Downhill Mountain Bike Gearbox Josh Filgate, Jesse Kuhn, Morgan Misek Jay Seiter, Michael Witonis Jay Seiter, Michael Witonis

Downhill Mountain Bike Gearbox

Josh Filgate, Jesse Kuhn, Morgan MisekJosh Filgate, Jesse Kuhn, Morgan Misek

Jay Seiter, Michael WitonisJay Seiter, Michael Witonis

December 4th, 2007Design Team: Joshua Filgate, Jesse Kuhn,

Morgan Misek, Jay Seiter, Michael Witonis

Problem Statement

Problem Statement:

When subjected to the abusive environment of downhill mountain biking, current drive train designs perform unreliably, require constant maintenance, and are easily damaged by a wide variety of external factors.



Proposed SolutionProposed Solution: To remedy these problems, it is our intention to design and construct an internal gearbox transmission.



Design Goals The final design will take into account: The final design will take into account:

1.1. Max rider input of 115 N-m at 90 RPMsMax rider input of 115 N-m at 90 RPMs2.2. Existing gear ratios of current drive trains (2.1-3.3)Existing gear ratios of current drive trains (2.1-3.3)3.3. High impacts resulting from crashing High impacts resulting from crashing 4.4. G-CON 2.0 mounting standardsG-CON 2.0 mounting standards5.5. Sealing against mud, snow, and dustSealing against mud, snow, and dust6.6. Industry standard shifters, cranks, and bottom bracketsIndustry standard shifters, cranks, and bottom brackets7.7. Targeting racers accustomed to spending between $4000 Targeting racers accustomed to spending between $4000

and $7000 for a complete bikeand $7000 for a complete bike



Gearbox vs. Current Drive System

Ingress Protection Separate sensitive surfaces from exposure to

elements Contain lubrication within a controlled

environment

Impact Protection Encloses potentially fragile components within

a protective case

UPDATE ME

Low Maintenance Less frequent lubrication and tuning required Less repairs due to impacts

Improved Center of Gravity Mass of shifting mechanisms (chain guide, derailleur,

and cassette) moved to a lower and more central point in the frame

Improved handling

Gearboxes offer:



What is Downhill Mountain Biking?

High Speeds:High Speeds: Up to 50+ mph

Natural Obstacles:Natural Obstacles: rock gardens boulders roots steep terrain

Stunts:Stunts: drop-offs over 10 vertical ft gap jumps of over 35 feet

Downhill Races Involve:Downhill Races Involve:



Downhill Mountain Biking



HIGH SPEEDS

ROOTS & VEGETATION

TRAIL DEBRIS

LARGE OBSTACLES

Downhill Mountain Biking



Examples of Harsh Environments



Current Drive Train is Fragile

EXPOSED DRIVE TRAIN COMPONENT FAILURE

IRREPAIRABLE FRAME AND COMPONENT DAMAGE



State of the Industry: Market Research

Online Study: “How many Derailleurs did you Online Study: “How many Derailleurs did you break in 2007?”break in 2007?” 192 responses via forums on www.bustedspoke.com and

www.ridemonkey.com 47% of riders broke at least one derailleur in 2007 2 Pro riders broke more than 10 derailleurs



State of the Industry: Early Prototypes

First internal tranmission mountain bike prototypes introduced in First internal tranmission mountain bike prototypes introduced in the late 1990sthe late 1990s

First bikes used existing technologies modified into centralized First bikes used existing technologies modified into centralized locationslocations

Derailleur-in-a-box Multi-speed hubs



State of the Industry: Future Growth

Creation of G-CON 2.0 standardCreation of G-CON 2.0 standard Growing number of frame manufacturers Growing number of frame manufacturers

designing gearbox compatible framesdesigning gearbox compatible frames Interfacing between gearboxes and Interfacing between gearboxes and

frames becoming more standardizedframes becoming more standardized

Frame weldmentCrank Input

Bolt pattern

Three current prototype designs that conform to the G-CON standards

G-CON 2.0 Gearbox Interface



Design Process

Phase 1: Shifting MechanismPhase 1: Shifting MechanismPhase 2: Gear AssemblyPhase 2: Gear AssemblyPhase 3: Case and InterfacingPhase 3: Case and Interfacing

