“Explosive” actuators power tiny robot to carry payload 22 times its body weight

Tiny combustion-powered microactuators propelled an insect-sized microbot capable of crawling and jumping, according to a new study. “The high frequencies, speeds, and strengths allow [the] actuators to provide microrobots with locomotion capabilities that were previously available only to much larger robots,” writes Ryan Truby in a related Perspective. Small insect-scale robots have the potential to fulfill a variety of needs, ranging from exploration in high-risk environments to healthcare. However, microrobotic systems are limited by existing microactuator technologies, which are driven by low-energy density power sources, such as batteries, and only able to produce small mechanical forces. These challenges are further compounded by performance losses due to component miniaturization, fabrication and manufacturing. In general, as energy sources and robotic actuators are made smaller, the power output and load-bearing capacity of robots diminish. These challenges have led researchers to search for alternative strategies to power small robots. Combustion of chemical fuels – which can have energy densities many times greater than those of lithium-ion batteries – could provide a solution, yet developing actuators that can convert chemical energy to mechanical work has proven difficult. Here, Cameron Aubin and colleagues present a lightweight, soft microactuator driven by the combustion of hydrocarbon fuels. Aubin et al.’s design, which weighs only 325 milligrams, features a three-dimensional printed combustion chamber, an inflatable elastomeric membrane, a pair of electrodes, and tubing for fuel injection. Methane in the combustion chamber is ignited via a spark from the electrodes, which drives expansion of the actuator’s elastomeric membrane. As these combustion gases are vented, the actuated membrane deflates, reversing the cycle. The resulting actuator achieved displacements of 140%, operated at frequencies greater than 100 hertz, and generated forces larger than 9.5 newtons. To demonstrate the actuator’s capabilities, Aubin et al. incorporated them into an insect-scale quadrupedal robot, which was capable of nimble locomotion across a variety of surfaces and obstacles, as well as carrying a payload 22 times its body weight.