traction performance of wheel and track for soft...
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Traction Performance of Wheel and Trackfor Soft-Soil Traversal
Kazuya Yoshida, Keiji Nagatani,Junya Yusa
Tohoku University, Japan
ICRA‘10 Planetary Rovers WorkshopMay 3rd, 2010
Traction Performance of Wheel and Trackfor Soft-Soil Traversal
IntroductionResearch Setup
The Sand BoxThe Test Beds
Traction Performance EvaluationExperimental Results for Wheel v.s. TrackHow can we improve the wheel traction?
Summary
Rover Test Beds in Tohoku Univ. since 1997
“Kaguya”a Japanese Lunar Orbiter
Launched on September 14, 2007.Orbiting 100km lunar polar orbit for global mapping and
remote sensing of the Moon.
Apollo mission © NASA
Lunar Rovers
Most of lunar surface is covered with soft soils (regolith).
Wheel slippages/skids are unavoidable.
Critical situations (immobility due to wheel spin, side slide, or tip over) should be avoided.
Maximize the traction performance and power efficiency
Modeling and control based on substantial analysis of traction mechanics is important.
Wheeled rovers can be stuckin loose soil
NASA’s Mars Exploration Roversalso experienced difficulty.
© NASA
© JAXA
Do tracks work better than wheels?
Advantages of Tracked Vehicles:• Higher slope-climbing capability• Higher bump-crossing capability*
(*This is only true when the length of the track is larger thana “wave length” of the bumps.)
Disadvantages of Tracked Vehicles:• Higher mass and higher energy consumption• Higher complexity of mechanism• Higher risk of track jamming or other mechanical
failures
Traction Performance of Wheel and Trackfor Soft-Soil Traversal
IntroductionResearch Setup
The Sand BoxThe Test Beds
Traction Performance EvaluationExperimental Results for Wheel v.s. TrackHow can we improve the wheel traction?
Summary
18
Toyoura-sand: a standard soil in Terramechanics research community
The Sand Box
19
Mono-Crawler Inline Four-Wheels
Length = 400 mm, Width = 40 mm, Weight = 6 - 18 kgfor Crawler: 375 - 1125 kg/m2 (0.53 – 1.60 psi)for Wheels: 1.5 - 4.5 kg/wheel
The Test Beds
20
Mono-Crawler Inline Four-Wheels
Slope Angle: 0 – 16 degs (physically)
0 – 30 degs (equivalently)
The Test Beds
Traction Performance of Wheel and Trackfor Soft-Soil Traversal
IntroductionResearch Setup
The Sand BoxThe Test Beds
Traction Performance EvaluationExperimental Results for Wheel v.s. TrackHow can we improve the wheel traction?
Summary
Slip Ratio
vd : circumference velocity of crawler belt or wheelv : body velocity of the test bed
22
Slip Ratio - Drawbar Pull Slip Ratio - Slope Angle
1d
d d
v v vsv v−
= = −
Performance Evaluation
Drawbar Pull (DP)
DP = Traction Force - Resistance
23
Q: Is the slope climbing condition equivalently tested by the increased horizontal load?
1tan x
z
FF
θ −=
24
Q: Is the slope climbing condition equivalently tested by the increased horizontal load?
A: Yes, that seems true as long as no landslide (avalanche) occurs.
Experimental Result 0 (track)
25
26
0
1
2
3
4
5
6
7
8
9
10
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
draw
bar pu
ll [kg]
slip ratio [‐]
8.8kg11.8kg14.8kg17.8kg
Experimental Result 1a (track)
The Drawbar Pull increases along with the vertical load Fz.
Experimental Result 2a (track)
27
0
5
10
15
20
25
30
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
slop
e an
gle [deg]
slip ratio [‐]
8.8kg11.8kg14.8kg17.8kg
But the ratio of DP/Fz (= slope angle) is not affected by Fz.This fact suggests that the traction force Fx is in proportion to the vertical load Fz (like friction), and the resistance R is relatively small. DP/Fz = Fx/Fz - R
28
0
5
10
15
20
25
30
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
slop
e an
gle[de
g]
slip ratio[‐]
2cm/s
4cm/s
Experimental Result 3a (track)
Velocity dependency is not observed between 2 and 4 cm/s.
