한국형 인공월면토를 이용한 달탐사 로버 휠 성능평가 실험 연구

한국형 인공월면토를 이용한 달탐사 로버 휠 성능평가 실험 연구 97

한국지반공학회논문집 제32권 11호 2016년 11월 pp. 97 ～ 108

JOURNAL OF THE KOREAN GEOTECHNICAL SOCIETYVol.32, No.11, November 2016 pp. 97 ～ 108

ISSN 1229-2427 (Print)

ISSN 2288-646X (Online)

https://doi.org/10.7843/kgs.2016.32.11.97

한국형 인공월면토를 이용한 달탐사 로버 휠 성능평가 실험 연구

Experimental Study of Lunar Rover Wheel’s Motion Performance

on Korean Lunar Soil Simulant

왕 성 찬1

Wang, Cheng-Can

한 진 태2

Han, Jin-Tae

Abstract

Lunar rover plays an important role in lunar exploration. Especially, performance of rover wheel related to interaction

with lunar soil is of great importance when it comes to optimization of rover’s configuration. In this study, in order

to investigate the motion performance of lunar rover’s wheel on Korean Lunar Soil Simulant (KLS-1), a single wheel

testbed was developed and used to carry out a series of experiments with two kinds of wheel with grousers and

without grousers which were used to perform the experiments. Wheel traction performance was evaluated by using

traction parameters such as drawbar pull, torque and sinkage correlated with slip ratio. The results showed that the

single wheel testbed was suitable for evaluation of the performance of wheel and rover wheel with grousers which

was likely to have higher traction performance than that without grousers in Korean Lunar soil simulant. The

experimental results could be utilized in verification of the optimum wheel design and effectiveness of wheel traction

for Korean lunar rover.

요 지

달 탐사시 탐사 로버는 반드시 필요하며, 특히 월면토와 로버 휠의 상호작용에 의한 로버 휠의 성능은 로버의 최적

형상을 결정하는데 있어서 매우 중요하다. 본 연구에서는 한국형 인공 월면토(KLS-1)에서 달 탐사 로버 휠의 거동

성능을 평가하기 위하여 단일 휠 성능평가 실험장비를 개발하였고, 이를 이용하여 그라우져 유무에 따른 휠 성능

평가 실험을 수행하였다. 휠 성능은 슬립율에 따른 견인력, 토크, 침하 등으로 평가하였으며, 실험 결과 개발된 단일

휠 성능평가 실험장비는 휠 성능을 적절히 평가하는 것으로 나타났으며, 한국형 인공 월면토에서 그라우져가 있는

휠이 그라우져가 없는 휠에 비해 높은 견인 성능을 보여주었다. 향후 본 실험은 한국형 로버의 최적 휠 결정을 위해

사용될 수 있을 것으로 판단된다.

Keywords : Lunar rover, Single wheel testbed, Drawbar pull, KLS-1, Grouser

1 정회원, Member, Graduate Student, Dept. of Geo-Space, Univ. of Science & Technology

2 정회원, Member, Senior Researcher, Dept. of Geotechnical Eng., Korea Institute of Civil Eng. and Building Tech., Tel: +82-31-910-0259, Fax: +82-31-910-0563,

[email protected], Corresponding author, 교신저자

* 본 논문에 대한 토의를 원하는 회원은 2017년 5월 31일까지 그 내용을 학회로 보내주시기 바랍니다. 저자의 검토 내용과 함께 논문집에 게재하여 드립니다.

Copyright © 2016 by the Korean Geotechnical Society

This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

98 한국지반공학회논문집 제32권 제11호

1. Introduction

Since 1959, the Soviet Union and United States have

started lunar exploration program, followed by various

kinds of lunar exploration activities from other developed

countries. Recently, there have been research programs

on rovers for lunar exploration in South Korea. In order

to accomplish difficult missions on the moon, there is a

continuous need for developing an unmanned exploration

rover with high performance which can adapt to the complex

environment on the moon and pass the soft soil and

negotiate obstacles successfully. In the stage of lunar

rover’s development, rover’s locomotion performance on

the deformable terrain should be investigated in order to

plan the moving path. In order to improve negotiation

and mobility performance, optimizing rover wheel’s design

is very important. Therefore, investigating mechanical

characteristic of wheel-soil interaction has a critical signi-

ficance for optimization of wheel design and development

of lunar rover with high mobility performance (Ding et

al., 2011a).

