ME 8843A t ti Bik T i iAutomatic Bike Transmission

Final Presentation4/20/09

Todd Sifleet - Razid Ahmad- Brandon Borm

IntroductionGoals

Bicycle that can shift gears at the appropriate time withoutBicycle that can shift gears at the appropriate time without user interventionBicycle should retain easy to ride natureEnhance enjoyment of leisurely rides as well asEnhance enjoyment of leisurely rides as well as commuting

VisionMechanical ShiftingEffective User InterfaceSensors to capture necessary real-time datap yController to put it all together

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Gear Actuation

Design ConsiderationgHigh TorquePosition Control

RC ServosHigh TorqueSimple Position Control

ImplementationSpool DesignMountingGear Mapping and Control

P bl E tProblems EncounterPower ConsumptionMounting

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Fabrication

Water JetWater JetServo MountsEnclosuresEnclosuresPlexiglass

N D t tiNon-Destructive Mounting

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Hall-Effect Sensor

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R = Vin / Isink = 5 V / 5 mA = 1 kΩCapacitors block high and low frequency noise

Electrical FabricationPower and I/O consolidated onto a single daughter board.Made connection of sensors and motors to microcontroller easy.

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AccelerometerDesign Consideration

High accuracy, compact, low power consumption, sufficient range to sense bicycle accel/decelbicycle accel/decel.

ImplementationFreescale MMA7260QT (sparkfun.com)

With 12bit A/D, 1.52 x 10-3G per divisionT i l iTriple axisUser selectable sensitivity from 1.5 to 6GRequires RC filter on each output

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Requires RC filter on each output

Code: BackendDesign Consideration

U h d f t t i i ffi i fUse hardware features to maximize efficiency of codeUse interrupts to drive program flowUse interrupts to drive program flow

ImplementationHardware modules used: Periodic Interrupt Timer, p ,Input Capture, Modulus Down Counter, Pulse Accumulator, Analog to Digital, Pulse Width Modulation SCI (debugging)Modulation, SCI (debugging)Module interrupts were used instead of polling; main loop is empty

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Code: FrontendLCD Update: Conveys relevant information to riderrider

Current or Average SpeedTrip DistanceTrip DistanceCurrent Gear

Front GearRear Gear

ControllerControl Action Based on Selected Mode

Functions called once per second by modulus down counter

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down counter

Control UnitLCD

C t GCurrent GearFrontRear

SpeedSpeedCurrent VelocityAverage Speed

Shifting ModeShifting ModeDistance Traveled

LEDShift Al tShift AlertFront Shift CompleteShift Complete

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Switches

Control TheoryyDesign Consideration

M i t i t t d li ff t / tMaintain constant pedaling effort / rateInputs

Accelerometer Data TiltAccelerometer Data - TiltWheel Speed (Hall Effect)Pedal Speed (Hall Effect)p ( )

ImplementationForce Controller

Shift based solely on pedal speedCadence Controller

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Shift based on change of tilt and pedal speed

Control Theoryy

Button 1

Yes

Mode = Manual

Button 1Pushed?

Is Mode =AutoForce?

Tilt

Is change intilt <

0.153g ?Shift UP

Is crankspeed <

30?

Yes

Yes Yes

Crank Speed

Is Mode =Manual?

No

2x

Shift DOWNIs Change in

tilt >0.153g ?

AutoForce?

Is crankspeed >

50?

Yes Yes

Manual?

2x

Yes

Mode = Manual

Button 2Pushed?

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Problems EncounteredFabrication difficultiesPart CostsWaiting for partsg pEffectively interpreting sensor dataConfiguring timers to record dataConfiguring timers to record data appropriatelyEff ti l tili i i t tEffectively utilizing interrupts

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Future WorkImplement smarter shifting algorithms

ProgrammableProgrammableSelf learningFurther utilize accelerometer data

Add feedback for chain positionModify mechanical actuation / derailleur system.

Self LockingRemove SpringRemove SpringReduce power consumptionImprove reliability

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Implement on adult sized bike

Webpagep g

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Questions?Q

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