Post on 26-Jun-2015
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1Dartmouth Formula Racing 1
Dartmouth Formula RacingDrivetrain and Driver InterfaceGroup 11: Samuel Axelrod, Joshua Bary, Zachary Currier, Ermira Murati
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Background Information
FSAE Student Design
Formula Hybrid
Background
Formula Hybrid CompetitionPresentation 100
Design 200Acceleration 150
Autocross 150Endurance 400
201174
185DNFDNF123
2012 Goal
WIN
201085
18211877
105
200991
192124DNFDNF
200810012715095
110
200799
200DNFDNF108
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Introduction
FALL TERM FOCUS
• Understanding the Car
• Designing Systems
• Fabricating components
WINTER TERM FOCUS
• Installation, Implementation, Assembly
• Rules Compliance
• Driving, Testing, Troubleshooting
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The 2011 Dartmouth Formula Hybrid racecar does not possess a reliable or
robust mechanical system that interfaces well with the driver
Problem Statement
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DFR needs to win the 2012 Formula Hybrid Competition.
Our group needs to design a functional drivetrain and integrate all mechanical systems by January to allow for optimization, so that the team can complete all events at competition.
Need Statement
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Deliverables
Primary Deliverables:
1. Implement a mechanism to start the racecar every time
2. Design a system that can shift consistently
3. Redesign the drivetrain to eliminate complexity and allow for improved alignment
4. Work with the Electrical Powerplant and Data Management groups to install and test their systems on the racecar
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Design Overview - Design Objectives
Simplicity — Time is our scarcest resource
Reliability — Failure rate must be very near zero
Durability — We plan for extensive testing and driving
Modularity — They will thank us next year
Transparency — Feedback critical for testing
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CostThe DFR budget is not unlimited, and our combined activities and purchases (including other 89/90 groups and DFR team projects) cannot exceed the collected funds of $8,000.
SizeThe overall size of the frame has been finalized, so every component must be designed to a specific size that will fit well in the assembly.
Rules ComplianceWe cannot race if we break any of the Formula Hybrid rules.
SafetyAs aspiring engineers, rules of ethical conduct require us to put the safety of all individuals above any other considerations.
Design Overview - Constraints
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• True dynamic loads are hard to predict
• All power is transmitted through the chain
• First part to fail should be the easiest to replace
• Design components so the chain is first to fail
Design Overview - Failure Strategy
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Previous design and reasons:‒ Fuel-injected internal combustion engine‒ Easy engine mapping and tune-ability ‒ No cutting out through corners‒ Problem: depended on high-voltage to start
Needed to design a mechanism to start the engine:‒Honda CRF250X with built-in electric starter‒Start with high voltage system‒External starter motor on the CRF 250R‒Mechanical linkage
Engine/Starter - Overview
http://twostrokemotocross.com/wp-content/uploads/2009/12/Keihin_PWK.jpg
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Engine/Starter - Specifications
Specification Justification Quantification Baseline Target
Cost DFR has a limited budget and numerous systems that must be improved
Price ($) <$1000 <$500
Weight A lighter car will perform better, all else equal
Pounds 10% increase from 2011
0% increase from 2011
Reliability The car must start every time, immediately. We cannot race if our car does not start.
Number of times engine starts out of 20
Starts 75% of the time
Starts 95% of the time
Durability Our starter mechanism must be durable enough to handle testing and competition. We do not want to worry whether our starter could fail
Number of broken parts during spring testing
No failures during testing
No failures during testing
Size The starter must be small enough to leave room for the other systems on the car
Volume 10% increase from 2011
0% increase from 2011
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Engine/Starter - Decision Matrix
Starter
Specification WeightHigh
VoltageStarter Motor
Internal Starter
Mechanical Linkage
Cost 0.00% 1 0 1 0
Weight 15.00% 1 0 1 0
Reliability 37.50% -1 1 1 0
Durability 25.00% -1 1 1 1
Size 22.50% 1 -1 1 0
-0.25 0.4 1 0.25
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• Design mounts and mount the engine
• Alter wiring harness to match the 2005 CRF250X
• Make and run new cooling hoses
• Design and fabricate new angled air filter
Engine - Methodology, Work Accomplished
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Engine - Finite Element Analysis
Factors of Safety: Front 4.5; Middle 1.1; Rear 1.9
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• Testing engine on the bench mounted in the car
• Drove the car on several track days
– Racecar started quickly both hot and cold
Engine/Starter - Testing
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Engine/Starter - Specifications
Specification Quantification Baseline Target Actual
Cost Price ($) <$1000 <$500 ~$300
Weight Pounds 10% increase from 2011
0% increase from 2011
<5% increase
Reliability Number of times engine starts out of 20
Starts 75% of the time
Starts 95% of the time
Starts >95% of the time
Durability Number of broken parts during spring testing
