Taking flight with robots the size of bees

The Laboratory for Computation Sensing and Robotics hosted Kevin Chen, an associate professor of electrical engineering and computer science at the Massachusetts Institute of Technology (MIT) on Wednesday, Sept. 25. In his talk, titled “Insect-scale Micro-Aerial-Robots Powered by Soft Artificial Muscles,” Chen explores the development of robots, the size of insects and their potential applications in our world. 

Chen began by introducing the world of robots and highlight the various types that exist in robotics research. He explained that traditional robots range from the large-scale machines seen in movies to tiny micro-electro-mechanical systems (MEMS) devices that can hardly be seen with the naked eye. However, there is a unique niche of robots that are the size of insects — robots that are one to five centimeters in size and weigh between ten milligrams. These “insect-scale robots” represent a growing area of research with promising potential.

“You can enable new functions in robots,” Chen said. “We show that [the insect-scale robot] is both able to fly and swim. More than that, you can use [insect-scale robots] as a platform to investigate interesting physics at the centimeter scale.”

Chen further discussed how insect-scale robots build upon these capabilities for different types of motion. He explained that because these robots are so small, they can exploit physical phenomena that are negligible at larger scales, such as surface tension and flow similarity, rather than phenomena like inertia that affect humans. Because of this, they are capable of hovering flight, impulsive jumps and fast running. 

“At this scale, the inertia becomes a lot less important, and surface effects become a lot more important,” he said. “So, as a consequence, new properties arise.”

Chen then delved into the development of a new class of insect-scale robots powered by soft artificial muscles, which sets them apart from previous robots. In traditional robots, the legs, wings and other appendages are moved by actuators (components of the machine that produce a force to move it). So, in essence, actuators can be thought of as the muscles of a robot. These are often rigid and unable to adapt to different environments and tasks. In contrast, soft artificial muscles are actuators made from flexible materials that can stretch and contract like real muscles. This enables the robots to be more robust and withstand collisions with other physical objects.

“[The soft actuators] retain relatively large strain,” Chen said. “And because they are soft, we can make a lot of them very cheaply. And finally, there are new properties that arise. For example, we can sense collisions in air, and we can also [collide] very hard. So they can do aggressive maneuvers such as a somersault.”

To demonstrate, Chen showed videos of the soft-artificial muscle robots flying and intentionally colliding with obstacles. The robots would lose their flight path but then restabilize themselves, illustrating robustness and resilience.

Chen continued the discussion by presenting challenges that prevent the robots from being widely adopted in practical applications. Primarily, the insect-scale robots struggled with achieving power autonomy. They currently rely on external power sources for their operations, which limits the range of their movement and practicality in real-world settings. External power sources are necessary because of the high amount of power necessary to power the soft artificial muscles. To address this issue, designing actuators that use less power would enable the robots to carry batteries on board that would power the soft artificial muscles. 

“Incorporating onboard computation is relatively easy, but developing onboard energy sources is extremely challenging,” Chen said.

Chen described the methods his lab is currently working on to work towards this goal. Researchers on his team are trying to refine the fabrication process of the soft actuators to reduce the required power without compromising performance. By making the elastic layers thinner and improving material properties, they have made progress towards lowering the operating power from around 2,000 volts to just 500 volts.  

“This really opens up the opportunity for making power electronics,” Chen said. “This is still very preliminary work, [though].”

Looking ahead, Chen envisions a swarm of these insect-scale robots working collaboratively in various applications such as environmental monitoring, search and rescue missions in hazardous areas and inspection of hard-to-reach spaces in machinery or infrastructure.

“We are still very far away from deploying a large number of microscale robots in complex environments. But hopefully, I’ve convinced you that we are making progress very quickly — putting on power electronics and enabling new flight abilities. I would argue the next ten to 15 years is going to be a very exciting time for people who work on micro-robotic systems.”