Step 1: Geometric Driven ModelingStep 1: Geometric Driven Modeling

Step 2: Calculations performed on Step 2: Calculations performed on simplified geometriessimplified geometries

Step 3: Detailed ModelingStep 3: Detailed Modeling

Step 4: FEA with COSMOSWorksStep 4: FEA with COSMOSWorks

Brainstorming and Initial Concept Modeling

Design Criteria Decision Matrix

Detailed System DesignProof of Concept Prototype

Concept Chosen for Design

Iterative Analytical Design



Decision Matrix

Conventional Conventional

SequentialSequential PlanetaryPlanetaryPlanetary Planetary

BarrelBarrelSequential Sequential SprocketsSprockets

Derailleur in a Derailleur in a boxbox

CriteriaCriteriaCriteria Criteria FactorFactor RatingRating ScoreScore RatingRating ScoreScore RatingRating ScoreScore RatingRating ScoreScore RatingRating ScoreScore

WeightWeight 55 22 1010 33 1515 44 2020 44 2020 44 2020

PackagingPackaging 55 44 2020 33 1515 55 2525 33 1515 22 1010

DurabilityDurability 55 55 2525 44 2020 55 2525 33 1515 22 1010

EfficiencyEfficiency 33 33 99 33 99 33 99 55 1515 55 1515

InterfacingInterfacing 44 22 88 44 1616 33 1212 33 1212 55 2020

Shifting feelShifting feel 44 55 2020 33 1212 33 1212 44 1616 22 88

Total Total Score:Score: 9292 8787 103103 9393 8383

High Score



Design Process

Phase 1: Shifting MechanismPhase 1: Shifting MechanismPhase 2: Gear AssemblyPhase 2: Gear AssemblyPhase 3: Case and InterfacingPhase 3: Case and Interfacing

Step 1: Geometric Driven ModelingStep 1: Geometric Driven Modeling

Step 2: Calculations performed on Step 2: Calculations performed on simplified geometriessimplified geometries

Step 3: Detailed ModelingStep 3: Detailed Modeling

Step 4: FEA with COSMOSWorksStep 4: FEA with COSMOSWorks

Brainstorming and Initial Concept Modeling

Design Criteria Decision Matrix

Detailed System DesignProof of Concept Prototype

Concept Chosen for Design

Iterative Analytical Design



Design Phase I: Shifting Mechanism

Model of Current Shifting System Configuration

SHIFTING BULB

PAWL RETURN SPRINGS

PAWLS

SHIFT BULB RETURN SPRING

SHIFT PULL CABLE







Governing Equations:

Assumptions:

Materials Selected:

Shaft: 4130 Steel Q&T

Pawl: 4130 Steel Normalized

τ = TcJ

ΣF = Σ ma = 0

2:1 Torque reduction from cranks to gearbox input

Torque distributed evenly over the three pawls

F.O.S. = 2

Cosmos FEA of Shaft and Pawl:

Max Stress: 370 MPa

Max Stress: 261 MPa Simplified Geometry Calculations:

Max stress calculated at outside diameter of shaft: 21.7 MPa



Design Phase II: Gear Assembly

Planetary Barrel

Hollow Drive Shaft

Output Gear

Support Plate

Sun Bearing

Barrel Bearing



Design Phase II: Gear Assembly Three types of gear analysis performedThree types of gear analysis performed

AGMA bending stress Buckingham gear wear Fatigue

GivensGivens Max rider input: 115 N-m at 90 RPMS 2:1 Gear reduction from cranks to gearbox input Product lifetime of 3 years

Independent VariablesIndependent Variables Tooth width Module Pitch diameter Material

J

KK

bmKKF ms

vt

0.10

AGMA Bending

Stress

Fw = K Q b Dp Buckingham Wear Load

Governing Equations:

