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ModularDevelopmentofMobileRobotswithOpenSourceHardwareandSoftwareComponentsMartinoMigliavacca,AndreaBonarini,andMatteoMatteucciPolitecnicodiMilano,DipartimentodiElettronica,InformazioneeBioingegneria,PiazzaLeonardoDaVinci32,20133,Milano,Italy{migliavacca,bonarini,matteucci}@polimi.
itAbstract.
Prototypingandengineeringrobothardwareandlow-levelcontroloftenrequiretimeandeortsthussubtractedtocoreresearchac-tivities,suchasSLAMorplanningalgorithmsdevelopment,whichneedaworking,reliable,platformtobeevaluatedinarealworldscenario.
Inthispaper,wepresentRapidRobotPrototyping(R2P),anopensource,hardwareandsoftwarearchitecturefortherapidprototypingofroboticapplications,whereo-the-shelfembeddedmodules(e.
g.
,sensors,actu-ators,andcontrollers)arecombinedtogetherinaplug-and-playfashion,enablingtheimplementationofacomplexsysteminasimpleandmod-ularway.
R2Pmakespeopleinvolvedinrobotics,fromresearchersanddesignerstostudentsandhobbyists,dramaticallyreducethetimeandeortsrequiredtobuildarobotprototype.
1IntroductionInrecentyears,severaldevelopmentframeworks[6,4,11,8]havebeenpro-posedtoassistresearchersinthedesignofroboticapplications.
Whiletheseprojectsreallyboostedthedevelopmentofhigh-levelsoftware,hardwarede-signandlow-levelrmwaredevelopmentarestillcriticaltasks.
Todevelopanewmobilerobot,designersalwaysfacetheproblemofselectinghardwarede-vices,controllingthem,andinterfacingthemwiththehigh-levelsoftware.
Thisslowsdowntheprogressofroboticresearch,asprototypingandengineeringof-tenrequiresmoretimeandresourcesthantasksstrictlyrelatedtothetargetapplication.
Tosimplifythedevelopmentofnewroboticapplications,wedevelopedRapidRobotPrototyping(R2P)[2,1],anopensourcehardwareandsoftwareframe-workfocusedonspeedinguptheprototypingofroboticsystems.
R2Ppro-videshardwaremodulesthatimplementbasicfunctionalitiesneededbycommonroboticapplications,andalightweight,real-time,middlewaretoeasilywritelow-levelcontrolsoftware.
R2Ptargetsspanfrommobileautonomousrobotsusedforresearchpurposestoentertainmentandserviceapplications,suchasgames,telepresence,andrescue.
ThelimitsofR2P,attheactualstageofdevelopment,areonlyimposedbythemodulesalreadyavailable;moreover,asR2PisanopenS.
Behnkeetal.
(Eds.
):RoboCup2013,LNAI8371,pp.
576–583,2014.
cSpringer-VerlagBerlinHeidelberg2014RapidRobotPrototyping577source,modular,framework,itcanbeextendedbyuserswithadditionalmodulestocoverotherapplicationelds.
2ModularHardwareandSoftwareDevelopmentWhenanewroboticapplicationisinvestigated,therststepsinvolveselect-ingthehardwaredevices,e.
g.
,sensorandactuators,andbuildingtheplatformneededtovalidatetheoverallidea.
Lookingattoday'spossibilities,wecanpickdeviceseitherfromtheautomationmarketorfromthehobbymarket.
Com-ponentsfromautomationmarketareoftenexpensiveandoeroverkillingper-formancewithrespecttotherequirementsofaroboticapplicationprototype.
Moreover,automationdevicesoftenrequirepowersuppliesnotsuitableforbat-terypoweredsystemslikemobilerobots.
Ontheotherhand,devicesfromhobbymarketareusuallycheap,buttheyshowpoorperformance,lowreliability,andnoreal-timecapabilitiesmakingimpossibleanydistributedcontrolloop.
