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CLIMBINGROBOTSINNATURALTERRAINTIMOTHYBRETL,TERESAMILLER,ANDSTEPHENROCKJEANCLAUDELATOMBEAEROSPACEROBOTICSLABROBOTICSLABORATORYDEPARTMENTOFAERONAUTICSANDASTRONAUTICSCOMPUTERSCIENCEDEPARTMENTSTANFORDUNIVERSITY,STANFORD,CA94305STANFORDUNIVERSITY,STANFORD,CA94305{TBRETL,TGMILLER,ROCK}SUNVALLEYSTANFORDEDULATOMBECSSTANFORDEDUKEYWORDSMOTIONPLANNING,CLIMBING,ROBOTICS,LEGGEDROBOTS,HIGHRISKACCESS,NATURALTERRAINABSTRACTTHISPAPERPRESENTSAGENERALFRAMEWORKFORPLANNINGTHEQUASISTATICMOTIONOFCLIMBINGROBOTSTHEFRAMEWORKISINSTANTIATEDTOCOMPUTECLIMBINGMOTIONSOFATHREELIMBEDROBOTINVERTICALNATURALTERRAINANEXAMPLERESULTINGPATHTHROUGHALARGESIMULATEDENVIRONMENTISPRESENTEDTHEPLANNINGPROBLEMISONEOFFIVEFUNDAMENTALCHALLENGESTOTHEDEVELOPMENTOFREALROBOTICSYSTEMSABLETOCLIMBREALNATURALTERRAINEACHOFTHEFOUROTHERAREASHARDWAREDESIGN,CONTROL,SENSING,ANDGRASPINGISALSODISCUSSED1INTRODUCTIONTHEWORKDESCRIBEDINTHISPAPERISPARTOFANEFFORTTODEVELOPCRITICALTECHNOLOGIESTHATWILLENABLETHEDESIGNANDIMPLEMENTATIONOFANAUTONOMOUSROBOTABLETOCLIMBVERTICALNATURALTERRAINTOOURKNOWLEDGE,THISCAPABILITYHASNOTBEENDEMONSTRATEDPREVIOUSLYFORROBOTICSYSTEMSPRIORAPPROACHESHAVEDEALTWITHARTIFICIALTERRAIN,EITHERUSINGSPECIAL“GRASPS”EG,PEGS,MAGNETSADAPTEDTOTHETERRAIN’SSURFACEOREXPLOITINGSPECIFICPROPERTIESORFEATURESOFTHETERRAINEG,DUCTSANDPIPES112DEVELOPINGTHISCAPABILITYWILLFURTHEROURUNDERSTANDINGOFHOWHUMANSPERFORMSUCHCOMPLEXTASKSASCLIMBINGANDSCRAMBLINGINRUGGEDTERRAINTHISMAYPROVEUSEFULINTHEFUTUREDEVELOPMENTOFSOPHISTICATEDROBOTICSYSTEMSTHATWILLEITHERAIDORREPLACEHUMANSINTHEPERFORMANCEOFAGGRESSIVETASKSINDIFFICULTTERRAINEXAMPLESINCLUDEROBOTICSYSTEMSFORSUCHMILITARYANDCIVILIANUSESASSEARCHANDRESCUE,RECONNAISSANCE,ANDPLANETARYEXPLORATIONMANYISSUESNEEDTOBEADDRESSEDBEFOREREALROBOTSCANCLIMBREAL,VERTICAL,NATURALTERRAINTHISPAPERCONSIDERSFIVEOFTHEMOSTFUNDAMENTALOFTHESEISSUESHARDWAREDESIGN,CONTROL,SENSING,PLANNING,ANDGRASPINGONEOFTHESEISSUESINPARTICULAR,THEMOTIONPLANNINGPROBLEM,ISDESCRIBEDINMOREDETAILAGENERALFRAMEWORKFORCLIMBINGROBOTSISPRESENTEDANDTHISFRAMEWORKISINSTANTIATEDTOCOMPUTECLIMBINGMOTIONSOFTHETHREELIMBEDROBOTSHOWNINFIGURE1SIMULATIONRESULTSARESHOWNFORTHEROBOTINANEXAMPLEVERTICALENVIRONMENT2MOTIVATIONTHERESULTSOFRESEARCHINTHISAREAWILLBENEFITANUMBEROFAPPLICATIONSANDHAVEIMPLICATIONSFORSEVERALRELATEDRESEARCHAREAS21APPLICATIONSTHISPAPERISMOTIVATEDBYANEEDFORROBOTICSYSTEMSCAPABLEOFPROVIDINGREMOTEACCESSTOHIGHRISKNATURALENVIRONMENTSTHEREAREMANYTERRESTRIALAPPLICATIONSFORTHESESYSTEMS,SUCHASSEARCHANDRESCUE,CAVEEXPLORATION,HUMANASSISTANCEFORROCKANDMOUNTAINCLIMBING,ANDTACTICALURBANMISSIONSEACHOFTHESEAPPLICATIONSREQUIRESCLIMBING,DESCENDING,ORTRAVERSINGSTEEPSLOPESANDBROKENTERRAIN,ANDTHUSINVOLVESCONSIDERABLEHUMANRISKSEVERALSPACEAPPLICATIONSCOULDALSOBENEFITFROMTHESEAGGRESSIVEROBOTICSYSTEMSFOREXAMPLE,SITESONMARSWITHPOTENTIALLYHIGHSCIENCEVALUEHAVEBEENIDENTIFIEDONCLIFFFACES13OFTEN,ITISNEITHERPRACTICALNORFEASIBLEFORFLYINGROBOTSTOACCESSTHESEFIG1ATHREELIMBEDCLIMBINGROBOTMOVINGVERTICALLYONNATURALSURFACESLOCATIONSTHEREFORE,TOREACHTHESESITES,ROBOTSMUSTCLIMB,DESCEND,ORTRAVERSESTEEPSLOPESFUTUREGOALSFOREXPLORATIONONOTHERPLANETARYBODIESMAYREQUIREACCESSTOEQUALLYRUGGEDTERRAIN22IMPLICATIONSINADDITIONTOFURTHERINGTHEDEVELOPMENTOFACLIMBINGROBOTFORVERTICALNATURALTERRAIN,THERESULTSOFRESEARCHINTHISAREACOULDPROVIDEFUNDAMENTALINSIGHTINTOSEVERALRELATEDRESEARCHAREASFOREXAMPLE,THISSTUDYCOULDLEADTOTHEDEVELOPMENTOFBETTERSTRATEGIESFORROBOTICWALKINGORDEXTEROUSMANIPULATIONHUMANCLIMBERSOFTENCOMMENTONANINCREASEINBALANCEANDANEXPANDEDRANGEOFMOVEMENTINEVERYDAYACTIVITYASTHEYBECOMEMOREPROFICIENTATTHESPORTTHISENHANCEDMOBILITYISOFTENREFERREDTOAS“DISCOVERINGNEWDEGREESOFFREEDOM,”ANDISRELATEDTOTHEIDEAOFDISCOVERINGUSEFULNEWMODESOFMOBILITYFOREXTREMELYCOMPLICATEDHUMANOIDROBOTSORDIGITALACTORSALSO,THEDEVELOPMENTOFPLANNINGALGORITHMSFORCLIMBINGROBOTSCOULDLEADTOABETTERSETOFCRITERIAFORTHEDESIGNOFTHESETYPESOFROBOTSTHESEALGORITHMSCOULDBEAPPLIEDTOCANDIDATEDESIGNSINSIMULATIONTODETERMINETHECAPABILITIESOFTHERESULTINGROBOTS,ANDTHUSTOSELECTADESIGN3FUNDAMENTALISSUESTHEREAREFIVEFUNDAMENTALISSUESINVOLVEDINCLIMBINGSTEEPNATURALTERRAINHARDWAREDESIGN,CONTROL,SENSING,GRASPING,ANDPLANNINGASUBSTANTIALAMOUNTOFWORKNEEDSTOBEDONEINEACHOFTHESEAREASINORDERTODEVELOPAREALCLIMBINGROBOTTHISSECTIONDESCRIBESTHECHALLENGESINVOLVEDINTHEFIRSTFOUROFTHESEAREAS；THEPLANNINGPROBLEMWILLBEDISCUSSEDINMOREDETAILINSECTION431HARDWAREDESIGNAGOODHARDWAREDESIGNCANINCREASETHEPERFORMANCEOFTHEROBOT,ANDOFTENCANMAKEEACHOFTHEOTHERFUNDAMENTALISSUESEASIERTODEALWITHHOWEVER,PASTUSEOFHARDWARESOLUTIONSINMAINTAININGEQUILIBRIUMGENERALLYRESULTEDINAFUNDAMENTALLIMITATIONONTHETERRAINTHATCOULDBETRAVERSEDWHEELEDROBOTICSYSTEMSHAVEBEENUSEDTOASCENDANDTRAVERSENATURALSLOPESOFUPTO50DEGREES,TODESCENDSLOPESOFUPTO75DEGREES,ANDTOCLIMBOVERSMALLOBSTACLESINROUGHTERRAINTHESESYSTEMSEITHERUSESOMEFORMOFACTIVEORROCKERBOGIESUSPENSIONASIN12,1416,ORUSERAPPELLINGASIN1SIMILARRESULTSHAVEBEENOBTAINEDUSINGLEGGEDRAPPELLINGROBOTS3,17ANDASNAKELIKEROBOT4THETERRAINTHATTHESEROVERSCANTRAVERSEROBUSTLYISIMPRESSIVE,BUTNONEOFTHEEXISTINGSYSTEMSHASBEENSHOWNTOBECAPABLEO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