Professor Full’s projects appeared in numerous popular magazines, newspapers, and books (as well as science literature, of course).
New Scientist. Leg spines make robots better scramblers 2007.
Science. Crab’s Downfall Reveals a Hole in Biomechanics Studies. vol. 315, p 325. 2007. Full text of this article in PDF
Forbes. The Robots are Coming – The Stickybot. Sept 2006. Full text of this article in PDF
Science. Scurrying Roaches Outwit Without Their Brains. vol. 307, p. 346. 2005. Full text of this article in PDF
Robosapiens, p. 90 – 95, by Peter Menzel and Faith D’Aluisio ( robosapien.pdf)
Sticky Secrets of the Gecko (SF Chronicle, 6/19/2000) SFChron6_19_00
Geckos Have Feet That Stick…(The Plain Dealer, 6/11/2000) PlainDealer6_11_00
Gripping Solution to Mystery of Geckos (The Daily Telegraph, 6/8/2000) DailyTelegraph6_8_00
The Sticky Point (The Guardian, 6/8/2000) Guardian6_8_2000
Secrets of Motion A new generation of robots is being modeled after the mesmerizing maneuvers of cockroaches and millipedes.
SECTION: Guardian Science Pages, Pg. 1
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HEADLINE: Science: The sticking point: Henry Gee on the surprising secrets of one of nature’s stickiest surfaces – the gecko’s atom-powered feet
BYLINE: Henry Gee
Robert Full’s laboratory is more than usually full of gizmos, even for a modern biologist. Full is a biological engineer. Like an industrial espionage outfit, he and colleagues at the University of California, Berkeley, look at nature and try to reverse-engineer it – taking nature’s solutions to pieces, learning how they work then putting them together in robot form, in new and exciting ways.
A big man with big enthusiasm, Full shows me a video of his team’s latest robot. This six-legged machine moves with all the natural assurance of an insect; the cartoon face painted on the front makes the creature (for that’s what it is) look animated. It crosses terrain that overturns other robots or stops them dead in their (caterpillar) tracks. How does it do it? By doing what insects do naturally: a bit of springiness engineered into the legs, combined with mechanical responses at a local level (rather than always being centralised through a “brain”) make for a flexible, robust system. Some feet, however, are the very opposite of springy; they are sticky with a vengeance. Full’s latest mission has been to understand what makes the feet of geckos so adhesive. No hot tropical night is complete without one of these small lizards darting up walls and across ceilings.
For decades, scientists have studied this trick. The anatomy is incredible. Each foot of a Tokay gecko (Gekko gecko) is clothed with a fine pile of microscopic hairs, around 5,000 per square millimetre – or around two million per gecko. These hairs have split ends, each dividing into as many as 1,000 frayed strands – the total, per lizard, running into billions.
As they show in today’s Nature (June 8, 2000), Full and colleagues have measured the force acting on isolated hairs as a gecko runs. The hairs on the foot point backwards. As the gecko takes a step and gains a purchase, the hairs are driven backwards and down, engaging with the surface. The force on each hair is minuscule, but the effect is cumulative: a totally stuck gecko would clamp on to a surface with a force equivalent to 10 atmospheres of pressure. No wonder they can stick to ceilings. But how does a gecko not get bogged down?
The answer is that the gecko doesn’t yank its feet off the surface all at once, but peels off its toes at a certain angle, rather like peeling off a strip of adhesive tape, or Velcro.
The puzzle is what makes them stick. Simple suction is out, because gecko feet work perfectly, even in a vacuum.
Clinging to very fine cracks or imperfections is also out: geckos can cope with polished glass.
It could be electrostatic attraction, like toy bal loons which, when rubbed vigorously on your shirt or sweater, can be suspended from a wall or ceiling.
But gecko feet work in ionised air, which would cancel out the electrostatic effect. That leaves old-fashioned glue: except that gecko feet have no suitable glue-secreting glands.
Back to square one, then – except that in the 1960s, a German scientist, Uwe Hiller, wondered whether gecko feet might work by tap-dancing their way into the molecular landscape of the surfaces they crossed. Many molecules have a slight electrical polarisation. Rather than being balanced throughout, they have spots of excess negative or positive charge. These allow different molecules to bind together very loosely, through a weak kind of electrostatic interaction called the van der Waals force. Although very weak, this force is highly important. It holds the strands of DNA together, and some of the unusual properties of water – such as its high boiling point – are connected to the fact that its molecules form loose, ever-changing associations, bound by the van der Waals force.
Uwe Hiller wondered if the fine hairs of gecko feet might exploit van der Waals forces. Supporting evidence came from an unusual finding: that geckos got stickier in proportion to the “free energy” – the degree to which surfaces have loose molecular ends – of the surfaces they crossed. Measurements by Full and colleagues on single gecko foot hairs are consistent with this idea: it sounds crazy, but geckos make their way by a kind of atomic energy.
How to reverse-engineer gecko feet into something useful? Forget Duck tape – Gecko tape could stick anything to anything else as securely as molecular bonds would allow, yet peel off gently, leaving no stain or trace. Sounds wonderful. Except that Full and colleagues admit defeat, at least for now: human technology is just too crude to manufacture structures as exquisitely tiny and precise as gecko foot hairs.
But, they suggest, the very contemplation of such structures could inspire those souls driven to create the perfect dry adhesive. After all, stranger things have happened: legend has it that the hooked burrs of plants inspired the invention of Velcro. And, these days, we’d certainly come unstuck without that.
Henry Gee is a senior editor of Nature. His book, Deep Time: Cladistics, the Revolution in Evolution, is published by Fourth Estate, price pounds 20
Author: Matt Crenson
Rabbits hop, turtles plod, peacocks strut and cockroaches skitter. In the animal world, there appear to be thousands of ways to get from Point A to Point B. But for all nature’s variety, recent research shows that every beast with legs, from ant to elephant, moves the same way.
After years of studying a menagerie of animals — humans, horses, crabs and cockroaches among them — biologists have come up with a unified theory of legged locomotion: Animals’ running legs work like pogo sticks.
Biologist Robert Full made the case for the pogo-stick theory in Durham, N.C., recently and suggested ways that the idea could be applied to robot design, paleontology and even moviemaking. The University of California, Berkeley, professor illustrated many of his points with movies and stop-action photographs of two-, four-, six-, eight- and many-legged animals walking, trotting, running and galloping. “All of these animals are bouncing along as they move,” he said at a meeting sponsored by the Council for the Advancement of Science Writing. It doesn’t matter how many legs an animal has, how they’re constructed or how the body is connected to them. It makes no difference what an animal’s skeleton is made of. Legs basically work like sticks with springs attached, Full said, flexing to absorb energy and then releasing it to propel the animal forward.
He and other researchers developed the pogo-stick theory by doing a natural experiment. Instead of manipulating nature to test a hypothesis, a natural experiment looks for cases that already differ in whatever character a researcher wants to understand better. In the case of legged locomotion, Full and his colleagues looked for animals that move in unusual ways –crabs, kangaroos and centipedes, for example. Despite their apparent differences, they all run the same way. “This turns out to be an extraordinarily powerful method,” Full said.
But it’s not always pretty. One of the most valuable experimental tools for studying locomotion is the 6-inch-long Madagascar hissing cockroach, Full said. Another species, known as the death-head cockroach, also makes a good subject.
“In most cases they’re disgusting animals that we look at. But they do reveal nature’s design lessons,” Full said.
They also misbehave. In one set of experiments, Full used a special substance to determine how cockroaches exert forces on the ground. When a cockroach stepped on the substance, the material conducted light differently, recording the direction and magnitude of the step’s force with a dark spot.
Although the setup has yielded a wealth of valuable information, early trials were less than successful.
Full explained that the high-tech substance, known as a photoelastic polymer, goes by a different name in the grocery store — Jell-O. So when he and his colleagues first set up their experiment, the cockroaches didn’t run at all. They chowed down.
