Sidewinder robots slither like snakes (video 4) Fluidizing sand using an air-fluidized bed. We constructed a setup to prepare a uniform and consistent state for the granular media before each trial. Our fluidized bed has a porous floor allowing the air to uniformly flow through the entire sand and letting it resettle into an equilibrium condition. As shown in this video, regardless of the initial state of the sand we were able to achieve a loosely packed granular media with a smooth surface after the fluidization process (movie 4 of 10.1126/science.1255718). - Sidewinder robots slither like snakes news.sciencemag.org/physics/2014/10/sidewinder-robots-slither-snakes In 2011, archaeologists needed to find out whether parts of ancient Egyptian boats were hidden in dangerously unstable humanmade caves by the Red Sea. Howie Choset, a roboticist at Carnegie Mellon University (CMU) in Pittsburgh, Pennsylvania, thought he had the perfect solution. He had built robotic snakes, so he outfitted one with a camera and sent it slithering through the caves narrow opening. But when the robot got inside, “we faced a challenge that we had not seen before,” Choset recalls. The robot couldnt make its way up the caves sandy slope, and the exploration was a bust. Now, Choset has found a way to climb that mountain. By teaming up with researchers studying how live snakes move, he and his colleagues have determined what it takes to make snake robots go uphill, even on slippery, sandy slopes. These reptiles, real and robotic, are sidewinders—they move forward not by slithering, but rather by wriggling their bodies perpendicular to the direction of travel in a undulating S-shaped wave. The motion is peculiar and, supposedly, “if you look too long at [a sidewinder] you’ll go mad,” says Daniel Goldman, a physicist at the Georgia Institute of Technology in Atlanta. And that motion will enable a snake to go uphill. But to maintain a grip on an incline, the snake modifies its motion to keep more of its body touching the ground as it moves, he, Choset, and their colleagues report online today in Science (1). Those insights could lead to robots that do better on rough terrain than robots with wheels, such as a Mars rover. “We don’t presently have machines that can climb steeply inclined fragile ground, and this work suggests new ways to build machines that can,” says Daniel Koditschek, an engineer at the University of Pennsylvania who was not involved with this work but who develops legged robots for desert explorations. “The opportunities and benefits for robotics here are significant.” Goldman specializes in studying how animals manage to move through sand and other granular materials that tend to give way. Curious about snakes, he and Hamidreza Marvi, now at postdoctoral student at CMU, went to Zoo Atlanta, where they filmed and analyzed the movements of six sidewinder rattlesnakes climbing in an enclosure with an inclined floor covered with sand. They varied the angle of the floor with each test and also observed several vipers, snakes that are not sidewinders, try to ascend the incline. The vipers slipped and failed to move up the slope, whereas the sidewinders had no problem, the researchers report. As it moves, a sidewinder sends a horizontal wave down its body. At the same time, it undulates up and down. As a result, the parts of the body on the ground push off while the airborne loops reach upslope, where they then make contact to push off. Marvi found that on flat ground, at any moment the rattlers have 25% of their body in contact with the ground. But the snakes tune their motion to the terrain. On a slope of 10°, 40% of the body remains in contact with the ground. That fraction increases to 45% on a 30° slope. In making the adjustment, a snake has to balance two factors. Too much contact and the reptile can’t lift the other parts of the body high enough to reach up the slope. Too little contact, and the sand gives way under the snake’s weight. “Apparently, these animals have found a sweet spot,” Koditschek says. Choset’s group programmed the robot to move in a similar manner, then altered the waves to change how much of the robot’s body was in contact with the sand at any one time. It, too, made it up through the sand. And by tweaking the two waves, “we can make our snake robots do what the snake can’t do,” Choset says, such as turn on a dime. These attributes may lead to robots that can snake their way through rubble in disaster zones to find trapped people or that can inspect nuclear power plants. “I’m smitten with this paper,” says Adam Summers, a comparative biomechanist at the University of Washington Friday Harbor Laboratories who was not involved with the work. “The biology is informed by the engineering and vice versa.” Choset, too, is quite pleased. He doesn’t have the permits needed to go back to the Egyptian caves, but has now used the robot on another archaeological expedition. There, “we did much better,” he says. Things are looking up for robotic snakes. References 1. Sidewinding with minimal slip: Snake and robot ascent of sandy slopes Science 10 October 2014: Vol. 346 no. 6206 pp. 224-229 DOI: 10.1126/science.1255718 sciencemag.org/content/346/6206/224 Editors Summary Whats that coming over the hill—is it a robot? Crossing a slope can be difficult, particularly if it is made of sand. Sidewinder rattlesnakes manage to climb sandy hills by adjusting the length of their body in contact with the sand. Marvi et al. designed robots based on this idea to determine what affects climbing ability on sandy slopes (see the Perspective by Socha). Based on the behavior of the robots, the authors performed further animal studies, and used an iterative approach to improve the robots capabilities and to better understand animal motion. Science, this issue p. 224 (1); see also p. 160 (2) Abstract Limbless organisms such as snakes can navigate nearly all terrain. In particular, desert-dwelling sidewinder rattlesnakes (Crotalus cerastes) operate effectively on inclined granular media (such as sand dunes) that induce failure in field-tested limbless robots through slipping and pitching. Our laboratory experiments reveal that as granular incline