AdaptiveBasketballShooterFinalProjectReport

June10,2014

Sponsor:SpecialOlympicsRegionalSportsManagerMichaelLara

Team:UPFBallers

JennaBecker

MechanicalEngineeringjnbecker@calpoly.edu

JustinHaleyKinesiology

jdhaley@calpoly.edu

RichardGalantiMechanicalEngineeringrgalanti@calpoly.edu

BrettNayudu

MechanicalEngineeringbnayudu@calpoly.edu

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StatementofDisclaimerSincethisprojectisaresultofaclassassignment,ithasbeengradedandacceptedasfulfillmentofthecourserequirements.Acceptancedoesnotimplytechnicalaccuracyorreliability.Anyuseofinformationinthisreportisdoneattheriskoftheuser.Theserisksmayincludecatastrophicfailureofthedeviceorinfringementofpatentorcopyrightlaws.CaliforniaPolytechnicStateUniversityatSanLuisObispoanditsstaffcannotbeheldliableforanyuseormisuseoftheproject.

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AcknowledgementsThismaterialisbaseduponworksupportedbytheNationalScienceFoundationunderGrantNo.0756210,AccessbyDesign:CapstoneProjectstoPromoteAdaptedPhysicalActivity.Anyopinions,findings,andconclusionsorrecommendationsexpressedinthismaterialarethoseoftheauthor(s)anddonotnecessarilyreflecttheviewsoftheNationalScienceFoundation.TheUPFBallerswouldliketothankthefollowingpeople:

Dr.JimWidmann,ourMechanicalEngineeringfacultyadvisor Dr.KevinTaylor,ourKinesiologyfacultyadvisor MichaelLara,oursponsorandpointofcontact MembersoftheFridayClubforallowingustocomeworkwiththemandobservethem Themechanicalengineeringshoptechs,fortheiradviceandassistanceinmanufacturing

difficultparts StaffofMinersAceHardwarefortheirpatienceandwillingnesstoprovidehelpful

advice IanGoodyearfromCentralCoastCreativeCuttingforhisworkonthecarriage

components

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TableofContentsStatementofDisclaimer...............................................................................................................................2Acknowledgements.......................................................................................................................................3ListofFigures................................................................................................................................................7ListofTables.................................................................................................................................................9ExecutiveSummary.....................................................................................................................................10Introduction................................................................................................................................................11

BackgroundandNeeds.........................................................................................................................11CurrentStateoftheArt........................................................................................................................12

PreExistingSolutions.....................................................................................................................12Mechanisms...................................................................................................................................15OtherBackgroundResearch..........................................................................................................18

ObjectivesandSpecifications...............................................................................................................20DesignDevelopment...................................................................................................................................23

DiscussionofConceptualDesigns........................................................................................................23ConceptSelection.................................................................................................................................24

ShootingMethod...........................................................................................................................24PullBackMechanism.....................................................................................................................24QuickReleaseMechanism.............................................................................................................25MountingandAimingMechanisms...............................................................................................25OtherConsiderations.....................................................................................................................26ProofofConcept............................................................................................................................26

DescriptionofFinalDesign.........................................................................................................................27OverallDescription...............................................................................................................................27DetailedDesignDescription.................................................................................................................28

FrameAssembly.............................................................................................................................28MountingofFrametoUPF............................................................................................................29WinchShaft....................................................................................................................................30RatchetandPawl...........................................................................................................................30RatchetArmLever.........................................................................................................................31Carriage..........................................................................................................................................32ReleaseMechanism.......................................................................................................................33

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SafetyMechanism..........................................................................................................................33UserInterface................................................................................................................................34AimingAssembly............................................................................................................................35

AnalysisResults....................................................................................................................................38CostAnalysis.........................................................................................................................................40SafetyConsiderations...........................................................................................................................41RepairConsiderations..........................................................................................................................41

ProductRealization.....................................................................................................................................43Frame....................................................................................................................................................43BottomHinges......................................................................................................................................44WinchShaftandComponents..............................................................................................................44PawlBlock.............................................................................................................................................46TableTop..............................................................................................................................................46SupportPlate........................................................................................................................................47Carriage................................................................................................................................................47UJoints,LeadScrews,andLeadScrewHinge......................................................................................48SafetyCasing........................................................................................................................................48ReleaseBracket....................................................................................................................................49CableandRopeAttachments...............................................................................................................49

ChangesMadeDuringManufacture...........................................................................................................50StrongerElastic.....................................................................................................................................50CarriageBending..................................................................................................................................50CarriageTopPlate................................................................................................................................50ReleaseBearings...................................................................................................................................50ReleasePinRing...................................................................................................................................50SpoolHoseClamp.................................................................................................................................51LocationofRatchetArm/WinchShaftParts........................................................................................51HexBolt................................................................................................................................................51WinchShaftHoleforRatchetFlange...................................................................................................51PawlBlockShaft...................................................................................................................................51ACMECylindricalNutAssembly...........................................................................................................52ClevisPinLength...................................................................................................................................52

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PulleySizesandBelts............................................................................................................................52TableTopPegs......................................................................................................................................52EyeStrap...............................................................................................................................................52ReleaseLeverLength............................................................................................................................52UChannelSetScrews...........................................................................................................................52CountersunkScrews.............................................................................................................................53

DesignVerification......................................................................................................................................54RecommendationsandConclusions...........................................................................................................56References..................................................................................................................................................57AppendixAQFDandPughMatrices........................................................................................................58

QFD(HouseofQuality).........................................................................................................................58PughMatrices.......................................................................................................................................60

AppendixBBillofMaterials.....................................................................................................................65AppendixCSupportingAnalysis...............................................................................................................67

EnergyRequiredtoShoot3Pointer....................................................................................................67TotalPotentialEnergyRequired(+Carriage).......................................................................................68ImpactLoadingofFrame,LeadScrews,andBaseHinge.....................................................................69FindingReactionsduetoImpactForce................................................................................................70LatexTubingEnergyStorageandSizeSelection..................................................................................72StaticAnalysisofWinchShaft..............................................................................................................75

AppendixDGanttChart...........................................................................................................................78AppendixEDrawingPackets....................................................................................................................80AppendixFOperationandSafetyManual.............................................................................................134

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ListofFigures Figure1.AphotographoftheMillerTwins.Theirbasketballshootingdeviceisnotshown.__________________12Figure2.Aflywheelstyleshooterisdepictedabove._________________________________________________12Figure3.AnOhioUniversitymechanicalengineeringstudentteststheteamsbasketballlauncher.____________13Figure4.PatentsketchofSportsballlauncher,patentedbyChristopherL.Hansen_______________________14Figure5.ShootAWayReboundMachine._________________________________________________________14Figure6.PoolLoungeChair_____________________________________________________________________15Figure7.ConceptDrawingofFiringAngleChangeMechanismforacannon______________________________15Figure8.Amotoroperatedwinch________________________________________________________________16Figure9.3RingQuickRelease___________________________________________________________________16Figure10.SpringLoadedSlingshotRelease________________________________________________________17Figure11.SolidModelofaDogClutch____________________________________________________________17Figure12.DimensionsofaNCAAregulationbasketballcourt__________________________________________18Figure13.UniversalPlayFrame(UPF) ____________________________________________________________19Figure14.DimensionsoftheUPFtableholesfordeviceattachment.____________________________________19Figure15.SketchesdepictingpossibleattachmenttotheUPFTableTopforacatapultandflywheel,respectively 23Figure16.Smallscalefunctionalmodelsofacatapultandslingshot,respectively__________________________23Figure17.LatexTubing,atypeofelasticband______________________________________________________24Figure18.Atabletopmounteddeviceversusalowerbarmounteddevice_______________________________25Figure19.Thetotalassemblyoftheadaptedbasketballauncher. ______________________________________27Figure20.Framesubassembly.__________________________________________________________________28Figure21.FrameattachingtotheUPFbyhinges. ___________________________________________________29Figure22.Winchshaftassembly,withratchetandpawl._____________________________________________30Figure23.Ratchetarmleverextendsfrombottomofframe. __________________________________________31Figure24.Carriageassembly.___________________________________________________________________32Figure25.Releasemechanismintheattachedposition.______________________________________________33Figure26.Theuserinterfaceallowsanathletetohaveasmuchcontrolofthesystemaspossiblefromawheelchairposition.____________________________________________________________________________________34Figure27.Workingportionoftabletopmountshowingsupportfin _____________________________________35Figure28.Pulleysystemforaimingmechanism. ____________________________________________________36Figure29.Universaljointthatwillallowforthetransmissionoftorqueto________________________________36Figure30.Leadscrewofaimingmechanismwhichcontrolsthetiltofthedevice.__________________________37Figure31.Custombracketcontainingcylindricalnuttoguidetheleadscrewasitisturnedandallowsthedevicetotilt. ________________________________________________________________________________________37Figure32.Inordertodrillpreciseholesinourframemembers,themillwasused. _________________________43Figure33.Allshortframememberscuttolengthwithholesdrilled._____________________________________43Figure34.ThesteelrectanglewasMigweldedtothecustomuchannel._________________________________44Figure35.Thebottomhingeassembledtoboththeframeandtheuchannel._____________________________44Figure36.Theratchetflangeattachestothewinchshaftviaasetscrew.________________________________45Figure37.Toattachtheratchetgeartoitsflange,fourholesweremilledandthreaded.____________________45Figure38.Thespoolattachestothewinchshaftviaasetscrew.Thewinchropeissecuredaroundthespoolthroughanotherhole._________________________________________________________________________45Figure39.Thepawlblockassemblymountstwoaframememberwithtwolongbolts.______________________46Figure40.Thetabletopassembly,withthepegsattachedtotheanglestock,isshown.TheassemblyfitsintotheholesshownintheUPF.________________________________________________________________________46Figure41.Thecarriagepieceswerecutandboltedtogetherwith_______________________________________47Figure42.Ujointsattachedtothepulleyshafts,andtheleadscrewsabovethem _________________________48Figure43.LeadscrewhingeswiththeACMEnutimbedded ___________________________________________48Figure44.Backsafetycasingwiththereleasecableslots_____________________________________________48Figure45.Releasebracket,freshlymilledandtapped,withthepullpininstalled.__________________________49Figure46.TestingattheFridayClub______________________________________________________________55

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Figure47.TheEngineeringTeamattheSeniorProjectExpo___________________________________________55Figure48.FBDoftheframeatimpact,withrelevantdimensions._______________________________________70Figure49.Testingtheelasticavailabletouseforlaunch. _____________________________________________73Figure50.Shearandmomentdiagramofwinchshaft._______________________________________________75Figure51.Effectivelengthforafixedfixedbeam.ImagefromBeersMechanicsofMaterials,6thEd.__________77

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ListofTables Table1.EngineeringSpecifications_______________________________________________________________21Table2.AbbreviatedBillofMaterials_____________________________________________________________40Table3.Designverificationtable,listingtestingofallcomponentsandmechanisms._______________________54Table5.FullBillofMaterials____________________________________________________________________65Table6.Testingtheelastic._____________________________________________________________________72

