Analysis of Angle of Attack for Efficient Slope Ascent by Rovers

100 Pages·2016·4.27 MB·English

Analysis of Angle of Attack
for Efficient Slope Ascent by Rovers
Hiroaki Inotsume
CMU-RI-TR-15-22
Submitted inpartialfulfillment of
therequirementsforthedegreeof
MastersofScienceinRobotics
TheRoboticsInstitute
CarnegieMellonUniversity
Pittsburgh, PA15213
August2015
ThesisCommittee:
DavidWettergreen,Chair
William”Red”Whittaker
Dimitorios Apostolopoulos
ChristopherCunningham
Copyright(cid:13)c 2015HiroakiInotsume. Allrightreserved.

Abstract
What direction should a rover drive to efficiently ascend slope of loose soil?
To explore the lunar poles, rovers will need to traverse craters where high slip will
hamper progress. Because of limited energy, rovers need to find efficient routes to
traverse such sloped terrain. It is an open question whether efficient and successful
slope-ascending is achieved in loose soil by driving directly uphill or in a diagonal
cross-slopedirection.
In this thesis, the influence of the rover’s angle of attack on slope-ascent per-
formance was analyzed based on a slope-ascent rover model that consists of force
equilibrium conditions and terramechanics-based wheel–soil interaction. The ter-
ramechanicmodelwasvalidatedinsingle-wheelexperiments. Roverslip,uphillve-
locity, and power efficiency were predicted and associated with the angle of attack.
Analysisshowstheascentinthedirect uphill direction resultsin mosteffectivemo-
tion, in terms of velocity and power efficiency, on most of the slopes analyzed even
ifthevehiclelongitudinalslipcanbereducedbydecreasingtheangleofattack. The
analysis also indicates that a rover can diagonally ascend steep slopes where it can
not drive directly up if the rover can generate sufficient lateral grip against downhill
slides.
Slope-ascent experiments using a rover were conducted to experimentally eval-
uate the effect of the angle of attack. The test results validated the model-based
analysisandtheusefulnessoftheproposedslope-ascentmodel.
A strategy to select slope-ascending routes is proposed based on the model and
experiment based analysis. The utility of the route selection method was demon-
stratedinsimulationsonvariousslopesandfordifferentrovers.
The findings in this research are useful to develop path planning strategies and
also to develop locomotion configuration and controls which can have high slope-
ascentcapability.
iv
Acknowledgments
First of all, I would like to thank my adviser, David Wettergreen, for his contin-
uous support and guideline for the development of this research and throughout my
student life in the Robotics Institute. He introduced me a lot of interesting research
topics, provided me advice from multiple points of view, and always tried to keep
mymotivation high.
IwouldalsoliketothankRedWhittakerforprovidingmeachancetotacklethe
researchtopicinthisthesis. Thediscussionswithhimandhisadvicegreatlypushed
theprogressofthisresearch. Inaddition,IwouldliketothankDimiApostolopoulos
andChrisCunninghamforhavingdiscussionsthatprovidedmevariouspossibilities
ofresearchdirections.
I thank the members of the Wheel Testbed Project: Chuck Whittaker, Jim Teza,
DavidKohanbash,JoeAmato,andMollyWhittaker. Withtheirhardworkandhelp,
Icouldconductvariousexperimentsandalsocouldhavetime forthisresearch.
The discussions with Scott Moreland, Chris Skonieczny, Colin Creager, Kyle
Johnson, Matt Heverly, and Patrick Degrosse helped me a lot to develop deeper un-
derstanding of terramechanics and important rover mobility issues. Also the testing
ofScarabrovercouldnotbedonewithoutColin’sgreathelp.
Lastly I appreciate the Funai Foundation for Information Technology for their
financialsupportthatrealizedmystudyatCMU.
