Post on 23-Jan-2021
FAURoboBoatTeam 1
V-BASS–3rdGenerationVision-BasedAutonomousSurfaceShipatFloridaAtlanticUniversity
Team:HaroldDavis,MichaelKaiser-Cross,JeanLapaix,AndrewLong,JorgeMartinez,BiancaMesa,TravisMoscicki,OwenPakledinaz,BrittanyRogers,Sven
Schneider,RyanZelaya
Advisor:Dr.KarlVonEllenrieder
DepartmentofOceanandMechanicalEngineering
FloridaAtlanticUniversity,SeaTech
Abstract:
FloridaAtlanticUniversity’sThirdGenerationVision-BasedAutonomousSurfaceShip(V-BASS)hasbeensuccessfullyoptimizedtocompeteinthisyear’s7thAnnualInternationalRoboBoatCompetition.Whilekeepingwiththepreviousgeneration’smodulardesignforefficiencyandreliability,thisgenerationofV-BASSboastsareengineeredelectricalsystem,modifiedsuperstructureandnewintegratedsensors.Layeredsoftwarearchitectureforplatformcontrol,ahigh-levelstateschedulerformissionmanagement,adaptivecontrolcapabilitiesusingcomputervisionandauniqueinteractivesimulatortoassistwithmissionplanningallcontributetomakingV-BASStheoptimalvehicleforthechallengesinthisyear’scompetition.
Figure1:theacclaimedV-BASSplatform
I. Introduction
AdvanceswithAutonomousSurfaceVehicles(ASV)arehighlyregardedandsoughtafterinresearchandindustry.Theeffectiveprocessingandexecutionoftasksbyavehicleinunpredictableenvironmentsisapressingtopicofinterest;itinspiresprofessionalsandcomprisesthemotivationforgroupsofdedicatedstudentstocompeteinsuchaneventasthe7thAnnualInternationalRoboBoatCompetition.
Bypresentingteamswithadistinctsetofmissionrequirementsandastricttimelimit,
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theInternationalRoboBoatCompetitionpromotesareal-worldsettingthatchallengestherapiddevelopmentofarobustandadvancedASVplatform.Objectivesforthecompetitionincludetheabilitytodemonstratethevehicle’spropulsionstrengthandspeed,itsagilitytonavigateabuoyfield,locateandengageobjectsofinterest,andidentifyandlocateobjects,soundsandlightsignalsbothaboveandbelowthesurfaceuponwhichthevehiclenavigates.
Waypointnavigationalonewillnotcompensateforaconstantlychangingenvironment,whichmakesV-BASS’svision-basednavigationsystemidealforanASVplatform.
FAU’sThirdgenerationV-BASS(Vision-BasedAutonomousSurfaceShip)isanASVwiththeabilitytoautonomouslyadapttoavarietyofobstacles.Itistheresultofacollaborationofamulti-disciplinarygroupofdedicatedengineeringstudentsfromtheOceanandMechanical,Electrical,ComputerEngineeringandComputerSciencedepartmentsandthewealthofexperienceatFAUfordevelopingsystemsforthemaritimeindustry.
II. DesignOverview
TheV-BASSplatformisacatamaranbydesignwithtwooutboardbrushedDCmotorsforpropulsion.Maneuveringemploysdifferentialthrust,whileelectricalpowerisprovidedbylithiumpolymer(Li-Po)batteries.Theplatformemploysvarioussensorsandauxiliarysystemstoincludea
LIDAR,twoLogitechwebcams(onefacingforwardandonedownward)andauniquehydrophonearray.
III. HullsandSuperstructure
Withadualhullconfigurationandwidebeamtoensuretransversestabilitywhilecompletingmissiontasks,thecatamaranplatformisidealforthethirdgenerationV-BASS.RepurposedhullsfromthesecondgenerationofV-BASSwererevitalizedwithstructuralmaintenance,anewpaintjobandmodifiedsuperstructure,makingthisplatformbothreliableandcosteffective.