The problem was, the experiment was conducted with orange Jell-O. “Now we use unflavored Jell-O. It works much better,” Full said.
The Jell-O experiments, along with high-speed films of cockroaches, centipedes, crabs and other animals running on treadmills, clearly showed Full that animals don’t progress smoothly as they run along.
“They were hitting the brakes and then stepping on the gas,” Full said, like a pogo stick lurching foward with each bounce.
Even a centipede, with dozens of legs, lurches forward as it walks. Progress that appears smooth in real time looks like a rhythmic sequence of pushing forward, then pausing, then moving along again.
“Anything that works like that can be described as a spring or a pogo stick,” said Tom McMahon of Harvard University in Cambridge, Mass.
The first part of each step is the release of energy as the spring uncoils, throwing the pogo stick and its rider up and forward. Then when the pogo stick hits the ground, the spring compresses, storing energy for the next hop.
Full has demonstrated that legs do the same thing, storing energy from one step and then releasing it on the next. And McMahon’s research has shown that in a wide variety of animals, legs have the same amount of stiffness no matter what they’re doing.
“The leg working as a spring doesn’t change its stiffness,” McMahon said. “It just works as an ordinary rubber band. And that was a big surprise.”
By looking at locomotion from a biomechanical point of view, the researchers have shown that some animals are really running when it looks like they’re walking. McMahon dubbed the process “Groucho running,” because the mustachioed Marx brother can be seen doing it in old movies. When Groucho running, an animal uses the leg as a spring, but never lifts more than one foot off the ground at once.
“It looks like the person is walking, but he’s not,” McMahon said. “That’s because in walking the body is highest in the middle of the time that the foot is in contact with the ground.”
But in Groucho running, a person — or any other animal — is lowest in the middle of each step, just as in normal running. Running used to be defined as locomotion in which at least one foot is always off the ground. But biologists now think of running as locomotion in which the leg acts like a spring, storing energy from one step and then releasing it on the next.
Walking, on the other hand, is more like rolling an egg end-over-end, McMahon said. With each step, a walking animal pushes itself over its extended leg like an egg being rolled over one of its ends. Then the animal falls downward onto another leg, or legs.
For the last few years, engineers have been applying concepts such as Groucho running and egg rolling to robots. Most robots can’t walk very well, Full contends, because they basically work as if they had wheels.
For example, a four-legged robot shifts its center of gravity so it can balance on its two rear legs and one front leg. Then it lifts the front leg that’s no longer needed for balance and sets it down farther forward. Then it pulls the rest of the legs forward, one by one, never lifting more than one leg off the ground.
“Dynamically, [robots] are more similar to a turtle than any other animal,” Full said.
Then he showed movies of one-legged robots that move like pogo sticks. The robots, built by engineers at the Massachusetts Institute of Technology, bounded down hallways and hopped over small obstacles. They looked so lifelike that the crowd cringed whenever one of the one-footed robots toppled over.
The goal of robot design isn’t to imitate animals, of course. But Full said his research can help engineers design better robots by revealing the basic principles of legged locomotion.
And it can also help people who do want to imitate animals. For example, Full said, he wasn’t too impressed by the dinosaurs in “Jurassic Park.” Animators drew those dinosaurs using computer programs that fine-tuned the creatures’ motion until it was as real as the artists could get it.
But the dinosaurs didn’t obey the basic physical laws he’s discovered, Full said, so they didn’t look completely real. By building computer animation programs that move animals around essentially like pogo sticks, using real information about their limb strength, weight distribution and other properties, he and his colleagues have been able to generate stunningly realistic animations of creatures running, jumping and falling.
The characters in the movies don’t look like much. The stars are imaginary animals that look like headless ostriches and kangaroos. But Hollywood is interested, Full said, because their motion is so real.
Using the same idea, Full said, the physical principles he has discovered could also be used to learn how dinosaurs, mastodons and other extinct creatures moved. In a recent issue of the Journal of Experimental Biology, he and biologist Anna Ahn of UC-Berkeley described a computer simulation of a cockroach leg that attempts to mimic the mechanics of the real thing.
“We are encouraged by the concordance of the model’s prediction and the `in vivo’ measurements on the animal,” the biologists wrote.
Because the computer simulation imitates the motion of living animals so well, presumably a similar one could be designed for extinct creatures. Using information from fossils, biologists might estimate how fast a tyrannosaur could run or how high a velociraptor could jump.
Full didn’t expect that he’d be dabbling in paleontology, computer animation and robotics when he began his animal-locomotion research.
“It’s only in the last three years or so that I’ve seen how these principles could be applied,” he said.
But he said the fact that nature has provided him with such a wealth of information illustrates an important lesson: “Even weird and disgusting animals should be preserved, because you can never predict where this research will lead.”
Two legs are a lot to move, and four legs are considerable. But Six legs are a quandary, and forty-four formidable.
Here, according to Nilesh Patel, is how you paint the legs of an ant: Begin by finding the right paint. Don’t use Wite-Out (it flakes off), and don’t use oil- based paints (they’re so thick that they make ants walk as if they’re wearing casts). Acrylic is best, says Patel. And be sure to get the thinnest, finest brush your local art supply store has to offer.
Next, chill the ant well. Patel, a 23-year-old senior at the University of California at Berkeley, takes his ants to the integrative biology department’s temperature-controlled room, which he cools to 40 degrees. Inevitably the cold- blooded ants become sleepy. To completely immobilize them, Patel first tried trapping them under a staple pushed gently into Styrofoam, but they managed to wriggle free. Now he Scotch-tapes three of their six legs to a table. Gently pulling the free legs straight with a pair of tweezers, he dabs them with his brush. “The more practice you have, the better you get at it,” says Patel. “When I first started, it took me about seven minutes, but now I can get an ant out in two.”
Patel learned to paint ants at the bidding of postdoctoral researcher Rodger Kram, whose work was spurred by a simple question: Do ants run?
The science of animal locomotion is full of such simple questions; getting the answers has always been the difficult part. In 1872, for example, Leland Stanford, a railroad tycoon and the founder of Stanford University, got into a heated debate as to whether all four legs of a horse leave the ground when it trots. Legend has it that he even bet $25,000 that they did. In any case, he did bankroll famed landscape photographer Eadweard Muybridge to find out.
Muybridge had horses trot down a path strung with threads connected to a row of cameras; when the horses snapped the threads, the cameras snapped the pictures. It took Muybridge years to perfect a shutter fast enough and film sensitive enough to capture the images (he also needed some time off to defend himself, successfully, against the charge that he had murdered his wife’s lover), but in 1877 he was finally able to give Stanford his answer: a series of pictures of a horse in motion, one of which showed the animal seemingly levitating, with all its legs in the air.
Like Muybridge, Kram wanted to take a series of pictures of an animal in motion, albeit a much, much smaller animal. And, like Muybridge, he had some technical considerations. Because even his high-speed video cameras couldn’t easily distinguish a moving ant’s six legs, he decided that the three facing the camera had to be painted white. Next, he and Patel built a narrow plastic chute for the painted ants to dash through, coating the walls with liquid Teflon to keep the ants from climbing up its sides. Patel then spent several weeks videotaping ants traveling down the chute. A prod from a pair of forceps or a puff of air was enough to get an ant moving. Patel would reach over to the camera and switch it on in time to tape the insect’s movements.
One morning last fall, one ant gave Patel some trouble. “As soon as I touched him he took off,” he recalls, “and I wasn’t fast enough turning on the camera.” By simply turning the camera on before prodding the ant, however, he succeeded in capturing the animal’s movements on tape. Later, watching the tape in slow motion, he and Kram saw something remarkable. In previous trials, the ants had used their normal gait, known as the alternating tripod, in which two legs on one side and one leg on the opposite side move in concert, the ant would raise, say, its middle left leg and its front and back right legs, bring them forward, plant them on the ground, then repeat the movement with its other three legs. But the tape of Patel’s swift ant showed that at one point all its legs actually left the ground. It was the first image of a running ant ever captured. “Unfortunately,” says Kram, “nobody had bet any money on it.”
