{"201371":{"#nid":"201371","#data":{"type":"news","title":"\u0022Terradynamics\u0022 Could Help Designers Predict How Legged Robots Will Move on Granular Media","body":[{"value":"\u003Cp\u003EUsing a combination of theory and experiment, researchers have developed a new approach for understanding and predicting how small legged robots \u2013 and potentially also animals \u2013 move on and interact with complex granular materials such as sand.\u003C\/p\u003E\u003Cp\u003EThe research could help create and advance the field of \u201cterradynamics\u201d \u2013 a name the researchers have given to the science of legged animals and vehicles moving on granular and other complex surfaces. Providing equations to describe and predict this type of movement \u2013 comparable to what has been done to predict the motion of animals and vehicles through the air or water \u2013 could allow designers to optimize legged robots operating in complex environments for search-and-rescue missions, space exploration or other tasks.\u003C\/p\u003E\u003Cp\u003E\u201cWe now have the tools to understand the movement of legged vehicles over loose sand in the same way that scientists and engineers have had tools to understand aerodynamics and hydrodynamics,\u201d said Daniel Goldman, a professor in the School of Physics at the Georgia Institute of Technology. \u201cWe are at the beginning of tools that will allow us to do the design and simulation of legged robots to not only predict their performance, but also to optimize designs and allow us to create new concepts.\u201d\u003C\/p\u003E\u003Cp\u003EThe research behind \u201cterradynamics\u201d was described in the March 22 issue of the journal \u003Cem\u003EScience\u003C\/em\u003E. The research was supported by the National Science Foundation Physics of Living Systems program, the Army Research Office, the Army Research Laboratory, the Burroughs Wellcome Fund and the Miller Institute for Basic Research in Science of the University of California, Berkeley.\u003C\/p\u003E\u003Cp\u003ERobots such as the Mars Rover have depended on wheels for moving in complex environments such as sand and rocky terrain. Robots envisioned for autonomous search-and-rescue missions also rely on wheels, but as the vehicles become smaller, designers may need to examine alternative means of locomotion, Goldman said.\u003C\/p\u003E\u003Cp\u003EExisting techniques for describing locomotion on surfaces are complex and can\u2019t take into account the intrusion of legs into a granular surface. To improve and simplify the understanding, Goldman and collaborators Chen Li and Tingnan Zhang examined the motion of a small legged robot as it moved on granular media. Using a 3-D printer, they created legs in a variety of shapes and used them to study how different configurations affected the robot\u2019s speed along a track bed. They then measured granular force laws from experiments to predict forces on legs, and created simulation to predict the robot\u2019s motion.\u003C\/p\u003E\u003Cp\u003EThe key insight, according to Goldman, was that the forces applied to independent elements of the robot legs could be simply summed together to provide a reasonably accurate measure of the net force on a robot moving through granular media. That technique, known as linear superposition, worked surprisingly well for legs moving in diverse kinds of granular media.\u003C\/p\u003E\u003Cp\u003E\u201cWe discovered that the force laws affecting this motion are generic in a diversity of granular media, including poppy seeds, glass beads and natural sand,\u201d said Li, who is now a Miller postdoctoral fellow at the University of California at Berkeley. \u201cBased on this generalization, we developed a practical procedure for non-specialists to easily apply terradynamics in their own studies using just a single force measurement made with simple equipment they can buy off the shelf, such as a penetrometer.\u201d\u003C\/p\u003E\u003Cp\u003EFor more complicated granular materials, although the terradynamics approach still worked well, an additional factor \u2013 perhaps the degree to which particles resemble a sphere \u2013 may be required to describe the forces with equivalent accuracy.\u003C\/p\u003E\u003Cp\u003EBeyond understanding the basic physics principles involved, the researchers also learned that convex legs made in the shape of the letter \u201cC\u201d worked better than other variations.\u003C\/p\u003E\u003Cp\u003E\u201cAs long as the legs are convex, the robot generates large lift and small body drag, and thus can run fast,\u201d Goldman said. \u201cWhen the limb shape was changed to flat or concave, the performance dropped. This information is important for optimizing the energy efficiency of legged robots.\u201d\u003C\/p\u003E\u003Cp\u003EAerodynamic designers have long used a series of equations known as Navier-Stokes to describe the movement of vehicles through the air. Similarly, these equations also allow hydrodynamics designers to know how submarines and other vehicles move through water.