PS08
月模擬砂を用いた走行試験場の開発と二輪小型ローバの走行性能検証
Development of a Driving Test Site Using MoonSimulated Sand and Verification of Driving Performanceof a Small Two-Wheeled Rover
堀口智輝 1, 野山剛志 2, 渡辺公貴 2, 田中和人 2, 川口正隆 2
Tomoki HORIGUCHI1, Koshi NOYAMA2, Kimitaka WATANABE2, Kazuto TANAKA2, and Masataka
KAWAGUCHI2
12同志社大学大学院，Doshisha University
同志社大学，Doshisha University

1. Introduction
In recent years, research on rovers capable of direct exploration of the lunar surface has attracted muchattention. The regolith deposited on the lunar surface causes the wheels to slip and the rover gets stuck, acondition that renders it from driving. To prevent the small rover, which has a small ground contact area,weak ground compaction, and poor traveling performance, from getting stuck; it is necessary to establish a
traveling system that can climb high slopes and to evaluate its traveling performance through hill climbing
tests on soft ground. Previous studies have only verified hill climbing with silica sand, and even tests using
moon-simulated sand have not been conducted at test sites where the angle can be changed to higher slope.
In this study, a traveling test site that can change the angle up to 30 degrees or more is constructed, andtraveling tests of a small-sized rover are conducted in both silica sand and moon-simulated sand to clarify theeffects of differences in soil environments on traveling performance.
2. Experimental procedure
2.1. Development of running test site
Figure. 1 shows the appearance and tilting mechanism of the moon-simulated sand running test site
developed in this study. The running test site has an acrylic water case at 2000 mm long, 1000 mm wide, and400 mm high fixed to the upper frame, and an electric lifting device mounted between the frames driving thecase to achieve an arbitrary tilt angle. The soil was made of moon-simulated sand (FJS-1，Shimizu Corporation)
spread to a depth of about 100 mm within the effective running surface of the acrylic case. The running testsite using silica sand is shown in Figure. 2. This running test site is 1820 mm long, 450 mm wide, and 308 mm
high. The soil was a 1 : 1 mixture of silica sand No. 5 and No. 6, spread to a depth of about 100 mm within theeffective driving surface. Angle adjustments were made by lifting one side of the running test using a lift table.
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Figure 1. Driving test site using moon-simulated sandFigure 2. Driving test site using silica sand2.2. Fabrication of a small lunar rover
Figure. 3 shows the appearance of the rover fabricated in this study. Fusion360 was used to create drawingsof the rover body and wheels, and a 3D printer (RAISE 3D) was used for laminated modeling. The rover isequipped with servo motors (XC330-M288-T，DYNAMIXEL) and Spresense (SONY) to rotate the wheels at
an arbitrary angular speed. In this test, the left and right motors were driven at 10 rpm. The wheels of the rover
are shown in Figure. 4. A cylindrical wheel with lugs and an eccentric wheel, in which the axle position of thecylindrical wheel is eccentric by 25 mm, were used. These wheel widths were set at 25 mm.

Figure 3. Appearance of Rover
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(b) Eccentricity(a) Cylinder

Figure 4. Drawing of wheels

2.3. Running test
Running time and slip rate were used as indicators of the rover’s running performance in this study. Theslip rate was calculated using the following equation defined by the running distance L，wheel circumference
length lw，number of revolutions per unit time n，and running time t.

𝐿∶ 𝐷𝑟𝑖𝑣𝑖𝑛𝑔(𝑙𝑤 𝑛𝑡 ≥ 𝐿)
𝑙𝑤 𝑛𝑡
λ=,
𝑙𝑤 𝑛𝑡
1−∶𝐵𝑟𝑎𝑘𝑖𝑛𝑔(𝐿≥𝑙𝑛𝑡)
𝑤{𝐿1−(1)The test was conducted with a travel distance of 700 mm and an inclination angle of 0 to 30 degrees inincrements of 5 degrees. The soil was leveled over the driving range using a leveling machine, and a vaneshear (FTD2CN-S，Nishinippon Tester) was used to confirm that the average shear torque at five points along
the driving course was less than 0.5 ± 0.1 cNm for silica sand and 0.3 cNm for simulant, thus providing theinitial conditions for driving tests.
3. Results
Figure. 5 shows the results of running tests. The rover with the cylindrical wheel was able to climb up to 30
degrees on silica sand but was not able to climb at more than 5 degrees on moon-simulated sand. Although
the rover with the eccentric wheel was able to climb hills up to 30 degrees even on moon-simulated sand, its
running performance was significantly lower than that on silica sand.

(i) Cylinder(ii) Eccentricity(a) Running time
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(i) Cylinder(ii) Eccentricity(b) Slip ratio
Figure 5. Results of running tests

4. Discussion
The moon-simulated sand used in this study (FJS-1) exhibits high dilatancy characteristics and is reported
to be much more sensitive to density than silica sand. When traveling in a loosely packed section, the densityof the moon-simulated sand changes from sparse to dense as the lugs scratch the soil to gain propulsive force.
As the lug moves, the soil volume also changes, and the lugs are unable to acquire sufficient reaction force tomove forward. When traveling on soft ground, the propulsive force received by the lugs of the rover
contributes significantly to its traveling performance. Therefore, the lack of reaction force from the lugs may
have accelerated the sinking of the rover, leading to a reduction in running performance.
5. Conclusion
A test site with a variable angle at a high slope was successfully developed, and a small rover was tested inboth silica sand and moon-simulated sand. Due to the characteristics of the density change of the moonsimulated sand, the rover could no longer obtain propulsion from the lugs, and its running performancedecreased. Eccentric wheels are also effective in moon-simulated sand.
References
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K. Iizuka and T. Kubota: Study on locomotion systems of lunar exploration roverson loose soil. Studies in Scienceand Technology, 1 (2012) 49, DOI: https://doi.org/10.11425/sst.1.49
H. Kanamori, S. Udagawa, T. Yoshida, S. Matsumoto and K. Takagi: Space 98, Amer Society of Civil Engineers(1998).DOI: https://doi.org/10.1061/40339(206)53
M. Sutoh, K. Nagatani, K. Yoshida, Traveling performance evaluation of wheeled rover climbing various soil slopes.
Proceedings of the 2012 JSME Conference on Robotics and Mechatronics (2012) 1A2-L06,
DOI: https://doi.org/10.1299/jsmermd.2012._1A2-L06_1© 2024 by the authors. Submitted for possible open access publication under
the terms and conditions of the Creative Commons Attribution (CC BY) license(http://creativecommons.org/li censes/by/4.0/).

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