Havingselectedhardwaredevices,hereitcomestheproblemofinterfacingthemwitheachother,andwiththehigh-levelcontrolsoftware.
Dierentmanufacturersgenerallyusedierentdatalinksandprotocols,increasingwiringcomplexityandrequiringspecializeddevicedrivers.
Asaconsequence,resultingplatformsarecommonlybasedoncustomsetups,whicharehardlyreusableindierentprojects.
Althoughmobilerobotshavebeenbuiltfordecadesbyintegratinghet-erogeneousdevices,orimplementingcustomsolutions,wermlybelievethatamodularapproachbasedono-the-shelfcomponentswouldstronglyhelprobotdesignersindevelopingnewapplications.
Tothebestofourknowledge,theonlyavailablemodularroboticplatforms,suchastheE-puckeducationalrobot[10],theKepherarobot[7],andafewothers,areaimedatdevelopingsmallmobilerobotsforapplicationslikeswarmroboticsandtheirusageisrestrictedtocontroltheplatformtheyaredesignedfor.
WithR2P,weaimatfulllingthelackofhardwarecomponentsfocusedonrobotprototyping,pushingdesignstrategiescommonlyexploitedinsoftwarede-velopment–suchasmodular,component-based,softwareengineering–downtothehardwarelevel.
R2Preliesontheprinciplethattherequirementsofagenericrobotapplicationcanbeimplementedbymodulesnotonlyatsoftwarelevel,asitiscommoninmostframeworks,butalsoathardwarelevel.
Basicfunctionalitiessuchasmotorcontrol,distancemeasurement,inertialnaviga-tionareimplementedbyspecic,standardizedhardwaremodules,withcorre-spondingrmware,thatcanbepluggedonacommonbusandcaninteractinreal-time.
Firmwaredevelopmenttools,andamiddlewaretofosterdistributed,reusable,softwaredevelopment,areprovided,supportingusersinwritingcodeonresource-constraineddevices.
UsingR2P,robotdesignerscanbuildgenericplatformsbychoosingthemodulestheyneed,conguringthem,andeasilyde-velopingthecontrolsoftware,implementingcomplexsystemsinaplug-and-playfashion.
Integrationwithhigh-levelroboticsframeworks,suchasROS[11],isprovidedbyagatewaymodule.
578M.
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Matteucci3R2P:TheRapidRobotPrototypingFrameworkInthissection,weintroduceR2Pdesignchoicesandarchitecture.
Then,areviewofsomeofthealreadyavailablehardwaremodulesarepresented.
3.
1PowerandDataLinkR2Pusesasingleconnectortotransportbothpoweranddata.
Powerconsump-tionislimitedto5V,200mA,foreachmodule,whichsuitestherequirementsofmostelectronicdevices,whilemodulesneedinghigherpower,suchasmo-tordrivers,mustrelyonauxiliaryconnections.
ModulesexchangedatausingtheCAN-Bus,whichhasbeendesignedtoworkinharshenvironmentsandisavailableonmanymicrocontrollers.
Itsmaximumdatarateof1Mbpsisgen-erallyenoughforadistributedsystemofsmartdevices,whereonlyhighlevelinformationneedstobesentoverthenetwork(i.
e.
,norawsensordataisex-changed),thusneedingarelativelysmallbandwidth[3].
AspartofR2P,wedevelopedRTCAN[9],aCAN-Busprotocoltargetedatroboticapplicationsthatsupportsbothsporadic,event-triggered,andperiodic,time-triggeredcom-munication,withsoftandhardreal-timeconstraints.
Toreducewires,adaisychainwiringschemaisadopted:eachmodulehastwoportstoconnecttothepreviousandthenextcomponent,asshowninFigure2(a).
Thisalsosupportseasyconnectionofnewmodulestoanexistingsystem.
3.
2EmbeddedFirmwareDevelopmentWritingcodeforresource-constraineddevices,suchasmicrocontrollersusedtointerfacewithsensorsandactuators,requiresspecicknowledgeandcompe-tence.