A variety of approaches to investigate wheel-soil interac-

tion performance have been developed and used. One of

the empirical methods was developed by US Army Water-

ways Experiment Station (WES). This method can evaluate

vehicle traction performance with respect to ground cha-

racteristics by cone index. However, this empirical method

has limitation in predicting certain performance parameter

of tyres accurately (Gee-Clough, 1978). Recently, numerical

simulation methods which use computer technology (i.e.,

FEM, DEM) to simulate the model for the traction of

a rover wheel on deformable terrain are widely applied

to this research field (Liu et al., 1996; Nakashima et al.,

2010). It also has limitations in simulating large, dis-

continuous terrain deformation. To tackle these problems

mentioned above, semi-empirical approaches using wheel-

terrain theoretical model and physical properties of soil

for evaluating vehicle performance on terrain have been

developed. A pioneering work in terramechanics was

conducted by Bekker, which came up with the relation

between rolling resistance and vertical stress for rigid

wheel rolling on the soft soils using Bekker pressure-

sinkage equation (Bekker, 1956). Bekker and Wong’s

model determined the wheel performance metrics such

as torque, drawbar pull, motion resistance, slope angle

and so on (Wong, 2010). When the drawbar pull comes

up, the shearing action of wheel on the soil causes it to

slip. Since the drawbar pull and resistance is a function

of slip, the relationships between the drawbar pull and

slip of a vehicle wheel are used to evaluate the mobility

performance of vehicle. Recently, in planetary researches,

due to small dimension of rover wheels and cost of

experiments, single wheel testing is thought to be a simple

and efficient way to investigate rover-wheel traction per-

formance under various situations with different terrain

types. Until now, many research works have been done

on the study of locomotion performance of small rigid

wheel on terrestrial soil such as sand.

In this study, a single-wheel testbed was developed

and used to experimentally evaluate traction performance

of rigid wheel on deformable soil in terms of drawbar pull,

torque and slip-sinkage versus slip ratio under different

wheel configuration and vertical load. As planetary rover

can get stuck into loose soil, wheel with grousers has been

studied because it has significant influence on wheel’s

performance (Liu et al., 2008; Sutoh et al., 2012). As

introduced in previous studies to implement and satisfy

the task of Korean lunar exploration, two kinds of wheels,

one with grousers and the other without grousers were

applied to investigate and compare rover wheel’s motion

performance. In addition, rover’s mobility highly depends

on mechanical properties of terrain. Due to the limitation

of use of water and organic material in the moon, properties

of lunar regolith are clearly distinguished from terrestrial

soil (Heiken et al., 1991). Due to the limited quantity

of available lunar soils, it is very difficult to carry out

experiments on the real lunar soils. Therefore, to satisfy

and accomplish the reliable analysis of wheel mobility

performance, Korean lunar soil simulant (KLS-1) having

similar physical and geotechnical properties of real lunar

soil was developed by Ryu et al. (2015) and utilized to

simulate lunar terrain in this study.

Though some previous studies aimed at similar experi-

mental investigation, this study is distinguished from them


Fig. 1. Force distribution of moving rigid wheel on soft soil

in terms of utilization of Korean rover wheel and Korean

lunar soil simulant. Thus, we believe this study could

contribute to the demonstration of the mobility of Korean

Lunar Rover in lunar environment condition for Korean

Lunar Exploration Project.

2. Wheel-soil Interaction Mechanics

The analysis of mechanical characteristics between

lunar rover wheel and soil interaction is the basis of

analyzing the lunar rover’s mobility performance. The

analysis of mechanical characteristics wheel-soil interaction

is related to the terrain characteristics and mechanical

model of wheel-soil interaction.

2.1 Terrain Characteristics under Stress Condition

The semi-empirical approach proposed by Bekker (1960)

is used to decompose the deformation of soil vertically and

horizontally, corresponding to normal pressure characterization

and shearing characterization, respectively.

A vehicle applies normal load to the terrain, which

results in sinkage. This causes motion resistance (Wong,

2010). Soil is considered as deformable material. To predict

the normal pressure distribution on vehicle-terrain interface,

the pressure-sinkage relationship for deformable terrain

can be defined using Bekker’s equation (Bekker, 1960)

as follows:

(1)

Where p is the normal pressure added on the wheel,

b is the smaller dimension of a contact rectangular plate;

n, kc, and are pressure-sinkage parameters for the

Bekker equation, z is sinkage, b is width of contacting

plate.

A vehicle applies shear load to the terrain surface

through its running gear, which results in the development

of thrust and associated slip (Wong, 2010). To predict

the tractive performance of vehicle, it is essential to

understand the shear stress-shear displacement relationship.