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ExecutiveSummaryTheFridayClubisajointventurebetweentheCalPolyKinesiologyDepartmentandtheSanLuisObispoSpecialOlympicsthatofferspeoplewithvaryingdegreesofdisabilitytheopportunitytomeetweeklyandlearnvarioussportsandgames.AtFridayClub,athletesinwheelchairswithlimitedarmstrengthusedevicesbuiltbyCalPolymechanicalengineeringstudentsinordertoparticipateinvarioussports.ManydevicesaredesignedtoattachtotheUniversalPlayFrame(UPF),awheelchairattachment.ThepurposeofthisprojectwastodesignandbuildaUPFdevicethatwilllaunchabasketball,sothatanathletecanparticipateinagameofHorse.Theprojectwasworkedonoverthecourseofthe20132014schoolyear.Tobegin,theteamdevelopedalistofobjectivesforthedevicetomeetandresearchedexistingsolutionsforvariousfacetsofourdesign.Thenextstepwastogenerateconceptsofourdevice,andusingPughmatrices,proofofconcepttesting,anddebatetonarrowdowntoasingleconcept.Next,thisconceptwastransformedintoafullyfledgeddesignbackedbyengineeringanalysis.Afterdesignapproval,allnecessarypartsandmaterialswereorderedandaprototypewasbuiltovera10weekperiod.ThefinalprototypewastestedwiththeFridayClubanddisplayedattheSeniorProjectExpoonMay31,2014.Thefinaldevicethatourteamdesignedisaslingshotthatlaunchestheballbyreleasingstretchedelasticbands.OurdesignattachestotheUPFattwopoints,andcanbeaimedtoshootabasketfromanywherebetween5and15feetaway.Theathletehastheabilitytocontrolthedirection,power,andreleaseofeachshot.Thedevicecanbesetupinunderfiveminutesbyasinglepersonandtakesonly30secondstoresetbetweenshots.Ofallcustomerrequirementsthatthedevicewastomeet,itonlyfailedtomeetoneofthem.Thefirstwasthatitshouldbeabletoshootathreepointer.Unfortunately,ourdeviceeitherdidnothavestrongenoughelastic,ordidnothaveenoughspacetopullbacktheballandcarriagesufficiently.Therefore,ourdevicecanshootabasketfromamaximumofonly15feetaway,orafreethrow.Otherfuturerecommendationsaretostrengthensomepartsthattakehighimpactsandtoreducetheweightofsomeunnecessarilybulkyparts.Ourbudgetforthisprojectwas$1,500butoverthecourseofthisprojectourteamspentalittleover$1,750.Afteranalyzingourspending,wefoundthatover$300wasspentbecauseofmanufacturingmistakesandmidconstructiondesignchanges.Ifweweretobuildanotherdevicewiththeexactsamedesignasourfinalprototype,andwithnomistakes,thedevicewouldcostabout$1,400.Inthisreport,ourteamsentiredesignprocessiscataloguedindetail.Alsoenclosedaredetailedpartdrawingsforeachmanufacturedpartofourfinaldevice,aswellasasafetyandoperationmanual.

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IntroductionBackgroundandNeedsTheFridayClubisajointventurebetweentheCalPolyKinesiologyDepartmentandtheSanLuisSpecialOlympics.EachFridayforthreehours,SpecialOlympicathletesmeetwithCalPolyKinesiologystudentsattheCalPolyRecCenterandaretaughtadifferentsportorformofexercise.Thisactivityallowstheathletestohavefunandgetphysicalexercise.Inordertoallowathletesofvaryingabilitiestoplaysportstogether,someathletesrequireadaptivedevices.Todesignandbuildtheseadaptivedevices,theKinesiologyDepartmentandSLOSpecialOlympicsturntoMechanicalEngineering(ME)seniorprojectstudents.Inthepast,MEseniorprojectgroupshaveconstructeddevicesallowingathletestoparticipateinavarietyofsportsandphysicalactivities,includinggolf,Frisbee,darts,andbaseball.MichaelLara,RegionalManageroftheSanLuisObispoSpecialOlympics,taskedourteamwithcreatinganadaptivebasketballshootingdevice.ThepurposeofthisdeviceistoallowanathleteinajoystickcontrolledwheelchairtoparticipateinagameofHorsewithotherathletes.Whilethedeviceshouldleveltheplayingfield,itshouldalsocreatetheLeastRestrictiveEnvironmentforthoseathletes.Inotherwords,itshouldmakethefewestadaptationspossible,allowingtheathletestoperformasmuchoftheactivityastheyareable.Ideally,thisdeviceshouldallowanathletetoshootaballfromavarietyofdistances,from5feetawaytoadistanceof20feet.Aboveall,thedeviceshouldbesafetosetupandoperate.

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CurrentStateoftheArtAfterreceivingourproject,thefirstthingourteamdidwasbeginbackgroundresearch.Theresearchfellintotwomaincategoriespreexistingsolutionstosimilarproblems,andgeneralinformationnecessarytodesignourdevice,includingspecificationsofbasketballandcourtdimensions,aswellasdimensionsoftheUniversalPlayFrame,whichourdevicemustattachto.PreExistingSolutions NormalforUs:TheMillerTwins

Figure 1. A photograph of the Miller Twins. Their basketball-shooting device is not shown.

WhilenotdepictedinFigure1,inNormalforUs:theMillerTwinsanadaptedbasketballlaunchingsystemisfeaturedthatattachestothesideofthewheelchair.Itisacatapultstyleshootermountedtotheseatbackofthechair(behindtheuser),withanestimatedthreefootarclengthsweeparm.Fromthevideo,itwasdifficulttotellwhatkindofenergystoragemechanismwasusedtopropeltheball.Itcouldshootabasketfromasfarawayashalfcourt.Itrequiredassistancetoresetthecatapultarm,butitwasaimedandshotbytheathlete.However,duetothemountingofthecatapulttothewheelchair,itisimpossibletoseethebasketballbeforeitisshot,meaningtheathletecannotseehowheorshehasthebasketballaimed.FIRSTRoboticsCompetition,2012BasketballLauncher(Flywheel)

Figure 2. A flywheel-style shooter is depicted above.

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ThedeviceshowninFigure2isaprototypemadebyahighschoolroboticsteamofabasketballlauncherusedonarobottoallowittoplayReboundRumble,abasketballlikegameplayedbyR/Crobots.Initscurrentform,thisisalight,portabledevicewithquicksetuptimeandlongdistancepower.Inavideoshowingthecapabilitiesofthisshooter,itwasabletomakeabasketfromfurtherawaythanthe3pointline.However,thisdeviceisnotdesignedtolaunchafullsizeball.Itrequirestwohandstooperate:onetoholdandaimthedevice,andanothertofeedtheballin.Feedingtheballdoesrequireasmallrangeofmovement,whichisbeneficial,butitisunsafetohaveoneshandssoclosetotheflywheels,whichspinathighspeeds.OhioUniversityBasketballLauncher

Figure 3. An Ohio University mechanical engineering student tests the teams basketball launcher.

Figure3showsaslingshotstylelauncher,producedbyanOhioUniversitymechanicalengineeringdesignteamin2010.Itisdesignedtobeoperatedbyawheelchairathletewithmusculardystrophy.Thedevicecanshootabasketballfrombetweenthefreethrowand3pointlines.Itresetsviamotorinaboutthirtyseconds,andisstructurallysound.However,itrequirestwohandstooperate:onetoaimandonetoreleasetheball.Inordertooperate,thedevicerequiresthattheathletehavearangeofmotionofabout2feetineacharm,andrequiresapushingmotiononthelevertoreleasetheobject.Itparksnexttothewheelchairandisoperatedfromtheside.

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SpringLoadedBallLauncherPatentUS7028682Thissystem,showninFigure4,wasonlyfoundasapatent,notasanactualdevice.Thedocumentationdescribesthedeviceasamechanismthatwilllaunchaninflatableball,suchasabasketball,volleyball,orsoccerball.Thisdevicestandsontheground.Thepurposeofthismechanismistoinitiateajumpballatthestartofagame.Theinternalspringsarecompressedviafootpumpactionbytheuser.Thestoredpotentialenergyisreleasedbytheathlete.Thedevicecanbeaimed,butdoesnotseemtobedesignedwithathleteswithdisabilitiesinmind.Footpowerisrequired,butitislikelythatthissolutioncouldbeadaptedforhandpumping.Itisunknownhowsafethisdeviceis,orhowfaritcanshootabasketball.

BasketballRebounderThesystemshowninFigure5istheonlyproductthatiscurrentlycommerciallyavailable.Itisusedtocatchballsshotbyathletesandshootthembackoutontothecourt.Thismachineisnotdesignedtoshootaballintothehoop,onlytosimulateateammatepassingaballtoanathlete.Asaresult,itislikelythatitcannotshootaballhighenoughtomakeabasket,becauseitisnotadjustablesinceitisdesignedforpassinginstead.Additionally,themachineislargeandbulky.Currently,itisfullyautomatic,needingnouserinputtoshootabasket.Themachinewillshootaballassoonasitreceivesone.

Figure 4. Patent sketch of Sports ball launcher, patented by Christopher L. Hansen

Figure 5. Shoot-A-Way Rebound Machine.

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MechanismsAfterresearchingexistingsolutionsthatshootbasketballs,welookedintoothercomponentsnecessaryforasuccessfuldesign.Themostimportantfunctionswereaiming,pullback,andreleasemechanisms.AimingMechanismsLoungeChairSeatbackAngleAdjust

Standardpoollounges,liketheoneshowninFigure6,haveanadjustableseatbackthatworksasasortofratchetingsystem.Tomovetheseatbackfromthereclinedtouprightposition,theseatbackismerelypulledforward.Alinearratchetsystemlockstheseatbackinitscurrentposition.Oneissuewiththisisthatitismoredifficulttolowertheseatbackthanitistoraiseit.Theratchetsystemmustbepulledupforthesystemtobeloweredbackdown.Thissystemfavorsonedirectionofanglechangemorethananother.

TheoreticalSystemCannonFiringAngleChangeInFigure7,aleadscrewcausesalargeringgeartorotateagainsttwosmallergears.Becausethecannonisattacheddirectlytothelargegear,itrotatesasthegearrotates.Whilethissystemfacilitatesanglechangeequallyinbothdirections,thesystemasawholeisquitelarge.Additionallylargegearsarequiteexpensivetopurchase,andsothissolutionmaynotbecosteffective,especiallywithourmodestbudget.

Figure 6. Pool Lounge Chair

Figure 7. Concept Drawing of Firing Angle Change Mechanism for a cannon

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PullBackMechanismsWinchThedeviceshowninFigure8isusedtodragorpullveryheavyloads.Itiscomposedmainlyofaspoolofcable.Whenoneendofthecableisconnectedtoanobject,themotorturnsthespool,windingthecableupanddraggingtheobjecttowardthewinch.Oneissuewiththisideaisthatitiselectricallyoperated.Thismeansthatitrequiresabattery,andthepeoplesupervisingourmachinewillhavetomakesurethatthebatteryissufficientlycharged.ReleaseMechanismsBecauseourballmustbereleasedbytheathlete,itisimportantthatthereleasemechanismrequireafairlylightamountofforceinordertoactuateit.Becauseofthis,ourteamresearchedmechanismsthatcanreleasehighloadswithalowamountofforce.ThreeRingQuickReleaseFigure9showsanintricateseriesofringsthatconnecttwocablesorstrapsintension.Toseparatethetwostraps,releasingtheload,thelongthincableissimplyremoved.Thisallows

allringstounfold,finallyreleasingthelargestringthatlinksthetwocables.Whilethissystemrequireslowforcetoactuate,thissystemhasflaws.First,thenatureofthismechanismrequiresthatitberesetaftereveryuse.Resettingwilltaketime,whichcanslowdownagameofHorse.Anotherissueishowcomplexthequickreleaseistoreset.Inordertousethisdevice,allkinesiologystudentswouldhavetobetrainedhowtoresetthisdevice.Ifresetincorrectly,theshootercouldmisfire,potentiallyharmingabystander.

