ME 8843 At ti Bik T i iAutomatic Bike...
Transcript of ME 8843 At ti Bik T i iAutomatic Bike...
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ME 8843A t ti Bik T i iAutomatic Bike Transmission
Final Presentation4/20/09
Todd Sifleet - Razid Ahmad- Brandon Borm
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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
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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
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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
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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
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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
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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
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Webpagep g
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Questions?Q
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