Kram and Patel, along with the dozen other Berkeley researchers who make up the PolyPEDAL lab (PEDAL stands for Performance, Energetics, and Dynamics of Animal Locomotion), are modern Muybridges. But instead of exposing the hidden complexities in the movement of tetrapods, animals like ourselves, with four limbs, the PolyPEDAL lab specializes in the even more complicated mysteries of arthropods, creatures that move on six or more legs and have external skeletons. Among the lab’s menagerie, in addition to the trotting ants, you’ll find galloping crabs, undulating centipedes, and a cockroach so fast it’s made the Guinness Book of World Records.
“We don’t study arthropods because we like them,” says Robert Full, the 36-year-old physiologist who directs the lab. “Many of them are actually disgusting. But they tell us secrets of nature that we can’t find out from studying one species, such as humans.”
They are also telling the researchers secrets that may soon be applied to some very unnatural creatures. For decades engineers and computer scientists have been convinced that walking, insectlike robots would be ideal for moving over rough terrain. Thus far, though, the slow, awkward machines they’ve built embody none of the speed and grace of insects. That, Full says, is because they’ve based most of their designs on old assumptions about how insects move, assumptions the PolyPEDAL lab has shown are false.
UNTIL THE POLYPEDAL LAB came along, researchers looking at animal locomotion concentrated on tetrapods even though there are several hundred times more arthropod species on this planet. It’s hard to blame the researchers, though. After all, it’s much easier to film and analyze the four heavy legs of a running dog than the six nearly weightless limbs of a skittering roach.
After completing his famous studies of horse movement, Muybridge went on to photograph many other tetrapods, including humans, and showed that, as a rule, they all lifted their legs off the ground simultaneously while running. That complete lack of contact with the ground, in fact, came to define the act of running. It’s a fairly crude definition, though, it tells you only about a brief moment in an animal’s gait and doesn’t describe the rest of the motion. These days researchers are constructing better definitions of walking and running by focusing on two simple models: pendulums and pogo sticks.
A pendulum can swing for a long time because it continually recovers its energy. On its downward stroke, it’s powered by the force of gravity; when it reaches the lowest point of its arc it has so much energy that it can counteract gravity and swing upward. When you walk, your body behaves like an upside- down pendulum: the foot you plant in front of you is the pendulum’s axis, your center of mass the hanging weight. In the beginning of your stride you work against gravity, vaulting your center of mass upward with your leg until you reach your highest point. Gravity then takes over, and your body swings downward until your other leg hits the ground. The next stride is even easier. You can use the energy given to you by gravity to vault yourself into your second and all successive steps, just as a pendulum reclaims its energy in each swing.
When you run, however, you stop behaving so much like a pendulum and begin behaving more like a pogo stick. Now when you first plant your leg, your body sinks down on it instead of rising up. Your leg actually acts as a brake for your body, and so your center of mass is at its lowest point when your acceleration is lowest. Meanwhile your tendons are acting as springs. As they stretch and snap back, they store and release energy, just like the spring in a pogo stick, and propel you upward and forward. Thus running, like walking, recovers energy and cuts down on your expenditure.
One intriguing implication of the pogo-stick model is that you don’t have to have both feet in the air to be running. In 1986 Thomas McMahon, a biomechanicist at Harvard, videotaped six runners trying to imitate that miracle of locomotion, Groucho Marx. They deliberately bent their legs deeply as they ran, so that they always kept one foot on the ground, yet their bodies still behaved like pogo sticks. So much for Muybridge.
At the time, Full was working in the laboratory of McMahon’s collaborator, Dick Taylor, investigating the intricacies of crab metabolism. One of the things he needed to know was what the crabs were doing with their limbs: Were they using any kind of energy-saving gait? The conventional wisdom at the time, which, as is often the case with conventional wisdom, had no real evidence to back it up, was that if tetrapods were pendulums and pogo sticks, then arthropods were wheels. Like a wheel, it was thought, an arthropod’s center of mass moved forward at a constant speed, never rising or falling, and so the animal never recovered energy as it moved.
To study crab locomotion, Full wanted to use one of the lab’s force plates, a device that measures the impact of an animal’s footsteps. Generally a force plate consists of a sheet of wood or metal sitting atop a grid of crisscrossing beams. Inside each of the beams are gauges that are squeezed by the pressure of the animal’s feet as it walks overhead; some gauges measure the up-and-down impacts while others sense forward-and-backward or side-to-side forces. But no one had ever tried to use a force plate to detect the steps of a half-ounce crab before. To do so, Full and a fellow postdoc gave the plate more sensitive gauges and a more complicated electronic configuration, then sent crabs scuttling over its surface.
When Full saw the force patterns the crabs were creating, he had a feeling of deja vu. Far from moving like a wheel, the crab’s center of mass rose and fell, and the crab itself slowed down and sped up rhythmically. At low speeds it walked like a pendulum, with gravity aiding its forward movement; and at faster speeds it ran like a pogo stick, with energy clearly being stored and released in some unidentified springlike structures. The crabs rarely became airborne, which meant that they, too, could run like Groucho. “I said, My goodness, there are so many similarities to the general model, it can’t happen!’ ” says Full.
To see if perhaps crabs were the exception rather than the rule among arthropods, Full decided to study cockroaches. But the insects, at a twentieth of an ounce, were too light for even the state-of-the-art Harvard force plates. Full had to wait until he came to Berkeley later that year, where he set up the PolyPEDAL lab. It took almost 12 months, but with the help of an undergraduate named Michael Tu he managed to build and calibrate a force plate that could measure the impact of a cockroach’s steps. The construction wasn’t easy. “You have 24 strain gauges made out of silicon slivers and gold wires about twice the thickness of a hair, and you have to glue all the gauges on the beams and solder the wires to terminals by hand,” Full explains. This was all then covered with a layer of wood a half-millimeter thick. It was worth the effort, however: Full and Tu promptly discovered that cockroaches walk and run like crabs, and horses and humans, by behaving like pendulums and pogo sticks.
But though an arthropod moves like a tetrapod, each of its many legs behaves uniquely. With student Lena Ting, Full measured the force of each individual cockroach leg by covering the lab’s force plate with a second thin sheet of wood, suspended just slightly above the first, with two cutout patches the size of a roach’s foot. Into these holes went cardboard plugs that sat on the lower plate. The force of the roach’s footsteps was thus detected only when the insect hit the plugs and indirectly struck the plate below. Using this device, Full and Ting found that when a running roach’s rear legs strike the ground, they push back against it to propel the roach forward; the front legs act like a set of brakes, decelerating the roach; and the middle legs act like human legs, like pogo sticks, to both accelerate and decelerate the body.
It was during these experiments that Full and his students discovered that the American cockroach can run five feet per second, a speed the Guinness Book of World Records recognized as the fastest of any insect on Earth. This means the roach travels 50 body lengths in a second. A human would have to run 200 miles an hour to match that pace.
It was also during these experiments that the researchers noticed something truly peculiar: the roach was running with its body tilted up 23 degrees. “The film wasn’t very good, and we couldn’t tell what the heck the animal was doing,” Full remembers. “And then we looked at the force platform.” Periodically it registered no forces at all, in other words, there were times when the roach had taken all its feet off the ground. Taken together with the images of the roaches tilting upward, this suggested that the bugs were getting up on their two long rear legs and running. “We thought the plate was broken, or maybe there had been a gust of wind, so we made the roaches do it again.” Eventually they looked at 40 roaches, using high-speed video with better resolution. In every case, they could see the roaches tilt up their bodies and sprint on their two back legs, just like humans.
Roaches turn bipedal at top speeds, Full suspects, because running on six becomes counterproductive. Their legs, he notes, are moving back and forth 27 times a second, which is probably as fast as their muscles can work. “The only way to go faster, then, is to take bigger steps,” says Full, “and since the front legs are a third shorter than the rear ones, they can’t possibly have the same stride length.”