Figure 9. 3-Ring Quick Release

Figure 8. A motor-operated winch

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SlingshotReleaseThismechanismisonlycompatiblewithslingshotdevices,whichlimitsitsuse.Theendoftheelastic,carryingtheload,isplacedbetweenthetwocylindricalpiecesontheright.Thesecylindricalpiecesareonswivelarms.Duetotheforceoftheelasticonthecylindricalpieces,thecylinderswanttomoveaparttoletitthrough,butcannotbecausethecircularpinontheleftisholdingtheswivelarmsintheircurrentposition.Toreleasetheslingshot,thepin,whichisspringloaded,ispusheddown,allowingtheswivelarmstoswing.Whilethisisaninterestingandseeminglyeffectivesystem,itcontains

manypartsandmaybetimeconsumingtomanufacture.Additionally,abasketballwillnotfitbehindthecylindersinthismechanismunlessthemechanismismadetobegigantic.DogClutchADogClutchismadeupoftwointerlockingpieces.Eachpiece,calledadog,isconnectedtoaseparateshaft.Wheninterlocked,thetwoshaftsactasoneandturntogether.Whenpulledapart,thetwoshaftscanrotateindependentlyofeachother.Thissystemcanbeusedtoallowaspoolofcabletounwindquickly,releasingtheball.Thissystemwouldrequireaspoolofcabletobeused,andwouldonlyworkwithelasticbandpowereddevices,suchasaslingshotorcatapult.

Figure 10. Spring-Loaded Slingshot Release

Figure 11. Solid Model of a Dog Clutch

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OtherBackgroundResearchBasketballandCourtDimensionsForaregulationbasketballcourt,thebasketiselevated10feetabovetheground.Inthehorizontaldirection,thefreethrowlineis15feetaway.Thethreepointline,ourdistancegoal,is19feet9inchesawayfromthehoopinthehorizontaldirection.AnNCAAmensregulationbasketballhasa9inchdiameterandweighs22ounces(1.375pounds).

Figure 12. Dimensions of a NCAA regulation basketball court

Horse ThisdeviceistobedesignedsothatuserscanparticipateinagameofHorse.Theobjectiveofthisgameistotaketurnsshootingbasketsuntiloneplayermakesashot.Atthatpoint,theotherplayersmustsuccessfullymakeabasketfromthesameplaceasthefirstplayer,orriskeliminationfromthegame.Becausethisgameisturnbasedandstationary,thisgamecanbeplayedeffectivelywithanassistivebasketballlauncher.

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UniversalPlayFrame(UPF)

Figure 13. Universal Play Frame (UPF)

OnerequirementofthisprojectwasthatourdevicemustattachtotheUniversalPlayFrame(UPF).TheUPFisastructurethatattachestoawheelchairandservesasamountforadaptivedevices.AdrawingshowingthedimensionsofthepointsofattachmentfromtheUPFtoourdeviceisshownbelow.

Figure 14. Dimensions of the UPF table holes for device attachment.

UserAbilitiesOurteamattendedtheFridayClubtomeettheathletesandobservetheircapabilities.Thisdeviceneededtobetailoredtoathleteswithlimitedrangeofmotionandstrengthintheirarms.Manyofthemhavelimiteduseoftheirhandsduetomuscularatrophy,andsotheirmotionislimitedbywhattheirwheelchaircando.Duetothis,thestrengthandrangeofmotionrequiredtooperateourdevicehadtobelowenoughtobeusedbytheseathletes,buthighenoughthattheyrequiretheathletestogetphysicalactivity.

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ObjectivesandSpecificationsTheoverallgoalofthisprojectistocreateanadaptivebasketballlauncherthatattachedtotheUniversalPlayFrame(UPF)andcanbeoperatedbyanindividualinawheelchairwhohaslittletonouseoftheirhandsorarms.WeplannedtogivetheseathletestheopportunitytoplayagameofHorseorAroundtheWorldwiththeirfriends.Thefirstgoalistomakeitsotheindividualusingourdevicecannotonlyshootabasketball,butcouldplayHorseatacompetitivelevel.Wedesignedthisdevicetoshootfromcloserange(insidethekey)aswellasfromthethreepointarcorpotentiallyevenfarther.Wewantedeveryonetofeelchallengedbyoneanotherinordertocreatetheleastrestrictiveenvironmentforallparticipantsinvolved.Firstandforemost,thedeviceneedstobecapableofbeingoperatedbythosewhohavelimitedmobilityintheirarms.Onerequirementistohavetheoperationofourlauncherrequireonlyasixinchsphereofmotion.Whateveractuationmechanismisused,ithastobedesignedinsuchawaythattheathleteneedstopullsixinchesatmost.But,sincemanyofourtargetathletesdonothavemuchupperbodystrength,wealsoneededtolimittheforceneededtoactivatethedeviceandensureitisintheidealdirection,whichisapullingmotiontowardstheuser.Inordertodetermineamaximumallowableforce,ourteammeasuredtheforcerequiredtopullthereleasemechanismofotherFridayClubadaptivedevices.Fromthistesting,itwasclearthatamaximumallowableforceof5poundswouldensurethatallathletescouldoperateourshooter.Fortheathletesthatdonothaveanyuseoftheirarms,weplannedtoallowforanattachment,suchasrope,tobesecurelyattachedtothereleasemechanismsoitcouldbetiedtothepersonswheelchair.Onceattached,theywouldbeabletomoveinreverseuntilthelauncheractivates.Inordertomeettherangerequirement(tomakeabasketfromascloseas5feetawayandasfaras20feetaway),thelaunchanglehastobeadjustable.Quickcalculationswerecompletedtodeterminetheidealanglenecessarytosinka3pointshot.Thisangleisroughly60degreesabovehorizontal.Becauseahigherangleisnecessaryforaclosershot,theangleoftheshooterhastobeadjustabletoanyanglebetween60degreesand85degreesabovehorizontal.Additionally,tosatisfytherangerequirement,themechanismhastoimpartsufficientenergyintotheballsothatitislaunchedfarenough.Again,fromroughcalculationswedeterminedthatoursystemneedstoprovide20footpoundsofenergytotheballinordertoensurethatthebasketballmadeittothehoop.ConductedanalysisthatledustotherequiredenergyvaluecanbefoundinAppendixE.Duringplay,theathleteshouldbeabletoseethehoop.Toensurethattheirlineofsightisunimpairedbyourlauncher,theheightofthelaunchercannotprotrudemorethanoneandahalffeetabovetheUPFTableTop.Oncetheathletelaunchesabasketballwiththedevice,wedonotwantthemwaitingforseveralminutesforthelaunchertobereadytofireagain.Ourtargetreloadtimeis30secondsorlesssothattheathletesdoesnotfeelasthoughheisholdingupthegame.

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Inadditiontorequirementsthatbenefittheuser,itisalsoimportanttoincluderequirementsthattakeintoaccountthekinesiologystudents,whosetuptheequipmentfortheathletesandoverseeitsuse.Oneengineeringrequirementisthatthedeviceasawholecanweighnomorethan30pounds,tofacilitateeaseoftransportationandmountingtotheUPF.Thelauncheralsoneedstobesimpleandquicktosetup.WeneededtomakesurethatthemountingtotheUPFandsetupofthebasketballshootertakesnomorethanfiveminutes.Thisway,wehopedtomaximizetheactivitytimeoftheathletes.InTable1,asummaryofallEngineeringSpecificationsareshown.Theriskcolumnreferstotheriskofmeetingeachofthespecifications.H,M,andLstandforHigh,Medium,andLow,respectively.Thecompliancecolumnreferstohoweachdesignrequirementwastobemet.ThefourmethodsusedhereareAnalysis(A),Test(T),SimilaritytoExistingDesigns(S),andInspection(I).

Table 1. Engineering Specifications

Spec.# ParameterDescriptionRequirementor

Target Tolerance Risk Compliance1 Weight 30pounds Max L I2 Height 1.5feet Max L I3 Range 20feet Min H A,T4 SetupTime 5minutes Max L I5 OperatingForce 5pounds Max M A,T6 ResetTime 30seconds Max L I,A7 RangeofMotion 6in.dia.Sphere Max L T,S

8 TimeBeforeMaintenance 2years Min M A9 Cost $1,500 Max L I10 WeightLaunched 22ounces Min M A,T

11 Dia.ofBallLaunched 9inches Min L I

12 ElectricalPowerReq'd 0Watts Max M I13 StorageSize 2x2x3ft2 Max M I,T14 StoredEnergyReq'd 20footpounds Min H A

15Angle(from

Horizontal)6085degrees MinMax L I

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Inordertoensurethatallcustomerrequirementsweremet,ourteamusedQualityFunctionDeployment(QFD),alsocalledaHouseofQuality,tocheckthattheengineeringspecificationswehavesetguaranteethefulfillmentofallcustomerrequirements.Thisdocument,whichcanbefoundinAppendixA,laysoutthegoalswesetforourdesignbasedonthewantsandneedsofoursponsorMichaelLaraandcomparingcompetitorsdesignstoours.Italsoallowedustoviewhowmuchcertainrequirementsaredependentoneachotherandifcertainrequirementswesetforaredesignarenecessary.ByphysicallylayingouttherequirementsforourdesignwiththeQFDwehadabetterideaofwhichonesarethemostimportantandcanfocusmoreonmeetingthoserequirements.

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DesignDevelopmentDiscussionofConceptualDesignsOurteambeganourgenerationofconceptualideasonagenerallevel.Alldecisionsdependedonwhattypeofshootingorlaunchingmechanismwaschosen.Severalconceptswereconsideredinthebeginning,includingflywheel,catapult,slingshot,andspringloaded.Conceptsweresystematicallyeliminatedastheproblembecamemoreclearlyunderstood.Tohelpusunderstandwhichmethodsmightworkbest,wefirstdrewsketchesofpossiblelayoutsforeach.Figure15showsexamplesofsketchesillustratingearlyideas.

Figure 15. Sketches depicting possible attachment to the UPF Table Top for a catapult and flywheel, respectively

Asateam,wealsomodeledsmallscaleprototypesforeachtodeterminetheirrelativeshootingabilityandeaseofmanufacture.TwoexamplesoftheseprototypesareshownbelowinFigure16.

Figure 16. Small-scale functional models of a catapult and slingshot, respectively

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ConceptSelectionShootingMethodOfthefourinitialshootingmethodsconceived,thespringloadedideawasthrownoutquicklybecausewedecideditwouldbedifficulttocompressaspringthatcouldstoresufficientenergytoshootabasketballfromthethreepointline.Safetyconcernsandspacelimitationssteeredthedesigncrewawayfromthecatapultandflywheel,sincetheathleteswouldhavetobeincloseproximitytothesesetupsinordertooperatethedeviceandcouldbehurtasaresult.Aslingshotwasseenastheeasiestdesigntocontainwithinasufficientlycompactbox,andbecauseofthisitwouldbeeasytoencloseallbutthetopoftheboxtoensurethesafetyofourusers.Theconceptwasthenbrokendownfromageneralslingshotstylelauncherintoahandfulofmechanisms.Keymechanismsforthedesignwerethequickrelease,thepullback,theaimingandtheUPFmountingmethod.Foreachofthemechanismslistedabove,aPughMatrixwascreatedinordertohelpwiththedecisionmakingprocess.APughMatrixisdecisionmakingtoolwhichlaysoutmanydifferentconceptsforagivenideaandcomparesthemtoastandardwhichiscalledadatum.Ourteamformedlistsofrequirementsforeachdeviceusesthoseliststocompareeachconceptagainstthedatumratethemaseitherbetter(+),thesame(S),orworse()thanthedatum.Ineachcolumn,the+s,sandSsareaddeduptoseethepotentialofeachconcept.Thisisnotadefinitivewayofdeterminingasolution,butrathershowsthebenefitsanddeficienciesofeachindividualconcept.PughMatriceswerecreatedforthreeseparateconcepts:thecrankmechanism,aimingmechanismandquickrelease.ThesematricesarelocatedinAppendixA.PullBackMechanismFirstthepullbackmechanismandthemethodofenergystorageneededtobeaddressed.Thefirstdecisionwastodeterminetheenergystoragemedium,andthiscamedowntousingeitherspringsorelasticbands.Betweenthetwo,thespringscreatemorepinchpoints,andadvicefromkinesiologyprofessorDr.Taylorsuggestedthatspringshavenotbeensuccessfulonpreviousadaptivesportsseniorprojects.Elasticbands,however,hadbeenshowntowork,asdemonstratedbytheOhioUniversitylauncher.Fromthere,itwasanticipatedthatacarriagewouldbeneededtoholdandcarrythebasketballinordertoensureitlaunchesproperly.Withoutacarriage,thestoredspringenergymaynotadequatelytransfertotheball,whichourteamconfirmedbytestingabasicslingshot.Buildingoffofthis,theideaofhavingguiderailstopositionthecarriagewasputforward.Thisistopreventtheballfrommisfiring,andtopromotestraightandconsistentshots.Thecarriagehadtobeattachedtothewinchshaftwhichwasabletoratchetback,stretchingtheelasticbandsandstoringenergy.Aratchetingleverwouldbeattachedtothewinchshaftinorderfortheathletetocrankithimself,orahelpercoulddoitifneedbe.

