P14007: Wheelchair Assit

P14007: Wheelchair Assist: Subsystem Design ReviewChe-An Lee Industrial and System EngineerDan Schuster Mechanical EngineerPhil Medalie Mechanical EngineerTom Elliot Electrical EngineerAgendaFunctional DecompositionSystem ArchitectureMovement Assist SystemCritical SubsystemsGradual GradeHill HolderCharging SystemUpdate CR and ERTest PlanRisk AssessmentProject ScheduleFunctional Decomposition

System Architecture

Movement Assist SystemConcept Validation and FeasibilityAnalysis of chosen designIntegration with Other SystemsResults and ConclusionConcept Validation and Feasibility

4 Main ConceptsFeasibility of Crank mechanismMechanical Advantage versus difficulty of integrationChosen Concept1234Comparison and Analysis of DesignsEvaluation of straight line crank mechanismShowed that the device can provide a mechanical advantage due to crank arm Main concerns and issues are due to actual construction binding and sticking in joints of links and moving the crank around two end points of arcRisk of trying to construct this crank versus the benefit resulted in going with regular crank armGear SetsLarge mechanical advantageRisks in cost and disengagementCouldnt find standard made planetary gear sets with the required footprint too thick/large

Regular Crank directly coupled to shaft provides lowest risk and best design due to ease of integration and has the benefits of a good mechanical advantageAnalysis of Chosen DesignFBD of Model and EOMMinimum Torque Required to move system uphillKey AssumptionsRolling without slipFrictionless bearingsLumped MassesTorque input from user is constant through Required Torque to turn generator is lumped into 1 term, Tmotor, and is constantStarts from Rest

Results With 1.5m Crank

Results with Hand on Wheel Rim

Conclusion of Movement AssistCrank Design is feasible by itself and should be able to be achievedDifficulty is in the user activation/disengagement and integration with other systemsFreewheelShaft attachmentIntegration with braking and ratchetBased on CR (component of lowest priority) we are putting this system on hold to focus on more critical systems = Hill Holder, Gradual Grade, and Energy RecoveryEntire System

Gradual Grade

Braking SystemAvid BB7 Disc BrakesControlled by bicycle brake handles160mm discsOffers more control and less wear than rim brakesEasily adjustable braking forceWear items easily and inexpensively replacedNormal state is disengaged

Braking System MountsMounting discThreaded onto end of shaftUsed as lock nut to allow shaft to spin with disc

Caliper MountBent sheet metalLocated with hole in frameCaliper attached via bolts through spacers

Hill Holder

Ratchet SystemW.M. Berg Ratchet and PawlR16S20-644 PD, 64 TeethCan handle ~600 lbfRoll back distance of ~1 inch

Pawl SystemSheet metal armLocating slot for vertical motionSpring pin at topUsed for engaging locking feature and for handlePawl is press fit onto end of armSystem weight will provide force to lock pawl in place

Shaft Design

Axle to Wheel AttachmentSpline exists in wheelNot a standard spline sizeMay end up cutting keyway into wheel

Moving Axle BackwardsMay need to move axle backwardsProvides more room for brakesLarger bearings can be usedShould not impact ergonomicsSimilar bracket already exists on chair

Advantages to DesignVery little modification to frame neededShould work for many chairsEasily removed to return to regular chairUses purchased parts where possibleShaft and pawl mount need to be madeWear items easily replacedStill folds up to small sizeHarnessing Power Electrical StagesGeneratorsRectifiersLog AmplifiersVoltage RegulatorsBattery InputsVoltage DividerSelecting a Motor for Generator* Two Motors are needed at to avg a electrical rate of .5-1 Amp at 5V Constantly. * Therefore 1.25-2.5 Watts needed on each motor when is spinning at 1.2mph(avg Wheelchair speed).* Torque to move the wheelchair be increased to a point where an elderly person cannot move the chair.Selected MotorSimple Full RectifierDifferent Kinds of Lin-Log AmplifierUp The Hill

Down The Hill

Battery2 Venom 2000mAh 7.4V 2S 1P 20C 1/16 LiPo Pack

Battery Type: Lithium Polymer (LiPO)Configuration: 2S1PWeight: 3.88 oz.Dimensions: 18 x 34 x 90mmCharge Rate: 1C (40A)Continuous Discharge: 20C (40A)Min Discharge Volts Per Pack: 5.5VMax Burst Rate: 30C (60A)Max Volts Per Cell: 4.2VMax Volts Per Pack: 8.4VWatt Hours: 14.8BatteryUpdated Customer Requirement

Updated Engineering Requirementsrqmt. #ImportanceSourceFunctionEngr. Requirement (metric)Unit of MeasureMarginal ValueTarget ValueIdeal ValueComments/StatusS193C13System OperationCurrent output to battery at 5V when moving 1 mphAmps0.1250.251S203C13System OperationCurrent output to battery at 5V when moving 4 mphAmps0.514S213C5System PortabilityRatchet System Weightlbf151210.5S223C5System PortabilityBrake System Weightlbf1087S233C5System PortabilityCharging System Weightlbf252017.5S249C7System OperationRachet System Cost$30015060Production level costsS259C7System OperationBrake System Cost$20010040Production level costsS269C7System OperationCharging System Cost$500250100Production level costsS279C1System OperationHill Holder Roll back distancein210.5S283C4System OperationWear Item Replacement Timeminutes30155S293C2System OperationUser Input Braking Forcelbf20105Test Planrqmt. #Engr. Requirement (metric)Test Procedure# of Tests RequiredEquipment RequiredTest CommentsS19Current output to battery at 5V when moving 1 mphTested by moving the chair at 1mph and mesuring the current going into battery.5MultimeterS20Current output to battery at 5V when moving 4 mphTested by moving the chair at 4 mph and mesuring the current going into battery.5MultimeterS21Ratchet System WeightWeigh all system components1ScaleS22Brake System WeightWeigh all system components1ScaleS23Charging System WeightWeigh all system components1ScaleS27Hill Holder Roll back distanceMark spot on wheel, match with so on ground. Measure distance between stops on ratchet5Tape MeasureS28Wear Item Replacement TimeTime study5NoneS29User Input Braking ForceUse force scale to determine force needed to full engage brakes5Fish hook scale or similarRisk Assessment

Project Schedule

Questions/ Comments?Holding Force Calculation

S = 60200 psiF = 0.375 inY = 0.426 for 64 teethDP = 16V Disregard for low speeds

W = 601 lbf of allowable tooth loadRoll Back Distance Calculation64 Teeth22 wheel diameter69 circumference69/64 Teeth = 1.08Sheet1Project: P14007Revision #:rqmt. #ImportanceCustomer RequirementComments/StatusC19"Hill Holder"C29De-acceleration downhillC31Movement assist up hillC43Detachable designC53Low weightC63CollapsibleC79Low costC89Medically approved for useC93Small turning radiusC103Size, overallC113Large user weight rangeC123Disengagable devicesC133Ability to provide electricity for user to charge personal electronics

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