Still, it was hard to accept that cockroaches could run on two legs, particularly because it seemed as if they were breaking the laws of physics. “When we calculated it, it seemed that they should just fall forward because they’re tipped so far over,” says Full. Their secret lies in their aerodynamics, a peculiar consequence of the insect’s small size and high running speed. Berkeley biomechanics expert Mimi Koehl teamed up with Full to do wind-tunnel experiments and showed that when the roach is sprinting, the air pushes against it so hard that it keeps the roach from falling down.
It’s difficult enough to decipher the mysteries of six-legged cockroaches and eight-legged crabs. What about a 44-legged centipede? Researchers have long assumed that a crawling centipede, at least, moves like a wheel, after all, it certainly looks as if it’s gliding as smoothly as a chair on casters. They also thought a centipede’s movement was rather uneconomical. Many centipedes bend like snakes when they move quickly, apparently wasting energy in undulations that could be used to move the animal forward. At fault, supposedly, was the centipede body plan. Centipede legs extend diagonally down from a long, flexible body. As each leg twists at the joint to propel the animal forward, the force also inadvertently swings the body around the joint.
To test these assumptions, PolyPEDAL lab member Bruce Anderson turned to the common Arizona centipede, a species with a particularly pronounced undulating walk. It’s a chilling creature, six inches long, with an orange body, 44 yellow legs, giant pincer jaws, and a painful bite, indeed, Anderson will handle it only with a gigantic pair of tweezers.
When he videotaped the centipede in motion, Anderson found what PolyPEDALists have almost come to expect: rather than moving smoothly forward like a wheel, the centipede’s body accelerates and decelerates as it travels. He also found that it’s a much more economical creature than was once thought. Anderson implanted electrodes in the centipede’s trunk muscles and found that whenever a segment of its body was curved out to the left, contracting muscles would then begin forcing that segment to curve to the right. When the segment was curved out to the right, the opposite action would occur. In other words, the centipede was not passively bending as a result of its anatomy; it was actively trying to undulate. And the bending seemed to be saving it energy, oxygen-consumption experiments showed that the centipede actually needed less fuel to move than most other animals of its weight.
To see how it was saving energy, though, meant seeing what each of the creature’s 44 legs was doing, and force plates just weren’t up to the task. For that the lab needed another device, known to the PolyPEDALists as the Jell-O track. The creation of engineering student Angela Yamauchi, it’s a clear plastic chute with a long, shallow tray of transparent gelatin sitting between two filters, one below the gelatin, the other just above it. Polarized light shines up from the bottom of the track.
POLARIZED LIGHT CONSISTS OF photons that have been filtered so they all vibrate in the same plane. If the light encounters a second filter oriented in the same direction, it can pass right through. But if you rotate the second filter 90 degrees, as is the case with the filter above the gelatin, all the light is blocked.
Viewed through the filter above the track, therefore, the clear gelatin looks black. But when an object, say, the foot of an insect, rests on it, the gelatin’s structure is transformed. It begins to interfere with the light passing through, changing its polarization. Photons that had been blocked by the second filter are then able to pass through. When an insect ambles down the track, little splotches of white light thus appear around its feet. By looking at the size of a splotch, Yamauchi can calculate the size of the force, and by analyzing its shape, she can tell you in what direction the force is moving.
When Anderson set his centipede on the Jell-O track, he discovered something remarkable. At any moment, most of the centipede’s legs are not on the gelatin, in fact, on average, only four touch the ground at a time. These four are the legs at the centermost point of the concave side of the four curves in the centipede’s body, two on the left side and two on the right. As the centipede undulates forward and the next foot in line reaches the center of a bend, the centipede lifts up the planted foot and sets the next foot down on the same spot. As different legs reach the center of the curves, they make the entire animal speed up or slow down, with the middle legs supplying most of the propulsive force.
How does this help the centipede save energy? “I made stick figures of these things until I was bleary-eyed,” says Anderson, but eventually he came up with a theory. Since the centipede is moving only four legs at a time, rather than 44, it takes less energy overall to operate its legs. This could pose a problem, of course; fewer legs on the ground means less support for the centipede’s long, flexible body. But by bending the body in the first place, which requires flexing its body muscles, the centipede keeps its body tight and stops it from sagging.
OF THE MANY ARTHROpods that have made their way into the PolyPEDAL lab, only one actually moves anything like a wheel. In 1979 Berkeley biologist Roy Caldwell encountered a species of stomatopod, a small, shrimplike creature, that had washed up on a beach in Panama. Lying on its back, it pulled its tail to its head to form a hoop and did a backward somersault, letting its back flop onto the ground. Then it pulled its tail up again and rolled on, slowly making its way back into the ocean.
When Full and his students videotaped some stomatopods in the lab in 1992, they found that for 40 percent of each “stride,” when the creature forms a hoop, it indeed moves exactly like a wheel. But during the other 60 percent, when it’s raising its body up and flopping it down, its center of mass rises and falls, slows down and speeds up. “It’s the ultimate example of something that is close to a wheel,” says Full, “but even there, it has forces that look like a leg, except that now the leg is the body.”
It’s not only in the animal world that legs seem to make more sense than wheels. Engineers have long wanted to make robots with legs for traveling over natural terrain, and robots with six legs or more make the most sense. There is already a long shopping list of uses for a walking robot, including exploring the moon and Mars and inspecting toxic waste sites. But today’s crop of robots is a long way from any moon walk. One of the most famous walking robots, a six- legged machine named Attila, from the laboratory of MIT engineer Rodney Brooks, is a case in point: it’s slow and it uses too much energy. “Attila can go three feet in 30 seconds,” explains Mike Binnard, a member of Brooks’s lab. “If you watch a video, it looks okay in fast-forward, but at regular speed it’s pretty boring.”
THE PROBLEM, ACCORDING to Full, is that engineers rely on the old conception of insects as having simple, wheellike locomotion. But Full has been preaching his new biomechanical gospel to robot designers for three years now, and they’re beginning to take his suggestions to heart. Binnard, for example, is in the process of building an Attila-style robot with cockroach legs. Using Full’s extensive data on the insect, he replaced its six identical limbs with three differently shaped pairs of legs: small front legs that act like brakes, longer middle legs that push in both directions, and even longer rear legs that push the robot forward. The savings in energy should help it travel five times faster than Attila.
Binnard and the other robot designers are not the only ones benefiting from this collaboration. The questions they ask have led Full and his PolyPEDAL students into entirely new areas of inquiry. For instance, Binnard recently asked Kram how he might teach his robot to climb over objects. It’s something robots are particularly bad at: they slowly plant one foot at a time, continually check their balance, and when they finally pull themselves up, they often strip their gears as they go. Cockroaches, on the other hand, can race over almost anything. Faced with the question, Kram realized he didn’t actually know how cockroaches do it. So he and Yamauchi built a step for the Jell-O track, ran roaches over it, and discovered that as the roaches approach the step, they tilt their front ends up with their middle legs and put their front legs on the ledge. But they don’t use their front legs to pull themselves up; instead they boost themselves over with a strong push of their back legs.
While Full loves the idea of a scurrying roach robot, his ultimate dream is a mechanical crab. Not only can a crab race across dry land, it can plunge into crashing surf and continue running underwater. A robot with a crab’s skills could do a number of remarkable things. Consider Marines trying to land on a beach laced with mines. Crab robots could jump out of the landing craft, run onshore, hunt the mines down, and set them off. Rockwell International recently gave a contract to Full and IS Robotics, a Massachusetts robotics company, to design such a robot for the Navy. A robot crab could also distinguish itself in civilian duty. Researchers surveying the ocean floor or engineers inspecting underwater construction use propeller-driven, tethered machines. In strong currents or crashing waves these devices get tossed around and are often rendered useless. A robot with a crab’s stability, on the other hand, could easily work in these inhospitable places.