Figure 17. Latex Tubing, a type of elastic band

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QuickReleaseMechanismNext,thequickreleasewasinvestigated,andvariousideasweregenerated:astandardpullpin,atriggerrelease,athreeringrelease,andadogclutch.Factorsthatweremostimportantinthequickreleaseweretheforcerequiredtoactivateit,thespacethatitconsumedanditsresettime.Thethreeringreleaseandtriggerreleasewouldrequireextrapartsinordertoattachthecarriagetothewinchshaft,whereasthedogclutchisapartofthewinchshaftitself.Withlesspartsinthedesign,itwouldbeeasiertoreset,andmoreconsistent.Weighingthesetogether,thedogclutchstoodoutatfirstasabettersolution,andwasincludedinourteamsfinalconceptualdesign.AfterdiscussingwithourpeersandadvisorduringourConceptualDesignReview,afewproblemswereexposedwiththedogclutch.Onesuchproblemwasthelargeamountoffrictionthatwouldbuilduponthedogclutchwiththehighamountoftorquebeingputonit.Anotherissuewouldbethatafreespinningwinchshaftmeantmuchmoreenergywouldbelostthroughspinningtheshaft.Additionally,withaquickspinningshaftcomesthepossibilityforlonghairorclothingtobecaughtaroundit,potentiallyharmingtheuser.Asaresult,ourteamdecidedforasimplisticapproach,andplannedtouseapullpinasarelease.Byusingapullpin,therewouldstillbefrictionbetweenthepinandcarriage,butreleasingthepinwouldnotaffectthewinchshaft,meaningitwouldnolongerspinfreelyathighspeeds.MountingandAimingMechanismsEarlyinthedesignprocesswebegantoconsiderhowtomountourfinaldevicetotheUPF.Originally,itwasthoughtthattheapparatuswouldbemountedtothetabletop.Thiswouldallowthedevicetobeaimedintwodifferentplanes,toadjusttheshotarcaswellastwistinthehorizontalplane(totheleftorright).Laterinthedesignprocess,though,itbecameapparentthatthedevicewouldneedtobemountedtosomethingotherthanthetoptable.Inordertostorethepotentialenergynecessarytolaunchabasketball20feet,thedevicewouldneedtoaccommodateenoughpullbackspace.Thetabletopwastoosmallforthis,however,andputtingtoolargeofasetuponthetoptablewouldobstructtheviewoftheathlete,aswellascausepotentialsafetyproblems.Thenextmostviableoptionwastomounttothefrontbar,andusethetoptableasastabilizer.Thisopeneduptheopportunitytoaimthedeviceusingleadscrewswhichpushandpullfromthetoptabletothedevice.LayoutsketchesforthetwomainmethodsofmountingareshowninFigure18.

. Figure 18. A table-top mounted device versus a lower-bar mounted device

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Thisconceptmettherequirementsofshootingdistanceandunobstructedview,withtheplacementofthelauncherinthefrontoftheUPFprovidingamplepullbackspacefortheelasticbands,andalsoclearingalineofsightfortheathletetothebasket.OtherConsiderationsOthermajorconsiderationstakenintoaccountduringtheconceptualdesignphasewerewear,noise,andsafetyconcerns.Someoftheathletesweretimidandfrightenedbysuddenloudnoises,soourdeviceshouldnotmakeastartlingnoise.Becausethecarriagewouldbemovingathighspeeds,ifitwasnotslowedafterreleasingtheballthecarriagewouldhittheframewithalargeimpact.Thiswouldbothcausealoudnoiseandcouldaffectthestructuralintegrityofthecarriageandsupportingframeovertime.Asaresult,ourteamdecidedthatplacingsomesortofcompressionspringorrubberstopperatthetopofeachguiderailwouldhelptoslowdownthecarriageinasafeandquietmanner.Thesafetyoftheuserswasimportantaboveallelse.Toaddresssafetyconcernswehadtwoprotocolsinplace.First,wedecidedthatthereshouldbewallscoveringthesidesofourshooterandanyexposedmechanicalparts,toensurethatuserscannotaccessanypinchpointsorareasofimpact.Also,weconsideredsafetymechanismswhereaballcannotbelaunchedaccidentallyuntilaspecificactionwastakenbyanassistant.Thesimplestmethodwastocreateawaytounhooktheathletesreleaseactuatorfromthequickreleasepinuntilallparticipantswerereadytoshootandtheareainfrontoftheshooterwasclearedofanybystanders.Thentheassistantwouldjointheusersreleaseactuatorandthequickreleasebycable,renderingthedeviceliveandreadytoshoot.ProofofConceptBeforeproceedinganyfurther,wewantedtomakesurethatourdecisiontostoreenergyinelastictubingwasaviablemethodforourdesign.Inordertotestwhetherthetubingwouldbecapableofshootingabasketballfrom20feetweneededatestingapparatus.Wedecidedtomakeacubewithrearlegextensionstogiveusashootingangleofapproximately60fromahorizontalsurface.Sinceweneededtomakesomethingquick,butstrong,weused1.5inchsquarewoodandcutitintotwofootsegments;twopieceswerelonger(about33inches)andangledatoneendtoanglethetestingapparatus.Wecreatedsomesimplejointssothewholedevicecouldbejoinedwithonlywoodglue.Onceitwasdriedwetookourelastictubingandcutitintofourequalpartstohavethesamesetupasourfinaldesign.However,insteadofusingeyescrewsandbungeehooksfortheelasticbands,wewrappedthetubingaroundthewoodonthetopoftheframeandtiedoffthetubingatourmakeshiftcarriage.Wethentiedastringaroundthebottomofthecarriagesothatwecouldmanuallypulltheballbacktoshootit.Aftertakingseveralshotsandgettingusetothedevicewewereabletomakeathreepointshotthusprovingthattheelastictubingwillhavesufficientenergystoragecapabilitiesandisdurableenoughtoshootrepeatedlyandconsistently.

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DescriptionofFinalDesignOverallDescriptionOurfinaldesignmountstotwoseparateareasoftheUniversalPlayFrame.First,thedevicesitsonhingesattachedtothelowerfrontbaroftheUPF,whichcarriesthebulkoftheassemblysweight.AnothersectionofthedevicealsomountstotheUPFTableTopvialongrodsthatrestinthetabletopholes.Thedeviceitselfcanbebrokenintothreemajorsubassemblies:theaimingsubassemblyshootingsubassembly,andreleasesubassembly.

Figure 19. The total assembly of the adapted basketbal launcher.

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DetailedDesignDescriptionFrameAssemblyTheframesizingwasverysimilartohowitwasfortheconceptualdesign.Ithadabasemeasuring13.5x13.5,anditis2feettall.Itwasmadeoutofstockaluminumbolttogetherframing,forwhichtherewerepremadeholesonallsidesforboltingattachmentbrackets.Thiswasidealforthedesignbecausethereareshaftsandeyeboltswhicharefastenedalongtheframeinveryspecificlocations.Loadsontheframewere200poundsmaximum,whichwaslowenoughthatthestructuralintegrityoftheframingneednotbequestioned.Thestockaluminumframingwascuttosize,andadditionalholesweremachinedtoattachtheguiderods

andwinchshaft.

Eachofthepremadeholesinthealuminumstockwas.328indiameter,allowingclearancefora5/16boltorrod.Theguiderodswere0.5indiameter,andsolargerholesoneithersideoftheframehadtobedrilled.Duringinstallation,theguiderodstouchedtheframeatfourdifferentpoints,andtwoboltsranhorizontallythroughframemembers,securingtheguiderodsintoplace.Thishelpedensurethestraightnessofourrods.Whilewedecidedtousetwoguiderodsinourdesign,wechosebetweenusingtwo,four,ornoguiderods.Overall,wedecidedthatitwasbesttohavejusttwoguiderods.Havinganyevennumberofrodsensuredthattheballwaslaunchedconsistently.Iftherewasaslightmisalignmentbetweentherods,thentwoguiderodswouldbemoreforgivingthanfour.Makingsurethat

theguiderodswereperfectlyparallelwasachallengewefacedinthemanufacturingprocess,butoneadvantageofhavingthepremadeholesinthealuminumstockisthatitwaseasiertoaccuratelylocatetheholesthatourteamdrilledfortheguiderods.Locatedoneachguiderodwerepolyurethanerubbertubeswithahardnessof40A.Theirpurposewastosoftentheimpactofthecarriageontheframe.Therubberwaschosenbasedonhowmuchitisabletocompress,andthushowmuchenergyitisabletostore.After

Figure 20. Frame subassembly.

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analyzingtheeffectofcarriageimpactforcesontherubbertube,itwasfoundthatatubelengthofthreeincheswouldprovideasufficientdistanceforthecarriagetodeceleratesafely.Eyehookswerefastenedtothefourtopcornersoftheframe,asdepictedinFigure20,whichwereforattachingtheelastictotheframe.Theelasticselectedwas3/8ODand1/8ID,andwouldbeformedintocordswithbungeehooksoneachend.Thefoursidesoftheframewerewalledwithpolycarbonatesheetstoensurethatnoparticipantscouldplacetheirhandsinsidewithintheframeduringuse,avoidinginjury.Thesheetswereboltedintotheframing,andoneofthesheetswashinged,actingasadoor,whichallowsanassistanttoreattachthewinchcabletothecarriagebetweenshots.MountingofFrametoUPFInordertomounttheframetotheUPF,wehadtwosteelhinges,twointermediatesteelplates,andtwosquaretubeswiththeirbottomscutoff.Whiledesigningthemountingofthisdevice,wedecidedthatwewantedtomakenomodificationstotheUPF.Asaresult,thehingesdidnotattachdirectlytotheframe;insteadwehadsteelspacerblocksforthehingestoboltinto.ThespacerblockswereweldedtotheUshapedsquaretubing,andthatsquaretubingsatontheUPFdirectly,withholesforsetscrewstoapplyhorizontalforcetotheUPFfrontbar.

Figure 21. Frame attaching to the UPF by hinges.

