Final presentation v final

Group 11: Samuel Axelrod, Joshua Bary, Zachary Currier, Ermira Murati

Dartmouth Formula Racing

1

1

Background Information

Background

FSAE Student Design

Formula Hybrid

Formula Hybrid Competition
Presentation 100
Design 200
Acceleration 150
Autocross 150
Endurance 400

2007
2008
99
100
200
127
DNF
150
DNF
95
108
110

2009
91
192
124
DNF
DNF

2010
85
182
118
77
105

2011
74
185
DNF
DNF
123

2012

W

2

2

Introduction

FALL TERM FOCUS

WINTER TERM FOCUS

• Understanding the Car

• Installation, Implementation, Assembly

• Designing Systems

• Rules Compliance

• Fabricating components

• Driving, Testing, Troubleshooting


3

3

Problem Statement

The 2011 Dartmouth Formula Hybrid
racecar does not possess a reliable or
robust mechanical system that interfaces
well with the driver


4

4

Need Statement

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.


5

5

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


6

6

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


7

7

Design Overview - Constraints

Cost
The 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.

Size
The 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 Compliance
We cannot race if we break any of the Formula Hybrid rules.

Safety
As aspiring engineers, rules of ethical conduct require us to put the safety of all
individuals above any other considerations.


8

8

Design Overview - Failure Strategy

• 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


9

9

Engine/Starter - Overview

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


http://twostrokemotocross.com/wpcontent/uploads/2009/12/Keihin_PWK.jpg

10

10

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 No failures during
during spring testing
testing

No failures during
testing

Size

The starter must be small enough to
leave room for the other systems on
the car

Volume

0% increase from
2011


10% increase from
2011

11

11

Engine/Starter - Decision Matrix

Starter
Specification Weight

High
Voltage

Starter
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


12

12

Engine - Methodology, Work Accomplished

•

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


13

13

Engine - Finite Element Analysis

Factors of Safety: Front 4.5; Middle 1.1; Rear 1.9


14

14

Engine/Starter - Testing

• Testing engine on the bench mounted in the car
• Drove the car on several track days
–

Racecar started quickly both hot and cold


15

15

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


16

16

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


17

17

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 No weight
last year
increase over
last year

Reliability

The driver will be required to shift
Consistency of
numerous times per lap and must
shifting and
be able to depend on the shifter
finding neutral
working when actuated. The shifter
must be able to shift up, down and
find neutral without missing shifts

Shifts 98%,
finds neutral
50%

Shifts 99%,
finds neutral
75%

Durability

The shifter should last through
testing and competition without
failing

No failures
during testing

No failures
during testing

Number of
broken parts
during spring
testing


18

18

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


19

19

Shifter - Decision Matrix

Shifter
Specification

Weight

Cost

3.57%

Electric
Solenoid
-1

Pneumatic (existing
system)
0

Mechanical
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%

Speed

20.24%

-1
1

-1
1

1
-1

0.1547

0.2143

0.0358


20

20

Shifter - Design Overview

• Last year – open-loop pneumatic system
Compressor

Pressure
Switch

Air tank

Regulator

Paddles

VCU

Solenoids

Cylinder

Schematic of last year’s shifting system

• Adjustments:
– How long air flows into cylinder
– Pressure in tank
– Pressure at regulator


21

21

Shifter - Design Overview

• This year – closed-loop pneumatic system
Compressor

Pressure
Switch

Air tank

Regulator

Paddles

VCU

Solenoids

Cylinder

Schematic of new shifting system

• Adjustments:
– How far cylinder travels
– Pressure in tank
– Pressure at regulator


22

22

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


23

23

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


24

24

Shifter - Testing

• 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


25

25

Shifter - Specifications

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

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


26

26

Drivetrain - Overview

• 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
Last year’s rear drive configuration

27

27

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

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


28

28

Drivetrain - Decision Matrix

Drivetrain
Specification

Weight

Current System

Switch Belt to
Chain

Clutch-less
System

Parallel
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


29

29

Drivetrain - Alternatives

1. Hybrid Type – Series or Parallel
2. Belt or Chain
3. Drivetrain Component Geometry
One Chain

Two Parallel Chains

Two Chains in Series

Engine

Engine
Engine

Transmission
Electric
Motor
Differential /
Wheels

Transmission

Chain

Chain

Electric
Motor

Transmission

Differential /
Wheels


Chain

Electric
Motor
Chain
Differential /
Wheels

30

30

Chain Tensioning

Adjustable motor and differential


31

31

Drivetrain - Motor Shaft

Alternatives

• Shaft with welded sprockets
- Simple
- Machinable

• Splined Shaft
- Elegant design
- Interchangeable sprockets
- Extra expense and machining
time

Electric Motor Assembly

Motor Shaft

32

32

Drivetrain - Chain Guards

• 0.125‖ x 2½‖ Stock
• Combine to cover both chains entirely
• Mount to frame and rear engine mount


33

33

Drivetrain - FEA Analysis

Electric Motor Shaft


34

34

Weld Analysis

• 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


35

35


Bearing Mount


36

36


Motor Mount


37

37

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


38

38

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


39

39

Drivetrain - Overall Evaluation

Did we improve over previous designs?
–
–
–
–
–

Easy, lasting chain tensioning
No alignment issues
Less space used overall
No custom parts
February completion


40

40

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

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


41

41

Future Design Work

• 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


42

42

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


43

43

Thank you!
Professors Douglas Van Citters and John Collier
Douglas Fraser
Jason Downs
Christian Ortiz
Graham Keggi
Review Board Members


45

45

Questions?


46

46

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