vi
Contents
1 Introduction 1
1.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2 Relatedwork . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2.1 Motion planningandcontrolonslopes . . . . . . . . . . . . . . . . . . . 3
1.2.2 Roverslopetesting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2.3 Modelingandanalysisofrovermobility onloosesoil . . . . . . . . . . . 5
1.3 Objectiveandapproach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.4 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2 Model-BasedAnalysisofSlope-AscentPerformance 9
2.1 Slope-ascentmodel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.2 Terramechanics-basedwheel–soilinteraction model . . . . . . . . . . . . . . . . 11
2.2.1 Modeldescription . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.2.2 Tuningofmodelparameters . . . . . . . . . . . . . . . . . . . . . . . . 16
2.3 Slope-ascentperformanceanalysis . . . . . . . . . . . . . . . . . . . . . . . . . 22
2.3.1 Simulation procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
2.3.2 Predictedwheelslip . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
2.3.3 Trajectoryanalysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
2.3.4 Uphill velocityandclimbing efficiency . . . . . . . . . . . . . . . . . . 30
2.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
3 Slope-AscentExperiments 35
3.1 Testroverandfield . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
3.2 Evaluationcriteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
3.3 Experimentprocedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
3.4 Experimentresults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
3.4.1 Rovertrajectory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
3.4.2 Roverslippage,uphillvelocity,andefficiency . . . . . . . . . . . . . . . 43
3.4.3 Comparison ofslope-ascentperformance ofAndy2andScarab . . . . . 46
3.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
4 SelectionofSafeandEfficientRoutes 49
4.1 Routeselectionbasedonslipregulation andefficiencymaximization . . . . . . . 49
4.2 Assessmentofslopetrafficabilitycharacteristics . . . . . . . . . . . . . . . . . . 50
vii
4.2.1 Slopetrafficabilitydiagram . . . . . . . . . . . . . . . . . . . . . . . . . 50
4.2.2 Climbing efficiencydiagram . . . . . . . . . . . . . . . . . . . . . . . . 52
4.3 Simulationofrouteselection . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
4.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
5 Conclusion 61
5.1 Summaryandconclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
5.2 Contribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
5.3 Futurework . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
Bibliography 63
A ValidityandLimitation ofSingle-WheelRepresentation 69
A.1 Analysisofweightdistribution . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
A.1.1 Weightdistribution model . . . . . . . . . . . . . . . . . . . . . . . . . 69
A.1.2 Weightdistribution ofAndy2andScarab . . . . . . . . . . . . . . . . . 70
A.2 Comparisonofsingle-wheelandfull-vehicle slipmodels . . . . . . . . . . . . . 71
A.2.1 Single-wheelandfull-vehicle models . . . . . . . . . . . . . . . . . . . 71
A.2.2 Simulation results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
A.3 Validityandlimitation ofthesingle-wheelmodel . . . . . . . . . . . . . . . . . 73
B Parametric Analysis of Wheel Grouser Configuration for Slope-Ascent and Tra-
verse 77
B.1 Single-wheelsideslipexperiments . . . . . . . . . . . . . . . . . . . . . . . . . 78
B.1.1 Experiment setupandprocedures . . . . . . . . . . . . . . . . . . . . . 78
B.1.2 Experiment results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
B.2 Slope-ascentandtraverseexperiments . . . . . . . . . . . . . . . . . . . . . . . 83
B.2.1 Experiment setupandprocedures . . . . . . . . . . . . . . . . . . . . . 83
B.2.2 Slope-ascentexperiment results . . . . . . . . . . . . . . . . . . . . . . 85
B.2.3 Slope-traverse experimentresults . . . . . . . . . . . . . . . . . . . . . 85
B.3 Assessmentofgrouserdesignforslope-ascentandtraverse . . . . . . . . . . . . 86
viii
List of Figures
1.1 Researchproblem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Temperaturemapofthecratersaroundthelunarsouthpole . . . . . . . . . . . . 2
1.3 Shackletoncraterandslopesaroundit . . . . . . . . . . . . . . . . . . . . . . . 3
1.4 TracksofOpportunity roverintheEaglecrater . . . . . . . . . . . . . . . . . . 4
1.5 Scarabroverwithactivesuspension . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1 Slopeascentwithanangleofattack . . . . . . . . . . . . . . . . . . . . . . . . 10
2.2 Drawbarpullandlateralforcerequiredtoascendslopes . . . . . . . . . . . . . . 11