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WinchShaft

Thewinchshaftbearsthestaticloadof65pounds,whichexistswhentheelasticisfullystretched.Itwas0.5indiameter,andextended13.5allthewaythroughbothsidesoftheframe.Thestaticforcecreatedabendingstressinthewinchshaft,forwhichtheshafthadasafetyfactorof1.72.Aspoolmadefromawoodencylinderwasplacedinthecenteroftheshaft.Thespoolwasdrilledthrough,aswellastheshaft,andthetwowereboltedtogetherwitha1/4diametersetscrew.Nylonropewastohavebeenattachedtothiswoodencylinderbytighteningahose

clampoverboththespoolandrope.Theotherendoftheropewasattachedtothequickreleasebracketviaaloopandropestop.Holesweredrilledintheframetoallowthewinchshafttofit,anditwassupportedbyoilimpregnatedbronzesleevebearingsoneithersidetoallowforfreespinningoftheshaft.RatchetandPawlTheratchetandpawlallowedforthenylontoberolledupvariousamountswithoutunrolling,andthereforetheelastictobestretchedatdiscreteincrements.Becausetheboreoftheratchetgearwaslargerthantheshaftdiameter,theratchetgearwasattachedtothewinchshaftbywayofaflangedcylinder.Theratchetgearwasfastenedtotheflangewithsetscrews,andthecylinderportionwasdirectlyfastenedtothewinchshaftviaanothersetscrew.Thepawlwaspositionedabovetheratchetsothatwheneveritwasdisplacedupwardbytheratchetteeth,itwouldfallintoplacebywayofgravityandwithouttheuseofaspring.Therefore,amountingblockforthepawlwasinstalledintotheframe,madeoutofthesamealuminumstockastherestoftheframe.

Figure 22. Winch shaft assembly, with ratchet and pawl.

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RatchetArmLever

Inorderforthewinchtospin,aratchetarmleverwasdesigned.OurleverwasbasedoffoftheratchetleverfortheFridayClubsbaseballbatswingingmechanism.Theratchetarmleverwascomposedofastandardratchetwrenchandtwowoodendowelswithadiameterof1.5.Theratchetwrenchfitintoaholelocatedonthefaceofoneofthedowels.Theotherendofthedowelhadaclearanceholeforapin.Thispinconnectedthetwodowelstogether.Thisresultedinajointedlever,whichmeantthattheleverarmcouldbeusedfroma

multitudeofangles.Ahexboltwasscrewedintoonesideofthewinchshaftandsetinplacewiththreadlockingadhesive.Toratchetbackthecarriage,wedecidedtoplacea9/16socketontotheendoftheratchetwrenchandplaceontotheboltthreadedintothewinchshaft.Then,crankingtheleverbackandforthwouldturnthewinchshaft,windingthenylonropearoundtheshaftandpullingbackthecarriage.Becausetheshaftwasjointed,theendcouldeitherbelocatedneartheuser,sotheusercancrankthelever,butitcouldalsobedetachedsothatanassistantcouldratchetfromalongsidethemechanism.

Figure 23. Ratchet arm lever extends from bottom of frame.

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Carriage

Thefourcarriagepiecesweremadeoutof1/8inchthicksheetaluminum.Alightmaterialsuchasaluminumwaschoseninordertoreducethetotalamountofenergyrequiredtolaunchthebasketballatthedesirablespeedof30ft/s.Aluminumwaschosenoveranevenlightermaterial,suchasplastic,becauseitneedstobeabletowithstandboththestaticforceoftheelasticinthefullystretchedposition,andthedynamicforceatimpact.Inthisdesign,weplannedtobendthealuminumcarriagepiecesat90degreeangle,creatingsurfacestoeasilyboltthepiecestogether.Twoflangedlinearsleevebearingswereselectedthatallowedthecarriagetorollalongtheguiderailswithminimalfriction,sothatrequiredlaunchenergywasaslowaspossible.

Figure 24. Carriage assembly.

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ReleaseMechanism Thereleasemechanismconsistedofabracketwithaspringplungerpinthatranthroughthecarriageandtotheothersideofthebracket.Thenyloncrankbackropewasloopedthroughthebottomholeofthebracketandpulledtheentirecarriagereleaseassemblybackintofiringposition.AtthetimeofourConceptualDesignReview,theleadingideaforreleasethesystemwasadogclutchwithaseparatingshaft.Sincethedogclutchwouldrequireasignificantamountofforcetodisengage,andthewinchshaftwouldbelefttospinatanuncontrolledspeed,thisideawasrejectedinfavorofapinreleasesystem

whichwasmoreeasilycontrolled.Toreducethefrictionactingagainstthepullpin,anoilimpregnatedbronzesleevebearingwouldhavebeeninsertedintoboththecarriagereleaseholeandthebracketholetoreducefrictionduringpulling.SafetyMechanismThesafetymechanismofthisdevicemadeithardertounintentionallydisengagethelauncher.Fromthepullpin,acableextendedthroughacutoutinthepolycarbonatetoacarabineerjustoutsideofthecutoutwhereitwasunabletoslipinsideoftheframe.Thiscarabineerallowedfortheothersideofthecableattachingtotheuserinterfacetobeengagedonlywhentheballandcarriagehadbeenpulledbackthedesireddistanceandallparticipantsandbystanderswereclearofthelaunchpath.Theslotsinthepolycarbonatewereincrementedsothatthecablewasasclosetoinlinewiththepullpinaspossible,minimizingtherequiredpullforce.

Figure 25. Release mechanism in the attached position.

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UserInterface

Figure 26. The user interface allows an athlete to have as much control of the system as possible from a wheelchair

position.

Fortheuserinterfaceportionofourdesign,whichsatonthetabletopoftheUPF,wehadabasemadeofanglestockaluminumwithasecondverticalfinwhichactedasasupportbracketfortheaimingmechanism.Fortheanglestock,wechose3/8inchthickaluminumwithfiveinchsides.Thethicknesswasdesignedtoprovideasufficientamountofstiffnesswhenloadedtopreventsignificantbending.ThewidthofthesidesallowedustoutilizethemajorityoftheUPFtabletop,givinggreaterstabilityandprovidingmorespaceforothercomponentstobemounted.Intheinitialdesign,sixaluminumpegswerefastenedtotheanglestockbyTigwelding.ThepegskepttheanglestockcenteredandgroundedwithrespecttotheUPF.Thecrankhandlewasmountedinthecenteroftheanglestockfacetoallowforeasyusewitheithertheleftorrighthand.Totherightofthecrankhandle,thereleaseleverwasmountedusingalongbracketwithapinforapivotpoint.Theleverhadapproximatelytwoinchesofclearancefromthecrankhandle.Wedecidedtomountthelevertotherightratherthaninthecentertoavoidinterferencewiththecrankhandle.Theratchetarmleverwastobemountedtotherightsideofthedevice.

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AimingAssembly

Figure 27. Working portion of tabletop mount showing support fin

and aiming mechanism components.

Allcomponentsoftheaimingassemblyweremountedonthesameanglestockasthecrankandreleaselever.Theaimingassemblyconsistedofshaftsandpulleystotranslaterotationalmotionintoananglechange,thecrankhandletoactuatetheaimingmechanism,andasupportplate.Theshaftsoftheaimingmechanismneededtorotate,sotoallowforsmoothrotationwepressfittedsleevebearingsintothefaceoftheanglestockwhichreducedfrictionwhilestillsupportingaradialload.Thesupportplateismadeof1/8thickaluminumsheetandprovidedtherotatingshaftsoftheaimingmechanismextraverticalsupporttopreventexcessivedeflection.Thinsleevebearingswerepressfitintoholesonthisplate,allowingforlowfrictionrotationwhilestillprovidingsufficientradialsupport.ThisplatewasmountedtotheanglestockaluminummentionedaboveusingfourLbracketsfastenedwithnutsandbolts.Thiswasdesignedtogivetheplateenoughstabilitytonotcollapseduringoperation.Therotatingshaftsoftheaimingmechanismthatfitthroughtheanglestockandfinweretobemadeof3/8diametersteelroundstock.Forthesecomponents,weneededamaterialwithagreaterstiffnessthanaluminumtopreventbending,anddecidedsteelwasthebestchoicesinceitisnearlythreetimesasstiffasaluminum.Therewerethreeparallelshafts,oneinthecenteroftheanglestockfaceandonetoeachsideofthecentralshaft.Thecentralshafthadthecrankhandlebondedtooneendandtwo10toothtimingpulleysmountedontheotherend,heldinplacewithsetscrews.Twotimingbeltsconnectedthethreeshafts,transmittingtheforceappliedonthecrankhandleequallytotheoutershafts.Theoutershaftshadslightlylarger(14tooth)timingpulleysthatwerealsoheldinplacewithsetscrews.Thethreepulleyshaftstransmittedthetorquefromthepulleystoadjoinedleadscrewsinordertotilttheentiredevice.Topreventtheshaftsfromslidingoutofplaceandmisaligningthetimingbelts,spacerswereplacedbetweenthepulleysandtwosupports,restrictingallshaftmovementintheaxialdirection.

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Figure 28. Pulley system for aiming mechanism.

Thetimingbeltsandpulleyschosenweredesignedtohavenoslipwhilebeingoperatedaswellastoprovideasmallmechanicaladvantagefortheuserastheyturnthecrankhandle.Thepulleysonthecentralshaftweretohave10teeth,andtheouterpulleyshave14teeth.Withourorientation(smallpulleytolarge)thiswouldgiveamechanicaladvantageof1.4,meaningtheuserwouldonlyneedtolessforcethaniftheyweretodirectlyturntheoutershafts.

Figure 29. Universal joint that will allow for the transmission of torque to

the lead screws of the aiming mechanism. Asthedevicechangedangle,theangleoftheleadscrewsneedtochangewithit.Becauseofthis,weneedtobeabletotransmitthetorquefromtheshaftsatanyangle.Todothiswechosetopurchaseunboreduniversaljointstomountattheendoftheoutershafts.Sincetheywereunbored,wewouldmachineoneendtofitaroundthe3/8shaftsandtheotherendtofittheleadscrewtip,andthenwewoulddrillholesineachendtopressspringpinsinsothattheleadscrewswouldtransmittorque.

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Figure 30. Lead screw of aiming mechanism which controls the tilt of the device.

ThenextcomponentoftheaimingmechanismwastheACMEthreadedleadscrews.Thesewerewhatcausedthefiringangletochange.WechoseanACMEthreadedleadscrewratherthanastandardthreadedrodbecauseAMCEthreadshadlessfriction.TheonlydownsidetousingAMCEthreadedpartswasthatwedidnothavetheresourcestotapACMEthreads;therefore,wehadtopurchaseACMEcompatiblepartsratherthanmanufacturingthemourselves.Toattachtheleadscrewstotheuniversaljoint,wedecidedwewouldturndownalengthof5/8ofoneendoftheleadscrewto1/4andwouldturndowntheavailableendoftheuniversaljointtobea1/4"shaft(theywouldfitwithoutneedingtobepressfitsincemachiningaholecausestheholetobeeitherthenominalsizeorbigger,andtheshaftwouldbeeitherthenominalsizeorsmaller).TheotherendoftheleadscrewranthroughacylindricalACMEnut,whichwaswhatmovedupanddownthelengthoftheleadscrew.Topreventtheleadscrewsfromfallingoutofthenutsorgoingtoofarthroughit,wesecuredacollaroneachendoftheleadscrew.

