development, design and verification of different wheel...

Development, Design and Verification of different

Wheel Concepts for NASA’s Field Integrated

Design and Operations Rover.

Diplomarbeit

zur Erlangung des Grades „Diplom – Ingenieur (FH)“

vorgelegt von: Alois Winterholler

betreuender Hochschullehrer: Prof. Dr.-Ing. Hans-Eberhard Schurk

vorgelegt am: XXXXXX

Fachbereich Maschinenbau Studienschwerpunkt: Konstruktion und Entwicklung

Fachhochschule Augsburg Hochschule für Technik – Wirtschaft – GestaltungUniversity of Applied Sciences

Alois Winterholler 18.07.2002

Table of Contents

1 Introduction............................................................................................................3

1.1 Purpose of Interplanetary Rover ....................................................................3

1.2 Problem Definition...........................................................................................5

2 Design Constraints ................................................................................................7

2.1 Lightweight Design .........................................................................................8

2.2 Space Environment .........................................................................................9

2.2.1 Vacuum ....................................................................................................10

2.2.2 Radiation ..................................................................................................11

2.2.3 Temperature.............................................................................................11

2.2.4 Martian Environment...............................................................................13

2.3 Dimensional and Load Constraints .............................................................14

2.4 Previous Wheel Designs...............................................................................16

2.5 Materials and Structures...............................................................................19

2.6 Design Decision.............................................................................................23

3 Wheel Design and Manufacturing ......................................................................25

3.1 Honeycomb....................................................................................................25

3.2 Carbon Fiber ..................................................................................................30

3.3 Hardfaom........................................................................................................30

3.4 Wheel Tread ...................................................................................................30

4 Wheel Comparison and Evaluation ....................................................................30

4.1 Cost and Manufacture Comparison.............................................................30

4.2 Weight and Stability Comparison ................................................................30

5 List of Illustrations...............................................................................................31

6 List of Tables........................................................................................................31

7 Reference .............................................................................................................32


1 Introduction An Indian proverb says: If you want to know where you are headed,

remember where you come from.

A human tendency is to discover, conquer, and populate new land. The first modern

humans emigrated from Africa approximately 80,000 years ago. In the next thousands of

years, humans settled over a majority of the earth. Christopher Columbus discovered,

on his attempt to find a new route to India, a new continent in the 15th century. Many

people immigrated to the newly discovered continent in search of a new and better life.

Mankind reached another exiting achievement in 1957 with the first launch of a satellite

into space. A new age, the space age, had begun. Soon after this, the first humans

experienced zero gravity flights into space. The United States sent people to the moon

and back in 1969. Space exploration has made a lot of progress and continues to

advance since this time.

At the beginning of the third millennium, the knowledge and tools are available to

prepare a manned space flight to our neighbor planet Mars. To reach such goals many

efforts have to be made. Scientists estimate a preparation time of 15 to 18 years for

such a mission. Several unmanned missions to the red planet could be accomplished

during this time. The data and information that could be gathered from the unmanned

missions is extremely important for the planning of a future manned mission.

Additionally, new mechanisms, techniques, and materials could be tested for their

functionality and reliability in such long time projects.

1.1 Purpose of Interplanetary Rover Alex Ellery writes in his book ‘An Introduction to space robotics’: “All manned missions to

planetary bodies, be it the Moon or Mars, will require prior unmanned exploration of the

surface for reconnaissance and surveying purpose by robotic rovers. They thus

compromise a central plank in all planetary exploration missions both manned and

unmanned from their ability to provide detailed in situ data not obtainable from orbital or

flyby missions. Robotic rovers are uniquely suited to special applications such as

seismic survey and local site preparation.”[1] NASA, National Aeronautics and Space

Administration, launched the Mars Pathfinder Mission on December 4th, 1996. The

instrumented lander, formally named the Carl Sagan Memorial Station after a space


scientist and professor from the Cornell University in Ithaca NY, landed safely with its

payload on the Martian surface on July 4th, 1997. The payload contained a free-ranging

robotic rover (Fig.1). The first mobile robot vehicle that was sent to planet Mars was

named Sojourner after American civil rights activist, Sojourner Truth. Scot Stride from

the Mars Pathfinder Microrover Telecom Team describes the rover on their Website as

follows: “Sojourner weighs 11.0 kg (24.3 lbs.) on earth (about 9 lbs. on Mars) and is

about the size of a child's small wagon. The Microrover has six wheels and can move at

speeds up to 0.6 meters (1.9 feet) per minute. This isn't very fast, but during the course

of a day on Mars the Microrover can cover a lot of territory (perhaps up to 3 meters).

However, that speed will be fast enough to accomplish many tasks during a day, since

we are not planning on driving the Microrover more than 10 meters (32.8 feet) away

from the lander.”[2]

The data and information received from the Pathfinder mission is described in a NASA-

report: “From landing until the final data transmission on September 27th, 1997, Mars

Pathfinder returned 2.3 billion bits of information, including more than 16,500 images

from the lander and 550 images from the rover, as well as more than 15 chemical

Fig. 1: Mars-Panorama-Picture taken at the Pathfinder-Mission (This picture is assembled from different pictures. Therefore you can see the Sojourner Rover in different positions.)


analyses of rocks and soil and extensive data on winds and other weather factors.