Thesuperstructureconsistsof1inchsquarebeamsthataremountedtothedeckviafour(4)metalbrackets.Theelectronicsboxrestsonthesuperstructureandissupportedbyfouraluminumcornerbrackets.
IV. PropulsionSystem
V-BASS’spropulsionsystemconsistsoftwo(2)Seabotixoutboardthrustersthataremountedtothehullswithspecializedmotormountsthatweredesignedandfabricatedin-house.Withamaximumrpmof6000,thethrusterssupplyrobustness,powerandreliabilitytotheplatformwhilemaximummaneuverabilityisachievedthroughdifferentialthrust.
Differentialthrustisachievedbydifferingtheamountordirectionofthrustproducedbyeachmotor.ThemotorsarecontrolledwithRoboteqSDC1130motorcontrollers,andareconnectedtothepropellershaftsviacustomcouplings.
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Figure2:Seabotixoutboardthruster
V. ElectronicSystem
Theelectronicsystem’scoreforV-BASSboastsaTS-7800single-boardcomputerwithARM9architecturethatisconnectedtoamotherboard(fabricatedin-house)andaBeagleBonemicrocontrollerforhigh-levelcommands.
Essentiallyabreakoutboard,themotherboardallowsthesubsystemaccesstothenecessaryportsontheTS-7800SBC.On-carddevicesonthemotherboardinclude:anR/CMaster/SlaveControlSwitch(togglesautonomousmodeintomanualmode),thePololuMaestroMini(generatesPWMsignals),powermonitoringandregulatingsystems(includingthreeanalogbuffers),aconnectorforthedigitalcompass,on-boardstatusLED’s,two(2)waterleakdetectionsensors,anH-bridgemotorcontroller,andhouse-keepinginputsforR/CandRFactivity.MotivationforimplementingtheBeagleBoneforthisgenerationofV-BASSinvolveditsbeingmorecosteffectivethanaTS-7800whileperformingwiththesameLinuxsystem.
OthermodificationstoV-BASSincludeabatterycharger,whichprovidestheoptiontochargethebatterieswithoutremovingthemfromthevehicle,andanaddedadapter(froma10pintoa16pin)thatallowsthemotorcontrollerconfigurationandthebatteriestocommunicatetotheelectricalbox.
Figure3:insideV-BASS’selectricalbox
VI. HydrophoneArray
Thehydrophonearraywasdesignedin-house.Thesystemismountedunderneaththevehicle’selectricalboxwiththehydrophonespositionedalongtheinnerhullsofthevehicle.
VII. LayeredSoftwareArchitecture
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TheV-BASSsystemimplements“layeredcontrol”architecturetosimplifyitsdesigncomplexitybyprovidingamodularcontrolofeachsubsystem.ItusesaLightweightCommunicationandMarshaling(LCM)interfacewithUDPprotocol,whichreduceslatencyascommandsareprocessed.Thisconfigurationallowsmultipleprocessestorunsimultaneouslyandatdifferentratesasnecessary.
AtitscoreistheTS-7800singleboardcomputerwithARM9architecture,madebyTechnologicSystems.ItusesaLinuxKernel2.6withafullDEBIANdistributionoperatingsystem.Toprocessallhigh-levelcommands,V-BASSisalsoequippedwithaBeagleBoneprocessor,whichfunctionsconjointlywiththeTS-7800toexecutemissiontasks.
Navigation,datafilteringandlogging,house-keepingfunctionsandcommunicationareallcontrolledbymiddle-layerprogramsandgeneratedbyhigh-levelcommands.Themiddle-layerprogramsdoubleascontrol-ware,whichcollaboratewithdevicedriverstocontrolmotorsandsensorsontheplatform.
Ahigh-levelmissionschedulerprioritizeseachmissiontaskbydividingeachmissionintoasetofobjectives,eachofwhichinvolvethecompletionofanumberoftasks.Tomanagetheseprocesses,severalprogramsmustrunindependentlyandarelinkedtogetherusingtheLightweightCommunicationSoftware(LCM).Awatchdogtimeronthemotherboardmonitorsthetimespentoneachtaskto
assisttheplatformwithcompletingallmissionsintheallottedtimeframe.