Figure 31. Custom bracket containing cylindrical nut to guide the lead screw as it is turned and allows the device to

tilt. Thelastcomponentsoftheentireaimingmechanismweretwocustombracketsthatwewouldmachineourselves.Theyweretobemadefromaonefootlengthpieceof6061aluminumbar

38

stockthatwas1x2.Wewouldfirstcutoffa1/2"thicksectionofthebarstockanddrilledaholewitha3/4"inchdiameterthroughthetophalfofthealuminumonthelargeface.TheACMEnutwouldfitinsidethisholeandwouldbesecuredwithsetscrewsthroughthesideofthealuminumbar.Then,onthelongersidefaceofthepieceofaluminum,wedrilledanotherthroughholethathadadiameterof5/16.Thisholewasforthepivotpointofthebracket.Thepinthatallowedforthepivotingwasalongclevispinwitharemovablepintopreventthebracketfromslippingoff.Thispinconnectedthebrackettotheframe.InordermaketheprocessofattachingourdevicetotheUPFeasier,itcouldbecompletedintwosteps.Priortoattachmenttheclevispinfortheleadscrewhingebracketwouldberemoved,formingourdeviceintotwoseparatepiecestheframeandtabletopmount.ThetabletopmountcouldfirstbeinstalledbyfittingthepegsintotheholesontheUPFtabletop.Next,theframecouldbesetontopoftheUPFbottomfrontbar.Then,thetwoassembliescouldbeattachedbytheclevispins.Splittingthedeviceintwoforassemblyanddisassemblymeantthattheassistantdidnothavetoliftmorethan30poundsatatime,meaninghecouldsetuptheUPFbyhimselfinatimelymanner.

AnalysisResultsInordertodesignourdeviceandtoverifydecisionsthathadalreadybeenmade,weconductedanalysisonvariousaspectsofourdesign.First,weusedprojectilemotionequationsandexperimentaldatatodeterminetheappropriateangleoflaunch(61.4degrees)andlaunchvelocityoftheball(30.3ft/s)thatisrequiredtomakea3pointshot.Bycombiningthatinformationwiththekineticenergyrequiredtoacceleratethecarriagetothesamelaunchvelocityandthepotentialenergyrequiredtoincreasetheheightofboththecarriageandballwithintheframe,thetotalenergythatmustbesuppliedbytheelasticbandswasdeterminedtobe36.3footpounds.Nextourteampurchasedfoursampleelasticbandsofvaryinginnerandouterdimensionsandperformedforcedisplacementtestingoneachusingaforcegaugeandruler.Fromthoseresults,wewereabletodeterminethenumberoftubesnecessaryandstretchedlengthrequiredofeachtostore36.3footpoundsofenergy.Wefoundthatusingfourofthesmallestbands(3/8OD,1/8ID)wouldgeneratethenecessaryamountofenergywhenstretchedthreetimeslongerthanitsunstretchedlength.Thetotalforcerequiredtostretchthesebandstothatlengthwas65pounds.Thisvaluewasthestaticloadingonthewinchshaftwhenthecarriagewaspulledbackthemaximumdistance.Fromthisinformation,wedeterminedthatasteelwinchshaftneededaminimumdiameterof0.28inches.Asaresult,wechoseawinchshaftdiameterof0.5inches,givingasafetyfactorof1.782.Wealsolookedatthecompressiveforcesontheguiderodstomakesurethatbucklingwasnotaconcern.Forthiscalculation,weassumedaworstcasescenario:thattheframewasnotsupportinganyofthestaticloadsotheguiderodsweretakingall65pounds(or32.5poundseach).Approximatingeachguiderodasafixedfixedbeam,andassumingtheguiderodismadefrom1/2inchdiametersteel,aguiderodwouldnotbuckleunlessitexperiencedaforceof6370pounds.Thisgivestheguiderodsasafetyfactorof196.

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Afterprovingthevalidityofourdesignunderstaticloading,weconductedananalysisduringimpactloading.Theimpactforcewascausedbythecarriagecollidingwiththetopbarsoftheframe.Inordertodetermineaplausibleimpactanalysisweusedknowndatafromtherubberstoppersweplantouse.Byestimatingthestiffnessthepolyurethanerubberandthelengthandcrosssectionalareaofthestopper,wewereabletousemechanicsofmaterialstosolvefortheforceperdisplacement,alsoknownasspringconstantk.Withthisinformation,wewereabletousetheknownenergystoredinthesystemtosolveforthedistancethattherubberstopperwillbedisplaced.Withthisdisplacementandthespringconstant,Hookeslawwasusedtoestimateanimpactforce.Usingthismethod,thetotalimpactforcewasfoundtoequal226pounds.Afreebodydiagramoftheframewasmadeatimpact,andforcesontheleadscrewandhingeweredetermined.Eachhingewasfoundtoexperiencealoadof136poundsandeachleadscrewfeltatensileloadof18.8pounds.Eachhingewasratedfora100poundloadandsurelyhadafactorofsafetygreaterthan1,sowewereconfidentthatourhingeswouldsupporttheframewithoutissue.Tensilestresscalculationswerecompletedontheleadscrewstodeterminethesizingofthem.Comparingourleadscrewsizetotheminimumsizeneededforourpurpose,wehadafactorofsafetyof23.3.Additionally,pressfitcalculationswereconductedforthefourassembliesthatwillbeattachedviainterferencefitpulleybearingtoanglestock,ACMEcylindernuttoleadscrewhingebracket,winchshaftbearingtoframe,andcranktocrankshaft.Allinterior,shaftpartswerepurchasedand,becausetheywereintendedtobepressfitted,weredesignedtobeslightlylargerthantheirnominalouterdiameter.Therefore,weonlyneededtoworryaboutholesizing.Foreachpressfit,wefoundthateachholecouldnothavebeensmallerthanthenominaldiameter,andcouldonlyhavebeen0.001inchlarger.Theseholeshadthetightesttoleranceofanypartofourdesign.Foramoredetailedlookatthesecalculationslistedinthissection,seeAppendixC.

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CostAnalysisAspartswereselectedanddesignedforourproject,ourteamkeptarunningtallyofallmaterialstobepurchasedandtheironlinepurchasingprice.Onceallpartshadbeendesignedandintegratedintoourfinaldesign,afullBillofMaterialswasconstructed,listingeverynamedpart,partdescription,vendor,partnumber,andcost.Thiswasupdatedthroughoutthemanufacturingphasewheneverourdesignchanged.ThefinalindepthBillofMaterialsfornecessarypartscanbefoundinAppendixB.AsummaryofallcostsisdetailedinTable2.

Table 2. Abbreviated Bill of Materials

FromthisBillofMaterials,thetotalcostofourprojectwasalittleover$1,750whichplacedusabout$250overoursuppliedbudgetof$1,500.Ourprojectwentoverbudgetduetoahandfulofsmallmanufacturingmistakesanddesignchanges.Forexample,webrokeauniversaljointwhileboringaholeinit,anditcostabout$50topurchaseanewone.Ifweweretomakeanotherbasketballshooterwiththeexactsamedesignasourfinalprototypeandmadenomistakesduringmanufacturing,thedevicewouldonlycostabout$1,400tomake,whichisunderbudget.

Part StockDescription CostFrame AluminumBoltTogetherFraming 122.20$Carriage 6061AluminumSheet 52.92$Carriage WaterJetCuttingServices 86.00$

TableTopPegs 6061AluminumRoundStock 20.89$LeadScrewHinge 6061AluminumBar 8.76$TableTopBase 6061AluminumAngle 57.18$BaseHinge LowCarbonSteelRectangularBar 4.07$BaseHinge A500SteelStructuralSquareTube 10.12$PulleyShafts 1144MediumCarbonSteelRod 21.70$RatchetFlange 1144MediumCarbonSteelRod 15.26$GuideRods 303StainlessSteelPrecisionShafting 28.00$WinchShaft 303StainlessSteelPrecisionShafting 14.00$ElasticTubing LatexTubing 12.25$

RubberStoppers PolyurethaneRubberTube 16.02$WoodenSpool RedOakDowelRod 6.84$RatchetArm OakDowelRod 26.44$ReleaseLever DelrinAcetalResinRod 7.37$

Spacers DelrinAcetalResinRod 11.55$SafetyCasing ImpactResistantPolycarbonateSheet 43.96$

FrameAccessories 160.15$Fasteners 203.46$Bearings 74.43$

Gears,Pulleys,andBelts 190.89$Addt'lRatchetArmParts 26.28$Addt'lAimingMech.Parts 152.01$Addt'lReleaseMech.Parts 61.12$SparePartsandMaterials 334.03$

TotalCost 1,767.90$

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SafetyConsiderationsBecausethisdevicewillbeoperatedincloseproximitytoalargenumberofpeople,itisimportantthatourdeviceisinherentlysafe.Whiletherearemanymovingpartswithintheframeandaimingassemblythatcouldcausepinchpoints,theseregionswillbecoveredwithpolycarbonatesheets,allowinguserstoseethemechanicalworkingsofourlauncherwithouttheriskofbeingharmedbyit.Anyedgeonourdevicewillbefileddownorrounded,ensuringthatnousercanbeinjuredbysharpedges.Becauseourdevicecontainsnoelectricalcomponents,thereisnoriskthatelectricalsystemsarenotproperlygroundedorthatlargeelectricalvoltageswillexist.Therearenoexplosivegasesorflammableliquidsinourdesign,andnomaterialsknowntobehazardoustohumans.Toensurethatourdevicedoesnotgeneratehighlevelsofnoiseuponimpact,rubberstoppersareinstalledatthetopofeachguiderod.Asthecarriageimpactsthesestoppers,therubberwillcompressandremoveenergyfromthecarriage,bringingittoastopmoregraduallythanifitweretohitthemetalframedirectly.Therubberstopperscushioningeffectshouldreducetheimpactnoisetolevelsthatwillnotfrightentheuserordamagetheusershearing.Whilethesystemdoescontainstoredenergyintheformofelastictubingandthesystemdoesproduceaprojectile,ourteamhasdesignedasafetymechanismtoreducetheriskofaccidentalfiring.Thereleasecablewillbetwocablesjoinedbyacarabineerhooksystem.Priortostretchingtheelasticbands,thecarabineerwillbedisengagedfromthehook,separatingthepullpinfromtheusersreleaselever.Thismeansthattheusercannotreleasethemechanisminitscurrentstate.Oncetheballhasbeenloadedandpulledbacktoitsintendeddistance,theassistantwillconfirmthatthelaunchpathoftheballisclearbeforereconnectingthecarabineertothehook,renderingthereleaseleverlive.Theusercanthenpullthereleaselever,shootingtheball.Duringresetofthepullpin,theassistantwillunhookthecarabineeragain.Duetothesesafetyconsiderations,wefeltitwouldbeagoodideatowriteanoperationandsafetymanualforanyhelperswhowillbesettingupandoverseeingtheuseofourdevice.ThesafetymanualcanbefoundinAppendixF.RepairConsiderationsOfallpartsonthisdevice,weanticipatethatthelatextubingwillbethefirstpartstorequirereplacement.Afteracertainnumberofstretches,thelatextubingwillbegintoplasticallydeformandmaynotprovideenoughenergyovertime.Toplanforthis,wehavedesignedthelatextubingtobeeasilychangedoutfornewtubing.Thetubinglengthsaremadebyfirstcuttinganappropriatelengthoftubeandknottingeachend.Bungeehooksarethenfastenedontoeachend.Toinstallonthedevice,oneendishookedontothecarriageandtheotherishookedontoaneyeboltatthetopoftheframe.Thisdesignmakesthetubinglengthseasytomanufacture,install,andreplace.

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Wecouldalsoanticipatethatthenylonropeusedtopullbackthecarriagecouldbeworndownovertime.Toreplacethis,apersoncouldcutoruntietheropefromthecarriageend,loosenthehoseclamponthespool,andremovetheropefromthatend.Theropewillnowbeunattachedandcanberemoved.Asimilarlengthofropecanbecutandinstalledinthesamemanner.Weanticipatethatthisreplacementcanbedoneinlessthantenminutes.Whilewedonotanticipateanyotherpartswearingoutwithintwoyears,wehavedesignedourdevicewitheaseofmanufacturinginmind.Becausenoneofourteammembersareveryexperiencedwelders,amajorityofcomponentsareassembledusingnutsandbolts.Thismeansthatnearlyallpartscanbeassembledandremovedwithbasictools,soitshouldnotbetoodifficultforthedevicetobeserviced.Manyofthepartsonourdeviceareofftheshelfparts,soifthosepartswearout,nomanufacturingshouldbenecessary.Areplacementpartcanbeboughtandinstalledinstead.