angle increases, sidewinder rattlesnakes increase the length of their body in contact with the sand. Implementing this strategy in a physical robot model of the snake enables the device to ascend sandy slopes close to the angle of maximum slope stability. Plate drag experiments demonstrate that granular yield stresses decrease with increasing incline angle. Together, these three approaches demonstrate how sidewinding with contact-length control mitigates failure on granular media. Supplementary Materials sciencemag.org/content/suppl/2014/10/08/346.6206.224.DC1/Marvi-SM.pdf Video Movie S1 sciencemag.org/content/suppl/2014/10/08/346.6206.224.DC1/1255718s1.mov A sidewinder rattlesnake climbing on loose sand. The videos illustrate sidewinding motion of a snake on inclinations of 0, 10, and 20° at real-time speed followed by 4-times slower speed. The side by side videos show each trial from two different angles. Movie S2 sciencemag.org/content/suppl/2014/10/08/346.6206.224.DC1/1255718s2.mov The CMU robot climbing loose sand at wave frequency of f = 0.08 Hz. At inclination of 10 degrees the robot pitched at contact length of l/L = 0.28 and slipped at l/L = 1. The CMU robot could successfully climb inclination of 10° at l/L = 0.55. The last two videos show the robot climbing inclinations of 5 and 20o at similar contact lengths successfully (l/L = 0.49 and 0.45, respectively). However, due to the presence of local slipping at the higher inclination angle (θ = 20°) the step length is shorter and thus the speed is slower. Movie S3 sciencemag.org/content/suppl/2014/10/08/346.6206.224.DC1/1255718s3.mov Movements of Other Crotaline Vipers on Horizontal and Inclined Sand. Sequence 1- A rock rattlesnake (Crotalus lepidus) uses lateral undulation on level sand. Sequence 2 - A speckled rattlesnake (Crotalus mitchellii) uses concertina with rectilinear locomotion on level sand (2x speed). Sequence 3 - A Mexican pitviper (Mixcoatlus melanurus) attempts to move using concertina locomotion on horizontal sand, but fails to make forward progress (3x speed). Sequence 4 - A pigmy rattlesnake (Sistrurus miliarius) attempts to move using lateral undulation on horizontal sand, but fails to make forward progress. Sequence 5 - A speckled rattlesnake (Crotalus mitchellii) uses concertina with rectilinear locomotion on 10° inclined sand (2x speed). Sequence 6 - A ridge-nosed rattlesnake (Crotalus willardi) attempts to move using lateral undulation on 10° inclined sand (uphill is upwards in the video), but fails to make forward progress. Sequence 7 - A Mexican pitviper (Mixcoatlus melanurus) attempts to move using concertina locomotion on 10o inclined sand, but fails to make forward progress. Sequence 8 - A pigmy rattlesnake (Sistrurus miliarius) attempts to move using lateral undulation on 10° inclined sand (uphill is upwards in the video), but fails to make forward progress. Movie S4 sciencemag.org/content/suppl/2014/10/08/346.6206.224.DC1/1255718s4.mov Fluidizing sand using an air-fluidized bed. We constructed a setup to prepare a uniform and consistent state for the granular media before each trial. Our fluidized bed has a porous floor allowing the air to uniformly flow through the entire sand and letting it resettle into an equilibrium condition. As shown in this video, regardless of the initial state of the sand we were able to achieve a loosely packed granular media with a smooth surface after the fluidization process. Movie S5 sciencemag.org/content/suppl/2014/10/08/346.6206.224.DC1/1255718s5.mov A sidewinder rattlesnake climbing loose sand at an inclination of 27°. The video is sped up 4 times and illustrates the extended contacts the snake makes during sidewinding motion on the highest possible angle (angle of maximum stability) on loose sand. 2. Of snakes and robots Science 10 October 2014: Vol. 346 no. 6206 pp. 160-161 DOI: 10.1126/science.1259970 sciencemag.org/content/346/6206/160.summary As anyone who has run up a sand dune can attest from burning calves, climbing a sandy slope is demanding. The root of the struggle—in animal and vehicle alike—comes from the behavior of the sand, a granular medium that can slip, slide, and flow like a fluid. Yet, desert-dwelling snakes can ascend sandy slopes with grace and energetic ease (1) through a process called sidewinding. Having no limbs to push off should make the matter worse, yet the snakes make it look simple. How do they do it? On page 224 of this issue, Marvi et al. (2) explore the physics of sidewinding in animal and robot, revealing how limbless locomotors can move up sandy slopes. 3. The social life of robots Science 10 October 2014: Vol. 346 no. 6206 pp. 178-179 DOI: 10.1126/science.346.6206.178 sciencemag.org/content/346/6206/178.full Autonomous machines have gripped our imagination ever since the first robot flickered on the silver screen, Maria (left) in the 1927 film Metropolis. Most of the robots we know today—unglamorous devices like robotic welders on car assembly lines and the Roomba vacuum cleaner—fall short of those in science fiction. But our relationship with robots is about to become far more intimate. Would you be comfortable with a robot butler, or a self-driving car? How about a robo-scientist toiling away next to you at the bench, not only pipetting but also formulating hypotheses and designing experiments? As robots become more sophisticated, psychological paradoxes are coming into sharper relief. Robots that look human strike many of us as downright creepy (as this weeks cover attests), while robots that act human—when they are programmed, for example, to cheat at cards—somehow put us at ease. And no matter how uncannily lifelike some of todays robots may seem, the resemblance is skin-deep. A stubborn challenge has been endowing robots with not only the capability to sense their environment, but also the wits to make sense of it. Robots will get there eventually, and when that happens well be confronted with a new array of ethical and moral questions. Questions like: Should robots be accorded rights as sentient beings? The rise of the machines will be anything but predictable.
Posted on: Tue, 21 Oct 2014 13:43:51 +0000
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