PS05
異なる車輪形状を有する四輪小型月面探査機の横滑り評価
Evaluation of skidding of a small four-wheeled lunar
rover with different shaped wheels
濵島優太 1, 和久井淳 1, 渡辺公貴 2, 川口正隆 2, 田中和人 2
Yuta HAMASHIMA1, Makoto WAKUI1, Kimitaka WATANABE2, Masataka KAWAGUTHI2 and Kazuto TANAKA2
1 同志社大学大学院, Doshisha University
2 同志社大学, Doshisha University

Introduction

1.

In recent years, the lunar exploration in the space development has again attracted attention. The lunar
exploration is necessary to unravel the solar origin and use moon resources. In order to conduct thisexploration smoothly, the necessity of small lunar exploration rovers increases, which are capable ofautonomous driving. When they drive on the moon, the soft ground formed by the lunar fine sand called
Regolith causes wheels used for rovers to slip. When climbing the slope such as craters, wheels can sink into
the soft ground and become inoperative called stuck. When crossing the slope, a slip called side skid occurs
and can cause the lowering of exploration efficiency by taking rovers off the target path. It also can causerovers to become inescapable because the wheel is buried into the soil1). We have developed small lunar rovers
with special shaped wheels2) such as an ellipse wheel and a 3blade wheel that is able to climb the slope of 30
degrees. However, effects of these special shaped wheels on the side skid have not been evaluated. Therefore,
this paper reveals the slope crossing performance of the small lunar rover with specifically shaped wheels.

2.

Design and experimental method for small lunar rover

2.1.

Design of a small lunar rover

Figure. 1 shows a small four-wheeled lunar rover used in this experiment. The sizes of the main body are
230 mm in length, 90 mm in width, and 73.5 mm in height and the total weight is 2 kg placing a weight.
Figure. 2 shows wheels attached to the main body. A circular wheel has a diameter of 110 mm, and an ellipse
wheel has a major axis of 110 mm and a minor axis of 66 mm. A 3blade wheel is inscribed in a circular with adiameter of 110 mm and a blade radius of curvature of 27.5 mm. Each wheel is designed with 15 lugs of 10mm high and 3 mm thick. The width of wheels is set to 30 mm.
2.2.

Road test track

Figure. 3 shows a test site. The size of test site is 1820 mm long, 450 mm wide and 308 mm high. The groundenvironment is set with a mixture of silica sand No. 5 (Takeori Kogyo Sho) with a particle size of 0.3 to 0.8 mm
1 of 6and silica sand No. 6 (Takeori Kogyo Sho) with a particle size of 0.2 to 0.3 mm, at a ratio of 1:1.
2.3.

Cross-slope test

The slope traverse test is conducted as shown in Figure. 4(a). The slope angle conditions are 5 °, 10 °, and 15 °.
The installation condition of the small lunar rover is 100 mm from the outer side of the test site above the slope to theinner side of the wheel above the slope. The power consumption and travel time of the small lunar rover are measured for
500 mm of travel.

Figure. 4(b) shows the location of the measurement of the amount of skidding. The horizontal

distance from the outer side of the test site above the slope to the inside of the ruts formed by the front wheels above theslope is measured. The amount of skid is calculated by dividing the difference between the measured value and theinstallation distance of 100 mm by the value of cos (slope angle). The motor speed is set at 10 rpm and driven by a 12 V
regulated power supply.
2.4. Measurement of wheel settlement relative to the ground
Measure the amount of wheel settlement and the lateral area of the settlement when traversing a 15° slope.
The amount of wheel settlement relative to the ground is calculated by measuring the distance from the centerof each wheel to the ground using ImageJ3). Furthermore, the measured values and the drawing data of eachwheel are used to measure the area of settlement of each wheel.

3.

Experimental results and discussion

3.1

Comparison of energy consumption and running time

Figure. 5 shows the power consumption of each wheel. The circular wheel consumes the least amount ofenergy at each inclination angle. It has a larger circumference than the other wheel shapes, which shorten therunning time, and this is thought to reduce the power consumption. In the wheel shapes except the circularwheel, it is thought to increase the amount of power consumption because of the extra torque generated in themotor which caused the vehicle body to move up and down.
3.2 Relationship between the amount of skidding and settlement of each wheel
Figure. 6 shows the amount of skid for each wheel. When comparing the ellipse wheel and the circular wheel,
the ellipse wheel has a smaller amount of skid at slope angle of 5°. However, there is no difference in theamount of skid at slope angle of 10° and 15°. When comparing the 3blade wheel and the circular wheel, the3blade wheel has a smaller amount of skidding at all slope angles.
Figure. 7 shows the amount of sinkage and the lateral area of the sinking part for each wheel. Comparing
the ellipse wheel and the circular wheel, there is no significant difference in the mean values of the amount ofsinkage and the lateral area of the sinking part of both wheels. The 3blade wheel sinks not only the lugs but
also the wheel itself during soil scraping. Therefore, the amount of sinkage and the lateral area of the sinking
part were the largest among the wheel shapes compared.
Figure. 8 shows how skidding occurs. Skidding occurs when the downward force due to the wheel's own
weight exceeds the support force from the soil, causing the soil to collapse. The bearing force immediately
before the soil collapses is called the passive earth pressure, which is defined in Rankine's theory3) of earthpressure by Equation (1).
1