To build such a robot, however, the researchers need to understand better just how crabs do what they do. Marlene Martinez, another Berkeley grad student, is therefore collecting data on real crabs. She’s seen crabs that live on rocky beaches wrap their legs around small rocks to resist the crashing waves, and she’s heard of species that live on sandy beaches vibrating their legs to liquefy the sand so they can jam their limbs down into it and hold on tight. She’s observed how, when a crab walks underwater, it adjusts the angle at which its body points so the water will lift and support it. This added buoyancy means the crab doesn’t need to keep as many legs on the ground for stability. A crab robot would do well to copy any or all of these strategies.
But no matter how deeply involved the PolyPEDALists get in robot design, their main focus is still on exploring how flesh-and-blood animals, or chitin-and- hemolymph arthropods, to be more precise, move. Despite having discovered the first airborne running ant, for example, Kram is convinced that ants don’t have to leave the ground to run. He thinks they, like crabs and humans, may be able to imitate Groucho Marx. To prove his hypothesis, he’s going to have to design the most sensitive force plate yet; an ant weighs a thousandth of an ounce. But when he’s done, chances are this research, like much of the other work that goes on in the PolyPEDAL lab, will uncover even more hidden similarities between ants and ourselves.
“I think what our research has said is that evolution is constrained,” says Full. “There are not an infinite number of ways to move, even though they can look very different. To say that a model of a pogo stick could apply to this kind of diversity, I can tell you, I never would have believed it unless I’d collected the data myself.”
If you’re fleeing a large indoor predator, it helps to be able to dash up walls and upside down across ceilings, pausing now and then to wave your antennae provocatively at your oafish floor-bound pursuer. Thanks to animal physiologists Alexa Tullis of the University of Puget Sound and Robert Full of the University of California at Berkeley, we are at last beginning to understand how cockroaches have perfected this art. They found that a roach burns three times as much energy running up a vertical wall as it does running upright on a flat surface–and, surprisingly, 50 percent more than it does running upside down.
Tullis and Full measured the oxygen consumption of roaches running on a tiny treadmill that was inclined at 45- and 90-degree angles, and also completely inverted for some tests. The treadmill was enclosed in a small chamber so the researchers could precisely monitor oxygen levels. Tullis and Full were surprised by their findings. “The cost of moving a given distance is highest when the roach runs up a vertical wall,” says Tullis.
Why do roaches find it easier to run upside down than straight up a wall? Tullis and Full aren’t entirely sure. A roach, says Full, apparently does more work against gravity when climbing a 90-degree incline than it does when moving on a level surface, even if that surface happens to be above the insect. The roaches have little hooks on their feet that probably help them cling to small bumps and fissures on a surface. Those hooks may help the roaches fight gravity, but the insect also takes fewer and longer steps when it’s upside down.
“It’s kind of like he knows he’s unstable, and if he lets go, it’s the end of him,” Tullis says. The change in gait, she speculates, may call different muscle groups into play that use less energy. What does it take to tire a roach out? Tullis had the roaches run for at least 15 minutes to get an accurate reading, and they showed no signs of tiring.
Ounce for ounce, rhinoceros beetles are the world’s strongest animals. But just how strong are they? And what makes them so powerful?
INSPIRATION CAN COME FROM THE STRANGEST PLACES. While perusing the Guinness Book of World Records, Rodger Kram saw a startling entry. “The claim that the world’s strongest animal is the rhinoceros beetle, and that it can support 850 times its own body weight,” he says. Kram, a physiologist at the University of California at Berkeley, decided to test that claim in the Poly-PEDAL lab.
Kram didn’t simply stack weights on beetles’ backs, since a little tilt would unbalance the load. Instead he created a yoke. He glued a patch of Velcro on each beetle’s back and attached to it a thin lead strip that extended over the beetle’s head and beyond its rear. On the ends he glued lead weights he had bought from a hobby shop (they’re normally used to give model trains traction).
When Kram put the rhinoceros beetles on a treadmill, he discovered that while they were not as strong as the Guinness Book claimed, they were still amazing. They could carry up to 100 times their own weight of one-tenth of an ounce, although under that load they could barely move. With 40 times their own weight, they plodded for about ten minutes before becoming exhausted. But with 30 times their own weight, things changed: after half an hour of walking, they still showed no sign of fatigue. “I got bored before they got tired,” says Kram.
The beetles’ feat is comparable to a 150-pound man walking a mile with a Cadillac on his head without tiring. To a physiologist like Kram, what was particularly mysterious was what fueled the beetles. “In humans and ponies and dogs,” he explains, “if you have them carry a weight equal to 10 percent of their body weight, their metabolic rate goes up by 10 percent: 10, 10; 20, 20; and so on in a proportional increase.”
For the rhinoceros beetles to follow this rule carrying 30 times their weight, though, they would have to speed up their metabolism by a factor of 30–something only a few creatures on Earth, such as bumblebees, can do. Kram didn’t expect ground-dwelling beetles to have a metabolism that could burn at such a high, sustained rate. But he also didn’t expect what he found when he sealed his treadmill in a test chamber and measured how much oxygen the beetles consumed, and thus how many calories they burned. While carrying 30 times their weight, the beetles consume only four times more oxygen than when walking unencumbered–an astonishing display of biomechanical efficiency. “If these beetles carry 50 percent of their own weight, it’s absolutely trivial,” says Kram. “They hardly notice it at all.”
Rhinoceros beetles don’t actually carry heavy loads on their backs in nature, but they do engage in strenuous tasks, such as plowing through forest litter to find food and locking horns with rivals. Kram has yet to figure out their secret. The mechanical tricks of other animals don’t apply. Hermit crabs, for example, can carry their heavy shells by dragging their abdomens; with the seafloor supporting most of the load, the crabs just have to move it forward. But rhinoceros beetles keep their bellies high. People practiced at carrying heavy loads on their heads conserve energy by turning some of the energy of their forward movement into the rise and fall of their stride. The beetles, on the other hand, walk too slowly to do anything of the sort. When carrying a load, they don’t change their walking style at all.
Kram plans to explore their skeleton and muscles to get to the bottom of this mystery. Like all insects, the beetles have a stiff exoskeleton, and it’s possible that it is so exceptionally strong that it can bear the beetle’s load without requiring much work from the muscles. But Kram suspects he’ll find the solution in the muscles–and he sees the beetles’ slowness as a clue. Muscles that contract and relax slowly, he says, can be powerful and metabolically efficient at the same time; the ones that clams use to keep their shells shut tight are an example. Rhino beetles may have muscles like that.
Uncovering their full story could be a great help to researchers trying to build many-legged robots for tasks like mining the moon. After all, a robot with legs of hollow steel is essentially a mechanical beetle. “The people who make robots haven’t been too concerned with energy consumption. They just plug the robot in, and there’s a nuclear reactor at the other end, and they have plenty of power,” says Kram. “But when we really start to make a practical, autonomous, payload-carrying robot, energy conservation will become much more important.”
Some critters walk, while others swim, fly, creep, or crawl to get around. Not the stomatopod, though. This tiny, shrimplike marine animal from the Pacific beaches of Panama rolls. And it’s the only known species in the animal kingdom that does.
So says Robert Full, an associate professor of integrative biology at the University of California in Berkeley, who has videotaped the strange cartwheeling crustaceans which were discovered by a colleague who brought several back to the United States for laboratory study.
Full says the creatures, whose Latin name is Nannosquilla decemspinosa, normally live in underwater burrows so cramped that they may have gradually learned to roll because evolution taught them that was the only way to turn around. Periodically waves or tides wash them ashore, and it is there, when surprised, that they arc their bodies tail-over-head into a ring and roll back to the safety of the water at a glacial 3.5 centimeters per second.
While the stomatopod can handle grades of 10 percent, it is unable to maneuver around obstacles and can only move in a straight line. It’s in a free roll less than half of the time, according to Full’s observations. The rest of the crustacean’s time is spent generating power by pushing off with its head and tail, the same way we use our legs.
