightning Bug from MIT

In addition to providing a low-cost method of tracking the robots, these artificial muscles that control the wings of lightweight flying robots also have the potential to allow the robots to converse. Credit: The researchers' kind permission

When it comes to communication, large-scale robots have access to a variety of instruments, including Bluetooth, wifi, and other technologies. But we must consider new forms of communication for a tiny, power-constrained robot. Kevin Chen, the D. Reid Weedon, Jr. Assistant Professor in the Department of Electrical Engineering and Computer Science (EECS), the head of the Soft and Micro Robotics Laboratory in the Research Laboratory of Electronics (RLE), and the senior author of the paper, says that this is a significant step toward flying these robots in outdoor settings where we don't have a fine-tuned, cutting-edge motion tracking system.

He and his colleagues made the artificial muscles glow by incorporating tiny electroluminescent particles into them. This procedure increases weight by only 2.5 percent while having no effect on the robot's ability to fly.

Recently, the study was released in IEEE Robotics and Automation Letters. Chen's co-authors on the work are Ningxia University associate professor Jie Mao, EECS graduate students Suhan Kim, the research's lead author, and Yi-Hsuan Hsiao, as well as Yu Fan Chen, SM '14, PhD '17.

These researchers have previously shown how to construct soft actuators, or synthetic muscles, that move the robot's wings. These robust actuators are created by rolling a stack of ultrathin layers of elastomer and carbon nanotube electrodes into a squishy cylinder. The electrodes on that cylinder squeeze the elastomer when a voltage is provided, and the mechanical strain causes the wing to flap.

The scientists had to overcome a number of obstacles in order to insert electroluminescent zinc sulfate particles into the elastomer and create a lighting actuator.

The group had to first develop an electrode that wouldn't block light. Carbon nanotubes, which are very transparent and only a few nanometers thick and allow light to pass through, were used to construct it.

But only in the presence of an extremely powerful, high-frequency electric field do the zinc particles light up. The zinc particles' electrons are excited by the electric field and release light photons, which are subatomic light particles. The researchers drive the soft actuator at a high frequency while using high voltage to generate a powerful electric field that causes the particles to glow brilliantly.

Since we only use the electric field at the frequency required for flight, we essentially acquire the electroluminescence for nothing. Traditionally, electroluminescent materials are quite expensive in terms of energy. We don't require any additional wires, actuators, or other components. To flash forth light, only roughly 3% additional energy is required, according to Kevin Chen.

They observed when they prototyped the actuator that adding zinc particles decreased its quality and made it more brittle. Kim only added zinc particles into the top elastomer layer to get around this issue. He increased the thickness of that layer by a few micrometers to account for any output power drop.

This led to a 2.5% weight increase for the actuator but had no negative effects on flight efficiency.

"We take great care to keep the elastomer layers between the electrodes in good condition. It was almost like adding dust to our elastomer layer when these particles were added. We developed a method to guarantee the quality of the actuator, but it required numerous strategies and extensive testing," claims Kim.

The light color can be altered by modifying the zinc particles' chemical composition. For the actuators they constructed, the study team created green, orange, and blue particles; each actuator emits a single solid color.

The actuators' ability to emit several colors and patterns of light was further improved by modifying the fabrication method. The top layer was covered with a small mask by the researchers, who then added zinc particles before curing the actuator. To generate a light pattern that spells out M-I-T, they went through this procedure three times using various masks and colored particles.

They examined the actuators' mechanical characteristics once they had optimized the fabrication process, and they utilized a luminescence meter to gauge the brightness of the light.

Then, employing a specially created motion-tracking system, they conducted flight tests. With the use of an iPhone's camera, each electroluminescent actuator acted as an active marker. A computer program they created tracks the location and attitude of the robots to within 2 millimeters of the most advanced infrared motion capture systems. The cameras identify each color of light.

When compared to the state-of-the-art, the tracking result is excellent, and we are quite happy of it. The tracking findings were remarkably similar even though we were employing inexpensive gear in comparison to the tens of thousands of dollars that these substantial motion-tracking systems cost, claims Kevin Chen.

They intend to improve that motion tracking system in the future so that robots may be tracked in real-time. In order for the robots to communicate more like actual fireflies and be able to turn on and off their lights while in flight, the crew is attempting to include control signals. According to Kevin Chen, they are also researching how electroluminescence can even enhance some characteristics of these soft artificial muscles.

According to Kaushik Jayaram, an assistant professor in the Department of Mechanical Engineering at the University of Colorado at Boulder who was not involved with this research, "This work is really interesting because it minimizes the overhead (weight and power) for light generation without compromising flight performance." The motion monitoring and flight control of many microrobots in low-light conditions both indoors and outdoors will be made easier thanks to the wingbeat synchronized flash generation presented in this work.

Pakpong Chirarattananon, an associate professor in the Department of Biomedical Engineering at the City University of Hong Kong, adds, "While the light production, the resemblance of biological fireflies, and the potential use of communication presented in this work are extremely interesting, I believe the true momentum is that this latest development could turn out to be a milestone toward the demonstration of these robots outside of controlled laboratory conditions."

In order to replace the current motion capture system and give real-time feedback for flight stabilization, the illuminated actuators may operate as active markers for external cameras. For application in the real world, electroluminescence would enable the use of less specialized tools and remote tracking of the robots, possibly using a larger mobile robot. That would be an amazing development.                                                                                                                                                                                                 MASSACHUSETTS INSTITUTE OF TECHNOLOGY                                                                                      

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