Implementation of Wheel Walking for a Mars Rover

Zhongliang Hu, Aarne Halme

Abstract— Mars is recently the most popular destination forplanetary exploitation. Due to the extremely long distance andhigh mission budge, present and near future research projectsare mostly based on unmanned mission, which normally reliedon mobile rover robots with good off-road mobility. Therefore,mobility control system of the platform plays an importantrole of the mission. This paper reviews a few of differentplanetary mobile robot platforms, which shows the wheelwalking motion mode tends to be the optimal solution foran unknown tough terrain roving missions. Then a wheel soilinteraction analysis gives a theoretical proof for the locomotionimprovement from this peristaltic motion mode. Based on theMars rover ’Marsokhod’, it presents the description of themechanical design and the implementation of the motion controlsystem using a CAN Bus system. At last, a series of testingresults and different proposed control strategies for this specialmotion are given.

I. INTRODUCTION

Mars has been known since prehistoric times. It has beenextensively studied with ground-based observatories and isstill a favorite of science fiction writers as the most favorableplace in the solar system for human habitation. Mars hassome of the most highly varied and interesting terrain of anyof the terrestrial planets. And the big variety of the landscapeand many unknown conditions make the landing vehiclesvery hard to move and navigate, which makes a high off-roadmobility system and a robust motion control system a must.Dozens of robotic spacecraft, including orbiters, landers, androvers, have been launched toward Mars since the 1960s.Many novel mobile platforms have been developed, some ofthem have been launched and a few of them are carryingon missions at this very moment. No matter how complexscientific payload they carry, a reliable and easy-to-controlchassis which has outstanding off-road capability is alwaysneeded.

This paper starts with a research on a wheel walkingmotion for a Mars rover in coping with difficult terrain withhighly restricted situations on Mars. Our work is based onan experimental ’Marsokhod’ type rover. This paper firstresearch a wheel walking motion for a Mars rover in copingwith difficult terrain with highly restricted situations on Marsand then present a fully developed control system includingthe hardware and software systems. At last a few controlstrategies are tested and analyzed to implement a peristalticmovement mode for the Martian rover.

Zhongliang Hu and Prof. Aarne Halme are with Department of Automa-tion and Systems Technology of Helsinki University of Technology, Otakaari1, FI-02150 Espoo, Finland firstname.lastname@tkk.fi

A. Wheel walking method

Building mobile robots able to deal autonomously withobstacles in rough terrain is a very complex task because thenature of the terrain isn’t known in advance and may changein time. This is the situation for a Mars exploration rover.There are a large variety of locomotion mechanisms thatenable a robot to move throughout its environment [1]. Seriesgenius inventions of different types of movement modes havebeen developed. Among them, a movement type called wheelwalking method is well received for planetary rover design.Walking robots probably offer the best maneuverability inrough terrain. However, they are inefficient on flat groundand need sophisticated mechanics and control.

Hybrid solutions, combining the adaptability of legs withthe efficiency of wheels, offer an interesting compromise.The Sojourner robot and the Shrimp robot represent suchhybrid passive solutions.

However active locomotion concepts using additional mo-torized degrees of freedom combined with walking wheelscan be more efficient in very rough terrain. Such mechanismsallow the robot to actively control the position of the centerof gravity with respect to the contact points with ground.High mobility is mainly insured by the quality of thecontrol strategy and the pertinent integration of sensors inthe structure. The Marsokhod robot, the Hybtor robot andthe Octopus Robot represent such hybrid active solutions.

Furthermore there is another combined locomotion mode,wheel walking motion mode, which simply means the legsbeing transferred to the next contact point with the endwheels rolling and attaching the ground all the time. Somepaper call this ’rolking’ or wheel walking motion. TheOctopus robot is an innovative off-road wheeled mobilerobot, able to deal autonomously with obstacles in roughterrain without getting stuck [1]. The payload support and thetwo bodies on each side are linked in a passive differentialconfiguration. This mechanism architecture allows the robotto have all the wheels touching the ground at the same time,independently of the terrain profile. With feedback of thetactile wheels, the robot can adapt its behavior to the terrain,which gives it a better mobility relative to its small size.

B. Wheel soil interaction

In aim to optimize the control for an off-road robot andspecially a robot with a crawling motion mode, namedperistaltic motion. To provide a better ground traction forthe mobile robot to climb up hill, Marsokhod was designedto have certain level of actuator redundancy, as shown inFigure 2.4. It has been proved that Marsokhod can climb 25degrees slopes in the all-wheels traction mode on a granular

soil [2]. On the contrary, with a peristaltic traction mode,Marsokhod is able to climb over 30 degrees slopes underthe same condition.

