Around three to four grains of rice.
That’s the approximate weight of the RoBeetle, a tiny robotic insect recognized by Guinness World Records as the world’s smallest liquid-fueled robot.
The 88-milligram RoBeetle – developed in part by Néstor Pérez-Arancibia, an associate professor in engineering at Washington State University – will be included in Guinness World Records 2022, which is set to come out this month. By comparison, a tiger beetle can weigh around 50 milligrams.
Pérez-Arancibia developed the RoBeetle alongside Xiufeng Yang and Longlong Chang during his time at the University of Southern California. He became a Flaherty associate professor with WSU Pullman’s School of Mechanical and Materials Engineering this year.
“There are no other robots of this kind,” Pérez-Arancibia said. “There are crawling robots, but those are all powered electrically and using electric actuators.”
RoBeetle’s creators published their first paper on the tiny bot in August 2020 in the research journal “Science Robotics.”
Powered by the catalytic combustion of methanol, the RoBeetle moves using a wire made of nitinol, a shape memory alloy. Shape memory alloys are metallic materials that return to their original shape under certain conditions, such as heat, according to the University of Birmingham.
The nitinol wire is layered with platinum, which reacts with the methanol to heat the wire, causing it to contract.
“At room temperature, they have a state in which they are long, and then if you apply heat in a controlled way, the wire contracts,” Pérez-Arancibia said. “Then if you can control the temperature on the surface, you can have a cycle, and you can use that for fluctuation. You can use this as a muscle.”
As a result, the RoBeetle can climb slopes and haul objects that weigh up to 2.6 times its own weight, about 230 milligrams. With a top speed of 0.76 mm/s, the RoBeetle can walk for two and a half hours without stopping.
Though Pérez-Arancibia said research and development on the RoBeetle took hundreds of thousands of dollars in work hours, don’t have a heart attack if you accidentally step on one. Most of the components are made of carbon fiber and polyimide film.
“Just to make one of these guys, when you have the technology to make one of those, is $10,” he said.
Pérez-Arancibia said the RoBeetle was developed as a “proof of concept.”
“Many roboticists say shape memory alloy-based actuators are always very slow, so one of the things we proved with RoBeetle and our other papers was actually you can do this very fast,” he said. “You can design actuators, you can design muscle, that behave very fast. It’s just that you have to understand the dynamics of the actuator itself and you have to understand the dynamics of the heating process.”
Pérez-Arancibia, a roboticist who earned his doctorate in engineering from the University of California, Los Angeles, first started working on microrobotics as a postdoctoral fellow at Harvard University. He then spent several years at USC, during which time he founded and directed the Autonomous Microrobotic Systems Laboratory.
Though the RoBeetle has set a world record, Pérez-Arancibia said he sees the robo-bug as a work in progress.
In the time since the “Science Robotics” paper, Pérez-Arancibia said he has worked on developing other robots to further the concept, including SMARTI, which stands for shape-memory alloy robotic traveling insect. This 60-milligram crawling microrobot, according to Pérez-Arancibia’s April paper on the subject, uses multiple high-frequency shape-memory alloy actuators to enable controlled steering and path following.
Pérez-Arancibia said his aim is to develop microrobots for use in other applications, such as surgery. And while nature is “an inspiration” for Pérez-Arancibia in these endeavors, he said replication is not the long-term goal.
“As an engineer, I don’t want to necessarily replicate everything that occurs in natural insects because we know that natural insects are the product of evolution,” he said. “We don’t know yet if we can do this, but theoretically speaking, we can do even better because we don’t have constraints related to development and all these things.”