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ProductRealizationAftercompletingourdetaileddesign,thenextstepwastomanufactureallpartsandassemblethemintoaprototype.Inordertoreduceproductiontime,commercialofftheshelfpartswereusedasmuchaspossible.However,modificationshadtobemadetomanyofthesecommerciallyboughtparts,andmanycustompartshadtobeproducedaswell.Manufacturingthisdevicewasachallengingfeatthattooktwelveweeksandover300manhoursofwork.FrameTheframewascutfromaluminumsquaretubingwithpredrilledholesonthechopsaw,andwasdeburred.Fourlongmembersandeightshortmemberswerecuttosize.Theonlyothermodificationstothisframewereholesforvariousattachments,suchastheholestothewinchshaft,theguiderodsandthemountinghinges.Lbracketswerepurchasedforattachingtheframetogetherwithbolts.Thebronzesleevebearingsforthewinchshaftwereinsertedintotheirholeswithanarborpress.Theguiderodswere1/2stainlesssteelrodsandhadholesdrilledateachendinordertopositionthemstraightlyandsecurelyintotheframe.Becausewefearedthatthebasketballmayhittheprotrudingboltheadsattachingtheguiderodstothetopoftheframe,theflatheadboltswereused,andthepertinentholesintheframewerecountersunksothatthetopoftheboltswouldlieflushagainsttheframe.

Figure 33. All short frame members cut to length with holes drilled.

Figure 32. In order to drill precise holes in our frame members, the mill was used.

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BottomHingesThebottomUPFattachmentpointwasmadefromsteelsquaretubing.Tocreateuchannelwithstraightwalls,onefaceofthesquaretubingwascutoffusingthechopsaw,andtheresultinguchannelwasgroundtoremovesharpedges.Becausetheofftheshelfhingesweremadeofanunknownmaterial,theycouldnotbeweldedtotheuchannel;insteadtheywouldhavetobeheldonwithfasteners.However,theuchannelwastoothintobe

threadedsoarectangularpieceofsteelwasMigweldedtotheuchannel.Aftergrindingdown

thewelds,holesweredrilledandtappedintothepartandthehingeswereboltedontoit.Theotherendofeachhingewasboltedontoaframemember,throughspeciallydrilledholes.

Figure 35. The bottom hinge assembled to both the frame and the u-channel.

WinchShaftandComponentsThewinchshaftwascuttolengthandtwosetscrewholesweredrilledintoitandtapped.Oneholewouldlocatethespool,whiletheotherwouldlocatetheratchetflange.Ononeendofthewinchshaftaholewasdrilledandtapped.Intothishole,acustomboltwithalongheadwasmadetoactasaninterfacebetweenthewinchshaftandratchetarm.Theboltwasmadefromapieceofsteelhexstock,withoneendturneddownto5/16.Thisroundportionwasthreadedtocreatea5/1624bolt.

Figure 34. The steel rectangle was Mig welded to the custom u-channel.

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Theratchetflange,whichadaptstheofftheshelfratchetgeartofitonthewinchshaft,wasmachinedfroma1diametercarbonsteelstockmetalcylinderonalathe,andthenturneddownononeendto3/4diameter,anddrilledthroughat1/2diameter.Holesweredrilledandtappedintothefaceoftheratchetflangetofastentheratchetviasetscrews,andanotherholewasdrilledandtappedintothebodyoftheflangeforasetscrewtolocatetheflangeonthewinchshaft.Theholesonratchetgearanditsflangeneededtobedrilledonamill

inordertolocatethempreciselyenough.Throughtrialanderror,wefoundthattheholeshadtobetappedwiththetwopartsclampedtogether,sothatthethreadswouldlineupcorrectly.Topreventthesharpsteelratchetfromwearingdowntheadjacentaluminumframe,aspacemadefromDelrinwaslathedtoserveasabarrierbetweentheratchetgearandframe,whilealsorestrictingaxialmotionofthewinchshaft

Thespoolwascuttolengthonabandsawfroma2diameter,4longwoodencylinder,andwassandedonaspindlesandertoachieveatapereddiameter.A1/2holewasdrilledallthewaythroughthespoolforthewinchshaft,andtwo1/4holesweredrilledinthroughtheradialdirectionofthespool.One,throughthecenter,allowedasetscrewtolockthespoolontotheshaftbothaxiallyandrotationally.Thesecondholewaswherethewinchropewassecuredtothespool.

Figure 36. The ratchet flange attaches to the winch shaft via a set screw.

Figure 37. To attach the ratchet gear to its flange, four holes were milled and

threaded.

Figure 38. The spool attaches to the winch shaft via a set screw. The winch rope is secured around the spool through another hole.

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PawlBlockThepawlblockwascutfromthesamestockasthealuminumframe.Anextraholewasdrilledonamill,becausetheexactlocationoftheholewasveryimportant;thepawlwouldinterlockwiththeratchetgearmosteffectivelywhenthecentersofthetwopartsare15/16apart.Alongboltwasinstalledthroughthishole,andactedastheshaftforthepawl.Becausetheboltwasslightlylong,aDelrinspacerwasmachinedonalathetouseuptheremaininglengthofthepawlshaft.Thispreventedthepawlfromslidingbackandforthalongitsshaft.Theentirepawlblockassemblywasattachedtotheframewithlongboltsputthroughthepredrilledframeholes.

TableTopThetabletopwasmadefromaluminumanglestockmeasuring5x5x3/8thick.Numerousholesweremilledinthisanglestockforvariousparts.Ontheverticalsideoftheanglestock,threeholesweredrilledandbronzesleevebearingsforthepulleyshaftswerepressedin.Twosmallerholesweredrilled,allowingthebracketforthereleaselevertobeboltedon.Another1/2holewasdrilledforreleasecableguiding.Onthebaseoftheanglestock,tenclearanceholesfor5/1618boltsweredrilled.FourofthesewereforLBracketsthatholdupthesupportplate,whoseprocessiscoveredbelow.Theothersixwereforthetabletoppegs.WhilethedesigninitiallycalledforthetabletoppegstobeTIGweldedtothetabletop,wedecidedthatboltingthepegsonwouldallowformoreprecisealignment.Thetabletoppegsweremachinedonalathefrom11/46061aluminumstock.Inoneend,aholewasdrilledandtappedfortheboltconnectingittotheanglestock.Ontheotherend,alargeamountofmaterialwasboredouttolightenthepegs.WhenwefirsttriedtofitthetabletopassemblyintotheUPF,wefoundthatthepegdiameterwasslightlytoolarge.Asaresult,weturneddowneachpegslightlytoallowforaclearancefitintotheUPF.

Figure 39. The pawl block assembly mounts two a frame member with two long bolts.

Figure 40. The table top assembly, with the pegs attached to the angle stock, is shown. The assembly fits into the holes shown in the UPF.

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SupportPlateTheoverallshapeofthesupportplatewascutonthebandsawfrom1/8thicksheetaluminum.Inthemill,holesweredrilledandbronzesleevebearingswerepressedintothem.Becausethebearingswerethickerthanthesupportplate,theprotrudingpartsofthebearingsweresandedoff.ThesupportplatewasattachedtothetabletopwiththesameLbracketsusedtoholdtheframetogether.CarriageThecarriagepartsareallmadefrom1/8thickaluminumsheet.ThecuttingofthesefourpartswasoutsourcedtoCentralCoastCreativeCuttingandwaswaterjetcut.Initially,ourteamhad

plannedtobendtheendsofthesepiecesto90degreeanglesandthenboltthefourpiecestogether.However,afterbendingsparealuminumstripsitbecameapparentthat6061aluminumwastoobrittleandwouldsnapratherthanbend.Oursolutionwastocutoffthematerialthatwouldhavebeenbent,andreplacedthemwithsmallofftheshelfLbrackets.Tousethissolution,newholeshadtobedrilledineachofthethreesupportmembers.Whiletheholesinthetopplate

weresufficient,wefoundthatthecarriagewasslightlytoolargeandwouldrubagainsttheplasticcasingontheframe.Tofixthis,thesidesofthetopplateweresandedflatinthefourplacesthatitcouldhittheplasticcasing.Thefourpieceswereboltedtogetherandsecuredwiththreadlockingglue.Linearslidebearings,boughtofftheshelf,wereinstalledintwoplacesinthecarriagetoensurethatthecarriageslidessmoothlyalongtheguiderods.

Figure 41. The carriage pieces were cut and bolted together with L-brackets

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UJoints,LeadScrews,andLeadScrewHingeTwomachinableUjointswereboughtforjoiningthepulleyshaftstotheleadscrews.A3/8diameter,5/16deepholewasdrilledinoneendofaUjointforthepulleyshafttobeinserted.Adiameter,5/16deepholewasdrilledintheotherendtoinserttheturneddownleadscrew.Theseholeswereboredoutonalathetoensuretheywerecentered

ontheUjointsaxis.Theleadscrewneededtobeturneddowntotheaforementioneddiameterononeendforalengthof5/16sothatitwouldfitintheUjointwhichwasalsodoneonalathe.ThepulleyshaftwasinsertedintotheUjointtodrilla1/16throughholeforaspringpintobeinsertedbymeansofapressfitwhichfixedthetwocomponentstogetherduringrotation.ThiswasrepeatedfortheleadscrewendoftheUjoint.Theleadscrewhingewasmadeoutofa2x1.5x0.5blockofaluminum,whichwascutouton

thehorizontalbandsawandthentheholeforthecylindrical3/812ACMEnutwasdrilledonamilltoensureitwascenteredonthefaceofthehinge.A5/16holewasdrilledthroughthebottomofthehinge,perpendiculartotheholeforthecylindricalnut,foraclevispinthatattachesthehingetotheframe.Thispinallowsthehingetopivotfreelyastheframetiltsforwardandback.A20holewasdrilledandtappedinthetopandsideofthishinge,perpendiculartotheholeforthecylindricalnut,sothatsetscrewscouldbeusedtofastentheACMEnutinsideofthehinge.One

hingewasmadeforeachleadscrew. SafetyCasingTwo1/16thick,2x3sheetsofpolycarbonatewereboughtandcutintofiveseparatepanelstomakeupoursafetycasing.Threeofthosepanelswerecuttobe13.5x24,oneofwhichhadsomeslotsmilledontoitforourreleasecable.Thispanel,whichfacestheuser,hasaseriesofslotssothatthereleasecablecanbeadjustedtodifferentheightsasthecarriageispulledback

Figure 42. U-joints attached to the pulley shafts, and the lead screws above them