In Andrades work, a soil model is proposed for studyingthe Marsokhods climbing capabilities. The soil is dividedin column cells. In a planar model, every cell has twoneighboring cells. The cell exchanges with its neighboringmass flow produced by internal forces, pressure and friction.With this soil model as well as 2D dynamic robot model, theyhave shown the difference between the normal rolling modeand the peristaltic motion peristaltic mode while only theback wheel is advancing. One can see the difference betweenthe two modes through the normal force distribution on thefront wheel contact surface. In the rolling mode, the anglebetween the direction of the resulting force on the contact,with the slope normal is less than 14◦, whereas it can reach35◦ in the peristaltic mode.

Fig. 1. Marsokhod Rolling and Peristaltic Mode Simulation, Rolling mode

Fig. 2. Marsokhod Rolling and Peristaltic Mode Simulation, Peristalticmode

II. MARSOKHOD PLATFORM

Our research is based on a so called Marsokhod rover. Themechanical platform is designed and developed in the MobileVehicle Engineering Institute (VNIITransmash) in Russia. InAutomation Technology Laboratory of Helsinki Universityof Technology, we have implemented a control system.

TABLE IPRINCIPAL DATA FOR SMALL MARSOKHOD

Mass of locomotion system , kg 30Payload mass, kg 15 . . . 20

Overall dimensions, m-length 0.8. . . 1-width 0.65-height 0.4

Stop length, m 0.1Wheel diameter, m 0.25Grouser height, m 0.01Quantity of drives 8

Motion speed on a horizontal sectionwith rigid surface, km/h,no less 1.2

Obstacles surmounted:-Friable soil slope, degr:

wheeled mode 20-separated rock (height) and

vertical obstacle, m 0.35-0.55

A. History and Background

The Marsokhod rover is an all terrain vehicle originallydesigned in Soviet Union for Mars exploration usage. Dueto the outstanding off-road capability and robust frame de-sign, Marsokhod becomes one of the most popular platformdesigned for Mars exploration. The design of Marsokhod isnot from one sudden great idea, it comes from more than 30years of knowledge and experience gathered from the veryfirst day of planetary rover development. Although all themoving vehicle design experience is the rich back-log fordeveloping the Mars rover.

The earlier exploration missions on the Moon has certainlyenriched the experience of Soviet space rover developmentand there are quite a few design of Marsokhod is from theseprecious experience. The Marsokhod robot even originallydesigned for Mars explorations has been extensively testedin volcanic surfaces such as in Kamchatka, Russia in 1993, inthe Amboy crater test in California in 1994 and the KilaueaVolcano test in Hawaii in 1995 [3].

There are several different versions of Marsokhod, whichvaries not only the dimensions but also the frame design(A.Kemurdjian, 1992). This thesis will be based on the module,JRover-2(2001) developed by the Mobile Vehicle Engineer-ing Institute (VNIITransmash) in Russia for the purpose oftesting control systems, navigation, scientific payloads andetc. for both planetary rovers and autonomous robots whenmoving over terrain with hard relief and soil conditions.These data were provided by the VNIITransmash.

B. Chassis of Marsokhod

The chassis consists of three pairs of independently driven,non-directional titanium wheels joined together by a threedegree of freedom passively articulated frame. The ampli-fiers, motors and batteries are mounted inside the wheels toproduce a very low center of gravity. The six independentlydriven wheels not only gives Marsokhod a good off-roaddriving capability but also fault tolerance. Practically noroad clearance is achieved by using conical wheels, occupiedpractically all the chassis, that provide a continuous support

surface for the rover, thus ensuring a cross-country capabilityfor terrains full of obstacles and ruling out the rover’s gettingstuck on a high center obstacle. These special designs enableit to overcome obstacles whose height is twice the wheels’diameter. For overcoming small crevasses, the sections canclamp together to form a rigid frame. The sections can movealternately to enable the wheel-walker to creep up friable soilslopes.