As the lunar soil is plastic soil, its characterization of

the shearing behavior can be evaluated based on Janosi’s

shearing model (Janosi, 1961). According to this model,

the relationship between shear stress of soil and shearing

displacement is shown as follows:

max

(2)

max

tan (3)

Where c is the apparent cohesion of soil, max

is the

maximum shear strength of soil, is the internal friction

angle of soil, k is shear deformation modulus, and j is

shearing deformation.

2.2 Rigid Wheel-deformable Terrain Interaction Model

Performance of an off-road vehicle refers to its ability

to overcome motion resistance, to develop drawbar pull,

to negotiate grade, and to accelerate straight-line motion

(Wong, 2010). Fig. 1 shows a picture of interaction force

distribution of rigid wheel moving on soft soil. In Fig.

1, r is wheel radius, is the total sinkage of wheel,

is the slip sinkage, is the wheel-soil interaction angle,

is the entrance angle, is the exit angle, is the

maximum stress angle, is the wheel angular velocity,

v is wheel travelling velocity, W is normal load, T is

traction torque, DP is drawbar pull, and are normal

stress and shear stress on wheel-soil contact surface,

respectively.

The drawbar pull plays an important role in the

evaluation of vehicles’ traction performance. Drawbar pull

is developed from soil thrust beneath a moving wheel.


(a) Single wheel testbed in MIT (Iagnemma, 2005)

(b) Single wheel testbed in CMU (Apostolopoulos, 2001)

(c) Single wheel testbed in HIT (Ding et al., 2011b)

Fig. 2. Existing single wheel testbed

Drawbar pull is the net force used to measure tractive

ability of vehicles. Drawbar pull (DP) indicates the difference

between the thrust F and the sum of all resisting forces

R on the vehicles. Wong’s model denotes DP as follows

(Wong, 1967):

cos

sin (4)

Where b is the width of wheel.

When a wheel moves on soft soil, shearing action takes

place on the wheel and terrain interface, which was

illustrated in the last section. Consequently, there is a

relative movement (or shear displacement) between wheel

and terrain in horizontal direction, which results in slip.

According to Wong (2010), slip generally happens when

the lunar rover is moving on the deformable regolith,

consequently leading to different wheel velocity from rover

travelling velocity. Therefore, slip ratio is a way of

expressing the slipping behavior of the wheel. It should

be considered to determine the vehicle acceleration. The

definition of slip ratio and relationship between shear

displacement and slip ratio are expressed by:

(5)

sinsin (6)

Where v is the actual moving speed of the vehicle,

ωr is the wheel’s velocity which is equal to the product

of angular speed ω and radius of wheel r.

As drawbar pull is a function of shear strength in

equation (4), shear strength is related to shear displacement

in equation (2)，shear displacement is related to slip ratio

in equation (6), drawbar pull is also a function of slip

ratio.

3. Single Wheel-soil Interaction Testbed

Until now, there are various kinds of testbed developed

for researches on the motion of a robotic wheel with small

dimensions. Fig. 2 (a) shows a single-wheel testbed which

was first developed for planetary rovers in Massachusetts

Institute of Technology (MIT) (Iagnemma, 2005). This

testbed was used to conduct the experiments of “Rocky”

wheel traction performance. It is used to measure drawbar

pull, driving torque, wheel velocity and carriage velocity,

and also analyze the force of wheel-soil interaction under


Fig. 3. Single wheel testbed developed by KICT

Table 1. Specification of single wheel testbed

Wheel diameter 150-250 mm

Wheel width 50-120 mm

Speed of carriage motor 190-1900 mm/min

Speed of driving motor 1-10 rpm

Vertical load 0-22.5 kg

Moving distance 0-600 mm

Maximum horizontal force 100 kg Fig. 4. Comparison of particle size distribution (Ryu et al., 2015)Fig. 4. Comparison of particle size distribution (Ryu et al., 2015)

different slip ratio by means of controlling wheel velocity

and carriage velocity. A single wheel testbed shown in Fig.

2 (b) developed by Robotics Institute in Carnegie Mellon

University is used to perform characterization of “Nomad”

locomotion with measuring driving power, endurance

and behavior of the wheel’s drive unit (Apostolopoulos,

2001). Fig. 2 (c) shows a testbed developed in Chinese

State Key Laboratory of Robotics and System in Harbin

Institute of Technology (HIT) is also used to measure

parameters such as drawbar pull, sinkage, slip ratio and

driving torque values (Ding et al., 2011b).

