Vodka-powered robots harness Cheerios-inspired physics for movement in bizarre experiment

In brief: In what is certainly one of the quirkiest science demonstrations we’ve seen, researchers have taken inspiration from a phenomenon observed in Cheerios to create tiny robots powered by vodka. It’s just a proof of concept for now, but the team says that the robots could potentially be used for environmental cleanup or industrial processes.

The bots were developed by a team led by Jackson Wilt at Harvard University. As reported by New Scientist, they experimented with 3D-printed plastic pucks around a centimeter wide, each containing an air chamber for buoyancy and a miniature fuel tank. But instead of traditional fuel, they filled the tanks with varying concentrations of alcohol ranging from 10-50%.

When the pucks were placed in water, the alcohol gradually leaked out, setting off what’s known as the Marangoni effect. This occurs when a fluid with lower surface tension rapidly spreads across a fluid with higher surface tension. As the alcohol with its lower surface tension spread over the water, it propelled the little robots across the surface.

This is the same phenomenon that allows some species of beetles to skim on the water surface. But instead of using alcohol, they use special secretions that act as a surfactant and propel the beetle forward.

The thing with vodka is that it’s pricier compared to some other types of alcohol, like beer. However, as New Scientist notes, going with the stronger beverage was a choice.

Higher alcohol concentrations simply worked better as a fuel source for achieving greater propulsion, with Wilt noting that beer would not be as effective. Indeed, some experiments saw the pucks motor along for up to 500 seconds at peak speeds of around 6 cm/second.

Soap was another candidate. However, alcohol bested that since it simply evaporates after propelling the robots, rather than contaminating and disrupting the water surface required for the Marangoni effect.

After nailing the basics, the team created more complex robot assemblies by 3D printing multiple fuel outlets into the pucks and linking them together. This allowed the robots to trace out curved paths or spin rapidly. Using multiple robots also helped demonstrate the “Cheerios effect” – the clustering of floating objects caused by attractive forces between the meniscuses they create on the water’s surface.

The experiments may seem like amusing novelties right now but the researchers believe the robots could have serious applications. Wilt suggests they could potentially be used to evenly disperse substances through bodies of water for environmental remediation or certain industrial processes that require timed material distribution.

The robots could also find use as educational tools, allowing students a hands-on way to learn about concepts like surface tension.

Image credit: Jackson K. Wilt/New Scientist