PS06
Effect of Wheel Rotation Speed on the Running
Performance of a Small Two-Wheeled Lunar Rover
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Yamato OTANI , Hiroto MORI , Kimitaka WATANABE2, Kazuto TANAKA2 and Masataka
KAWAGUCHI2
1Doshisha University
Doshisha University

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1. Introduction
In recent years, unmanned exploration of the Moon using rovers has been attracting attention because of thehazardous environment for human beings at the Moon. The problem with small two-wheeled rovers, which
can reduce development costs, is that regolith on the lunar surface causes them to become stuck1) , a condition
that prevents them from moving forward. This study aims to reduce the amount of having rovers getting stuckby adjusting the rotation speed of the wheels of a small two-wheeled lunar rover and to run with low power
consumption. The optimal speed of a small two-wheeled rover that can run with low power consumption will
be proposed.
2.

Experimental methods

2.1. Creation of a small two-wheeled rover
Figure. 1 shows a drawing of a small two-wheeled rover body and circular wheels. In this study, a 3D printer(Raise3D Pro3 Plus, JAPAN 3D PRINTER) was used to create the body and wheels in layers. ABS resin (RAISE3D) was used as the material. Two servo motors (XC-330-M288-T, DYNAMIXEL, ROBOTIS) were controlled
by a board computer (SPRESENSE, SONY) to control the phase and speed of the left and right wheels. The
circular wheel was 100 mm in diameter and 25 mm thick, with 12 lugs of 10 mm long mounted at equalintervals on the outside of the wheel.

(a)Two-wheeled rover(b)CircularFigure 1. Rover and wheel blueprints
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In this study, the created rover was driven on soil covered with a lunar soil simulant (FJS-1, ShimizuCorporation) as a substitute for regolith. The wheel rotation speed was adjusted in 2 min-1 increments from 6
min-1 to 14 min-1. Three parameters were used to evaluate the running performance: running time, energy
consumption during running and slip rate. The slip rate was calculated using the following equation, where𝑉 is the wheel's running speed, 𝛾 is the wheel's circumference and 𝜔 is the angular velocity.

𝜆 =1−𝑉: 𝐷𝑟𝑖𝑣𝑖𝑛𝑔(𝑟𝜔 ≥ 𝑉 )𝑟𝜔

(1)

𝜆 =1−𝑟𝜔: 𝐵𝑟𝑒𝑎𝑘𝑖𝑛𝑔(𝑉 ≥ 𝑟𝜔)𝑉(2)The running distance was set to 700 mm and the inclination angle was set to 0 degrees. The shear strength
at a depth of 40 mm was measured using a vane shear test apparatus (FTD2CN-5, Nishinihon Shikenki Co.,
Ltd.） The average shear strength of the test area before driving was set to 0.4 ± 0.05 by using a levelingmachine and a flat plate.
3.

Results
Figure 2 shows the results of the running test. The running time and energy consumption decreased as therotation speed increased, but the rotation speed and energy consumption increased at 14 min-1. Table 1 shows
the shear strength of the soil after running. The shear strength decreased as the rotation speed increased.

Figure 3. Runnning test results

Table 1. Shear strength and trend of soil in ruts after driving

Rotation [min-1]

Track [cNm]

Tendency

60.53

Increase

80.52

Increase

100.49

Increase

120.42

Increase

140.34

Decrease
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4.

Discussion
It has been reported that the main propulsive force for wheeled rovers in soft ground is the passive pressureof the wheel lugs1) . The passive pressure is related to the soil density, which increases as the soil densityincreases. It is reported that as speed increases, sand under the wheel escapes outward and the soil cannot becompacted2) . Therefore, as velocity increases, wheel sinkage increases. It is also reported that the density
increases with soil depth3) , and although the sinkage increases as the rotation speed increases, it converges toa constant value as the density increases. Therefore, it is considered that as the rotation speed increases, therunning time decreases, resulting in lower energy consumption. In addition, it is thought that above a certain
rotation speed, sufficient passive pressure could not be obtained, resulting in a decrease in running
performance.
5.

Conclusion
A small two-wheeled rover was created and its running performance was evaluated by adjusting wheel

rotation speed. Increasing wheel rotation speed shortens the running time and enables running with low
power consumption, but above a certain number of rotations, sufficient passive pressure cannot be obtained,and running performance deteriorates.
References
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2)

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K. Iizuka and T. Kubota: Study on locomotion on systems of lunar exploration roverson loosesoil. Studies in Scienceand Technology, 1 (2012) 49, DOI: https://doi.org/10.11425/sst.1.49.
K. Iizuka, Y. Sato, Y. Kuroda and T. Kubota: Study on Traversability with Consideration of Wheeled Forms for Lunarand Planetary Exploration Rovers. Transactions of the Japan society of mechanical engineers. C 72 (2006) 148, DOI:
https://doi.org/10.1299/kikaic.72.3842.
S. Wakabayashi, K. Matsumoto: Development of Slope Mobility Tested using Simulated Lunar Soil. JAXA Repository
5 (2006) 1, https://jaxa.repo.nii.ac.jp/records/2650© 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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