“The results of 350 million years of evolution tell us that wheellike movement is a possible but improbable method of locomotion on land,” says Full, noting that the curious rolling facility could have some practical applications in locomotion mechanics for tiny robots. “By studying the mechanisms of locomotion and learning how the muscles and skeleton work–looking at exceptions to rules like this–we could get some biological inspiration for robotics.”
The PolyPEDAL (Performance, Energetics, and Dynamics of Animal Locomotion) laboratory of Robert Full, physiologist and Chancellor’s Professor at the University of California at Berkeley, performs internationally recognized research programs in comparative physiology and biomechanics that examine the general principles of animal and insect locomotion. Using high-speed-camera and imaging techniques, Full’s research has progressed to the point where it now provides biological stimulus for computer animations and the design of multilegged robots.
To set the stage for taking real-time pictures of the creatures in motion (from many angles in a three-dimensional process), segments of images are videotaped and transferred to computer files using frame grabbers. The images are then computer-analyzed using various imaging-analysis software.
The PolyPEDAL laboratory focuses on four basic areas of study: the cost of locomotion, metabolic capacity and endurance, leg musculoskeletal mechanics, and biomechanics. To study small, skittering creatures, the laboratory makes use of a large amount of video, imaging, computer, and mechanical equipment. For instance, exercise physiology is examined using treadmills and aerobic measurements; biochemical analysis is performed by measuring lactic acid and high-energy phosphate; biomechanical performance is analyzed with force plates, photoelastic gelatin, and high-speed, three-dimensional (3-D) image-motion analysis; and locomotive behavior across species is predicted with high-performance simulation workstations.
Says Full, “The economy of locomotion is remarkably similar for animals that differ in leg architecture, leg number, skeletal type, and body temperature, if you remove the effects of size. For instance, a four-legged mouse, four-legged lizard, eight-legged crab, and 42-legged centipede of the same size have similar economics. Size alone can explain much of the variation we see. But we’ve uncovered some amazing differences in the cost of locomotion by studying even smaller life forms, such as insects”.
To examine the effects of variation in body form on the mechanics of animal locomotion, the PolyPEDAL laboratory intensely studies biomechanics, such as in their experiments with cockroaches (see “Pendulums and pogo sticks”). All the laboratory’s investigations start with the application of reflective markers to the insect in question, in this case, the American cockroach (mass = 0.83 g). These markers are used as points of reference for the imaging portion of the experiment. Minitreadmills are used to measure the ground reaction forces and movements of the insects.
The miniscale or force platform at the PolyPEDAL laboratory required a structure that could measure the force generated by an insect that weighed just one-twentieth of an ounce. A force platform was eventually designed by Full and Berkeley undergraduate Michael Tu. Their force plate consists of 24 strain gauges made out of silicon slivers and gold wires about twice the thickness of a hair. All the gauges on the beams and the soldering of wires to terminals were done by hand, then covered with a layer of wood a half-millimeter thick.
To set the stage for taking real-time pictures of the creatures in motion (from many angles as locomotion is obviously a 3-D process), a runway is set up to include a gelatin track placed between crossed polarizing filters. The gelatin force platform is distinct from the treadmill and the force platform. Illuminated from below, a high-speed Redlake Imaging MotionScope HR1000 video camera records the stress-induced optical signals from above at 1000 frames/s. The size and skew of the optical patterns generated by the insect on the gelatin relate to the magnitude and direction of the force.
Segments of the images are videotaped and then transferred to computer files using a frame grabber (Neotech Image Grabber for the NuBus). The images are analyzed on an Apple Power Mac 9500 computer using different imaging-analysis soft ware packages, such as: NIH Image, and National Instruments’ Ultimage Concept VI and LabVIEW.
Images of the insects are also captured from different angles above the treadmill so that a 3-D image of insect leg movements can be recreated. Several high-speed digital cameras are used to capture images of the moving cockroaches at 1000 frames/s. The cameras include Kodak’s EktaPro 1000, the NAC 1000, and the Redlake HR1000.
Full says, “The Redlake [cameras] were recently added to the experimental setup because they were the first high-speed cameras on the market with a small form factor and reasonable cost. As a result, they are used to look at the action above and below the minitreadmill.”
The high-speed cameras download their data to a Peak Performance 3D Motus System at 10 to 30 frames/s. This Windows-based motion-capture system combines high-speed video-capture boards (a Matrox Marvel II frame grabber and a Matrox Studio Express compression card) with software for detailed analysis of the data. Motus software converts pixel locations from the images into units, such as meters. This is done by digitizing a calibration frame that has been placed in the plane of motion in which the roach moves. Kinematic calculations are then per- formed using linear displacements, angular displacements of the joint, lin-ear velocities, joint velocities, linear acceleration, and centers of mass. Full also uses the Motus software to transform 2-D data into 3-D graphics. This is accomplished by digitizing several views of the same image (collected by two to six cameras located at different angles from the insect) and a direct linear-transformation (DLT) mathematical process. With DLT, the original 2-D data can be converted into 3-D graphics, which are then rotated in space for viewing from different perspectives. This analysis reveals the changing position of the reference markers and, therefore, the roach’s locomotive behavior.
The results of Full’s research using high-speed imaging are interesting. For instance, he found that roaches use an alternating tripod-stepping pattern at 0.44 to 1.0 m/s, which is basically a running or bouncing gait. At their highest speeds (1.0 to 1.5 m/s), the roaches switch to quadrupedal and bipedal running. Basically, the roaches are able to run exceptionally fast on their two hind legs by taking advantage of their aerodynamic shape. Wind-tunnel experiments at the laboratory showed that when the roach is sprinting, the air pushes against it so hard that it keeps the insect from falling down. Furthermore, this heretofore unheard of running motion generates the same amount of mechanical energy per unit mass that is used by animals five times larger in mass.
The PolyPEDAL laboratory scientists have amassed an impressive collection of imaging instruments and computers. Several motion-kinematics workstations are available. They include two Kodak EktaPro 1000 high-speed video cameras capable of collecting image data at 1000 frames/s; a VideoLogic high-speed video camera (320 frames/s); a dedicated Intel-Pentium PC computer for studies on mechanics; a Peak Performance 3-D motion-analysis system with color monitor; two Panasonic VCRs for analysis, several Redlake high-speed video cameras (1000 frames/s); and two NAC high-speed, color video cameras (1000 frames/s).
For studying mechanics, five Power Mac 9500 computers are fully equipped with frame grabbers, LabVIEW software and National Instruments’ analog-to-digital converters. Moreover, separate workstations are for metabolic studies, EMG analysis, modeling, muscle studies, and data visualization, where Silicon Graphics’ computers and digital cameras for microscopes are used.
“Next,” says Full, “we are going to study the motion of nature’s smallest runners, such as ants. We are also working closely with engineers that use micro-mechanical system (MEMS) technology so that we can measure the force produced by a single leg of an animal 1 mm long. Discoveries in this area could inspire the design of 1-mm MEMS/silicon robots. We also hope to collect more three-dimensional motion data that will allow us to produce a complete three-dimensional, dynamic musculoskeletal simulation of a running insect. This will let us test the hypotheses behind the control systems that are ultimately used in robots. Most important, we await the development of smart agents that can image-process natural markers on animals and autotrack them through time.’
Adds Full, “We must preserve biodiversity even of the most disgusting animals, because they can lead to major discoveries about how animals work. Especially in the case of humans, these animals can tell us a lot about our muscles and skeletons. They can also help us learn about how we interact with our environment.”
Studying Animal Locomotion
Picture a horror movie, filled with insects fast insects so fast that some insects have even set speed records. Then, move the whole scene to California and the laboratory of Robert Full, physiologist at the University of California at Berkeley. He is a man with a penchant for the multilegged.
Full’s laboratory, the PolyPEDAL (Performance, Energetics, and Dynamics of Animal Locomotion) laboratory, contains trotting ants, galloping crabs, undulating centipedes, and a famous cockroach that holds the record for insect speed in the Guinness Book of World Records. Full and his students study how muscles and skeletons work during movement by exploring the extraordinary diversity of animals in nature. The focus on what many consider strange and less-than-lovable creatures because they are looking to answer questions related to the energy costs of locomotion. Does the cost depend on leg number? On leg design? On body form or type of skeleton being used? These are all interesting questions that are yielding some unexpected findings.