29
Experimental Result 1b (wheel)
0
1
2
3
4
5
6
7
8
9
10
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
draw
bar pu
ll [kg]
slip ratio [‐]
8.8kg11.8kg14.8kg17.8kg
0
1
2
3
4
5
6
7
8
9
10
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
draw
bar pu
ll [kg]
slip ratio [‐]
6kg9kg12kg
track wheel
Drawbar Pull v.s. Slip Ratio
30
Experimental Result 2b (wheel)
track wheel
Slope Angle v.s. Slip Ratio
0
5
10
15
20
25
30
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
slop
e an
gle [deg]
slip ratio [‐]
8.8kg11.8kg14.8kg17.8kg
0
5
10
15
20
25
30
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
6kg9kg12kg
slip ratio [‐]
slop
ean
gle[deg]
Experimental Result 1b (wheel)
31
This fact suggests that the wheel traction is NOT like friction, because of relatively large the resistance R due to wheel sinkage.
In wheel, DP is not much affected by Fz.
0
0.5
1
1.5
2
2.5
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
draw
bar pu
ll [kg]
slip ratio [‐]
6kg
9kg
12kg
DP/Fz = Fx/Fz - R
Traction Model for a Rigid Tire on Soft Soil
( ) ( ){ }
( ) ( ){ } θθθσθθτ
θθθτθθσ
θ
θ
θ
θ
drbDP
drbW
f
r
f
r
∫
∫−=
+=
sincos
sincos
( ) ( )( )( ) ( )( )[ ]θθθθ
ϕσθτ
sinsin1
1tan)(
−−−−−=
−+=
ff
sa
skrsa
ec
(Bekker 1956, Wong 1978)
∫= f
r
dbrTθ
θθθτ )(2
33
Weight = 9kg , slope angle = 10°
Slip Ratio = 0.054 Slip Ratio = 0.774
Comparison of Track and Wheel
35
116m
m
202m
m327m
mQ: How can we improve the traction
performance of the wheels?
Wheels with Different Dimensions
36
D=100mm D=200 D=300diameter [mm] 116 202 327lug height [mm] 5 9 15number of lugs 24 24 24width [mm] 50, 100, 150 50, 100, 150 50, 100, 150
D=100 D=200 D=300
With Larger Diameter
37(width = 100mm)
38
各車輪径におけるスリップ率 と斜度の関係(車輪幅 = 100mm)
θ = 12°φ300mm s = 0.056
θ = 12°φ100mm s = 0.741
θ = 12°φ200mm s = 0.229
With Larger Diameter
39
(D = 200mm)
With Larger Width
40
各車輪幅におけるスリップ率 と斜度の関係(車輪径 = 200mm)
θ = 14°w50mm s = 0.471
θ = 14°w100mm s = 0.320θ = 14°w150mm s = 0.247
With Larger Width
41
0
5
10
15
20
25
30
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
slop
e an
gle [deg]
slip ratio [‐]
8.8kg11.8kg14.8kg17.8kg
0
5
10
15
20
25
30
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
slop
e an
gle [‐]
slip ratio [‐]
w50mm
w100mm
w150mm
track wheel
Comparison of Track and Wheel
42
Q: How can we improve the traction performance of the wheels?
Yeswith increased contact areawith decreased wheel sinkage
Example:Michelin Tweel®
Deformable Tire
Traction Performance of Wheel and Trackfor Soft-Soil Traversal
IntroductionResearch Setup
The Sand BoxThe Test Beds
Traction Performance EvaluationExperimental Results for Wheel v.s. TrackHow can we improve the wheel traction?
Summary
Summary
The traction performance was experimentally studied to compare track (mono-crawler) and wheel (inline wheels).The slope climbing condition was equivalently tested by the increased horizontal load.The track showed higher performance than wheels.The track performance can be modeled like a surface friction, with very small sinkage related resistance. The wheel performance is largely disturbed by the wheel sinkage.But the performance of the wheels can be improved with grater diameter and width, which resulting in smaller sinkage.
The Space Robotics Lab.Dept. of Aerospace Engineering
Tohoku University, JAPANDirected by Prof. Kazuya Yoshida
[email protected]://www.astro.mech.tohoku.ac.jp/home-e.html
Free-Flying Space Robot
Planetary Exploration Rovers Asteroid Sampling
Robotic Systems on ISS
The SPACE ROBOTICS
Lab.