Fig. 3. Moving axis of Marsokhod

The drive-wheels of the front and rear axles are mountedon the ends of levers able to turn forward/backward bymeans of mechanisms for walking which are installed onthe frame. At the same time the front and rear axles canturn about longitudinal axis of the robot (two longitudinalhinges). The central free hinge ensures turning the semi-frames about axes of the middle drive-wheels (the transversalhinge). As a result, the constant contact between wheelsand unevenness of surface, i.e. ability of the chassis toaccommodate the relief of the terrain, is ensured. Thus, cross-country capability is essentially improved and impact loadsare reduced. When moving over terrain with great numberof obstacles mechanical stops limiting mutual displacementsof chassis elements, are installed in hinges. All the chassisdrives are provided with parking brakes. Each of the chassissections has a platform for mounting blocks of the controlsystem and scientific equipment. There is a special design forthe ’arm’ motor, a self-braking two-shoe clutch. It helps theMarsokhod to ’stand up’. It makes the arm joints can only bemoved from inside, e.g. when the arm motors start to move,it will release the brake and the move freely, but when themotor stop moving, it will lock the joint from inside andprevent the joints from changing the angles.

C. Wheel walking modes

There are two modes of the chassis motion: wheeled modeand wheelwalking mode. The wheeled mode is realized withthe different constant wheel bases resulting by conditions ofmotion. Turning the chassis is fulfilled on the spot or usingthe tractor type turning. The wheel-walking mode used undercomplex soil conditions and when going up steep friablesoil slopes. This mode is realized with the drive-wheels andmechanisms for walking. This is the original strategy for

TABLE IIMOTORS AND RELATED COMPONENTS INSTALLED FOR MARSOKHOD

Motor Module Maxon DC motor RE 118798Diameter (mm) 36

Weight (g) 350Nominal Voltage (V ) 24.00

Speed/Torque Ratio (rpm/mNm) 8.05Torque Constant (mNm/A) 36.4Terminal Resistance (ohm) 1.11Terminal Inductance (mH) 0.20

Reduction Gear Gearhead 110407 d=42mmReduction Ratio 216:1

Weight (g) 720Max.Perm.Load (N) 294

Recommended Input Speed(rpm) ¡5000Motor Encoder HP HEDS 5540

Supply Voltage (V ) 5Output Singal TTL Compatible

Counts per Turn 500

Marsokhod, this will be studied in depth in later chapters.There can be many other combination of the wheel-walkingmodes, e.g. instead of the three separated phases, the last twoparts can stretch back together with the back arm locked.Although, the three phase mode is naturally the optimalwheel walking motion mode.

Fig. 4. Wheel-Walking Motion Mode for Marsokhod

D. Kinematics Model

In order to describe the location of each link relative to itsneighbors, a frame is attached to each link. These link framesare named by number according to the link to which theyare attached. Hence, any robot kinematics can be describedby giving the values of four quantities for each link. Twodescribe the link itself, and two describe the link’s connection

to a neighboring link. The definition of mechanisms bymeans of these quantities is a convention usually called theDenavit-Hartenberg notation.

Fig. 5. Marsokhod Moving Unit Views, Cuts View

Fig. 6. Marsokhod Moving Unit Views, Axes View

The Marsokhod is designed as a symmetric body, soto develop a kinematic description for it, one unit can beenough. Although, to construct a matrix and do all the controlcalculations based on it will certainly increase the complexityof the program which inevitably decrease the performance ofthe control strategy. In this implementation, one simplifiedpure triangle calculation will be employed for calculation.

As shown in Figure 7, a triangle is constructed to resemblethe front part of Marsokhod. One should notice, here, we didnot take in consideration of the ground adaption joint. Thisis because our calculation is based on two dimension. Andin this thesis, we assume there is no lateral change of theground profile.

Fig. 7. Simplified Kinematics Model of Marsokhod

From Figure 7, we can form a relation equation betweenthe joint angle θ and the length X.

X2 = L21 +L2

2−2cosθ ·L1 ·L2 (1)

In this equation , the changing variable with respect oftime is X and θ . The equation can be re-write as follow.

X2(t) = L21 +L2

2−2cosθ(t) ·L1 ·L2. (2)

When the wheel is moving in the x direction, the jointangle θ will change accordingly, to keep the wheel on theground, e.g. the X side remains on the same direction.

Take the derivative of both sides with the respect of t andre-arrange the equation, we have:

X(t) · X(t) = sinθ(t) ·L1 ·L2 · θ(t). (3)

Since X(t) is the wheel joint movement speed with respectto ground, the equation can be re-write into:

θ(t) =V ·X(t)

L1 ·L2 · sinθ(t). (4)

To make the calculation only involve with the knownvariables, we substitute X(t), and the final equation will be:

θ(t) =V ·

√L2

1 +L22−2cosθ ·L1 ·L2

L1 ·L2 · sinθ(t). (5)

Until here, we have a ready being used mathematic modelfor the control. The results will be introduced in laterchapters.

