jean-christophe fauroux improving...

1IFToMM 2007, The 12th World Congress in Mechanism and Machine ScienceJune 1721, Besançon, FRANCE

ImprovingSkid-steering

Fauroux / Vaslin / Douarre

Improving skid-steering on a 6x6 all-terrain vehicle

Philippe [email protected] / UBPClermont-Ferrand, France

Jean-Christophe [email protected]

Guillaume DOUARRELaMI / IFMA / UBPClermont-Ferrand, France

Laboratoire deMécanique &Ingénieries

KOKOON projectwww.kokoon.fr.st

IFToMM 2007, The 12th World Congress in Mechanism and Machine ScienceJune 1721, Besançon, FRANCE

A preliminary experimental

study

http://www.kokoon.fr.st/




Introduction to the problem

Introduction

Vehicle

Experiment

Results

Two existing principles for steering a wheeled vehicle

Our purpose● To keep the robustness and mechanical

simplicity of skid-steering vehicles

● Trying to minimize the energy consumption of such vehicles during steering

Conclusion

Future work

● Ackermann steering● Skid-steering

A complex phenomenon, difficult to modelPreliminary experimental results to check consistency

● Evaluate the ripping forces● Try to minimize them...● ...by adjusting normal contact forces




Mobile crane, Liebherr 15008.1 6 steering axles out of 8

Ackermann steering

With N axles, (N-1) axles must steer at least

C

Mostly for hard ground

Ackermann (1817) / Jeantaud (1870)For wheeled vehicles that steer with minimal skid

Tricycle scooter, Piaggio MP3

Power lift truck, Manitou M26

Minimal skid vs. complexitySemitrailer

1 steering axle out of 5 + 1R

Introduction

Vehicle

Experiment

Results

Conclusion

Future work

● Ackermann

● Skid-steering

Mobile mortar, Patria NEMO




For wheeled and tracked vehiclesMechanical simplicity (no steering mechanism, only suspension)

Skid-steering

Simplicity vs. turning resistance

CC

Wheels cannot roll laterally

Tracked tractor, Caterpillar D6R III

Amphibian ATV, Oasis LLC Max 6x6 Mobile robot, Pioneer 3 AT

AT wheelchair, Modul Evasion

Mostly for low friction / soft grounds Introduction

Vehicle

Experiment

Results

Conclusion

Future work

● Ackermann

● Skid-steering

Two versions of the same mobile mortarAckermann and Skidsteering tracked,

Patria AMOS




Overview of the 6x6 Kokoon vehicle

An ATW (All-Terrain Wheelchair)6x6 transmission and 2x1330W electric enginesOleo-pneumatic suspension on all wheelsClimbing capacity: 20cm obstacles, 36% slopesSpeed: 8 km/h Autonomy: 4h Introduction

Vehicle

Experiment

Results

Conclusion

Future work

● Overview

● Transmission

● Suspension

Designedat IFMA from 1999




Overview of the 6x6 Kokoon vehicle

Skid steering for robustness and allterrain mobilityA reconfigurable vehicle A research platform with sensors

Controlled by joystick

Safetyharness

Rollbar

Independent oleopneumatic suspensions

6x6 allterrain vehicle

2 DC electric engines of 1330W each

Lead batteries 24V 160Ah

Top caseor transporting platform

Sliding sport seat

Improved access: sliding seat

Transport position

Multiple functions

Research configuration with onboard camera, double

acquisition laptop and suspension sensors

Introduction

Vehicle

Experiment

Results

Conclusion

Future work

● Overview

● Transmission

● Suspension




Vehicle transmission

Belt transmission: 3 wheels at the same speedCompatible with suspension displacementsGood efficiencyClutching

Introduction

Vehicle

Experiment

Results

Conclusion

Future work

● Overview

● Transmission

● Suspension




● Track width = 93 cm● Wheel base = 47 cm

Introduction

Vehicle

Experiment

Results

Conclusion

Future work

● Overview

● Transmission

● Suspension

6 Independent wheels

Trailing arm suspensions● Robust● Easy to adjust● Oleo-pneumatic

shock-absorber

Vehicle suspension

● Length = 175 cm● Width = 103 cm

175 cm

103 cm

47 cm

47 cm93 cm

● Wheel diam. = 40 cm● Wheel width = 7 cm

40cm

7 cm




The force plate

Introduction

Vehicle

Experiment

Results

Conclusion

Future work

● Force plate

● Mass

● Suspensions

Steadystate circular turningA force plate to measure contact reaction forces

● Rx longitudinal force provided by the engines● Ry lateral force due to ripping● Rz normal force due to mass dispatching

