Scientists build methanol-powered beetle bone

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Scientists have long thought of building small robots capable of navigating environments that are accessible or dangerous to humans – but finding ways to keep them moving and moving is impossible to achieve .

A team from the University of Southern California has now made a breakthrough, building an 88-milligram (one three-hundredth of an ounce) “RoBeetle” that runs on methanol and uses an artificial muscle system to crawl, climb and carry on wear the back for up to two hours.

It’s just 15 millimeters (.6 inches) in length, making it “one of the lightest and smallest autonomous robots ever made,” its inventor Xiufeng Yang told AFP.

“We wanted to create a robot that has a weight and size comparable to real insects,” added Yang, who on Wednesday was lead author of a paper describing the work in Science Robotics.

The problem is that most robots need motors that are even bulky and require electricity, which in turn requires batteries.

The smallest available batteries weigh 10-20 times more than a tiger beetle, a 50 milligram insect that the team used as a reference point.

To overcome this, Yang and his colleagues created an artificial muscle system based on liquid fuel – in this case methanol, which stores about 10 times more energy than a battery of the same mass.

The “muscles” are made of nickel-titanium alloy wire – also called Nitinol – which creeps in length when heated, unlike most metals that expand.

The wire was coated in a platinum powder which acts as a catalyst for the combustion of methanol vapor.

While the vapor from RoBeetle’s fuel tank burns on the platinum powder, the wire gets stuck, and an array of micro valves closes to stop more combustion.

The wire then cools and expands, reopening the valves, and the process repeats itself until all fuel is expended.

The expanding and contracted artificial muscles are connected to the front legs of the RoBeetles via a transfer mechanism, allowing it to crawl.

The team tested their robot on a variety of flat and sloping surfaces made of materials that were both smooth, such as glass, and rough, such as mattress blocks.

RoBeetle could carry a load of up to 2.6 times its own weight on its back and run two hours on a full tank, Yang said.

By contrast, “the smallest battery-powered crawling robot weighs one gram and works for about 12 minutes.”

In the future, microbots can be used for a variety of applications such as infrastructure inspection or search-and-rescue missions to natural disasters.

They might also help with tasks like artificial pollination or environmental control.

Robotists Ryan Truby and Shuguang Li, from MIT and Harvard, respectively, wrote in an accompanying commentary that RoBeetle was “an exciting milestone of microrobotics”, but added that there were also opportunities for improvement.

The robot, for example, is limited to continuous forward motion, and taking electronics out of the equation reduces its capacity to perform sophisticated tasks.

© 2020 AFP