Insect-Sized Robots Powered by Internal Combustion Engines

Insect-Sized Robots Powered by Internal Combustion Engines
Insect-Sized Robots Powered by Internal Combustion Engines - Credit: CA Aubin et al

A four-legged robot with soft actuators can carry up to 22 times its body weight while crawling or jumping from one place to another.

Mobile, centimeter-scale robots have numerous uses across a range of industries, including agriculture, healthcare, exploration and communications. Imagine a fleet of small robots exploring dangerous or inaccessible locations. Because batteries and other power sources have low energy density, robots of this scale have traditionally relied on force-limited microactuator technologies.

The cycle rate, force, or displacement of other microactuators used in robotics, such as electrostatic, thermal, and magnetic types, are insufficient to perform more important tasks.

In addition, the power output and load carrying capacity of actuators decrease as they become smaller.

These problems were resolved by Cornell University researchers who served as thesis advisors. For example, methanol has a much higher energy density than lithium batteries, which have an energy density of only 1,0 MJ/kg. The 29-mm-tall quadruped robot shown here, with actuators positioned on two front legs and two hind legs, was built by Aubin, Shepherd, and colleagues using a lightweight (325 mg) microactuator and its integration into a working model was demonstrated.

An order of magnitude more force can be generated by each microactuator in submillisecond pulses than current actuators of comparable size, weight, or composition can produce (i.e., 9 N).

To power the micro-actuators, the researchers created a 3D-printed combustion chamber into which a gaseous combination of methane and oxygen is pumped through tubes. A small spark is then generated between two chamber electrodes to ignite the methane. At the top of the chamber, an elastomer membrane, like a piston, is inflated and expanded by the product gases of the exothermic reaction. The explosion can activate an actuator, launch objects, or perform other tasks. When gases are released from the chamber, the membrane deflates, signaling the beginning of a new cycle.

The researchers demonstrated actuator displacements of 140%, which is higher than modern microactuators. They were also able to tune the performance of the actuator by operating it at various frequencies and fuel concentrations. Thanks to its adaptability, the robot was able to navigate various terrains by crawling or jumping. The robot was able to jump 20 and 5,5 times its body length, or 59 cm high and 16 cm forward, respectively. Additionally, it could lift a load 22 times its own weight.

The robot's temperature rose to the point where it constantly ignited the room when operated at frequencies higher than 50 Hz. The device showed good endurance below this frequency. In one of their tests, the team ran the four-legged robot for 8,5 cycles over 750.000 hours.

Source: Physics Today

📩 18/09/2023 09:29