January 25, 2007 | David F. Coppedge

Robot Legs Can’t Keep Up With Animals

Robot designers are envious of animals.  Insects, crabs and lizards leave them in the dust.  Alison Abbott in Nature (Jan 18) described the latest attempts to get the bugs out of insect-imitating “biological robots.”1  “Programming a robot to think like an insect is tough,” the subtitle reads, “but it could help breed machines as manoeuvrable as flies.”  Which animals are robot designers looking at?

  • Flies:   Abbott described a German robot named Tarry II with six legs that creaks with every step.  Building legs, though, is the easy part.  The legs need to be programmed to work.  Tarry II’s designer is envious of the software in a fly: “Although our encounters with flies often leave an impression of aimless and irritating meandering,’ Abbott writes, “these tiny creatures’ decisions are just as purposeful as those of other animals.  A fly scans its environment with eyes and antennae, processes this information in its brain and then makes a decision, perhaps to turn away from potential danger or hurry towards food.”
        Much of the information processing in an insect occurs outside the brain.  Circuits of nerves in the fly’s nerve chord direct some of the movements.  This can be seen when a fly is decapitated and a neurotransmitter is applied onto the chord: “then it will start to walk around like – well, like a headless chicken.”  A headless fly can even be stimulated to groom eyes that are no longer there.  This kind of distributed processing has not escaped the notice of robot designers.  “These basic movement programmes are well studied and have been transferred to robots” like the predecessor to Tarry II, which “has been walking with the confident coordination of a decapitated stick insect for more than a decade.”  The “cleverer stuff” like decision making and coordinated movement, of course, requires a brain.  Designers are also observing how insects use stereo vision and parallax to sight their targets, and how they vary step size and walking rate to achieve optimum energy efficiency.
  • Cockroaches:  “If only the Mars rovers had been more like cockroaches, sigh insect biologists, they might have been able to extricate themselves from the sand dunes and rocks on which they have occasionally come a cropper and had to be carefully steered to safety by their human controllers,” Abbott writes.  Roland Strauss, builder of Tarry II, said, “We are very happy if what we learn from nature can be put to use to make better robots.”  Cockroach brains are about 50 times bigger than fly brains.  Using “brain damage” experiments, designers learn how the cockroach software works to encounter obstacles.  It’s a challenge to detect an obstacle, decide whether it needs to be avoided, and decide which way to turn.
        “Insect biologists are eager to model ever more intricate types of insect behaviour in their robots, such as walking uphill or climbing,” Abbott writes.  “….But until these robots can be programmed with more sophisticated and autonomous software – precisely the directions that biologists are extracting from insect’s brains – they cannot pass for true robotic insects.”  Autonomous control is a highly-sought-after skill being watched by NASA, the European Space Agency and other groups into robotics.  That’s why they are watching these experimental labs with great interest.  “Just a few of an insect’s effortless navigational skills would be a boon for many of today’s applied robots, which can negotiate obstacles only via human intervention and remote control.”  Abbott envisioned insect lookalikes someday navigating the moon or “confidently striding” the canyons of Mars.
        On Earth, too, we can all benefit from these studies.  The military will be able to perform safer surveillance.  Victims of natural disasters might some day be met by friendly search-and-rescue robots with a marked resemblance to spiders or cockroaches.
  • Crab Legs:  When robots have mastered insect navigation, they might be ready for the big time.  It’s hard enough to walk on a hard surface.  Sand provides a new challenge: the foot slips with every step.  The ghost crab, however, is king of the sand hill.  Elisabeth Pennisi writes in Science (Jan 19),2 “With legs that are a blur to the naked eye, Ocypode quadrata scoots up to 2 meters per second on hard-packed sand” – the Olympic champion of sand locomotion, at least when it is firm. 
  • Leapin’ Lizards:  “But soften up the sand a bit,” Pennisi continues, “and the gold medal instead goes to the zebra-tailed lizard, an animal that spends little time on the grainy material.”  It clocked 1.5 meters per second on soft sand that slows the ghost crab to a gecko-like crawl.
        Daniel Goldman and a team from the Georgia Institute of Technology built an artificial sand track to learn from the abilities of animals having to negotiate a variety of surfaces in the wild: mud, gravel, sand, and debris-covered surfaces.  The zebra-tailed lizard has long, gangly toes that spread out when hitting the sand and curl up with lifting the foot.  Robot designers want to invent machines that can navigate all kinds of surfaces.  That’s why they study the animal experts for clues.

Lest you envy the foot feats of lowly insects and crabs and lizards, you have some pretty remarkable legs yourself.  Lucy Odling-Smee in Nature (Jan 19) discussed a mathematical model developed by Herman Pontzer (Washington State U of St. Louis) that measures an animal’s leg length, body weight and other physical factors to determine the efficiency of walking and running.  Although Odling-Smee and Pontzer both assumed humans developed long legs by an evolutionary history, they agreed the proportions in the modern human transportation system are good at saving energy.


1Alison Abbott, “Biological robotics: Working out the bugs,” Nature 445, 250-253 (18 January 2007) | doi:10.1038/445250a.
2Elisabeth Pennisi, “Crab’s Downfall Reveals a Hole in Biomechanics Studies,” Science, 19 January 2007: Vol. 315. no. 5810, p. 325, DOI: 10.1126/science.315.5810.325.

Evolution has nothing to do with it; these stories are about design through and through.  We can observe design, we can study it, and we can imitate it.  When we do, science progresses and leads to wonderful inventions that improve our lives and extend our reach.
    Go to the ant, thou sluggard evolutionist; consider her ways, and be wise.  When you’ve learned those ways, go to the fly, the cockroach, the crab, the lizard, and all the other examples of optimized hardware and software in the living world.  Catch up to the design-theoretic scientists who are way ahead of you.

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