Mostrobotdesignersareusedtowritesoftwareondesktop-levelcom-putersystems,andtheyhavetospendtimeandeortstostartdevelopingcodetargetedtoembeddeddevices.
Toreducethiseort,theuseofanoperatingsystemcansignicantlysupportsoftwaredevelopmentevenforsmallembeddedsystemsasitfeaturesthreads,memorymanagement,messagepassingprimi-tives,andotherservicesprogrammersarecommonlyusedtodealwith.
More-over,anoperatingsystemwithreal-timecapabilitiesisimportanttomanagecritical,high-prioritytasks,whichareofteninvolvedinroboticsystems,e.
g.
,forclosed-loopcontrol.
Forthementionedreasons,R2PreliesonChibiOS/RT[12],areal-timeoperatingsystemdesignedfordeeplyembeddedrealtimeapplications.
ChibiOS/RThasbeenpreferredtootheralternativesforitsportability,easeofuse,richfeaturesset,andextremelyhigheciency;anyway,areviewofavailableembeddedoperatingsystemsisoutofthescopeofthispaper.
ChibiOS/RTalsoincludesaHardwareAbstractionLayer(HAL),whichabstractsthehardwareimplementationofdierentlowlevelperipherals,relievingthedeveloperfromacquiringspeciccompetenceoneachspecicplatformandmakingeasiertheportofexistingcodetodierenttargets.
RapidRobotPrototyping579!
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1.
ThedistributedarchitectureoftheembeddedsoftwarecontrollingTriskar23.
3Publish/SubscribeMiddlewareTosupportthedevelopmentofmodularsoftwarecomponentsonembeddedtar-get,R2Pfeaturesalightweightcommunicationmiddleware.
R2Pmiddlewaremaingoalsaresoftwarereuse,real-timecommunication,ecientimplementa-tion,andeaseofuse.
Itfollowsthepublish/subscribeparadigm[5]:datapro-ducerspublishmessagesonatopic,i.
e.
,acommunicationchannel,whiledataconsumerssubscribetothecorrespondingtopictoreceivemessages.
Identifyingdatabyitscontent,i.
e.
,thetopicitispublishedon,insteadofbyitsproducer,alsopromotesloosely-coupledsoftwaredesignand,thus,codereuse.
Themiddle-wareprovidesconceptscommontomostroboticsframeworksusedoncomputersystems,suchassoftwarenodes,topics,publishers,subscribers,andmessagequeues.
R2PmiddlewareiswritteninasubsetofC++,totakeadvantageofsomeobject-orientedprogrammingfeatureswithoutcompromisingperformanceonembeddedtargets.
Itsimplementationisfocusedoncodeeciencyandmes-sagingperformance.
Softwarenodescansubscribetobothlocalandremotepublishers,withnodierencefromtheuserpointofview.
Themiddlewaresup-portsbothperiodicandsporadicpublishers,whichcanspecifyreal-timecom-municationconstraints:updateperiodfortime-triggeredmessages,anddeliverydeadlineforevent-triggeredones.
Finally,asimpleAPI,whichremindstheROSsyntax,enablesdeveloperstowriteembedded,distributedcodeastheyareusedtodooncomputersystems,fosteringcodereusethroughdierentprojects.
3.
4IntegrationwithROSWhileR2Psupportsrapiddevelopmentofroboticsystemsusingo-the-shelfhardwareandsoftwarecomponents,applicationsinvolvingcomputation-intensivetaskssuchascomputervision,localization,andcomplexplanning,mustalsorelyonacomputersystemand,eventually,asoftwareframework.
Amongthemanyavailabledevelopmentframeworksforroboticssoftware,ROS[11]iscurrentlythemostwidelyadoptedinacademiaandresearchlaboratories,and,recently,ithasbeenconsideredalsobyindustrialdevelopers.
Tonativelyintegrateresource-constraineddeviceswithinROS,wedevelopedμROSnode,alightweight,open580M.
Migliavacca,A.