Figure 43. Lead screw hinges with the ACME nut imbedded

Figure 44. Back safety casing with the release cable slots

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differentdistances.Byhavingtheslots,wewereabletokeepthereleasecablepullingdirectlyinlinewiththequickrelease,springloadedpin,thusreducingtheforcenecessarytopullthepinout.Theothertwopanelswerecuttobe13.5x12,oneofwhichwasmadetobeouraccessdoor.Usingastandardboltlatch,theaccessdoorallowsanassistanttoeasilyadjustandresetthelauncherorsafelyreleaseamisfire.Thepolycarbonatesheetshadseveral5/16holesdrilledthroughtheminordertofixthesheetstotheframeusing5/1618boltsandnuts.Thiscasingpreventsanypotentiallyharmful,fastmovingpartsfromfailingandhittinganyoneinthevicinityaswellasstoppingpeoplefromstickingtheirhandsintothedevice.ReleaseBracketOurreleasebracketwasmadefromapieceofsquare,6061aluminumbarstock.Itwasfirstcutonthecutoffsawtoalengthofapproximately1.5.Itwasthentakentoamilltofirsthavebothendsfacedtoensureallfaceswereparallelorperpendicular.Oncethepieceofaluminumwasfacedtosize,a5/16throughholewasdrilled3/8fromthelongedgeand1.25fromoneoftheshortends.Thisholewasthentappedtohave3/816threadssothatourspringloadedquickreleasepincouldbeinserted.Theringonthequickreleasepinisweldedsothatitdoesnotcomeapartwhenitispulledforlaunch.Thenadiameterthroughholewasdrilled,perpendiculartothetappedhole,3/8fromalongedgeofthebracket,and3/8fromthesameshortedgeasthetappedhole.Thisholewasfortheropetoconnectthereleasebrackettothewinchshaftspool.Aftertheholesweremade,a7/8deepslotwasmadeperpendiculartothetappedholeusingtheedgeclosesttothetappedholeastheopenendoftheslot.Thisslot,ratherthanbeingcentered,was0.22fromalongedgeofthebracket.Thisslotismeanttofitapieceofthecarriageinitandthereforemustbeatleast1/8wide,soa1/8or3/16endmillissufficientforthejob.Eithercanbeusedasonewillnotdiminishorlimitthefunctionalityofthebracketorthereleasepin.A3/16endmillwasusedforthereleasebracketcurrentlyinuse.CableandRopeAttachmentsThereleaseleverisa1longDelrincylinder,whichhasoneendmachinedflatonbothsidesonamillandaholedrilledthroughitforthepivotonthetabletop.Aholeisdrilledthrough2abovethispivotforthereleasecabletogothrough.Fromthereleaselevertothereleasebracket,thereisasteelcablewithacablestopatoneendtokeepitslippingthroughthelever,whichrunsthroughthetabletopandisloopedwithacableferruleandarubberendcaptokeepitfromfraying.Thisloopstopsjustshortofthesafetycasing,whereitconnectstoacarabineertiedtoanylonropewhichrunstotheweldedringonthereleasepin,loopedaroundthiswithaferrule.Anothernylonropesegmentloopsthroughthereleasebracketbottomholewithaferrule,extendsdowntothespoolandloopsthroughaholeinthespoolwhichwashanddrilled,andsecuredinplacewithaferruleaswell.Anextraferrulewasincludedonthereleasebracketendofthenylonropetoholditmoresecurely,asthisropeundergoessignificanttension.

Figure 45. Release bracket, freshly milled and tapped, with the pull pin installed.

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ChangesMadeDuringManufactureThroughoutthemanufacturingprocess,werealizedthatpartsofourdesignwereinsufficientforasuccessfulprototype.Asaresult,wemademanychangestothedesignofourfinalprototype.Thesechangesareshowninthedrawingpacket,foundinAppendixE.Adescriptionofallchangescanbefoundbelow.StrongerElasticWehadcalculatedearlyonthatfoursinglebandsofelastictubingwithandIDof1/8andanODof3/8wouldbesufficienttolaunchthebasketballfromthethreepointarc,butthiswasnotthecase.Wetrieddoublingtheelasticanditstillwasntenough.Atthatpoint,however,thebungeehookswerefailing;thewireclipscouldnttaketheloadwithoutslippingoutofthebungeehooks.Thisrequiredanewmethodtosecuretheelastic.Wedecidedwirecableclampscouldprovideenoughholdingforceandalsomadetheelasticmorereadilyadjustableandremovable.TogetenoughpowerwehadtostepupourelasticfromthesizementionedbeforetohaveanIDof1/8andanODof1/2.Thisprovideduswithenoughpowertomakeabasketfromthethreepointline.CarriageBendingOurcarriagewascutwithawaterjetandmadeof1/8thick6061aluminum.Ourdesignrequiredtheverticallyorientedmemberstobebent90attheends,but6061aluminumistoobrittleforthatandbreaks.WedecidedtogrinddowntheendsandusesmallLbracketstoconnectthecarriagetogether.CarriageTopPlateThetopplateofthecarriagewasoriginallysupposedtobecompletelyround,butasweputonthesafetycasing,wefoundthatthetopplateinterferedwiththepolycarbonate.Tomitigatethisproblemwegrounddowntheproblemareastoaflatedgetohavesomeclearancebetweenthecarriageandthesafetycasing.Wealsochangedthemethodusedtoconnecttheelastictubingtothecarriagewhicheliminatedtheneedforbungeehooks.Instead,wedrilledtwoholesthroughthetopplatesothatwecouldfitournew,largerelasticthroughthemanduseourwirecableclampstosecuretheelastictothecarriage.ReleaseBearingsWeplannedonpressfittingasleevebearingintothereleasebracketandtheholeinthecarriageforthereleasepininordertoreducethefrictiononthereleasepin,thusreducingtheactivationforce.However,wefoundthatthebearingsactuallyincreasedthefrictionbecausetherewasnotenoughclearancebetweenthebearingsandthepin.Weleftoutbothbearingswhichmadetheactivationforcemorereasonable.ReleasePinRingDuringinitialtestingofourdevice,wefoundthatthekeyringthatattachedthepullpintothereleasecablewasnotmeanttohandletheforcerequiredtopullthepinfromthereleasebracket.Asaresult,whenthereleasecablewasfullyloaded,thereleasepinunwound.Thismeantthereleasecablewasnolongerconnectedtothepullpinandthedevicecouldnotbe

51

shot.Tofixthissolution,weusedaMigweldertotackthetwoendsofanewringcoiltogether.Thispreventedtheringfromunfoldinginfuturelaunches.SpoolHoseClampAtfirstwewantedtouseahoseclamponthespooltosecuretheropetoit,butwefoundthattheropewasrubbingagainstthewormonthehoseclampwhichwascausingtheropetofray.Topreventtheropefromfrayingandsnapping,wedrilledanoffcenterholeinthespoolbigenoughfortheropetofitthrough.Wefedtheropethroughthisholeandthroughaloopoftheropetosecuretheropetothespool.Theloopofropewillnotcomelooseasitisclampedbyaferrule,ametalsleeveyouflattenovertheropetoholditinplace.LocationofRatchetArm/WinchShaftPartsWeoriginallyhadtheratchetarmonthesamesideasthereleaselever,buttheyinterferedwitheachother.Wehadtomovethereleaseleverfartheroutwardbecauseapersonshandwouldhavehititwhileusingthecrankhandleifitwereplacedintheoriginallocation.Flippingthewinchshaftandhavingtheratchetarmontheleftwasaneasysolutiontopreventinteractivepartsfrombeingtooconfined.HexBoltInordertocrankbackthecarriage,weintendedtouseastandard5/1624hexboltwithoursocketwrenchratchetarm.Wefoundthatthesocketwasunstableasitrestedontheheadofthebolt,sowemanufacturedourownhexboltwitha1longhead.Thisextralengthmadetheratchetarmfarmorestablewhilecrankingthecarriageback.WinchShaftHoleforRatchetFlangeInourfirstdesign,weplannedtosecuretheratchetflangetothewinchshaftbyasetscrew.Therewasinitiallynocorrespondingholeinthewinchshaft,andtherigidityoftheflangedependedontheforcebetweenthetightenedsetscrewandthewinchshaft.However,duetothehightorsionloadsontheratchetgear,andthereforeontheflange,wedecidedwewouldfeelmorecomfortablehavingthesetscrewthreadthroughthewinchshaft.PawlBlockShaftOriginally,theshaftforthepawlwasdesignedtobeashoulderscrewthatrunsthroughonesideofthepawlblock.Weencounteredtwoproblemswiththis.First,becausetheshaftwasonlysupportedbyonesideofthepawlblock,itwasinherentlyunstable.Second,theshoulderscrewweorderedwastoolargeforthepawl.InsteadoforderinganappropriatelysizedshoulderscrewfromMcMasterCarrandwaitingforittoarrive,weoptedtogotoalocalhardwarestoreandpurchasealong1/420boltwithalongunthreadedportion.Thisboltwaslongagotorunthroughbothsidesofthepawlblock,andthepawlwasabletorotatefreelyontheunthreadedportion.

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ACMECylindricalNutAssemblyInitially,weplannedtopressfitourcylindricalACMEnutsintotheleadscrewhinges.However,theholewedrilledendedupjusttoolargeforapressfit.Instead,weusedsetscrewstoholdthecylindricalnutsintotheleadscrewhinges.ClevisPinLengthForourleadscrewhingesweinitiallyhad1.75clevispinsbecausewedidntintendonputtingthepinsthroughtheentireframe,onlyonewall.Welaterdiscussedthatthepinswouldbetoounstablelikethat,sowepurchased3.5longclevispinssothattheywouldhavetwosupportpointsfromtheframeratherthanone.PulleySizesandBeltsFortheaimingmechanismweplannedonusingfourpulleys;twowith10teethinthecenter,andtwowith14teeth,oneoneitherside.However,our20.2beltwastoobigandwouldslipduringoperation,soweorderedanew19.5belt.Thisnewbeltwastoosmall,sowehadtoordertwopulleyswith12teeth.Ourfinalorientationwaswithtwo10toothpulleysinthemiddle,a12toothpulleyoneithersideofthesmallpulleysandthe19.5belt.TableTopPegsWeweregoingtoweldthetabletoppegstotheanglestock,butwewereconcernedabouthowstraightthepegswouldbeafterwelding.Insteadwedrilledandtapped5/1618holesinoneendofthepegstosecurethemtotheanglestock.Weboredouttheotherendinanattempttoreducethetotalweightoftheaimingmechanism.EyeStrapToroutethereleasecabletothereleaselever,weinitiallyplannedtouseabrasstubetoguidethecable,butsecuringthebrasstubetotheanglestockseemedproblematic.Insteadweusedaneyestopwhichwescrewedintotheanglestocktosecureitinplace.Theeyestopprovidesacurvedsurfaceforthecabletoslideoverandalsofeedsthecabledirectlytothereleaselever,preventingitfrombeingpulledtothesideatsomeangle.ReleaseLeverLengthInitially,thereleaseleverwasdesignedtobesixincheslong.Thiswasbecausewehadplannedtosecurethereleasecabletwoinchesfromtheleverspivot,anda3to1mechanicaladvantagewascalculatedassufficienttolowertherequiredforceto5pounds.However,theshortestlengthofthematerialwewantedwasonefoot.Wedecidedtousethewholelengthbecausethereseemedtobenodownsidetoimprovingtheusersmechanicaladvantage.Thislaterprovedtobeanecessarychange,becausethefrictionalforcegeneratedwhenthickerelasticwasemployedwasmuchgreaterthanbefore.UChannelSetScrewsWethoughtaboutdrillingandtappingsomeholesintheverticalfacesofthehingesthatmountontotheUPF,butthematerialisnotthickenoughtohavetheminimumthreethreadsactive.

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WedecidedtoforgousinganyfastenersonthehingesandhaveitrestingontheUPFfrontmember.CountersunkScrewsWhenshootingtheball,wefoundthattheballoftenhittheheadoftheboltthatwentthroughtheguiderodcausingittonotproperlyfire.Toreducetheprofileofthisbolt,wereplaceditwithaflatheadboltandaddedacountersinktotheinsideholesothattheboltwouldbeflushwiththeframemember.Thisallowedthebasketballtobeshotwithoutanyinterferencefromthebolt.

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DesignVerificationTherewerenumerousdesignrequirementsthatneededtobetested,somequantitativelyandothersqualitatively.AsummaryoftheresultsisfoundinTable3below.Acceptancecriteriaaredefinedbythesamemethodasourdesignspecifications:Inspection(I),Analysis(A),Test(T),andSimilaritytoExistingDesigns(S).Foralltests,theteststag