In this research, the single wheel-soil interaction testbed

shown in Fig. 3 was developed to measure the wheel

drawbar forces, torques and sinkage. This testbed dis-

tinguished from other apparatus as the soil box below

can be separated from the upper part which is favorable

for the experiment in the freezing chamber in KICT.

However, experimental results under freezing condition

were not included in this paper. The size of soil box of

the testbed is 2000 mm × 600 mm × 500 mm. It was

designed to conduct experiments on a wheel with a

diameter ranging from 150 mm to 250 mm and width

ranging from 50 mm to 120 mm. The testbed consists of

a driving motor, a carriage motor, LVDT, a counterweight

system, and a torque sensor. The driving motor and the

carriage motor are used to make the wheel and vehicle

body move independently. The slip ratio can vary by

controlling the linear velocity of the wheel carriage in

the horizontal direction and angular velocity of the wheel.

LVDT is used for measuring wheel singkage on the soil.

The load added on the wheel can be controlled by a

counterweight system attached upon the wheel carriage.

The detailed information of the testbed is shown in Table 1.

4. Lunar Soil Simulant and Experimental Setup

4.1 Korean Lunar Soil Simulants (KLS-1)

In order to validate reliable mobility of rover wheel’s

mobility performance, the experiments were carried out

on the Korean lunar soil simulant (KLS-1). Korean Lunar

soil Simulant was developed by KICT in 2014 to offer

simulant lunar terrain for lunar rover’s motion performance

tests. KLS-1 was made from basalt in Yeoncheon through

crushing, screening, grinding, sieving and recomposition

(Ryu et al., 2015). A group of laboratory tests were carried

out to measure the geotechnical properties of KLS-1.

Particle size distribution is considered as one of the most

fundamental parameters to evaluate the geotechnical cha-

racteristic. The test results showed that the particle size

distribution of KLS-1 matched with real lunar soil and

other lunar soil simulant such as JSC-1 and FJS-1 as

shown in Fig. 4. Other geotechnical properties from direct

shear test, relative density test and specific gravity test


Table 2. Geotechnical properties of KLS-1

GS C (kPa) Φ (°) γd D50 (mm) Cu

2.94 1.716 40.6 1.46~1.80 0.03 12.50

Fig. 5. Wheel developed in KATECH

(a) Wheel without grousers (b) Wheel with 16 grousers

Fig. 6. Test wheels

Table 3. Experimental conditions and cases

Terrain Wheel design Relative density (%) Moving velocity (mm/s) Vertical load (kg) Slip ratio

Rigid plate Without grousers -

10 6

0.1, 0.2,

0.3, 0.4

0.5

KLS-1 Without grousers 60

KLS-1 With grousers 60

shown in Table 2 were also similar to those of other

lunar soil simulants such as JSC-1 and FJS-1. In addition,

since the relative density of lunar soil is 65 ± 3% in

depth of 0-15cm from lunar surface, in keeping with the

lunar regolith condition of surface layer, the relative density

of soil was prepared as 60% in experiments (Mitchell

et al., 1974).

4.2 Wheel Designs

A wheel shown in Fig. 5 was designed in Korea

Automotive Technology Institute (KATECH) for Korean

lunar rover. Regardless of influence of wheel’s weight,

size of wheel with diameter of 170 mm and width of

80 mm was adopted in this study. To compare effect of

grousers on wheel’s traction performance, two kinds of

cylinder aluminum wheels with 16 grousers (height of

10 mm, spacing of 36° and thickness of 3 mm) and

without grousers were applied based on comparison with

past experimental results. Pictures of wheels are shown

in Fig. 6.

4.3 External Conditions

Due to the limitation of mobility of a lunar rover and

energy supply, the rover is not available to move at a

high speed. The maximum moving velocity of rover

developed in KIST. In this experiment, to ensure stability

of wheel’s motion performance on the testbed, a lower

velocity of wheel was set to be 10 mm/s. As mass of

Korean four-wheel rover is 20 kg, which means that the


Fig. 7. Procedure diagram of experiments

Fig. 8. Example of drawbar pull, torque and sinkage time histories

(Vertical load 6 kg, wheel with grouser, slip ratio 0.2)

average vertical load on each wheel is 5 kg, vertical

loads added to the wheel were controlled to be 6 kg

through counterweight in this experiment. The experimental

cases are shown in Table 3 below.