For instance, the laboratory scientists have discovered that the mechanical energy that a human, a crab, a cockroach, a dog, or a horse generate to move 1 m is 1 J relative to body mass; this energy value is the same despite the fact that humans differ radically from other creatures. What’s more, two-, four-, six-, and eight-legged animals all can push the ground to move in the same way, like a pogo stick, despite their differences in structure. Studying the exercise physiology of crabs, as well as cockroaches running on treadmills, reveals, like humans, some creatures are extraordinary athletes and others are couch potatoes.
According to the laboratory scientists, these creatures play crucial roles in Professor Full’s internationally recognized research program in comparative physiology and biomechanics, a program that shows how examining a diversity of animals leads to the discovery of general principles of animal locomotion. Moving far beyond insect locomotion, Full’s research has progressed to the point where it now provides biological stimulus for computer animations and the design of multilegged robots that will be used for checking pipes at nuclear plants, cleaning toxic wastes, and performing fire and police work.
Pendulums and pogo sticks
Until the PolyPEDAL Laboratory was established, researchers studying animal locomotion concentrated on tetrapods (dogs, horses, and so forth) to construct models of walking and running. Even though there are several hundred times more arthropod species in this world, it’s much easier to film and image-analyze the four heavy legs of a running dog than the six nearly weightless limbs of a wriggling ant. But, as a result, it was generally believed that running was defined by all of an animal’s limbs leaving the ground.
Today, researchers such as Robert Full are focusing on two simple locomotion models: pogo sticks and pendulums. In 1986, while Full was conducting postdoctoral research in the laboratory of Thomas McMahon, a biomechanicist at Harvard University, it was discovered that running can occur when one foot is kept on the ground, if the human body behaves like a pogo stick.
When a human plants one leg on the ground, the body sinks down on the leg instead of being pushed upward. Meanwhile, the leg’s tendons act like springs. They stretch and snap back, and they store and release energy, just like the spring in a pogo stick. This movement propels the body upward and forward. Therefore, running, like walking, recovers energy and cuts down on energy expenditure.
The other current model of locomotion compares animal movement to the movement of a pendulum. When a human walks, the body behaves like and upside down pendulum. The foot set down in front is the pendulum’s axis; the center of mass is the hanging weight. As the stride is begun, the body works against gravity, forcing the body’s center of mass upward with the leg until the body reaches its highest point.
Gravity then takes over, and the body swings down until the leg comes in contact with the ground. The next stride is even easier because the body can use the energy provided by gravity to vault into successive steps, just as a pendulum reclaims its energy with each swing.
Magazine: International Design
Issue: Sept/Oct 1997
“Secrets of Motion”
EDITOR’S NOTE: DESIGN + BIOLOGY = BUGS
by Chee Pearlman
A quick glance through the current issue could lead one to believe that we at I.D. have gone a bit buggy. More than a bit, in fact, by devoting this issue to the subject of bugs. Bugs? Yes, we were bitten and smitten by bugs, and here’s how it happened:
First, we wandered into the movie Microcosmos, an exquisite live-action narrative about a day in the life of a community of insects. The movie is not extraordinary merely in its focus on the drama of these creatures’ existence, but also for the years that went into its making and the battery of equipment specially designed in order to film this micro-universe. (I confess to seeing the movie three times, right in the second row where you can really commune with the protagonists.)
Then, at last February’s TED conference, we met up with the ebullient bug man, Dr. Robert Full, whose investigations into the motion mechanics of creepy crawlies will inform the next generation of robot designs for IS Robotics and Rockwell. In our report, senior writer Peter Hall encounters Dr. Full’s menagerie of cockroaches, poisonous centipedes and scorpions some of the most remarkably designed moving life forms on earth. Each, as Full has shown, has plenty to teach creators of machines designed to navigate land mines or otherworldly environments.
It was about this time that we realized that Hollywood was becoming as alive to bugs as we were. A spate of digitally designed movies with insects in starring roles are in the pipeline from animators at Pixar, Dreamworks and Tippett Studios. The last has produced tour-de-force sequences of an especially mean class of Warrior bugs, managing to key directly into some of our worst cultural fears about insects.
After that, the horse was out of the barn, to mix our animal metaphors. We were on to bugging devices, computer bugs and – how could we miss the cute new VW bug, which will come onto the market next year. What’s fascinating, scary and little known about the VW beetle is that the “people’s car” was originally designed, in part, by Hitler. (“It should look like a beetle,” he said in 1934, “for we need look no further than nature to find out what streamlining is.”) Contributor Phil Patton takes us through a 65-year time line of the Love Bug’s remarkable history.
There was no end to the sources of inspiration for this issue, but we owe a particular debt of gratitude to Dr. Thomas Eisner, a leading researcher and biologist who took time out from this summer’s peak bug-studying season to write our introductory essay. When I contacted him to ask whether he agreed that bugs were the embodiment of great design, his response was rapid: “Insects are designed for success,” he said enthusiastically. “They won’t take over the world. They own it now!” That’s when we knew we were onto something. Enjoy.
Secrets of Motion
A new generation of robots is being modeled after the mesmerizing maneuvers of cockroaches and millipedes. Could they soon roam Mars? I.D Magazine, Sept/Oct 1997. By Peter Hall
Filmed under a high intensity light and played back in slow motion, the glowing legs of a poisonous centipede dance with a fearful symmetry. Its six-inch-long body undulates like a snake, with the legs inside each curve of the torso taking turns to strike the ground and propel the body forward. At full speed, the dance comes close to flight: only 3 of the centipede’s 44 legs are on the ground at any one time.
Revelatory footage of nature’s most loathsome creatures doesn’t just serve to fascinate the TV nature-show-viewing public. When the sequence – from a Discovery Channel show was shown as part of a presentation at the TED conference in Monterey last year, several design educators extended invitations for follow-up lectures at their schools. They hadn’t missed the fact that the presenter of the centipede’s leggy ballet, Robert Full, of the University of California in Berkeley, is a bubbling fount of biological design inspiration. But the invitations were all tactfully declined. Full is also possibly the busiest bug man on earth.
A broad, effusive, 39-year-old Homo sapien from Buffalo, New York, Full is the director of UC Berkeley’s Poly-PEDAL laboratory (the acronym PEDAL stands for performance, energetics and dynamics of animal locomotion), which studies the mechanics and physiology of creepy crawlies. His distinctly uncreepy, warm-blooded and media-friendly enthusiasm for bugs has landed him appearances on the Discovery Channel, the Today Show, in a variety of magazines and even some unwarranted attention in the National Enquirer. He was consulted on the making of animated bugs for RAID commercials and Pixar’s upcoming movie A Bug’s Life and has advised on the creation of animatronic bugs in the recent Miramax release, Mimic. But his most intriguing collaboration has been with the people who design autonomous vehicles with artificial intelligence: the Poly-PEDAL lab’s findings are influencing a whole new generation of robots.
Conversations with Bob Full are held preferably by e-mail, but with a word of caution. He confesses to occasionally consigning the entire contents of an overbrimming inbox to the trash. One can see why. A question that twangs Full’s pedagogical heartstrings received a reply several pages long. This is a jackpot for the recipient: Full-mail is not littered with scientific jargon, but with catchphrases, emphatic punctuation and descriptive analogies that even a mental millipede could understand.
