One of the world’s smallest microrobots is able to carry 2.6 times its own body weight thanks to a muscular system powered by alcohol.
Conventionally, the “muscles” of small robots have been tethered to an external power source. Alternatively, they have been powered by batteries, the weight and size of which have limited efficiency and how small the robots can be. Top-of-the-range batteries have an energy density of around 1.8 megajoules per kilogram, a fraction of what you get from animal fat, which is about 38 MJ/kg. The methanol-powered muscles used by RoBeetle, an 88-milligram microrobot, can use catalytic combustion to reach energy levels up to 20 MJ/kg.
“The energy density of batteries is very low, so we needed new sources of power,” says Nestor Perez-Arancibia at the University of Southern California, who designed RoBeetle with his colleagues. “We were able to make it so light and small because we’re not relying on batteries.”
The methanol, stored in a fuel tank that weighs 95 milligrams when full, triggers an energy-releasing chemical reaction with oxygen that warps composite wire muscles to a preprogrammed shape. That twitching of the muscles allows the microrobot to crawl like a beetle. It is still able to move when carrying a cylindrical object weighing 230 milligrams on its horns – 2.6 times the weight of RoBeetle itself, or 1.3 times the weight of Robeetle and its fuel tank.
The paper is “a first step towards intelligent robotics”, says Samuel Sánchez at the Institute for Bioengineering of Catalonia, Spain. “I like the idea of replicating and engineering biomimetic systems like the RoBeetle, but using chemical reactions as highly powered energy sources.” While Sanchez points out the idea of small robots isn’t new, the use of the fuel and the potential to do more than just move is.
Research is under way to improve RoBeetle’s performance by using other fuel sources, including propane, which has an energy density of 50 MJ/kg.
The next step for RoBeetle? To grow wings, courtesy of funding from DARPA, the US Department of Defense’s research arm. “We want to create the first completely autonomous flying robot at beetle scale,” says Perez-Arancibia.
Journal reference: Science Robotics, DOI: 10.1126/scirobotics.aba0015