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
2IFToMM 2007, The 12th World Congress in Mechanism and Machine ScienceJune 1721, Besançon, FRANCE
ImprovingSkid-steering
Fauroux / Vaslin / Douarre
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
3IFToMM 2007, The 12th World Congress in Mechanism and Machine ScienceJune 1721, Besançon, FRANCE
ImprovingSkid-steering
Fauroux / Vaslin / Douarre
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
4IFToMM 2007, The 12th World Congress in Mechanism and Machine ScienceJune 1721, Besançon, FRANCE
ImprovingSkid-steering
Fauroux / Vaslin / Douarre
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
5IFToMM 2007, The 12th World Congress in Mechanism and Machine ScienceJune 1721, Besançon, FRANCE
ImprovingSkid-steering
Fauroux / Vaslin / Douarre
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
6IFToMM 2007, The 12th World Congress in Mechanism and Machine ScienceJune 1721, Besançon, FRANCE
ImprovingSkid-steering
Fauroux / Vaslin / Douarre
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
7IFToMM 2007, The 12th World Congress in Mechanism and Machine ScienceJune 1721, Besançon, FRANCE
ImprovingSkid-steering
Fauroux / Vaslin / Douarre
Vehicle transmission
Belt transmission: 3 wheels at the same speedCompatible with suspension displacementsGood efficiencyClutching
Introduction
Vehicle
Experiment
Results
Conclusion
Future work
● Overview
● Transmission
● Suspension
8IFToMM 2007, The 12th World Congress in Mechanism and Machine ScienceJune 1721, Besançon, FRANCE
ImprovingSkid-steering
Fauroux / Vaslin / Douarre
● 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
9IFToMM 2007, The 12th World Congress in Mechanism and Machine ScienceJune 1721, Besançon, FRANCE
ImprovingSkid-steering
Fauroux / Vaslin / Douarre
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
10IFToMM 2007, The 12th World Congress in Mechanism and Machine ScienceJune 1721, Besançon, FRANCE
ImprovingSkid-steering
Fauroux / Vaslin / Douarre
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
11IFToMM 2007, The 12th World Congress in Mechanism and Machine ScienceJune 1721, Besançon, FRANCE
ImprovingSkid-steering
Fauroux / Vaslin / Douarre
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
12IFToMM 2007, The 12th World Congress in Mechanism and Machine ScienceJune 1721, Besançon, FRANCE
ImprovingSkid-steering
Fauroux / Vaslin / Douarre
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
13IFToMM 2007, The 12th World Congress in Mechanism and Machine ScienceJune 1721, Besançon, FRANCE
ImprovingSkid-steering
Fauroux / Vaslin / Douarre
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
14IFToMM 2007, The 12th World Congress in Mechanism and Machine ScienceJune 1721, Besançon, FRANCE
ImprovingSkid-steering
Fauroux / Vaslin / Douarre
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
15IFToMM 2007, The 12th World Congress in Mechanism and Machine ScienceJune 1721, Besançon, FRANCE
ImprovingSkid-steering
Fauroux / Vaslin / Douarre
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:
16IFToMM 2007, The 12th World Congress in Mechanism and Machine ScienceJune 1721, Besançon, FRANCE
ImprovingSkid-steering
Fauroux / Vaslin / Douarre
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
Reaction forces (N)Standard suspension
Straight line
Rx
Rz
Ry
Rx
Rz
Ry
Rx
Rz
Ry
Wheel 1 Wheel 2 Wheel 3
Reaction forces (N)Standard suspension
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
17IFToMM 2007, The 12th World Congress in Mechanism and Machine ScienceJune 1721, Besançon, FRANCE
ImprovingSkid-steering
Fauroux / Vaslin / Douarre
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
Reaction forces (N)Modified suspension
Turn R = 3m
Reaction forces (N)Modified suspension
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)
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
Reaction forces (N)Standard suspension
Straight line
Rx
Rz
Ry
Rx
Rz
Ry
Rx
Rz
Ry
Wheel 1 Wheel 2 Wheel 3
Reaction forces (N)Standard suspension
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
18IFToMM 2007, The 12th World Congress in Mechanism and Machine ScienceJune 1721, Besançon, FRANCE
ImprovingSkid-steering
Fauroux / Vaslin / Douarre
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
19IFToMM 2007, The 12th World Congress in Mechanism and Machine ScienceJune 1721, Besançon, FRANCE
ImprovingSkid-steering
Fauroux / Vaslin / Douarre
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
20IFToMM 2007, The 12th World Congress in Mechanism and Machine ScienceJune 1721, Besançon, FRANCE
ImprovingSkid-steering
Fauroux / Vaslin / Douarre
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
21IFToMM 2007, The 12th World Congress in Mechanism and Machine ScienceJune 1721, Besançon, FRANCE
ImprovingSkid-steering
Fauroux / Vaslin / Douarre
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