VIII. MissionCommandStructure
V-BASS’scommandandcontrolstructureisderivedfromthedistributionofresponsibilitiesonanavalvessel.Aseparatenomenclaturewasadoptedtoidentifyeachresponsibilitywithinthesystem.
Captain
TheCaptainisresponsibleforthemissionandsystemmanagement.ItinterceptsdatafromtheSpotterandreferstothestateofthevehiclebeforemaking“decisions”toproceedwitheachtask.
Spotter
TheSpotterreceivesdatafromthevisionsystems(andOpenCV),hydrophonesandotherexternalcomponentsataparticularrate.Thisinformationisrelayedtothe“Captain”forthedecision-makingprocess.
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Navigator
ThiscomponentisresponsibleforallGPSandNavigationdataandwaypoints,whichareusedbytheCaptainalongwithdatafromtheSpotter.Whenadesiredheadingandtransitspeedisdetermined,thenavigatortranslatesallwaypointstogeographicalwaypointswhichuseaNorthEastDownreferenceframe.
Engineer
Responsibleforalllowlevelprocessesrelatingtothevessel,theengineermonitorsthevehicle’sstatus.Ifafailureweretooccuronthevehicle,theengineerwilldeterminewhetherornotitcanbefixedandrelaysthisknowledgetothecaptaintoinferhowtoproceed.
IX. VisionSystem
Thevehicle’svisionsystemiscomprisedoftwoLogitechwebcams:oneofwhichismountedonthesuperstructurefacingforward,whiletheotherfacesdownwardandispositionedbelowthevehicle’swaterline,andaLIDARsystem.
TwoPlexiglasspanelssupportedbyangledaluminumconstituteasplashguardfortheforwardfacingwebcam.Thedownwardfacingwebcamismountedbyoneofthehullsviathesuperstructureandhousedinawaterproofcasing.ThecasingconsistsofmilledPlexiglassthatissealedwithanO-ringandanaluminumplate.Boththesplashguardandthewaterproofcasingwerefabricatedin-house.
Onemajorrevisiontothesecondgeneration’svisionsysteminvolvesastate-of-the-artLIDARsystem.Usingasingleforwardfacingcameraforthevisionposesmajorlimitationstotheplatform,sinceitimpedesthesystem’sabilitytoeasilydeterminedistancetoanobject.IntegratingtheLIDARsysteminvolvescalibratingitwiththecamera’sframeofviewtoaccuratelydeterminedistance.Onceimplemented,theLIDARwilleliminatetheneedforacamera-baseddistancealgorithmthatutilizesthenumberofpixelsonascreen,thusrelievingmuchofthischallenge.
ThevisionsystemalsoemploysanOpenComputerVision(OpenCV)librarytoapplymultiorsingle-channelfilterstobetterfindcontours(outlines)oredgemapsofadesiredobject.TheuseofOpenCVoptimizesthexypositionsforthecentersof
eachbuoyduringmissions.
Figure4:usingOpenCVtomanipulatecolorspaces
X. NavigationSystem
Theplatform’sstatemachinecontrolsthevehicle’snavigationforeachmission.Each
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objectivepresentsuniquenavigationdirectives,whichcanbesatisfiedbyGPSwaypointandcompassheadingcontrolor(mostcommonly)thevehicle’svisionsystem.Expectedfeedbackforthenavigationsystemincludesbuoycolorinputsfromthevisionsystem,speedovergroundfromtheGPSandthevehicle’sorientation(yaw).
WaypointNavigation
UsingtheprovidedGPScoordinatesforeachmissionlocation,alookuptablewasprogrammedintoahigh-levelmissionconfigurationfiletobeaccessedbytheNavigatorcomponentofV-BASS’ssystemarchitecture.Thevehicle’sdestinationandsourceofnavigationiscomputedbytheNavigatorwhilereal-timeprocessedvisioninformationisprovidedbytheSpotterinthecaseofarequiredobstacleavoidancemaneuver.