Bonarini,andM.
Matteucci(a)Daisy-chainwiringofhardwaremodules(b)R2PIMU(c)R2PDCmotorcontrollerFig.
2.
R2Phardwaremodulessource,ANSICROSclientlibrary.
R2Pprovidesagatewaymodule(seeSec-tion3.
5),whichactsasaproxybetweentheR2PmiddlewareandROSsystems.
TopicspublishedontheR2PnetworkcanbeaccessedfromROSnodes,and,atthesameway,R2PmodulescansubscribedatapublishedbyROSsoftware.
3.
5O-the-ShelfHardwareComponentsWehavedesignedandbuilt,aspartoftheR2Pframework,asetofplug-and-playhardwaremodulesthatimplementbasicfunctionalitiesrequiredbycommonroboticsapplications.
ModulesarebasedonSTM32Cortex-M3microcontrollerswith20KbofRAMand128KbofFlashmemory,runningtheChibiOS/RTandtheR2Pmiddleware.
EachmodulehastwoRJ45portsfordaisy-chainconnectiontothebus,aserialporttodownloadnewrmwareandfordebuggingpurposes,andaJTAGheaderforadvanceduserswhowanttodirectlyaccessthemicro-controller.
Anoverviewofthecurrentlyavailablemodulesfollows.
PSUModule.
Thisisthepowersupplyunit,whichpowersallthemodulesconnectedtothebus.
Inputvoltagerangeisfrom5.
5Vto36VDC.
ADC-DCconverterproducesa5Vregulatedoutputwithmaximumcurrentsupplyof4Aandshortcircuitprotection.
Bothbatteryvoltageandcurrentdraincanbepublishedoverthenetworktomonitorpowerconsumptionandtoestimatetheresidualbatterylife.
DCMotorModule.
Thishigh-powermotorcontrollerboardcandriveDCmotorsupto36V,deliveringacontinuous20Acurrent.
Itfeaturesclosedloopcontrol,withpositionfeedbackfromaquadratureencoderandcurrentmea-surementfromtheon-boardHall-eectsensor.
TheDCmotormoduleacceptsposition,speed,andtorquesetpoints,andcanpublishpositionandspeedmes-sages,exploitingdatafromtheencoder,andthemeasuredcurrentdrawn.
IMUModule.
A10-DoFInertialMeasurementUnitfeaturingMEMSac-celerometer,gyroscope,magnetometerandpressuresensor.
AnadditionalserialporttoacquireGPScoordinatesfromanexternalGPSreceiverisalsoprovidedonthismodule.
Theon-boardsensorfusionalgorithmproducesheading,atti-tude,andpositionmessages.
RapidRobotPrototyping581ProximityModule.
AmoduletointerfacewithproximitysensorssuchastheSharpIRrangersorMaxBotixultrasonicsensors.
Eachmoduleconnectstoupto4sensors.
Calibrationanddatalteringalgorithmsrunonthemicrocon-troller,whichproducesdistancemeasurements.
GatewayModule.
ThisisthegatewaymodulementionedinSection3.
4.
ItfeaturesanEthernetportandamorepowerful,Ethernet-enabled,microcon-trollertohandletheTCP/IPstack.
R2PmessagescanbeforwardedfromtheCAN-BustotheIPnetwork,andtheotherwayaround.
ThegatewaymodulerunsROSnode,whichenablesadirectintegrationofR2PmoduleswithROSsystems.
3.
6OpenSourceDevelopmentR2Pisfullyopensource,bothhardwareandsoftware,toencourageitsadoptionandtotakeadvantageofcommunity-drivenimprovementstobecameamatureandwidespreadproject.
Thedesignoftheboards,thecodetheyrunandthemiddlewareareavailableontheR2Prepository:http://github.
com/openrobots-dev.
Atthemomentofwriting,R2Phasreacheditsmaturity(see,e.
g.
,theusecaseinthenextsection),butitsdevelopmentisstillactivelyprogressing,thus,therepositoryisfrequentlyupdated.