The Poly-PEDAL lab’s favorite subjects, arthropods, are creatures Full likes to distinguish with scorpions, centipedes, millipedes and cockroaches; any one of over a million species of invertebrates with segmented bodies, jointed limbs and external skeletons. Full maintains that he has no particular fondness for them, but believes after the Danish physiologist August Krogh – that their relatively simple muscles and skeletons contain general architectural principles for all animals and, by extension, for the design of robots. “I think, like most people, that bugs are actually disgusting,” he says. “But they are simply extraordinary at telling us the secrets of nature.” This philosophy yields a conservationist refrain, “diversity enables discovery.” Strange and disgusting creatures must be preserved, argues Full, because they can lead to unanticipated discoveries that change the way we interact with our environment. “It pains me to see things become extinct,” he says, “because that’s a wonderful set of design ideas that are gone. Every organism has a story to tell.”
RUN, ROACHES, RUN
At the lab, nature’s crunchy creatures are put through a series of tests in torturous-looking contraptions. Roaches and crabs run on force-measuring platforms, Plexiglas stairs and treadmills in boxes that measure oxygen consumption. Tiny wires are placed into tiny muscles to determine when they are active. Our friend the poisonous centipede, meanwhile, is put in an ingenious “Jell-O trap” a long acrylic box with a gelatin-coated floor layered over two polarizing filters that are illuminated from beneath by a high-intensity light. The construction examines the forces the centipede generates when running. As each of the creature’s feet strikes the Jell-O, the opaque surface is disrupted, allowing light to shine through at the same specific angle. The stronger the force of the leg, the brighter the light. On film, the effect is startling: the monstrous, jawed centipede appears to be creating stars with it’s tiptoes.
The lab’s choicest findings are relayed to the public as a series of astounding revelations of nature. Full’s students notified the Guinness Book of World Records that the world’s fastest land insect is a cockroach, which moves at 50 steps a second (the equivalent of humans running at 200 miles per hour). At top speeds, the roach rears up on its hind legs and runs like a bipedal human. Another feature shared by cockroaches and humans is the amount of mechanical energy we (along with dogs, horses, crabs, lizards and mice) use per pound of body weight when we walk or run.
Particularly startling is the manner in which creatures with six or more legs move. Previous theories had it that they trundled along rather like a wheel, placing one leg down after another at a regular pace. Under observations at the Poly-PEDAL lab, however, it emerged that the arthropods propel their legs in alternating tripods, with two legs down on one side, one leg down on the other, maintaining an impressive stool-like stability in motion. Most significantly, the legs of a running roach, crab, centipede and human do not move at a smooth, constant speed like wheels, but like pendulums when they walk and springs when they run, bending and bouncing, accelerating and decelerating. The tendons in our legs, in other words, function like energy-efficient pogo sticks, storing and releasing energy as they go.
DESIGN LESSON FROM LOW LIFES
About six years ago, Full got together with a group of researchers in robot development, including Rodney Brooks and Mark Raibert from the Massachusetts Institute of Technology’s Artificial Intelligence Lab. Brook’s lab had been working on an array of autonomous vehicles, or artificial creatures, for traversing difficult and hazardous terrains, such as the surface of Mars. Raibert’s Leg Lab, meanwhile, had been building a series of one-, two- and four-legged hopping mechanisms that moved with an eerie naturalism. (They were accordingly cast, as robots, in a bit part with Sean Connery in the 1993 film, Rising Sun.) The contract between Brooks’s and Raibert’s robots was revealing. The former were very stable and moved very slowly with back-and-forth leg movements and little up-and-down oscillation of the body. Raibert’s robots, on the other hand, were capable of extraordinary mechanical feats running at 13 mph, leaping over obstacles and climbing simplified stairs but they fell over when they were not moving.
Balance, as biologists, engineers, ecologists and Yoga enthusiasts all agree, is the key to moving forward. But Raibert had demonstrated that moving forward is also the key to balance. His robots were built on the pendulum/pogo stick principle. “I would never have guessed that many-legged sprawled postured animals would move dynamically by bouncing, ” says Full. “Once we discovered this in several species, we looked at Raibert’s work very carefully. Quire simply, he is a genius. He showed the importance and beauty of dynamic-legged locomotion.”
A series of collaborations began. Full and Raibert decided to test the theory that insects “bounced” by building a computer simulation of a six-legged creature. Faithfully copying the Poly-PEDALists’s detailed account of a cockroach’s leg structure and positions during movement, the Leg Lab team (and subsequently Raibert’s firm, Boston Dynamics) created 3-D computer renderings of a roach that resembled a hemisphere on legs. Sure enough, it bounced, and moved remarkably like New York’s most reviled insect. Raibert’s lab was also able to establish how much the muscles controlled the leg and the extent to which the tendons stretched. “Almost nothing is known about how people or animals control themselves,” says Raibert, “and watching them doesn’t always tell you how they work.”
At the same time, Brooks and Raibert saw how Full’s insight and amassed data on the design advantages and flaws of the roach and other creatures could influence their mechanical creations. “Seeing his critters,” says Raibert, “has provided huge motivation.” An early exploration of Poly-PEDAL findings was a bouncing, six-legged terrestrial robot powered by compressed air, built at Brooks’s lab by researcher Mike Binnard. He called it Boadicea, after the fearsome queen of Britain who defeated the Romans in the first century A.D. While its lumbering, comical movements – which can be viewed in a series of mini-movies on the MIT Web site – bear little relation to the motions of Boadicea’s thundering chariot, they do come several steps closer toward an approximation of a cockroach’s dynamic. Like the roach, and unlike earlier robots, Boadicea’s legs overlap each others’ workspaces as they move, allowing for longer strides and therefore faster movement. It also strives to replicate the dynamic and static stability of a six-legged creature, such that three legs are always on the ground, forming a tripod.
RISE, ROBOTS, RISE
Champions of the robotic leg will point out that about half of the earth’s landmass is inaccessible to a wheeled vehicle, and that’s not counting the rest of the planets: A legged robot might have an easier time sightseeing on Mars than the wheeled Sojourner Rover. Legs often do less damage than wheels. A team at Ohio State University developed an “adaptive suspension vehicle” that showed how a legged tractor might pick its way gingerly through crops rather than flatten paths through wheatfields.
Such projects are no longer confined to the realm of academia. The Poly-PEDAL lab is collaborating with companies like Rockwell and IS Robotics, a commercial firm founded by Rodney Brooks, on commercial robots for a variety of uses, including medical and hazardous clean-up jobs. For IS Robotics, Full’s team provided videotapes of crabs roving on beaches as references for the design of an amphibious six-legged vehicle named Ariel, which is designed to find landmines in the surf zone by moving over sand and underwater. Following the Poly-PEDAL lab’s suggestions, Ariel adopts the flat orientation of a crab’s body and leg design to minimize drag, and a variable stance width for high stability and high bottom clearance.
It’s not that nature – or Full – have all the design answers. The idea that gazelles or ghost crabs are objects of perfection is a popular misconception. Evolution marches not toward perfection, but aims at the “just good enough” principle, such that many animals are constrained by their history. Full likes to use an automotive design analogy: Animals must make small changes in what their ancestors left them, like trying to modify a used car,” he says. ‘Humans can create a new car from scratch, using different designs and materials.” With the design of Ariel, for instance, the crab’s various efforts to avoid being flipped over by waves could be happily ignored by making the robot invertible, a distinctly non-biological solution.
Are six legs better than four, three or two, or even wheels? Some experts, such as Robert Ringrose, an MIT graduate student who worked on the roach simulation, believe that fewer legs is better for speed and maintenance. “I see adding more legs as moving back,” says Ringrose. “Four legs gives you more pieces to break. And consider how fast an ostrich can run.” Even Raibert is reluctant to say that the Sojourner Rover would have fared better with legs, given the current state of the technology. ‘When you take into account the competing demands on a Mars mission, such as reliability, cost and communication, they’re doing a magnificent job,” he says.
In Full’s view, however, a six-legged paradigm holds the key to the future, bringing speed and maneuverability to stable robots. The next robotic generation will fuse the static stability of the Sojourner Rover (it doesn’t fall over when it stops) with the dynamic stability of a Raibert hopper. “Bugs have both!” says Full. “Nature is telling us that the bouncing six-legged design will result in the most maneuverable land vehicles ever built. “I cant wait to see them.”