VisionNavigation
Forvisionnavigation,thevisionsystem(twoLogitechwebcams)actsasasensorwhosedataisinterpretedbytheSpotterfunction.TheSpotterwillprovideadesiredheadingforthevehicleaccordingtoitscurrentandupcomingtasks,whicharedelegatedbyanindependentlyrunningcontrolloop.TheSpotter’soutputispublishedtoaspecifiedchannelonLCM.ThisoutputisreceivedbytheCaptainfunction,whocallstheNavigatorfunctiontofilterandconvertthedesiredheadingintoanactualbearing.
XI. ControlSystem
Throughtheuseofdifferentialthrust,amomentaboutthevehiclecausesittoturnwhilesteering.Thisqualityofdifferentialsteeringallowsthevehicletopossessasmallerturningradiusandtheabilitytosteerwithoutaforwardspeed.
VBASSutilizesheadingandspeedcontrollerstomaintainadesiredheadingandvehicleposition.Thecontrollersmustbetunedasacoupletocompensateforthecouplingeffectofdifferentialsteering.
Twoseparateproportionalcontrollawsallowthemotorheadingcontrollerstogovernthevehicle’sdirection.WithayawofNorth-East-Downconvention,theportcontrollerwouldexhibitapositiveslopewhilethestarboardcontrollerhasanegativeslope[1].
Theboat’sforwardspeedisexpressedasapercentageofmaximummotorpower.Thispercentageisusedtosetabiasvalue(tobiastheproportionalcontrollaw)toadesiredsteady-statespeedforthevehicle.Aspeedcontrollershiftsthisbiasvalueasitassiststhevehicleinreachingadesiredsteady-statespeed.
XII. OpenGLSimulation
WhencodeismodifiedforV-BASS,werequireanalternativewaytotestitwiththeplatformthatallowsforfrequentandeasydevelopment.OpenGLisanopen-sourcegraphicslanguagewhichallowsustodisplaybothcommonsensorvaluesfortheplatform(toincludetheboat’sposition,
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compassreading,speed,objectsinview,etc.),anda3Dvisualizationofthecourse.
TheframeworkforthesimulationisastrongModel-View-Controller,where“Model”isthephysicalcourse,“View”isOpenGL’s3DrepresentationoftheModel,and“Controller”implementsinputsfromthekeyboardandhandlesfileinput,outputandbasicmessaging.LCMallowsOpenGLsimulationtobecomeintegratedwiththevehicle’shigh-levelcode.
Forthisyear’scompetition,OpenGLallowedustoimplementanewcommandstructureforbuoyfieldnavigation.Usingsimulation,wewereabletodevelopV-BASS’sbehaviorbeforeintegratingitwiththemotors,computervisionandothersensors.
XIII. MissionTasks
Missionmanagementforeachtaskisaccomplishedwithhigh-levelcommandandcommunicatedthroughtheLCM.
V-BASS’swatchdogtimermonitorstheallottedtimeforthevehicletocompleteeachobjective,whichconsistsofaseriesoftasks.Forthisyear’scompetitionthevehiclesareallottedtwentyminutestocompleteatotaloffourmissiontasks,excludingthe“SpeedGate”.
SpeedGate
Theobjectiveofthismissionistonavigatethroughastartinggateandspeedthroughasuccessive“SpeedGate”inaslittletimeaspossible.Thisisaccomplishedviadead-
reckoningsincevisionnavigationwouldlikelyhinderthevehicle’sabilityforspeedbyattemptingtoperfectthevehicle’sdesiredheading.V-BASS’shydrodynamichullsprovidedirectionalstabilitythatisoptimizedasthevehicle’sspeedincreases,thusreducingtheneedofavisionsystemtostayontrack.
1. BuoyChannel/ObstacleAvoidance
Whereaslastyear’schallengepresentedachannelofbuoysfortheobstacleavoidancemission,thisyear’smissionintroducesabuoyfield.Thismissioninvolvessuccessfullynavigatingthroughthefieldwithouthittingany“obstacles”,meanwhileenteringandexitingthroughthecorrectgates.