2.3 Wheel–soilinteraction model . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.4 Typicalpressure–sinkagecurves . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2.5 Typicalshearstress–sheardisplacementcurvesofloose,granularsoils . . . . . . 15
2.6 Andy2rover . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.7 Singlewheeltestrig . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.8 Modelpredictiveforcesandsinkageplottedwithexperimentalresults . . . . . . 20
2.9 Resultoftheparametertuning . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.10 Slip-forcerelationship . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
2.11 Predictedlongitudinal andlateralslipofAndy2 . . . . . . . . . . . . . . . . . . 23
2.12 PredictedslipratioofAndy2rover . . . . . . . . . . . . . . . . . . . . . . . . . 24
2.13 PredictedslipangleofAndy2 . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
2.14 Predictedtrajectorieson20o slope . . . . . . . . . . . . . . . . . . . . . . . . . 27
2.15 Predictedtrajectorieson25o slope . . . . . . . . . . . . . . . . . . . . . . . . . 28
2.16 Predictedtrajectorieson30o slope . . . . . . . . . . . . . . . . . . . . . . . . . 29
2.17 Definitionsoftheuphill velocityv andtheuphillforceF . . . . . . . . . . . . 30
Y Y
2.18 Estimateduphill velocityofAndy2 . . . . . . . . . . . . . . . . . . . . . . . . 32
2.19 Estimatedclimbing efficiencyofAndy2 . . . . . . . . . . . . . . . . . . . . . . 32
3.1 Scarabroverusedfortheslope-ascentexperiments . . . . . . . . . . . . . . . . 36
3.2 SLOPELaboratoryatNASAGlennResearchCenter . . . . . . . . . . . . . . . 36
3.3 Setupoftheslope-ascentexperiments . . . . . . . . . . . . . . . . . . . . . . . 38
3.4 Rovertrajectoriesonθ = 10o slope . . . . . . . . . . . . . . . . . . . . . . . . 40
0
3.5 Rovertrajectoriesonθ = 15o slope . . . . . . . . . . . . . . . . . . . . . . . . 40
0
3.6 Rovertrajectoriesonθ = 20o slope . . . . . . . . . . . . . . . . . . . . . . . . 41
0
3.7 Rovertrajectoriesonθ = 25o slope . . . . . . . . . . . . . . . . . . . . . . . . 41
0
3.8 Comparisonsoftherovertrajectoriesfromthesimulations andexperiments . . . 42
3.9 SlipratiovsangleofattackrelationshipoftheScarab . . . . . . . . . . . . . . . 44
ix
3.10 Slipanglevsangleofattackrelationship oftheScarab . . . . . . . . . . . . . . 44
3.11 Uphillvelocityvsangleofattackrelationship oftheScarab . . . . . . . . . . . . 45
3.12 Climbing efficiencyvsangleofattackrelationship oftheScarab . . . . . . . . . 45
3.13 Comparisonsoftheslope-ascentperformancesofAndy2andScarabrovers . . . 47
4.1 SlopetrafficabilitydiagramofAndy2andScarabrovers . . . . . . . . . . . . . 51
4.2 ClimbingefficiencydiagramofAndy2for20o slope. Multi-levelsofslipthresh-
oldarerenderedwithdifferentcolors. Thediagramindicatesclimbingefficiency,
slope-ascendability,andsliplevelsforvariousanglesofattack. . . . . . . . . . . 53
4.3 RouteselectionforAndy2over20o slope . . . . . . . . . . . . . . . . . . . . . 56
4.4 RouteselectionforAndy2over25o slope . . . . . . . . . . . . . . . . . . . . . 57
4.5 RouteselectionforAndy2over31o slope . . . . . . . . . . . . . . . . . . . . . 58
4.6 RouteselectionforScarabover15o slope . . . . . . . . . . . . . . . . . . . . . 59
A.1 Steadystateslope-ascentbyafour-wheeled rover . . . . . . . . . . . . . . . . . 70
A.2 SchematicviewofaplanarCGpositionofarover . . . . . . . . . . . . . . . . . 70
A.3 Weightdistribution ofAndy2andScarabonslopes . . . . . . . . . . . . . . . . 72
A.4 Comparisons of slip of Andy2 predicted based on the single-wheel model and
thefull-vehicle model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
A.5 Comparisons of slip of Scarab predicted based on the single-wheel model and
thefull-vehicle model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
A.6 PredictedsinkageandforcesofAndy2wheelsforvariedangleofattack . . . . . 75
B.1 Testwheelwithsideslipconfigurations . . . . . . . . . . . . . . . . . . . . . . . 78
B.2 Relationshipbetweenthewheelslipandwheel-soilinteractionforces . . . . . . 79
B.3 Influenceofgrousercountondrawbarpullduringsideslip . . . . . . . . . . . . 81
B.4 Influenceofgrousercountonlateralforceduring sideslip . . . . . . . . . . . . . 81
B.5 Influenceofgrouserheightondrawbarpullduring sideslip . . . . . . . . . . . . 82
B.6 Influenceofgrouserheightonlateralforceduring sideslip . . . . . . . . . . . . 82
B.7 Testroverandtestfield . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
B.8 Wheelsusedtoevaluatetheeffectofgrousercount . . . . . . . . . . . . . . . . 84
B.9 Wheelsusedtoevaluatetheeffectofgrouserheight . . . . . . . . . . . . . . . . 84
B.10 Slope-ascentexperimentresults . . . . . . . . . . . . . . . . . . . . . . . . . . 85
B.11 Rovertrajectorieswithdifferent grouserconfigurations . . . . . . . . . . . . . . 86
B.12 Slipratioduringslope-traversing fordifferent grouserconfigurations . . . . . . . 87
B.13 Slipangleduring slope-traversing fordifferentgrouserconfigurations . . . . . . 87
x