Robots still can’t compete with the fastest-jumping insects and other small-but-powerful creatures. New research helps explain why nature still beats robots, and describes how machines might take the lead.
Take the smashing mantis shrimp, a small crustacean not much bigger than a thumb. Its hammer-like mouthparts can repeatedly deliver 69-mile-per-hour wallops more than 100 times faster than the blink of an eye to break open hard snail shells.
Or the unassuming trap-jaw ant: In a zero-to-60 matchup, even the fastest dragster would have little chance against its snapping mandibles, which reach speeds of more than 140 miles per hour in less than a millisecond to nab their prey.
One of the fastest accelerations known on Earth is the hydra’s sting. These soft-bodied aquatic creatures defend themselves with help from capsules along their tentacles that act like pressurized balloons. When triggered, they fire a barrage of microscopic poison spears that briefly accelerate 100 times faster than a bullet.
Strike, chomp, jump
A new mathematical model reported in Science – a study co-authored by Saad Bhamla, assistant professor of Georgia Tech's School of Chemical & Biomolecular Engineering – could help explain how these and other tiny organisms generate their powerful strikes, chomps, jumps, and punches.
Further, the model suggests ways to design small, nature-inspired robots that come closer to their biological counterparts in terms of power and speed.
The secret to these organisms’ explosive movements isn’t powerful muscles, but rather spring-loaded parts they can cock and release like an archer’s bow, says Sheila Patek, associate professor of biology at Duke University.
Tough yet flexible tendons, cuticles, and other elastic structures stretch and release like slingshots, powering their jumps and snaps.
A short-legged insect called the froghopper, for example, has a bow-like structure called the pleural arch that acts like a spring. Latch-like protrusions on their legs control its release, allowing them to leap more than 100 times their body length despite their short legs. A person with that much power could jump nearly two football fields.
But, how do these mechanisms work together to enhance power? That’s not clear, says Mark Ilton, a postdoctoral fellow at the University of Massachusetts Amherst.
While traditional mathematical models of performance take into account the inherent physical tradeoffs of muscle—which can contract forcefully, or quickly, but not both—they fail to factor in the tradeoffs inherent to springs and latch-like mechanisms as well.
In other words, nothing can be faster, stronger, and more powerful at the same time. “Until now these other components have been mostly black-boxed,” Patek says.
The new mathematical model of fast motion at small scales incorporates constraints on springs and latches.
“Part of our goal was to try to develop a model that is equally generalizable to biological or engineered systems,” says Manny Azizi, an assistant professor of ecology and evolutionary biology at the University of California, Irvine, who studies jumping frogs.
First, they compiled data on the size and top speeds and accelerations for 104 species of elite plant and animal athletes. They compared the data to similar measurements for miniature robots inspired by ultrafast movements such as unfurling chameleon tongues, snapping Venus fly traps, and hopping insects.
Finely tuned parts
By incorporating the performance tradeoffs of biological and synthetic springs and latches, the researchers hope to better understand how variables such as spring mass, stiffness, material composition, and latch geometry work together with muscles or motors to influence power.
The model allows researchers to input a set of spring, latch, and muscle or motor parameters and get back details about an individual’s theoretical maximum speed, acceleration, and other aspects of performance at a given weight.
There are major implications for engineers, the researchers say. It suggests that robots can’t yet outjump a flea in part because such quick, repeatable movements require components to be exquisitely fine-tuned to each other.
But the model also gives researchers a tool to design small, fast-moving robots with more precisely matched components that work better together to enhance performance, says Sarah Bergbreiter, associate professor of mechanical engineering at the University of Maryland who makes jumping robots the size of ants.
“If you have a particular size robot that you want to design, for example, it would allow you to better explore what kind of spring you want, what kind of motor you want, what kind of latch you need to get the best performance at that size scale, and understand the consequences of those design choices,” she says.
For biologists, the model can also be used to pinpoint the upper and lower weight limits of different groups of spring-powered organisms, given variables such as which elastic materials their bodies are made of, Azizi says.
The US Army Research Laboratory and the US Army Research Office, the Royal Society of London, the US National Science Foundation, and the John Simon Guggenheim Foundation funded the work.
CITATION: "The Principles of Cascading Power Limits in Small, Fast Biological and Engineered Systems," Mark Ilton, M. Saad Bhamla, Xiaotian Ma, Suzanne M. Cox, Leah L. Fitchett, Yongjin Kim, Je-sung Koh, Deepak Krishnamurthy, Chi-Yun Kuo, Fatma Zeynep Temel, Alfred J. Crosby, Manu Prakash, Gregory P. Sutton, Robert J. Wood, Emanuel Azizi, Sarah Bergbreiter and Sheila Patek. Science, April 27, 2018. DOI: 10.1126/science.aao1082
News story by Robin Smith, Duke University
NOTE: Click on media below to play gifs of flea and trap-jaw ants launching.