4UseCase:AnOmnidirectionalRobotWeusedR2PtodeveloptheomnidirectionalwheeledrobotTriskar2,showninFigure3(a).
Therobotsports3R2PDCmodules,aPSUmodule,aProximitymodule,andtheGatewaymoduletointerfacewithacomputerrunningROS.
Thelow-levelcontrolsoftwareembeddedonthemodules,whichexploitstheR2Ppublish/subscribermiddleware,isreportedinFigure3.
SoftwarecomponentsareenclosedinR2Pnodes,whichimplementbasicfunctionalities,performingaspe-cictask.
Then,nodesarecomposedasadistributedarchitecture,implementingacomplexsystemfrombasic,reusable,components.
Thisdesignstrategyisnotinnovative,beingcommonlyusedinsoftwaredevelopment;themaincontribu-tionofR2Pmiddlewareistobringthesameapproach,and,thus,thesameadvantages,toembeddedrmwaredevelopment,withthesameprogramminginterfacesknowntomostrobotdevelopers.
SoftwarenodeshavebeendeployedonthemodulesasshowninFigure3(b).
Somenodeshavetorunonspecicboards(e.
g.
,thosethataredirectlycon-nectedtothehardwarelikemotorcontrollernodes),whileotherscanrunonanyconnectedmodule.
Forexample,inourtests,theinversekinematicsmodeltocomputewheelspeedswasrunontheMotor1module,whiletheodometrynodewasdeployedonMotor2.
Inthisway,wecanbalanceprocessorloadandreducelatency,easilymovingnodesfromanhardwaremoduletoanother.
ThankstotheR2Pgateway,Triskar2canbecontrolledbyanyROSappli-cationpublishingnativeROStopics.
WerstlyteleoperatedtherobotbyusingstandardROSteleopmessages,thenwedevelopedaroboticgame,involvingtheTriskar2robotandaquadricopter,bothcontrolledbyROSsoftware.
582M.
Migliavacca,A.
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3.
TheTriskar2omnidirectionalplatform(a)andtheR2Phardwaremodulescontrollingtherobot(b)5ConclusionsInthispaper,wepresentedR2P,anopensourcehardwareandsoftwareframe-workfortherapidprototypingofrobots.
Bringingdesignstrategiessuchasmodulardevelopment,andcomponentsreuse,downtohardwarelevel,R2Pen-ablesrobotdesignerstobuildandcontrolaroboticplatformusingo-the-shelfmodules.
ExploitingtheR2Pframework,genericmobilerobotscanbebuiltbottom-upinadistributedplug-and-playfashionbysimplyselectingthehard-waremodulestosatisfytheneededfunctionalrequirementsandeasilyprogram-mingtheirinteraction.
Integrationwithhigh-levelsoftwareframeworks,e.
g.
,ROS,allowstodevelopcomplexapplication,whilelow-levelcontrolisimple-mentedbymeansofamodulardistributedarchitecture,withreal-timeper-formance,withouttheneedforadvanceddomain-specicknowledge.
WeareexploitingR2Ptodesignnewrobotsinourlaboratory,asshownbytheusecasepresentedinSection4,andtoupgradeourpreviousplatforms,therstbeingabalancingwheeledrobot,adierentialdriveheavy-dutyrobot,andanautonomouswheelchair.
TheopensourcelicenseencouragesrobotdesignerstoadoptexistingR2Pmodulestocontroltheirplatforms,andtodevelopnewhard-waremodulesandsoftwarecomponentsthatimplementnewfunctionalities.
Acknowledgements.
Thisworkhasbeenpartiallysupportedbytheresearchgrant"RoboticsfortheMasses"fromSTMicroelectronicsandRegioneLom-bardia,andbytheItalianMinistryofUniversityandResearch(MIUR)throughthePRIN2009grant"ROAMFREE:RobustOdometryApplyingMulti-sensorFusiontoReduceEstimationErrors".
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