No failures during testing
No failures during testing
No failures during testing
Size Volume 10% increase from 2011
0% increase from 2011
0% increase
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Shifter Overview
• 2011 team designed a pneumatic paddle-shifting system
• Clutch-less upshifts and downshifts using spark cut
• Tested only on the dynamometer
• Mounted on the car with universal joints, in a different location than designed
• Shifted inconsistently
• Could not find neutral
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Shifter - Specifications
Specification Justification Quantification Baseline Target
Cost DFR has a limited budget and numerous systems that must be improved
Price ($) < $1000 <$500
Weight A lighter car will perform better, all else equal
Pounds 5lbs more than last year
No weight increase over last year
Reliability The driver will be required to shift numerous times per lap and must be able to depend on the shifter working when actuated. The shifter must be able to shift up, down and find neutral without missing shifts
Consistency of shifting and finding neutral
Shifts 98%, finds neutral 50%
Shifts 99%, finds neutral 75%
Durability The shifter should last through testing and competition without failing
Number of broken parts during spring testing
No failures during testing
No failures during testing
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Shifter - Specifications (Continued)
Specification Justification Quantification Baseline Target
Size The car has limited space. A new shifting system should not take up more space that the current pneumatic system
Volume Same size as last year
10% smaller than last year
Power Requirement
The shifter may require power to function. If so, it must be a low enough requirement so that the power does not run out during the endurance race
Power draw (W) 36W (last year’s system)
No increase in power draw
Speed The system must quickly execute shifts to improve acceleration and decrease lap times
Time per shift 0.2 seconds 0.1 seconds
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Shifter - Decision Matrix
Shifter
Specification WeightElectric
SolenoidPneumatic (existing
system) Mechanical
Cost 3.57% -1 0 0
Weight 4.76% 1 0 0
Reliability 26.19% 0 0 0
Durability 17.86% 0 1 1
Size 10.71% 1 0 -1
Power Requirement 16.67% -1 -1 1
Speed 20.24% 1 1 -1
0.1547 0.2143 0.0358
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Shifter - Design Overview
• Last year – open-loop pneumatic system
• Adjustments:– How long air flows into cylinder– Pressure in tank– Pressure at regulator
Schematic of last year’s shifting system
CompressorPressure Switch
Air tank
Paddles Solenoids Cylinder
Regulator
VCU
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Shifter - Design Overview
• This year – closed-loop pneumatic system
• Adjustments:– How far cylinder travels– Pressure in tank– Pressure at regulator
Schematic of new shifting system
CompressorPressure Switch
Air tank
Paddles Solenoids Cylinder
Regulator
VCU
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Shifter - Methodology, Work Accomplished
• Cylinder Sizing– Measured force and distance required to shift– Purchased Bimba Position-Feedback cylinder
• Power consumption– Air compressor draws 20A at 12V so 240W if
running continuously– Rated for 15% duty cycle – 36W on average– 14Ah battery – will last at least 0.7 hours (longer
than endurance race)
• Mounting– Solid mount to secure the cylinder position– Eliminates lateral motion
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Shifter - Methodology, Work Accomplished
• Shifter control– Moved from Arduino to Vehicle Control Unit (VCU)– VCU already weatherproofed– Eliminated the problem of wires falling out
• Spark cut– Program to cut engine spark for time of cylinder travel– Removes all load on transmission to ensure
consistent shifting– VCU triggers a relay to ground the kill input on the
ignition control module– Will trigger as soon as a paddle is pressed
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• Bench test– Ran through the gears in sets of 20– Listened for shift and monitored
wheel speed
• Track day tests– Shifting without spark cut – Shifting with spark cut
• Neutral– Found neutral on bench at least
50% of the time
Shifter - Testing
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Specification Quantification Baseline Target Actual
Cost Price ($) < $1000 <$500 $350
Weight Pounds 5lbs more than last year
No weight increase over last year
No increase
Reliability Consistency of shifting and finding neutral
Shifts 98%, finds neutral 50%
Shifts 99%, finds neutral 75%
100% bench, >95% outside
Durability Number of broken parts during spring testing
No failures during testing
No failures during testing
No failures
Size Volume Same size as last year
10% smaller than last year
Same as last year
Power Requirement
Power draw (W) 36W (last year’s system)
No increase in power draw
Same as last year
Speed Time per shift 0.2 seconds 0.1 seconds 0.1 – 0.4 secs
Shifter - Specifications
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Drivetrain - Overview
Last year’s rear drive configuration
• Last year’s configuration was designed to allow the electric motor to start the internal combustion engine
• Incorporated a “launch clutch” to disengage the electric motor and engine from the wheels
• Chain between engine and motor and belt from motor to differential
• Misaligned and difficult to adjust
Clutch
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Drivetrain - Specifications
Specification Justification Quantification Baseline Target
Cost DFR has a limited budget and numerous systems that must be improved
Price ($) <$1000 <$500
