Hardware Design Considerations for an Electric Bicycle ...

1 ApplicationReportSLVA642 June2014 HardwareDesignConsiderationsfor an ElectricBicycleUsinga BLDCM otorSrivatsaRaghunathABSTRACTA traditionalbicycleis a two-wheelvehiclethat is propelledby the riderwhodeliversmusclepowerthroughpedals that rotateone of the two ridersteersthe frontwheelto createa forcethatreturnsand maintainsthe vehiclecenterof gravityinto a stablezonewhenevernecessary,thuskeepingt he electricbicyclecarriesbatteriesthat deliverelectricpowerto a motorthat iscoupledto mostelectricbicyclesthe ridercan choseto use musclepowerto deliverall,part,or noneof the propulsionpowerrequiredto maintainan commandthe motorto delivermorepowerwheneverthe ElectricalCharacteristicsof of Figures1 Rangeof June2014 HardwareDesignConsiderationsfor an ElectricBicycleUsinga BLDCM otorSubmitDocumentationFeedbackCopyright 2014, of Tables1 Rangeof an ElectricBicycleUsinga BLDCM otorSLVA642 June2014 SubmitDocumentationFeedbackCopyright 2014, controllerfor an electricbicyclemustdeliverpowerthat variesfromzeroto the ratedpeakof thepropulsion-motor,at motorspeedscorrespondingto bicyclespeedsfromzeroto 48 km per hour(30 mph).

2 WithDC propulsionmotors,powercan be controlledwith pulse-widthmodulated(PWM) designof an Electric -bicyclecontrolarepostulatedand basicblocksalongwith theirusageare electricbicyclehas a conventionalbicycleframe,pedals,cranks,c hain,and addsto the bicyclean electricmotor,gearreducer,battery,and followingdefinesthe requirementsof an electricbicycle: The completebicyclemusthavethe massmustbe hauledoverhills withenergysuppliedby the the battery. Bicyclestabilityis affectstability,but theplacementof massis lists the rangeof massthat is consideredto be Rangeof MassCOMPONENTMASSIN KGBicycleassembly10 Motorand gear6 Powercontrol1 Battery6 Cyclist80 Totalweight106 Figure1 showsthe requiredpowerto developthe necessarywheeltorquefor the indicatedtravelconditions:Fwf= windageand frictiondragFd= downhillforcefromgravityFP= propulsionforce= Fwf+ FdVb= bicyclespeed= 20 km/hrFd= m sinx= 106 kg = 63 NPd= F Vb= 63 = 350 WHeadwindspeed= 25 km/hr,adds30-Wpowerto propelFigure1.

3 Rangeof MassHencethe powerrequiredby the motorto propelthe bicycleand rideris 380 June2014 HardwareDesignConsiderationsfor an ElectricBicycleUsinga BLDCM otorSubmitDocumentationFeedbackCopyright 2014, lists the comparisonsof the differentDC DC MotorsTYPEADVANTAGESDISADVANTAGESTYPICAL APPLICATIONT ypicalDrivePrecisionpositioningSlowspeed RequiresaPositioningin printersand floppyStepperDCMultiphaseDCStepperDC HighholdingtorquecontrollerdrivesLonglif espanBrushlessDCHighinitialcost RequiresHarddrivesCD/DVDplayersElectricL ow maintenanceMultiphaseDCelectricmotora controllervehiclesHighefficiencyHighmain tenanceBrushedDCLow initialcostTreadmillexercisersAutomotive (brushes)LimitedDirect(PWM)electricmotor SimplespeedcontrolstartersToyslifespanBa sedon Table2, a BLDC motorcan be selectedfor its (BLDC)

4 Motoris a type of synchronousmotor,wheremagneticfieldsgene ratedby bothstatorand rotatehavethe BLDC motorhas a longerlife becausenobrushesare ,it has a high startingtorque,high no-loadspeedand BLDC motorcan be configuredin 1-phase,2-phase,and mostpopularamongall the configurationsand are widelyusedin structureof a BLDC motoris dividedinto two parts: Movingpart calledthe rotor,representedby permanentmagnet Fixedpart calledthe stator,representedby phasewindingsof magneticcircuit3 StatorThe statorof a BLDC motorconsistsof stackedsteellaminationswith windingsplacedin the slotsthat areaxiallycut alongthe ,the statorresemblesan inductionmotor;however,thewindingsare distributedin a constructedwith numerouscoilsthat are interconnectedto forma or morecoilsare placedin the slotsand they are interconnectedto makea statorperipheryto forman evennumberof rotoris madeof permanentmagnetand can vary fromtwo to eightpole pairswith alternateNorth(N)and South(S) polesFigure2.

5 BLDCM otorMechanicalStructure4 HardwareDesignConsiderationsfor an ElectricBicycleUsinga BLDCM otorSLVA642 June2014 SubmitDocumentationFeedbackCopyright 2014, brushedDC motor,BLDC motorcan be rotatethe BLDC motor,thestatorwindingsmustenergizedin a rotorpositionmustbe knownin ordertounderstandwhichwindingwill be rotorpositionis sensedusingHall Effectsensorsthat are embeddedin the sensorsembeddedin the statoron the non drivingend of the rotormagneticpolespassnearthe Hall sensors,they generatea high or low signal,whichindicatesthat N or S pole is passingnearthe the combinationof theseHall Sensorsignals,the exactsequenceof commutationcan be the increasingpopularityof ebikes,motorsdesignedspecificallyfor ebikeapplicationsare a greatdeal in how they are mountedto a bicycleand in howthe poweris appliedto themThe followingpowertrainand motortypeshavemultipleexamplesin the markettoday.

