Most robots use electric actuators, but this little guy does a lot more. Researchers have created a new type of miniature internal combustion engine that gives the little frog robot explosive jumping abilities and fine motor control.
The idea of burning fuel to power a robot may seem like it's from the last century, but as a research team from Cornell University's Organic Robotics Laboratory points out, today's batteries are heavy and don't carry much energy -- so the performance of electric actuators is limited.
These limits would be even higher if high-energy chemical fuels were used instead, so the team set out to design a new type of fast, high-frequency robotic actuator that would operate much like a regular internal combustion engine.
The tiny actuators, which are about 5 millimeters (0.2 inches) in diameter, draw methane and oxygen into a simple 0.09 milliliter combustion chamber and ignite it with a spark. The top of the combustion chamber is covered with a layer of highly elastic silicone dragon skin film, which functions a bit like a piston in a car engine. When fuel is burned, it stretches to expand the volume of the combustion chamber, and then quickly recovers to discharge the exhaust gas from the small holes on the side.
It all happens very quickly, but the end result is: the bigger the impact, the more the membrane pops off. These actuators can handle impacts with cavity volume expansion of up to 140%, with forces exceeding 9.5N, and are very fast, operating at a frequency of more than 100 times per second if required.
The Cornell team embedded 3D-printed prototypes of these small combustion actuators on top of the foot pads of a tiny rigid quadruped frog robot, so that whenever a certain actuator's membrane pops off, the feet are pushed down. They designed a control scheme that varied the actuator's spark frequency, fuel equivalence ratio, and fuel flow, then combined those controls with control of two left legs and two right legs, and then began to see what they could get the robot to do.
They succeeded in getting the robot to crawl forward in an oscillating gait and jump forward at various heights, including onto higher surfaces. They created a serpentine forward gait based on rotation and had it rotate clockwise or counterclockwise on the spot.
To demonstrate the actuator's explosive power, they made the robot jump an impressive 56 centimeters (1.8 feet) in the air, and they also demonstrated that the robot could move on a variety of solid, high-friction, low-friction and loose surfaces. They also loaded the robot with 32 grams of cargo (more than 22 times the robot's own weight) and demonstrated that they could still control the robot's movement.
Finally, these little actuators could give roboticists a handy extra option when ultra-fast movement is required - just imagine how nice it would be if Atlas could provide explosive assistance with its leg hydraulics, or fire-powered punches.
The research was published in the journal Science. Watch the video below.