Traction Performance of Wheel and Track for Soft-Soil Traversal

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1 ICRA 10 Planetary Rovers Workshop May 3rd, 2010 Traction Performance of Wheel and Track for Soft-Soil Traversal Kazuya Yoshida, Keiji Nagatani, Junya Yusa Tohoku University, Japan

2 Traction Performance of Wheel and Track for Soft-Soil Traversal Introduction Research Setup The Sand Box The Test Beds Traction Performance Evaluation Experimental Results for Wheel v.s. Track How can we improve the wheel traction? Summary

3 Rover Test Beds in Tohoku Univ. since 1997

5 Kaguya a Japanese Lunar Orbiter Launched on September 14, Orbiting 100km lunar polar orbit for global mapping and remote sensing of the Moon.

6 Apollo mission NASA

7 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.

9 Wheeled rovers can be stuck in loose soil

10 NASA s Mars Exploration Rovers also experienced difficulty. NASA

11 Do tracks work better than wheels? JAXA

12 Advantages of Tracked Vehicles: Higher slope-climbing capability Higher bump-crossing capability* (*This is only true when the length of the track is larger than a 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

13 Traction Performance of Wheel and Track for Soft-Soil Traversal Introduction Research Setup The Sand Box The Test Beds Traction Performance Evaluation Experimental Results for Wheel v.s. Track How can we improve the wheel traction? Summary

14 The Sand Box Toyoura-sand: a standard soil in Terramechanics research community 18

mm, Weight = 6-18 kg for Crawler: 375-1125

15 The Test Beds Mono-Crawler Inline Four-Wheels Length = 400 mm, Width = 40 mm, Weight = 6-18 kg for Crawler: kg/m 2 ( psi) for Wheels: kg/wheel 19

16 The Test Beds Mono-Crawler Inline Four-Wheels Slope Angle: 0 16 degs (physically) 0 30 degs (equivalently) 20

17 Traction Performance of Wheel and Track for Soft-Soil Traversal Introduction Research Setup The Sand Box The Test Beds Traction Performance Evaluation Experimental Results for Wheel v.s. Track How can we improve the wheel traction? Summary

18 Performance Evaluation Slip Ratio s v v v = d = 1 v v d vd : circumference velocity of crawler belt or wheel v : body velocity of the test bed Drawbar Pull (DP) DP = Traction Force - Resistance d Slip Ratio - Drawbar Pull Slip Ratio - Slope Angle 22

19 Q: Is the slope climbing condition equivalently tested by the increased horizontal load? θ = tan 1 F F x z 23

20 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. 24

21 Experimental Result 0 (track) 25

22 Experimental Result 1a (track) 10 9 drawbar pull [kg] slip ratio [ ] 8.8kg 11.8kg 14.8kg 17.8kg The Drawbar Pull increases along with the vertical load Fz. 26

23 Experimental Result 2a (track) slope angle [deg] kg 11.8kg 14.8kg 17.8kg slip ratio [ ] 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 27

24 Experimental Result 3a (track) slope angle[deg] cm/s 4cm/s slip ratio[ ] Velocity dependency is not observed between 2 and 4 cm/s. 28

25 Experimental Result 1b (wheel) track wheel drawbar pull [kg] slip ratio [ ] 8.8kg 11.8kg 14.8kg 17.8kg drawbar pull [kg] slip ratio [ ] 6kg 9kg 12kg Drawbar Pull v.s. Slip Ratio 29

26 Experimental Result 2b (wheel) track wheel slope angle [deg] kg 11.8kg 14.8kg 17.8kg slope angle [deg] kg 9kg 12kg slip ratio [ ] slip ratio [ ] Slope Angle v.s. Slip Ratio 30

27 Experimental Result 1b (wheel) 2.5 drawbar pull [kg] slip ratio [ ] 6kg 9kg 12kg In wheel, DP is not much affected by Fz. This fact suggests that the wheel traction is NOT like friction, because of relatively large the resistance R due to wheel sinkage. DP/Fz = Fx/Fz - R 31

28 W DP T Traction Model for a Rigid Tire on Soft Soil (Bekker 1956, Wong 1978) = = rb τ ( θ ) = a = r 2 θ θ rb b r f θ θ θ θ r f { σ ( θ ) cosθ + τ ( θ ) sinθ } r f dθ { τ ( θ ) cosθ σ ( θ ) sinθ } dθ a( s) ( c + σ tanϕ) 1 e r k τ ( θ) dθ ( ) () s = [ θ θ ( 1 s)( sinθ sinθ )] f f

29 Comparison of Track and Wheel Weight = 9kg, slope angle = 10 Slip Ratio = Slip Ratio =

30 Q: How can we improve the traction performance of the wheels? 327mm 202mm 116mm 35

31 Wheels with Different Dimensions D=100mm D=200 D=300 diameter [mm] lug height [mm] number of lugs width [mm] 50, 100, , 100, , 100, 150 D=100 D=200 D=300 36

32 With Larger Diameter (width = 100mm) 37

33 With Larger Diameter θ = 12 φ100mm s = 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 = θ = 12 φ200mm s =

34 With Larger Width (D = 200mm) 39

35 With Larger Width θ = 14 w50mm s = 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 w150mm s = θ = 14 w100mm s =

36 Comparison of Track and Wheel track wheel slope angle [deg] kg 11.8kg 14.8kg 17.8kg slope angle [ ] w50mm w100mm w150mm slip ratio [ ] slip ratio [ ] 41

37 Q: How can we improve the traction performance of the wheels? Yes with increased contact area with decreased wheel sinkage 42

38 Deformable Tire Example: Michelin Tweel

39 Traction Performance of Wheel and Track for Soft-Soil Traversal Introduction Research Setup The Sand Box The Test Beds Traction Performance Evaluation Experimental Results for Wheel v.s. Track How can we improve the wheel traction? Summary

40 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.

41 The Space Robotics Lab. Dept. of Aerospace Engineering Tohoku University, JAPAN Directed by Prof. Kazuya Yoshida Free-Flying Space Robot Robotic Systems on ISS Planetary Exploration Rovers The SPACE ROBOTICS Lab. Asteroid Sampling

Traveling Performance Evaluation of Planetary Rovers on Loose Soil

Traveling Performance Evaluation of Planetary Rovers on Loose Soil Masataku Sutoh Department of Aerospace Engineering Tohoku University Aoba 6-6-, Sendai 98-8579, Japan sutoh@astro.mech.tohoku.ac.jp Tsuyoshi