∅2

2

𝑃 = 𝑟𝐻 2 𝑡𝑎𝑛2 (45° + )(N/m2)(1)
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Therefore, it is considered possible to increase the passive earth pressure and obtain high bearing capacity byincreasing the amount of settlement H into the soil. It is also considered effective to increase the lateral area ofsettlement to reduce the pressure on the soil to less than the passive earth pressure.
The ellipse wheel does not differ from the average values of settlement and lateral area of settlement of thecircular wheel. Therefore, there is no difference in the total amount of support force received from the soil
during the measurement time, suggesting that the ellipse wheel is not effective in suppressing sideslip at highslopes. The 3blade wheel has the largest settlement and the largest lateral area of settlement among the wheelscompared. Therefore, it is considered that the support force is increased by decreasing the pressure on the soil
while increasing the passive soil pressure, and that the wheel is effective in preventing sideslip even at highslopes. These results are based on Equation (1) and show Rankine's soil pressure theory is appropriate.

4.

Conclusion

The findings of this study are as follows.
1) When traversing a slope, the circular wheel can run with the lowest power consumption and in the shortest
time. This may be due to the fact that the circumference of the circular wheel is the largest and no torqueloss occurs due to the vertical motion of the vehicle body.
2) The 3blade wheel is more effective than other wheels in suppressing skidding. This is because the wheel
itself also sinks when the 3blade wheel scrapes the soil, and both the amount of sinkage and the lateralarea of the sinking part are larger.
3) When traversing a slope, the greater the amount of settlement of the wheel relative to the ground and thelateral area of the settlement, the higher the support from the soil and the more effective the control ofskidding.

Figure 1.

(a)Small four-wheeled lunar rover used in this experiment

Circular wheel(b) Ellipse wheel

Figure 2.

(c)3blade wheel

Shape of each wheel
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Figure 3.

(a)Test site

Schematic of driving
Figure 4.

(b)

Measurement position

Schematic diagram of a cross-slope test

1530

10

Time [s]Power consumption [mWh]

Circular wheel
Ellipse wheel
3blade wheel

Circular wheel
Ellipse wheel
3blade wheel

2051005(a)1015
Slope angle [°]Power Consumption

Figure 5.

05(b)1015
Slope angle [°]Running TimePower consumption and running time（N=5, mean ± S.D.）

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Slip distance [mm]150
Circular wheel
Ellipse wheel
3blade wheel

10050051015

Slope angle [°]Figure 6.

(a)Amount of skid（N=5, mean ± S.D.）The amount of sinkage

Figure 7.

(b)

The lateral area of sinkage

Amount of sinkage and the lateral area of sinkage for each wheel

Figure 8.

Mechanism of skidding

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References

1)

H. Inotsume, et al, Study on the Effect of Shifting Center of Gravity on Mobile Robots Traversing Loose Soil Slopes
Laterally, Dynamics and Design Conference Motion and vibration control Movic, vol. 12 (2011) pp. 76.
K. Watanabe, et al, Effect of Elliptic Column Wheels on the Running Performance of Small Lunar Exploration Roveron Soft Ground, The Harris science review of Doshisha University, vol. 62, no. 3 (2021) pp. 189.
Rasband, W.S., ImageJ, U. S. National Institutes of Health, Bethesda, Maryland, USA, https://imagej.nih.gov/ij/, 19972018.
T. Watanabe, et al, Proposal of Walking to reduce Slipping Behavior using Compaction Effect of Loose Soil caused bya Propagation of Vibration for Small Light Lunar Planetary Exploration Rovers with Legs, Transactions of the JSME,
vol. 86, no. 886 (2020) pp. 19.

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© 2024 by the authors. Submitted for possible open access publication under theterms and conditions of the Creative Commons Attribution (CC BY) license(http://creativecommons.org/li censes/by/4.0/).

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