Assumptions:K0 = 1.25

Kv = 1

Ks = 1

Km = 1.2

J = 0.35

F.O.S. = 1.25

Available Gear Materials:

l7-4 PH Stainless Steel

2024 T4 Aluminum

303 Stainless Steel

416 Stainless Steel




Ring GearRing Gear

Material Selected: Material Selected: 2024 T4 Aluminum

Module: 1 Gear width: Module: 1 Gear width: 5.6 mm

Fatigue Stress Limit: Fatigue Stress Limit: 324 MPa

Yield Strength: Yield Strength: 325 Mpa

AGMA Stress x F.O.S: AGMA Stress x F.O.S: 266 MPa

Wear Stress: Wear Stress: 19.9 MPa

Planet GearPlanet Gear

Material Selected: Material Selected: 416 Stainless Steel

Module: 1 Gear width: Module: 1 Gear width: 5.6 mm

Endurance Limit: Endurance Limit: 277 MPa

Yield Strength:Yield Strength: 277 MPa



Sun GearSun Gear

Material Selected: Material Selected: 416 Stainless Steel

Module: 1 Gear width: 5.6 mmModule: 1 Gear width: 5.6 mm

Endurance Limit: Endurance Limit: 277 Mpa

Yield Strength:Yield Strength: 277 MPa



Example of Gear Analysis: Gear Set 4Example of Gear Analysis: Gear Set 4




Gear material was selected by optimizing AGMA bending stress Gear material was selected by optimizing AGMA bending stress and fatigueand fatigue

AGMA Fatigue AGMA Fatigue AGMA Fatigue AGMA Fatigue

Set 1

Selected Material2024 Aluminum 303 Stainless Steel 416 Stainless Steel 17-4 PH Stainless Steel

Planet N N N N N N Y Y 17-4 PH Stainless SteelSun N N N N N N Y Y 17-4 PH Stainless SteelRing N N N N N N Y Y 17-4 PH Stainless SteelSet

1

Set 2

Planet Y N Y N Y N Y Y 17-4 PH Stainless SteelSun Y N N N N N Y Y 17-4 PH Stainless SteelRing Y Y N N N N Y Y 2024 AluminumSet

2

Set 3

Planet Y N Y N Y Y Y Y 416 Stainless SteelSun Y N Y N Y Y Y Y 416 Stainless SteelRing Y Y Y N Y Y Y Y 2024 AluminumSet

3

Set 4

Planet Y N Y N Y Y Y Y 416 Stainless SteelSun Y N Y N Y Y Y Y 416 Stainless SteelRing Y Y Y N Y Y Y Y 2024 AluminumSet

4

Set 5

Planet Y N Y Y Y Y Y Y 416 Stainless SteelSun Y N Y Y Y Y Y Y 303 Stainless SteelRing Y Y Y Y Y Y Y Y 2024 AluminumSet

5

Set 6

Planet Y N Y Y Y Y Y Y 303 Stainless SteelSun Y N Y Y Y Y Y Y 303 Stainless SteelRing Y Y Y Y Y Y Y Y 2024 Aluminum

Set 7

Set 6

Planet Y N Y Y Y Y Y Y 303 Stainless SteelSun Y N Y Y Y Y Y Y 303 Stainless SteelRing Y Y Y Y Y Y Y Y 2024 AluminumOutput Y Y N N Y N Y Y 2024 Aluminum

Set 7



Design Phase III: Case and Interfacing

Mounts to G-CON 2.0 standard Mounts to G-CON 2.0 standard framesframes

Supports gears and shaftsSupports gears and shafts Structural member of frameStructural member of frame

Max Left Leg

Loading

Max Right Leg

LoadingFd

.2*Fd

.2*Fd

.2*Fd

.2*Fd

.2*Fd

Threaded Bottom Bracket Shell

Barrel Bearing Support

Support Flanges

Output Shaft Bearing Support

G-CON 2.0 Mounting Feature

Drive Shaft Bearing Support

Free body diagram



Design Phase III

Loading Conditions:Loading Conditions:

Rider transmits 100% of load from vertical impact to

pedals via legs

0% absorption with bike suspension

Maximum force rider’s legs can transmit = 500 lb

Material Selected:Material Selected:

6061 T6 Aluminum

COSMOS FEA of Case:COSMOS FEA of Case:

Max Stress: 7 MPa



Design Phase III: Case and Interfacing

Shifting Cable Scalar

Industry Standard Bottom

Bracket and Cranks

Gasket

Impact Resistant Bash

Guard

Input Sprocket

Output Sprocket

Industry Standard Component Compatibility: Industry Standard Component Compatibility: Shifting cable scalar interfaces with indexed shiftersShifting cable scalar interfaces with indexed shifters Case sized and threaded for integration with standards bottom brackets and cranksCase sized and threaded for integration with standards bottom brackets and cranks Standard mountain bike sprockets used for input and outputStandard mountain bike sprockets used for input and output



Final Design

Weight:Weight: 7.5 lbs

Estimated Cost:Estimated Cost: $4000

Gear Ratios:Gear Ratios: 2.1, 2.3, 2.5, 2.7, 2.9, 3.1, 3.3

Materials:Materials: 416 Stainless Steel, 303 Stainless Steel, 17-4 PH Stainless Steel, 4130 Steel, 1045 Steel, 2024 Aluminum, 6061 Aluminum



Proof of Concept Prototype

Weight: Weight: 8 lbs

Cost:Cost: $1500

Gear Range:Gear Range: 2.1, 2.5, 3.3

Materials:Materials: SLA, 303 Stainless Steel, 6061 Aluminum, 1045 Steel, Carbon Steel, Nylon



Concluding Thoughts

Proof of concept testingProof of concept testing Shifting mechanism functions Gear configuration provides three distinct ratios Case supports internal systems and interfaces with industry standard

components Sub systems mechanically integrate

Further developmentFurther development Build and test final design prototype Reduce weight Extend lifetime Improve manufacturability



Questions?

Special thanks to the following individuals for their technical and moral support:

Randy Moore, Brian Weinberg, Jim Forte



Extra Slides



Images



Images



b - Face Width

m - Module

sK - Size Factor = 1

mK - Mounting Factor = 1.3

0K - Overload Factor = 1.5 (1 - 2.25)

vK - Velocity Factor (precision, pitch velocity)

tF- Transmitted tangential load

J - Geometry Factor: .45

RT

Ltall KK

KS

AGMA

tS - Material Yield Strength

LK - Life Factor

TK - Temperature Factor

RK - Reliability Factor

J

KK

bmKKF ms

vt

0.10



Different Suspensions with G-CON 2.0

ONLINE VIDEO OF MORE PIVOT DESIGNS



Slide Graveyard




Final Design Prototype

Weight:Weight: 7.5 lbs

Cost:Cost: $4000

Gear Ratios:Gear Ratios: 2.1, 2.3, 2.5, 2.7, 2.9, 3.1, 3.3

Materials:Materials: 416 Stainless Steel, 303 Stainless Steel, 17-4 PH Stainless Steel, 4130 Steel, 1045 Steel, 2024 Aluminum, 6061 Aluminum


Weight: Weight: 8 lbs

Cost:Cost: $1500

Gear Range:Gear Range: 2.1, 2.5, 3.3

Materials:Materials: SLA, 303 Stainless Steel, 6061 Aluminum, 1045 Steel, Carbon Steel, Nylon



Final Design

PLANETARY STACK

INPUT SPROCKET

STANDARD MOUNTAIN BIKE CRANKSET, BOTTOM BRACKET. AND

BASHGUARD

SHIFTING CABLE SCALER

OUTPUT SPROCKET

Documents

Downhill Mountain Bike Gearbox Josh Filgate, Jesse Kuhn, Morgan Misek Jay Seiter, Michael Witonis Jay Seiter, Michael Witonis