4.4 Experimental Procedure

In order to avoid sinkage in the locomotion, the slip

ratio of exploring rovers should be well controlled, for

instance, the maximum slip ratio of Mars rovers of USA

is controlled to be less than 0.4 (Ding, 2010). In this

study, to compare performance of rover wheel traction,

the slip ratio was set to be from 0 to 50% and slip ratio

was controlled by varying motion velocity of carriage

motor. In order to ensure the repeatability and reliability

and to reduce measurement error of the experiments, all

the experiments were carried out three times under the

same condition. The mean values were utilized to derive

the correlation between drawbar pull, torque, sinkage and

slip ratio, respectively.

Fig. 7 shows the procedure of experiments. Before

performing experiments, all sensors were calibrated and

the test wheel size and the rover moving velocity and wheel

angular velocity were considered as input parameters.

Soil conditions were cautiously managed to be kept constant.

During experiments, the value of drawbar, torque and sinkage

were recorded from a computer program.

5. Results and Analysis

All the tests for the drawbar pull, torque and slip-

sinkage were measured under slip of 0-0.5. Since the


Fig. 9. Experiments on the rigid plate

Fig. 10. Drawbar pull, Torque and Sinkage vs. Slip ratio on rigid plate Fig. 11. Drawbar pull, Torque vs. Slip ratio (Ding et al., 2011b)

measured data of drawbar pull and torque have large

fluctuation, the data of drawbar pull and torque were

processed by using adjacent averaging smooth at point

of window of 300. As data of sinkage did not fluctuated

greatly, data of sinkage were not processed. The results

are shown in Fig. 8. Each test was conducted around

40s. In the beginning stage, it takes about 10s for wheel

interacting with soil to reach a steady data. Therefore,

the data of drawbar pull, torque and sinkage from 10s

to 40s at steady-state response were utilized to calculate

the mean value and standard deviation in each case. The

obtained data were adopted to plot the curve of drawbar

pull, torque and sinkage as a function of slip ratio.

5.1 Performance of Wheel on Rigid Plate

Before carrying out experiments on KLS-1, the pre-

liminary tests were conducted on the rigid plate shown

in Fig. 9. Drawbar pull, torque and sinkage were measured

at vertical loads of 6 kg for the verification of single

wheel testbed developed by KICT. Fig. 10 presents the

results of drawbar pull, torque and sinkage value versus

various slip ratio of a wheel without grouser, respectively.

Because the experiments were conducted on the rigid plate,

sinkge is nearly zero as shown in Fig. 10 (a). The graphs

of Figs. 10 (b), (c) illustrate that torque and drawbar pull

increase sharply with increasing slip ratio at between

0-0.2, and the maximum value of drawbar pull and

torque are generated at slip ratio of about 0.2 and then

gradually becomes converged similar to other research


(a) With grouser (b) Without grouser

Fig. 12. Tracks of wheel

as shown in Fig. 11 (Ding et al., 2011). Therefore, this

equipment was considered to be verified in terms of the

performance evaluation for the single wheel.

5.2 Performance of Wheel Mobility on KLS-1

As wheel design is a key factor evaluated in this study,

a series of experiments with 2 kinds of wheels (with

grousers and without grousers) were performed on the

KLS-1. While a wheel moves on the deformable terrain,

tracks are generated.

Fig. 12 shows the picture of tracks for wheel with and

without grousers under the slip ratio of 0.1, 0.2, 0.4 and

0.5, respectively. It can be seen that as the increase of

slip ratio from 0.1 to 0.5, interval of tracks decreases

and soil becomes denser. At slip ratio of 0.5, soil is

disturbed heavily. Furthermore, interval of tracks at each

slip ratio in Fig. 12 (a) is smaller than wheel without

grousers shown in Fig. 12 (b) because grousers has effect

on enhancing soil’s compactness. Whereas, at high slip

ratio of 0.5, grousers digging into soil results in increasing

soil’s disturbance when wheel entering into soil and leaving

from the soil. According to tracks of wheel, Figs. 13 (a),

(b) show the smoothing data of drawbar pull for wheel

with grousers and without grousers under slip ratio of

0.1, 0.2, 0.4 and 0.5, respectively. Drawbar pull is

developed by shear stress applied on the soil depending

on soil’s density and strength. Value of drawbar pull

increases depends on increment of slip ratios from 0.1

to 0.4, and most important factor is larger drawbar pull

developed under denser soil while a wheel is spinning on

the soil. On the contrary, drawbar pull decreases at slip

ratio of 0.5, and the large slip causes the grousers digging

the soil and stuck in the soil. As a result, distrurbance

of soil reducing shearing on the interface of wheel and

soil greatly leads to the decrement of drawbar pull.