Todominatethistask,V-BASSwillcommunicatewiththe“Spotter”todetermineaperpendicularlinetotheplaneoftheentrancegate.Thevehiclewillexitthroughthecenteroftheentrancegate,collectaspecificheadingandcontinueinthedirectionofthatheadinguntilanobjectisrecognizedasanobstruction.Thisisdeterminedbasedonthebisectingangleforthefieldofviewoftheforwardcamera.Intheinstanceofanobstacle,thevehiclewillevadebymovingacomputeddistancetotheleftorrightoftheobject,andwillattempttoregainitspreferredheadingafterthedetour.ThisobstacleavoidanceprocesscontinuesuntilitcrossesaGPSthreshold,atwhichpointV-BASSwillstopandscanfortheexitgate.Oncetheexit
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gateisidentified,thevehiclewillheadtowardstheexitgatewhilecommencingwithobstacleavoidance.
2. AutomatedDocking
GiventheGPScoordinatesforthedock,thegoalofthischallengeisforV-BASStodockinthecorrectspace(withthecorrespondingsymbolforitsrun).
ThegoalofthismissionisforV-BASStodockatafloatingdockinaspotcorrespondingtothecorrectsymbolforitsrun.
Thisisaccomplishedthroughthevehicle’svisionnavigationsystem,whichwillidentifythecorrectsymbolanddetermineabearingforthevehicletotravel.Whenthedockisataspecificrangewithinthecameravision,thevehiclewillidentifythebottomofthedockanddetermineitsdistanceviaadistancefindingalgorithm.Upondeterminingitsdistancetothedock,V-BASSwillexecuteashortburstforwarduntilabuttononthebowispressed,indicativeofhavingreachedthedock.Atthispointthevehiclewillreverse,stop,andnavigatetowardsthecoordinatesforitsnextchallenge.
3. AcousticBeaconPositioning
GiventheGPScoordinatesofafieldofbuoys,V-BASSmustidentifythebuoywithanactivepingerandrelayitspositionandcolor.Tocompletethismission,thevehiclewillutilizeitsvisionnavigationsystemandhydrophonearray.Thevehiclewillfirstnavigatetothelocationandheadingofthe
buoyfieldwithallbuoysintheiruniquepositions,thenuseitshydrophonearraytodeterminetheheadingofthepinger’ssoundandtraveltowardsit.Thevehiclewillstopnexttothebuoy,identifyandrelayitscolorandpositionandthenproceedtopickanewdesiredheadingtowardsthenextmission.
4. UnderwaterLightIdentification
Forthismissiontask,V-BASSmustactivateandreportasequenceoflightsthataresubmergedatagivenlocation.Thevehiclewillinitializethemissionbytravelingtothedesiredlocationandusingthedownwardfacingcameratolocateasolidwhitelight.Itwillhoveroverthelightandsendamessageofitslocation,thenreadthelightpatternusingitsvisionsystem.Thelightsequencewillbecommunicatedandtheboatwillcompletethemissionbyreturningtothedock.
XIV. Conclusion
Thisyear’sgoalhasbeentoimprovetheV-BASS2ndGenerationplatformwhilemaintainingitsreliableandeffectivemodulardesign.Toachievethisgoal,theteamhasdonatedmanyhourstoV-BASStomakethisplatformourmostreliableandhighperformancevehicletodate.
XV. Acknowledgments
Advancesforthisyear’splatformwouldnothavebeenachievedwithoutthededicationandpracticebyindividualsfromaplethoraofengineeringdisciplinesandinterests.
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ContributionsbypastmembersoftheV-BASSteamwerevitaltothisyear’sdevelopments:MarioMirandaandIvanBertaska.
ContributionsbyEdHendersonandJohnKielbasa,membersoftheFAUfacultyandstaff,havealsobeengreatlyappreciated.
SpecialthankstoDr.KarlVonEllenriederforpresentingourteamwiththeRoboboatchallenge.
XVI. References
[1]Bertaska,I.etal.,2013.“ExperimentalEvaluationofApproachBehaviorforAutonomousSurfaceVehicles”.InProc.ASMEDynamicSystemsandControlConference,2013.