III. MARSOKHOD CONTROL SYSTEM

A. Hardware Design

A central computer is placed to coordinate the motionand scientific exploration missions of Marsokhod, as wellas communicate with the ground station. Basically, there areeight active motor joints. A control bus is needed for theindividual operation for every each of them. With the coor-dination of the central computer, eight identical controllersare installed locally with the motors, e.g. inside the wheels,to accept and execute the commands from the ground stationwith the relay of the central computer, as well as monitor thelocate state of the system and give feedback. And there canbe a direct link with control system with navigation system,power system and so on, although this is beyond the rangeof study of this paper.

Fig. 8. Block Diagram of the Marsokhod Control System

As shown in Figure 8, the overall control diagrams isdesigned as such. The connection built in between the groundstation(GS) and the central control unit(CC), is via WirelessLAN. This can be used also as a simulation of the real spacemission situation, e.g. the communication delayed situation.

As for the control bus, a controller area network (CAN)bus is chosen. The CAN is a serial communications protocol

which efficiently supports distributed realtime control with avery high level of security. Its domain of application rangesfrom high speed networks to low cost multiplex wiring. Inautomotive electronics, engine control units, sensors, etc. areconnected using CAN with bit rates up to 1 Mbit/s. At thesame time it is cost effective to build into vehicle body elec-tronics to replace the wiring harness otherwise required. Itprovides a safe communication channel to exchange betweenseveral network nodes.

Due to the fact that the batteries packs are installedinside the wheels for each of the motors, there is a powerdistributing recharging bus being included in the main bus.This bus is used to control and monitor the batteries packs,as well as generate the recharging sequence for them fromdifferent power source (solar, wind , etc.) by the groundstation through the central computer.

1) Central Control Unit: We chose one recent mod-ule PC104 embedded computer(ReadyBoard 700, AmproComputers Incorporated), for the mainframe of the con-trol system. For testing purpose, we used a WLAN USBadapter(A-LINKWL54USB), to resemble the telecommuni-cation situation. And inside the lab we installed a WLANrouter(Rangebooster, LINKSYS) to connect the ground sta-tion(GS) computer. An open source Linux system (Debiandistribution) is installed as an operational system.

There is also DC-DC converter (ECW24-0525, FAB-RIMEX) and one signal distributor board been developedand put inside the unit with the central computer. It providea steady output of +5V for the central computer as wellas the micro-controllers inside the wheels, and has a largerange of an operating voltage (+9V...+36V), which could beused for different setup of the power levels, e.g. the batteriesstacks. For the CANBus communication and control, aPC104 compatible CANBus interface card(AIM104-CAN,ARCOM) is installed. The system have the capability withthe AIM104-CAN running at 1Mb/s on the central computerunit.

Fig. 9. Picture of Central Control Unit

2) Local Motor Controller: As for each of the motorcontrol and state monitor, a local motor controller, whichconsists of a micro-controller and a H-bridge, is imple-mented. They are intended to control and monitor the motorslocally. They are designed to be installed inside the wheelsto keep the center of gravity as low as possible, and also,

Fig. 10. Block Diagram of Central Control Unit

perhaps more importantly, to minimize the control interval,with the limited computing power of the central computer.

Every motor controller has a unique ID in the CANBussystem. As for the ’Arm motor’ 1 and 2, the controllers areplaced inside Wheel 2 and Wheel 5 respectively.

Fig. 11. Picture of Marsokhod Local Controllers in Wheel 5

As shown in Figure 11, the local control hardware systemconsists of two Printed Circuit Boards (PCB) , a micro-controller board and an H-bridge board. The micro-controllerboard is used to be the interface of the CANBus system viaa CAN transceiver. The transceiver is designed to providedifferential transmit capability to the bus and gives the micro-controller the capability to operate a CANBus at speeds up to1 Mbps. The program runs inside the chip (AT90CAN128)also operate the power gate (+24V) for the H-bridge. Fordriving the motor, it provides the Pulse-width modulation(PWM) signal as well as the direction for the H-bridge,and receives feedback signals, such as the driving current ofthe motor and the temperature sensor information inside thewheels preventing over heating. As a feedback of the motordriving, the controller board also reads back the encoder(Digital Encoder HP HEDS 5540) ticks from the motor,which then feed through a CMOS quadrature clock converterand be converted to a clock and an up/down directioncontrol.This setup makes the close loop control of the motors

Fig. 12. Block Diagram of the Marsokhod Wheels Local Control System

possible, the PID control is implemented within the softwareof the micro-controller, which will be explained in latersections. The system diagram is shown in Figure 12.