6 Belt-drivetransmission a speciallydesignedmotoris mountedlow in the frame,and drivesthe rearwheelby use of a beltDirectdrive(in-linechain-drive) this methodhas the motorworkingwith the primarybicyclechain the samechainthat the the motorvarieswith anothercommonmethodis to mounta motortothe bicycleframenearthe hub of the rear wheel,oftenon one motorhas its own smallchainthat drivesa planetarygearon the rear specializedchainis separatefromtheprimarybicyclechainthat remainsin use with the themanufactureror this is apancakeordish platemotor,sometimesevencalledaFrisbeemo tor, installedon one or be placedon bothwheels,effectivelydoublingthe poweravailableto the ,thesemotorsincreaseweightand centrifugalforceon ideally.

7 The termhub motorrefersto a motorthat replacesthe hub of a can be a flat disk motor,othertimesit is not a disk eithercase,the motoris thehub insteadof beingmountedbesideit or this type of electricdriveinstallsthe motorvery closeto one shaftextendsfromthe motor,and this rotatingshaftdrivesthe wheelby spinningin directcontactwith motordoesnot interactwith the the motorare this type of electricdriveis like a havea motorand the pedalsapplypowerto a sealedand protectedshaftthat has bevelgearsin frontand (speeds)are summarizesof the June2014 HardwareDesignConsiderationsfor an ElectricBicycleUsinga BLDCM otorSubmitDocumentationFeedbackCopyright 2014, Typesof DriveTrainPOWERTRAINTYPEADVANTAGESDISADV ANTAGES Allowsfor a greatdeal of customizationinMightreducethe performanceof pedalingwhenBelt-drivetransmissiondesign motoris not used Silentoperation No additionalchainneeded Perceived(standard)draguponthe chain Monocoqueframescan hide the motorDirectdrive(conventionalin-with greatprotection Chainremainsvisible,perhapsvulnerabletol ine chain)dirt The motormightinheritas manygearsasare availableto the rider.

8 Potentialfor noise Low centerof gravity A secondchainand planetarygeararerequired A dedicatedchaincan attaingoodpowerFrame-mountedmotorwithtra nsferwithoutcomplications Multiplegearsfor the motormay or may notdedicatedchainbe available. A dedicatedchaincan attaingoodpowertransferwithoutcomplicati ons Multiplegearsfor the motormay or may notbe available. The mostefficientapproachso far Placesa greatdeal of weightin the wheels,Wheel-mounteddisk motorwith potentialhandlingissuesat higherspeed. No planetarygearsor spinningshaftsare(pancakemotor)neededfor power Multiplegearsfor the motormay or may notbe present. Retainsgoodprotectionfromelements Addsweightto the wheel No interactionwith the primarybicycle Torquefactorscan enteroperationalHub-motor(non-disk)chain requiredconsiderations.

9 No additionaltransmissionrequired Un-sprungweightor mass Inefficient no gearing Inexpensive Frictionwearsout tires. Easyto mount Pressureagainstthe shaftmightstrainmotorFriction-basedshaft drivefunctionsovertime. By far the mostmechanicallysimpleconcept Motormustsustainvery high RPMsat and reinstallingthe wheelmay Multiplegearsare commonshaftdrivebecomemoredemandingthanw ith othermethods Multiplegearsare commonBasedon the informationlistedin Table3, a 500-Wrear hub motoris selectedwith the followingperformancedetails: Model:HBS36R RearHub MotorVoltage:36 V (brushless) PowerRate:500 W Weight:5 Kgs6 HardwareDesignConsiderationsfor an ElectricBicycleUsinga BLDCM otorSLVA642 June2014 SubmitDocumentationFeedbackCopyright 2014, (V)I (A)P1 (W)M (Nm)n (RPM)P2 (W)EFFICIENCY(%)No June2014 HardwareDesignConsiderationsfor an ElectricBicycleUsinga BLDCM otorSubmitDocumentationFeedbackCopyright 2014, (V)I (A)P1 (W)M (Nm)n (RPM)P2 (W)EFFICIENCY(%) an ElectricBicycleUsinga BLDCM otorSLVA642 June2014 SubmitDocumentationFeedbackCopyright 2014, the followingequationsto calculatethe rangefromamperageand voltage.

10 Ah (Amphours) V (volts)= Wh (Watthours)(1)Selecta 48-V,10-AHbatterywith 480 (power)= Work/ t (time)(2)P t = Work= Force distance(3)Force= mass acceleration(4)Distance= Wh / Force(5)Distance= Wh / Force(6)Electricbicyclesare oftenrestrictedto a speedof 30 largerwattageincreasesthe rangeand can increasethe uphilltorque,however,a largerwattagedoesnot typicallyincreasethemaximumspeedwhichis previouslylistedequations,a 480-Whbatterycan roughlyprovidea rangeof total 55 lists a comparisonof the AvailableBatteryTypesPOWERTRAINADVANTAGE SDISADVANTAGESTYPE Inexpensiveand simpleto manufacture Mature,reliableand well-knowntechnology Not to be storedin a dischargedcondition Low self-discharge the self-dischargerate is Low energydensity poorweight-toenergyamongthe lowestin (sealed)densityCapableof high dischargerates.