\u003C\/p\u003E\u003Cp\u003E\u201cTerradynamics\u201d could provide designers with an efficient technique for understanding motion through media that flows around legs of terrestrial animals and robots.\u003C\/p\u003E\u003Cp\u003E\u201cUsing terradynamics, our simulation is not only as accurate as the established discrete element method (DEM) simulation, but also much more computationally efficient,\u201d said Zhang, who is a graduate student in Goldman\u2019s laboratory. \u201cFor example, to simulate one second of robot locomotion on a granular bed of five million poppy seeds takes the DEM simulation a month using computers in our lab. Using terradynamics, the simulation takes only 10 seconds.\u201d\u003C\/p\u003E\u003Cp\u003EThe six-legged experimental robot was just 13 centimeters long and weighed about 150 grams. Robots of that size could be used in the future for search-and-rescue missions, or to scout out unknown environments such as the surface of Mars. They could also provide biologists with a better understanding of how animals such as sand lizards run and kangaroo rats hop on granular media.\u003C\/p\u003E\u003Cp\u003E\u201cFrom a biological perspective, this opens up a new area,\u201d said Goldman, who has studied a variety of animals to learn how their locomotion may assist robot designers. \u201cThese are the kinds of tools that can help understand why lizards have feet and bodies of certain shapes. The problems associated with movement in sandy environments are as important to many animals as they are to robots.\u201d\u003C\/p\u003E\u003Cp\u003EBeyond optimizing the design of future small robots, the work could also lead to a better understanding of the complex environment through which they will have to move.\u003C\/p\u003E\u003Cp\u003E\u201cWe think that the kind of approach we are taking allows us to ask questions about the physics of granular materials that no one has asked before,\u201d Goldman added. \u201cThis may reveal new features of granular materials to help us create more comprehensive models and theories of motion. We are now beginning to get the rules of how vehicles move through these materials.\u201d\u003C\/p\u003E\u003Cp\u003E\u003Cem\u003EThis research was supported by the Burroughs Wellcome Fund, the Army Research Laboratory Micro Autonomous Systems and Technology Collaborative Technology Alliance (CTA W911NF-08-2-004), the Army Research Office (W911NF-11-1-0514), the National Science Foundation (NSF) Physics of Living Systems program (PHY-1150760) and the Miller Institute for Basic Research in Science at the University of California, Berkeley. Any conclusions are those of the principal investigators, and do not necessarily represent the official position of the Army Research Laboratory, the Army Research Office or the NSF.\u003C\/em\u003E\u003C\/p\u003E\u003Cp\u003E\u003Cstrong\u003ECITATION\u003C\/strong\u003E: Chen Li, Tingnan Zhang, Daniel I. Goldman. \u201cA Terradynamics of Legged Locomotion on Granular Media,\u201d Science (2013): \u003Ca href=\u0022http:\/\/dx.doi.org\/10.1126\/science.1229163\u0022 title=\u0022http:\/\/dx.doi.org\/10.1126\/science.1229163\u0022\u003Ehttp:\/\/dx.doi.org\/10.1126\/science.1229163\u003C\/a\u003E.\u003Cbr \/\u003E\u003Cbr \/\u003E\u003Cstrong\u003EResearch News\u003C\/strong\u003E\u003Cbr \/\u003E\u003Cstrong\u003EGeorgia Institute of Technology\u003C\/strong\u003E\u003Cbr \/\u003E\u003Cstrong\u003E177 North Avenue\u003C\/strong\u003E\u003Cbr \/\u003E\u003Cstrong\u003EAtlanta, Georgia\u0026nbsp; 30332-0181\u003C\/strong\u003E\u003Cbr \/\u003E\u003Cbr \/\u003E\u003Cstrong\u003EMedia Relations Contact\u003C\/strong\u003E: John Toon (404-894-6986)(\u003Ca href=\u0022mailto:jtoon@gatech.edu\u0022\u003Ejtoon@gatech.edu\u003C\/a\u003E).\u003C\/p\u003E\u003Cp\u003E\u003Cstrong\u003EWriter\u003C\/strong\u003E: John Toon\u003C\/p\u003E","summary":null,"format":"limited_html"}],"field_subtitle":"","field_summary":[{"value":"\u003Cp\u003EUsing a combination of theory and experiment, researchers have developed a new approach for understanding and predicting how small legged robots \u2013 and potentially also animals \u2013 move on and interact with complex granular materials such as sand.\u003C\/p\u003E","format":"limited_html"}],"field_summary_sentence":[{"value":"Researchers have developed a new technique for predicting how robots will move on granular media."}],"uid":"27303","created_gmt":"2013-03-21 13:20:17","changed_gmt":"2016-10-08 03:13:55","author":"John Toon","boilerplate_text":"","field_publication":"","field_article_url":"","dateline":{"date":"2013-03-21T00:00:00-04:00","iso_date":"2013-03-21T00:00:00-04:00","tz":"America\/New_York"},"extras":[],"hg_media":{"201321":{"id":"201321","type":"image","title":"Terradynamics robots 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