Force plate

Ground

Circular trajectory

Z

X

Y● Turning




The force plate

A sixcomponent force plate (TSR, France)

Force measurement ranges: Rx: 1000N Ry: 900N Rz: 2000N

Force transducers

Base plate

Top plate

Groundlevel

Wooden box

80cm

60cm

3 twocomponent strain gauge transducers at 120°

Z

Y

X

3 normal components (Rz)3 tangential components (RxRy)

Wooden box

Acquisition chain: 6 channels, 16 bits, 100Hz, Labview

F x

F y

F z

M x

M y

M z

=[C ] V 1

V 2

V 3

V 4

V 5

V 6

Wrench = 6x6 Calibration matrix x Tensions

Introduction

Vehicle

Experiment

Results

Conclusion

Future work

● Force plate

● Mass

● Suspensions

● Turning




Mass dispatching

Centre of mass is computed with the CAD modelHypothesis : uniform density in each partEmpty mass: 367 kg

Introduction

Vehicle

Experiment

Results

Conclusion

Future work

● Force plate

● Mass

● Suspensions

● Turning




Mass dispatching

Experimental measurement6 scales with the same height

Good correlation Experiment / CAD

Lifting rectangle

Central axle axis

Real CM

CAD CM

Introduction

Vehicle

Experiment

Results

Conclusion

Future work

● Force plate

● Mass

● Suspensions

● Turning




Suspension reconfiguration

Reconfigurable suspension

● Reference configuration● Three identical suspensions

● Modified configuration● Differentiated suspensions

● Central suspension becomes more loaded

Reference dimensions

Fw

Fs

hs

vs

B

O S1

S2

θa

θs

C

l2

la

ls

z

x

e

● Adjustment with hs

● Initial hs = 145mm

● New hs = 045mm

Parameter Value

180 mm

145 mm

45 mm

210280 mm

170 mm

350 mm

e 15 mm

vs

hs std

hs mod

ls

l2

la

● A new mass dispatching

108 kg 158 kg 183 kg

80 kg (26%) 250 kg (+58%) 120 kg (35%)

Introduction

Vehicle

Experiment

Results

Conclusion

Future work

● Force plate

● Mass

● Suspensions

● Turning

● Includes a 83kg driver




Turning experiment

Introduction

Vehicle

Experiment

Results

Conclusion

Future work

● Force plate

● Mass

● Suspensions

● Turning

Three types of trajectories for the external wheelsRadius R Infinite ( => straight line) 6m 3m

Acquisition at 100Hz is enough for low speed (around 45 kph)

Duration: from 1.5s (straight line) to 2.5s (3m turn)

Z

X

YR = 3m

R = 6m

Lines drawn with flour




0 0,5 1 1,5 2

500

0

500

1000

1500

2000

Rx (N)

Ry (N)

Rz (N)

Time (s)

Reaction forces (N)

Standard suspension

Turn R = 6m

Typical curves

Introduction

Vehicle

Experiment

Results

Conclusion

Future work

● Reference

● Modified

● COP

Curves of Rx, Ry, Rz are providedOne or two wheels on the force plate at the same timeFive zones appear on the time axis

● Curves

● Explanation

Wheel 1 Wheel 2 Wheel 3Wheels 1+2 Wheels 2+3

Average values on each zone (vibrations on gravel and electric perturbations)

Rz1 = 627N Rz2 = 972N Rz3 = 905N (one side only)

● Wheels 2 and 3 prevail for Rz > confirms weight dispatching● Wheels 1 and 3 prevail for Ry and turning moment● Wheel 2 generates most of the traction force Rx (belt sliding ?)