Fig. 14 shows the relation of drawbar pull, torque and

slip-sinkage as a function of slip ratio for a wheel without

grouser and with grouser of 10 mm height, 36° spacing

and 3 mm thickness at vertical load of 6 kg. It can be

observed in Fig. 14 (a) that sinkage of wheel increases

with increasing slip ratio because the relative density of

soil is low compared to the rigid plate. If the slip ratio

is less than 0.2, the trend of two types of wheels is similar,

however, at slip ratio of 0.5, value of sinkage for wheel

with grousers is 1.68 times higher than smooth wheel


(a) With grousers (grouser height 10 mm)

(b) Without grousers

Fig. 13. Drawbar pull time histories with slip ratio

(a) Sinkage vs. Slip ratio

(b) Torque vs. Slip ratio

(c) Drawbar pull vs. Slip ratio

Fig. 14. Drawbar pull, Torque and Sinkage vs. Slip ratio on KLS-1

It can be seen that grousers have not obvious effect on

sinkage at low slip ratio. Whereas, if the slip ratio is

greater than 0.2, sinkage increases exponentially for the

wheel with grousers. Under slip ratio of 0.5, wheel with

grousers increased by 2.2 times from slip ratio 0.2, whereas

wheel with grouser increased by 1.7 times. It can be

explained that at less slip ratio, grouser has not obvious

influence on slip sinkage, but the grouser’s effect of digging

in the soil plays an important role of increasing motion

resistance and sinkage. Figs. 14 (b), (c) that torque and

drawbar pull increased rapidly with the increase of slip

ratio from 0-0.1 at the initial phase and then after reaching

a maximum value, torque gradually becomes converged.

However, drawbar pull decreases with the increase of slip

ratio from 0.4-0.5. At slip ratio from 0.4-0.5, decrement of

shear stress caused by soil’s heavy disturbance leads to

reducing drawbar pull. In addition, as the effect of grousers

on digging into soil, the drawbar pull’s decrement of wheel

with grousers is 3 times greater than wheel without grousers.

The results also indicate that the value of drawbar

pull, torque and sinkage are higher in the case of wheel

with grouser than without wheel. The peak value of


torque on wheel with grousers is only 1.5 times more

than smooth wheels. However, the peak value of drawbar

pull is 4.7 times higher than wheel without grousers. It can

be explained that grousers of wheel have an influence

on traction performance of a wheel. Thrust of a wheel

is obtained from shear stress developed by the interaction

of wheel and soil. A wheel with grousers is able to

generate larger thrust by increasing the shear stress while

interacting on the soil to move the rover forward. The

results could be utilized in the evaluation of drawbar

efficiency for a rover.

6. Conclusion

In this study, a single wheel testbed was developed

and used to evaluate the traction performance of two

lunar rover wheels (with grousers and without grousers)

on Korean lunar soil simulants (KLS-1) whose geotechnical

and physical properties were experimentally validated to be

similar to real lunar soil and other lunar soil simulants. The

traction performance parameters such as drawbar pull,

torque and sinkage were measured by the single wheel

testbed in order to evaluate the performance of the wheel

under the normal load of 6 kg at the speed of 10 mm/s.

The tests performed on rigid plate were to evaluate

the calibration of equipment and to compare with the

experimental results on KLS-1. Torque and drawbar pull

increased with slip ratio at from 0-0.2 and then were

stabilized like the results in literature. In the case of the

tests on KLS-1, wheel with grousers obtained much higher

performance than smooth wheel at a small slip ratio. It

can be seen that wheel configuration and terrain conditions

significantly influence the motion performance of the wheel.

The results may be useful in optimizing wheel design

and verifying preferable slip ratio for Korean planetary

rover’s mobility performance. To analyze the optimum

wheel configuration and evaluate the reliability of rover’s

locomotion performance better, more experiments in terms

of changing wheel grouser shape, wheel size, soil conditions

and temperature conditions should be implemented in the

future works.

Acknowledgements

This research was supported by a grant from “Geo-

technical Engineering Preparations for Lunar Exploration-

Soil Mechanics with Lunar Soil and Laboratory Demon-

stration of Lunar Environments” which is funded by the

Korea Institute of Civil Engineering and Building

Technology (KICT).

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Received : October 17th, 2016

Revised : November 15th, 2016

Accepted : November 16th, 2016

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