Weight A lighter car will perform better, all else equal
Pounds No increase in weight
10% decrease over 2011
Reliability Must be able to operate consistently. The system should not lose alignment or constantly require adjustment
Service time required between track days (hours)
<2 hours <1 hour
Durability Must be able to operate through testing and competition without failure
Number of broken parts during spring testing
No failures during testing
No failures during testing
Size Must leave room for other components that will be installed on the car
Volume No increase in size
10% decrease over 2011
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Drivetrain - Decision Matrix
Drivetrain
Specification Weight Current SystemSwitch Belt to
ChainClutch-less
SystemParallel Chains
Cost 0.0% 1 0 0 -1
Weight 8.3% -1 -1 1 0
Reliability 21.4% -1 0 0 0
Durability 13.1% -1 0 0 0
Size 11.7% -1 -1 1 0
-1 -0.35 0.35 0
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Drivetrain - Alternatives
1. Hybrid Type – Series or Parallel2. Belt or Chain3. Drivetrain Component Geometry
Engine
Electric Motor
Transmission
Differential / Wheels
Chain
Engine
Electric Motor
Transmission
Differential / Wheels
Chain
Chain
Engine
Electric Motor
Transmission
Differential / Wheels
Chain
One Chain Two Parallel Chains Two Chains in Series
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Chain Tensioning
Adjustable motor and differential
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Drivetrain - Motor Shaft
Electric Motor Assembly Motor Shaft
• Splined Shaft - Elegant design- Interchangeable sprockets- Extra expense and machining
time
• Shaft with welded sprockets- Simple- Machinable
Alternatives
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Drivetrain - Chain Guards
• 0.125” x 2½” Stock• Combine to cover both chains entirely• Mount to frame and rear engine mount
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Drivetrain - FEA Analysis
Electric Motor Shaft
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• Analyzed the welds between the motor shaft and the sprockets
• Static Analysis– Factor of Safety = 1
• Fatigue Analysis– Welds fail due to large bending stresses created by the maximum tension
force of the chain of 7000lbf
– Calculations demonstrate that no possible weld size, weld material, or shaft material will fix this problem
• Future Plan– Conduct a three-point bending stress test to determine at what bending
stress the weld will fail
– Investigate the problem further and fabricate two to three motor shafts with welded sprockets as reserves
Weld Analysis
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Bearing Mount
Drivetrain - FEA Analysis
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Motor Mount
Drivetrain - FEA Analysis
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Drivetrain - Differential
• Taylor Race Engineering - 4:1 Automatic Torque Biasing (ATB) Differential
• One wheel can have up to 4X the torque of the other wheel
• Output Range of 220 hp
• 17 lbs including the differential housing and oil
Current Differential
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Drivetrain - Specifications Evaluation
Specification Quantification Baseline Target Actual
Cost Price ($) <$1000 <$500 $478.32
Weight Pounds No increase in weight 10% decrease over 2011
No increase in weight
Reliability Service time required between track days (hours)
<2 hours <1 hour <15 min
Durability Number of broken parts during spring testing
No failures during testing
No failures during testing
No failures during testing
Size Volume No increase in size 10% decrease over 2011
No increase in size
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Did we improve over previous designs?
– Easy, lasting chain tensioning– No alignment issues– Less space used overall– No custom parts– February completion
Drivetrain - Overall Evaluation
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Subassemblies Price Manufactured Price
Shift Mechanism
$865.50 $479.02
Engine $5,381.15 $2,926.37
Drivetrain $3,427.32 $2,085.32
Total $9,673.97 $5,490.71
Economic Analysis – Market Analysis
• Target Market : Amateur weekend racecar drivers
• SCCA has over 55,000 members that compete in over 2000 events every year
• NASA has more than 10,000 members in 15 chapters nationwide
• Secondary Market: Hybrid industry, FSAE and Formula Hybrid teams, motorcycle and dirt bike enthusiasts
• Followed FSAE rules to price components for 1,000 unit per year production
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• Final Drive Ratio– Will choose a final drive ratio after more driving, with a better understanding
of traction and engine performance
• Pedal Package
• Gas Tank– Design will be guided by simplicity, the need to place it above the engine,
and need to install in it a level sensor
• Steering Wheel
• Engine Tuning and Efficiency Testing– Carburetor re-jetting and fuel efficiency testing
• Manuals and Competition Presentations
Future Design Work
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Deliverables
1. Installed the CRF250X with an electric starter so that our racecar starts every time
2. Improved the pneumatic system so that we can shift consistently
3. Redesigned the drivetrain to eliminate complexity and allow for improved alignment
4. Worked with the Electrical Powerplant and Data Management groups to install and test their systems on the racecar
Moving Picture
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- Professors Douglas Van Citters and John Collier- Douglas Fraser- Jason Downs- Christian Ortiz- Graham Keggi- Review Board Members
Thank you!
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Questions?