B. Software System Design

For achieving a successful mission, a solid software sys-tem is needed for the Marsokhod. The software systemdesigned and implemented can be generally divided intothree parts, ground station part, central control unit part andthe micro-controller part.

Fig. 13. Block Diagram of the Marsokhod Software System

1) Ground Station Software: The ground station software(GS), allows the user to send commands for Marsokhodswitching in between different motions modes, as well asacquiring and monitoring the overall state of the Marsokhod.It also employs a dynamic model of Marsokhod and theground, using an Open Dynamic Engine (ODE), to developa simulation environment. Then it can be feeded in theMarsokhod feedback information combining the dynamicsimulation, which can be used as a virtual ’real-time’ displayfor the operation of Marsokhod during the Mars operation

using the so called ’predictive display’. It will also providea user interface for the ground station users to control andmonitor the Marsokhod from a remote console. It should alsoinclude the communication interface with the central controlunit. Although these is not yet implemented by the time ofthe thesis.

2) Central Computer Software: The central computersoftware (CC), is to act as a relay for receiving the groundstation commands and pass them to the individual motorsand instruments, and acquiring the needed data and put thatraw data into a right order and send it back to the groundstation for the users to monitor the Marsokhod. And moreimportantly, it will generate a series of combined movementsof the joints to perform different motion modes, i.e. wheel-legged motion.

The commands of the motion control for the Marsokhodis generally developed in three layers plus the CANBusinterface functions.• Bottom Layer. As the lowest motion commands for

the Marsokhod, it simply gives the direct command foreach of the joints. It includes the velocity commands,raw PWM control commands, and the encoder, currentand temperature information to and from the localcontrollers via the CANBus interface functions.

• Middle Layer. The middle layer commands are em-ployed to drive each ’parts’ of the Marsokhod. Each twoparallel wheels and the are controlled and monitored asa ’part’ for a more intuitive upper level control.

• Top Layer. For controlling the Marsokhod as a whole,the top layer commands is developed. The commandsinclude drive, turn and different arm-wheel combinedmotions, which can be used to test for the wheel-leggedmotion control strategies (will be explained in laterchapters).

As a central computer, there is a potential it can be usedfor other tasks, i.e. the scientific data pre-operation.

3) CANBus Motor Controller Software: The lowestpart software are inside the wheels, the micro-controllersoftware(µCs). They are designed to accept messages sentvia the CANBus, and interpret them into motor control andsensor reading commands. They shall also take care of thecontrol of the motors, with some defined control mechanism,e.g. close loop digital PID controller.

IV. TEST CONDITION AND RESULT

A few preliminary test results are listed in this chapter.Different motion modes have been implemented and someanalysis are presented.

4) Central Control Unit Test: The central control unitconsists of: central computer, CANBus Card, , WLAN card,DC-DC converter and power-signal distributor, as shown inFigure 10. Testing shows the central control unit is workingproperly.

5) Local Controller Test: To test the individual localcontrollers, a wooden test bed is constructed to make thewheel run freely, as shown in Figure 15.

Fig. 14. Software Structure of the Motor Controllers

Fig. 15. Wooden Testbed for Unit Test

For testing the hardware and software system of the localcontrollers, all the commands are tested. Connect the motorto drive and read the feedback information with the resultshown in the following Figures.

Figure 16 and 17 show the response and accelerationperformance of the motor with a load, and the same PIDparameters and acceleration rate setup. This shall reflect themotor reaction in real working conditions.

The tests results are shown based on the test of wheel 3.Same tests are performed for the other local motor controllersand results are similar, which proves the functioning of eightof the subsystems. The tests also include the mechanicalstructure of the central computer container, the wiring con-

TABLE IIIMOTOR MONITOR TEST RESULTS

Function Test Condition ResultCurrent Monitor multi-meter Max.3A±50mAEncoder Counter MC board 2/Tick

Temperature Monitor DMM −7.5mV/DegJoint Angle Sensor angle with scale 0.26mV/Rad

0 0.5 1 1.5 2 2.50

3

6

9

12

15

18

21

24

Time (s)

Ang

ular

Spe

ed (

mR

ad/s

)

Fig. 16. Motor Response Performance

0 1 2 3 4 50

60

120

180

240

300

360

420

480

540

600

Time(s)

Ang

ular

Spe

ed (

mR

ad/s

)Fig. 17. Motor Acceleration Performance

nections inside the Marsokhod main frame, the holding frameof the local controllers and so on, to make the over all systemworking. The results are positive.

