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.