Main results:




Results for reference vehicle

Introduction

Vehicle

Experiment

Results

Conclusion

Future work

● Reference

● Modified

● COP

● Curves

● Explanation

0 0,5 1 1,5

Rx (N)

Ry (N)

Rz (N)

Time (s)

0 0,5 1 1,5 2

Time (s)

0 0,5 1 1,5 2 2,5

Time (s)

Reaction forces (N)Standard suspension

Turn R = 3m

2000

1500

1000

500

0

500

2000

1500

1000

500

0

500

2000

1500

1000

500

0

500


Straight line

Rx

Rz

Ry

Rx

Rz

Ry

Rx

Rz

Ry

Wheel 1 Wheel 2 Wheel 3


Turn R = 6m

Wheels 1+2 Wheels 2+3

Influence of radius RRz does not changes with R

Ry is quasi null in straight lineRy increases when R decreases

Rx is quasi null in straight lineRx increases when R decreasesThis phenomenon was experienced by the driver




Introduction

Vehicle

Experiment

Results

Conclusion

Future work

● Reference

● Modified

● COP

● Curves

● Explanation

0 0,5 1 1,5

Time (s)

0 0,5 1 1,5

Time (s)

0 0,5 1 1,5

Time (s)

Reaction forces (N)Modified suspension

Straight line

2000

1500

1000

500

0

500


Turn R = 3m


Turn R = 6m

Rx

Rz

Ry

Rx

Rz

Ry

Rx

Rz

Ry

2000

1500

1000

500

0

500

2000

1500

1000

500

0

500

0 0,5 1 1,5

Rx (N)

Ry (N)

Rz (N)

Time (s)

0 0,5 1 1,5 2

Time (s)

0 0,5 1 1,5 2 2,5

Time (s)


Turn R = 3m

2000

1500

1000

500

0

500

2000

1500

1000

500

0

500

2000

1500

1000

500

0

500


Straight line

Rx

Rz

Ry

Rx

Rz

Ry

Rx

Rz

Ry

Wheel 1 Wheel 2 Wheel 3


Turn R = 6m

Wheels 1+2 Wheels 2+3

Results for modified vehicle

A 38% decrease of Rx on Wheel 2

A 36% decrease of Ry on Wheel 3

Turn is shorter on modified

vehicle




Introduction

Vehicle

Experiment

Results

Conclusion

Future work

● Reference

● Modified

● COP

● Curves

● Explanation

Centre of pressure (COP)

0

10

20

30

40

50

60

80706050403020100

X (cm)

Y (cm)

Goingstraight

TurnR=6m

TurnR=3m

COP = the point where the moment of contact wrench is nullPhases are visible (one or two wheels on the force plate) The COP follows circles => Trajectories were correct




Physical explanations

Introduction

Vehicle

Experiment

Results

Conclusion

Future work

● Reference

● Modified

● COP

● Curves

● Explanation

Strong influence of mass dispatching on turning abilityAnalogy with the behaviour of a road tire

Slipangle

Lateral force RY

RZ1

RZ2

RZ3

RZ1

> RZ2

> RZ3

s

sl

V3

X

Y

Circular trajectory of radius R

Forceplatform

V1

V2s1 s3

● Lateral force Ry increases with normal force Rz● Lateral force Ry depends also on slip angle

s

● Linear behaviour up to sl

● During skidsteering, two slip angles s1

and s3

appear on wheels 1 and 3




ConclusionSkid-steering can be greatly improved......only by minor adjustments on the suspensions10cm adjustments only decreased normal force of 30% on front and rear axlesPropulsion forces decreased of 30% when steeringMulti-axles vehicles without steering systems are robust. They can now be efficient when skid-steering

Introduction

Vehicle

Experiment

Results

Conclusion

Future work




Future work

Replace belts by chains to suppress slidingAdd 6 force sensors inside the wheels for continuous measurementBuild analytical modelTowards an active correction system

AcknowledgementANVAR : French

National Agency for Development of

Research

...and many more onwww.kokoon.fr.st

TIMS Research FederationMobility pole

MichelinCompany

3 Videos

TSR force sensor in a wheel

Introduction

Vehicle

Experiment

Results

Conclusion

Future work

jean-christophe fauroux improving...

Documents