A. Wheel Walking Motion Control Strategies and Tests

To realize the wheel walking motion mode of the Mar-sokhod, a few three different drive strategies are implementedand tested.

1) Independent Drive: This test is the most simple way ofdriving the arm joint to the designed position/angle. Drivethe Arm joint and the wheel motor drive to the requiredposition/angle with an arbitrary constant speed, and stop bothwhen the designed angles are reached. This method causethe two (three) motors work against each other, which is notpower efficient nor provide improvement for the climbing.In certain conditions, there could be quite a lot of slippageand the system will take much more current. There is alsothe danger of pushing the Marsokhod down hill. The indoortest results under this driving method, with exception to themiddle of the movement, are that the wheels are experiencinga big slippage. Even by tuning of the arm joint angular speed,the slippage can not fully be eliminated. In some of the tests,the current consumption of the motors are very high dueto the motion error. This situation also appears during theoutdoor tests.

2) Kinematics Drive: According to the kinematics model(Function. 5), a kinematics drive strategy is carried out. First,the front two wheels run in a constant speed with the speedcontrol. With the angular velocity of the front arm jointcalculated accordingly, an updated velocity is given to the

Fig. 18. Outdoor Test of Marsokhod

arm motor local controllers with a control interval. Becausethe controller rate is quite high (>2KHz), the speed jumpsare not visible through the velocity data. This method willwork under the assumption that there is no slippage onthe wheels, and the ground is flat (not necessarily withoutslope), at least on the lateral direction there is no significantdifference. The micro-controller will update this speed tomake them follow the velocity curve (depends on the currentposition / angle). The same control program is tested underthe outdoor test environment.

3) Torque Drive Strategy Test: According to the currentmeasurement, the value of the torque applied on the armmotor can be calculated. From this, the wheel can be drivenfirst in a speed according to the kinematics calculation, whichis the same as the geometry drive. After this, by keep monitorthe torque on the joint, it should be able to increase the wheelspeed to overcome the slippage and also help the ARM jointto proceed for the stretching. This drive can work for theslippage condition, which is the most difficult state for therover to climb up hill. The control scheme shall be decided togive the best performance. Although during the tests, thereis no visible difference shown in the arm angular velocitychart. It appears to consume less current during the test.

V. CONCLUSIONS AND FUTURE WORKS

A. Conclusions

After a introduction of the importance of having a highmobility rover, Marsokhod, the Mars rover is studied thor-oughly. For this a control system of Marsokhod is imple-mented and proved to be functioning. This includes bothhardware and software development. For hardware, the PCBs(about 20 pieces and some Off-the-shelf unit) of local con-trollers and the central control unit are designed, developed,installed and integrated. For the software, programs in motorcontrollers as well as the central control unit are devel-oped and implemented. Some supporting Matlab simulation

programs and a 3D simulation model, which is based onthe kinematics model of Marsokhod is also developed. Theplatform, including both the mechanical chassis and thecontrol system can be used for many following studies.Tests of the individual parts of the control system are donethoroughly. And some control strategies are proposed andanalyzed.

B. Future Works

Due to the testing and time limitation, the tests are notall fully implemented. For example, some extreme conditiontests shall be done, to make sure the robustness of theplatform and the control system. Moreover, other types ofwheel walking motion modes(e.g. 2-phase wheel walking)can be also tested. Moreover the sandy ground is not uni-versal through the test and the conditions are very crucial inmany ways, which make the results somewhat inaccurate.Although the tests shows the effectiveness of the controlsystem and an enhanced mobility from the proposed motioncontrol strategies.

This thesis will be hopefully be useful for future work, byboth giving a documentation of the system and by pointingout things that could be improved in the future.

REFERENCES

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[3] G. Muscato, D. Caltabiano and S. Guccione, ”ROBOVOLC: A Robotfor volcano exploration C Result of first test campaign”, IndustrialRobot: An International Journal, Vol. 30, N.3, pp.231-242, 2003.

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