Tiny combustion reactions power itty-bitty, jumping robot

The robot can carry a payload of 22 times its weight and jump up nearly two feet in the air, all with little power.
Ameya Paleja
Burn of hydrocarbon can be controlled even to miniature levels for desired effect
Burn of hydrocarbon can be controlled even to miniature levels for desired effect


Researchers at Cornell University may have just made one of the world's tiniest and softest internal combustion engines. The team led by Robert Shepherd in collaboration with researchers at Northwestern University made quadruped insect-sized robots that can crawl and jump, a press release said.

Small-sized robots have been proposed to solve a wide spectrum of problems in many fields ranging from military to healthcare. For these small robots to function, one needs to deploy microactuators – parts that can enable their movement.

While humanity many have succeeded in making giant robots and machines, as one tries to miniaturize them, they lose their capabilities to generate high amounts of power and bear larger payloads. One of the contributing factors to this is the reliance on batteries that can only supply limited amounts of power output.

Powered by methane

With energy densities 20-50 times that of the best batteries, hydrocarbon molecules are a possible solution to this problem. Not only are they packed with power, but they can easily be scaled down to meet energy requirements without the heavy redesigning necessary for batteries.

The research team led by Shepherd works on organic control of robots and recently designed a small robot that is less than an inch (29 mm) long but can jump up nearly two feet (59 cm) in the air.

The robot is powered by methane inside a very tiny and soft internal combustion chamber. In half a millisecond after the combustion of methane, the chamber swells up like a balloon, generating 9.5 newtons of force. This cycle can be repeated 100 times every second, reports IEEE Spectrum.

By putting two of these actuators together, the researchers were able to design a quadruped robot.

Smaller than a penny

The microactuators weigh just 325 milligrams and are a quarter of the size of a penny. This has been achieved by offboarding a major part of the machinery required for the actuators' work. Right from the fuel to its mixing with oxygen and the source for the spark for the combustion to occur are all located outside the robot.

Nevertheless, the biggest challenge was to ensure that the actuator did not blow up when the methane was fired. For this, the researchers ensured that a small amount of fuel entered the combustion chamber but also added a fire-resistance elastomer to the design while integrating a flame arrestor. Put together, the soft and tiny actuator is quite robust and can handle 750,000 cycles of operation at 50 Hz, the researchers claim.

By controlling the gas pressure, the researchers have been able to direct the quadruped robot around. Firing both actuators moves the robot in front, while firing only one can help rotate it around. What the team has been working on to improve next is how to slow down the robot.

The technology is not limited to small robots alone. The team also wants to further explore if such tiny actuators could be put into a large robot to allow more dexterity, much like providing the robotic arm with individual muscles.

The research findings were published in the journal Science.


Insects perform feats of strength and endurance that belie their small stature. Insect-scale robots—although subject to the same scaling laws—demonstrate reduced performance because existing microactuator technologies are driven by low–energy density power sources and produce small forces and/or displacements. The use of high–energy density chemical fuels to power small, soft actuators represents a possible solution. We demonstrate a 325-milligram soft combustion microactuator that can achieve displacements of 140%, operate at frequencies >100 hertz, and generate forces >9.5 newtons. With these actuators, we powered an insect-scale quadrupedal robot, which demonstrated a variety of gait patterns, directional control, and a payload capacity 22 times its body weight. These features enabled locomotion through uneven terrain and over obstacles.

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