Findings from the investigations carried out by scientific instruments on both the lander

and the rover suggest that Mars was at one time in its past warm and wet, with water

existing in its liquid state and a thicker atmosphere.”[3] The Pathfinder mission was very

successful and exceeded even the boldest expectations. A lot of information could not

have been obtained without a mobile robot. The mobile rover provides the capability to

extend the action radius around the lander. The rover was controlled remotely from the

earth. This gave scientists the ability to look for interesting points and position the rover

there. The examination of different rocks with a spectrometer was performed in this way.

In addition, soil mechanics and material abrasion experiments were executed with the

rover wheels. The two experiments were monitored by using the rover cameras to image

the wheel trace and the wheel wear. A few other experiments were made using the

rover, such as Rover Thermal Characterization, Rover Imaging Sensor Performance,

Lander Assessment, and some other experiments.[4]

1.2 Problem Definition To try and verify new rover technologies for future Mars explorations NASA uses the so-

called FIDO-Rover (Fig.2). FIDO stands for Field Integrated Design and Operations. The

FIDO-Rover is an earth based

analog of the Mars Exploration

Rover (MER), which is send to

Mars in 2003 (Fig.2). NASA

describes the purpose of the

FIDO-Rovers on their Website:

“In particular, the FIDO rover

conducts mission relevant field

trials that simulate mission

operations scenarios and

validate rover technology in the

areas of rover navigation and

control, instrument placement,

remote sensing, scientific data collection, intelligent behaviors, telemetry processing,

Fig. 2: Field Integrated Design and Operations Rover (FIDO)


data visualization, and mission operations tools. … FIDO will conduct field trials in 2001

and 2002 to assist with training Mars scientists and operations personnel by allowing

these people the opportunity to operate a fully-instrumented rover within challenging

geological settings on Earth that are analogous to settings on Mars.”[5]

A FIDO-Rover similar to NASA’s was built by Matt Roman and Tim Hunt for the

Intelligent Robotics Lab at the University of Oklahoma. Prof. Dr. David Miller is the

director of the Intelligent Robotics Lab. The Intelligent Robotics Lab supports NASA in

the development of autonomous mobile robots. Prof. Dr. David Miller is a former NASA

scientist, who worked on the development of autonomous interplanetary rovers. He was

also in charge of the Sojourner rover project from the Pathfinder Mission. Prof. Dr. Miller

describes the research assignment for the diploma thesis as follows: “The project that I

have in mind is to do a series of tests and analysis on the wheel design for the OU

version of NASA’s FIDO rover. NASA originally designed this robot for going very slowly

(about 5cm/sec) over rough terrain. We have modified the robot so that it is capable of

speeds of up to 2m/sec on smooth terrain. An open question that would like you to

address is: what is a good wheel design that gives good climbing capabilities at low

speeds, reduces shocks at higher speeds, and still is reasonably energy efficient. I

would like you to do some preliminary analysis, and then fabricate at least two different

sets of wheels. Finally I would like to mount the wheels on the rover and analyze their

performance over a test track that includes obstacles of various sizes an shapes.”[6] The

reason for increasing the driving speed is to achieve a higher mobility. The daily driving

time of a planetary rover is limited. The onboard computers consume almost the same

power using either the slow or fast speed. If the same amount of energy can be used to

reach a higher speed, he radius of action will increase. This enables the mobile robot to

drive longer distances to survey different geological landmarks.

Prof. Dr.-Ing. Hans-Eberhard Schurk, my thesis advisor, assigned the following topic

‘Development, Design and Verification of different Wheel Concepts for NASA’s Field

Integrated Design and Operations Rover’ to me for my Diploma thesis after reading the

letter from Prof. Dr. Miller.


2 Design Constraints Principle thoughts had to be made before starting to develop different design concepts.

The wheels have to be manufactured with the equipment, machines, and tools that are

available at the University of Oklahoma. These machines include: CNC controlled mill,

manual mill, manual lathe, drill press, sheet metal shear, sheet metal roller, and several

types of hand tools.

In order to keep project costs low, only 'off-the-shelf products’ should be used. The use

of products that are easy available stands in contrast with the designing of wheels that

are suitable for space. The focus of this thesis is on the development of principle design

and manufacturing concepts. Therefore, it is not an interest of building rover wheels,

which are ready for space flight. Another condition, which has to be fulfilled, is that the

wheels fit without modification on the existing rover suspension.

Other questions that have to be answered are: How does the terrain look like? What are

the environmental conditions? How much weight do the wheels have to support? These

are only some of the open questions, which had to be clarified first. Answers to these

problems are discussed in the following paragraphs.

One requirement in the assignment was the energy efficiency. The efficiency of a wheel

depends mainly on the rolling resistance and the required torque to turn the wheel. The

Author Alex Ellery writes in his book: “Rolling resistance occurs when soil compaction

and bulldozing of the soil occurs and it can absorb between 5% and 35% of gross

engine power depending on the soil and vehicle speed.”[1]. According to the author M.

G. Bekker, the rolling resistance depends on different factors. A main factor for a rigid

wheel is sinking into soft grounds. The sinking depends on the wheel width, the wheel

diameter, the wheel load, and the modulus of the soil.[12] Different scientists have

compiled different solutions which are valid for certain defined conditions. Wheels for off

road vehicles generally have a high rolling resistance. This comes from the large wheel

contact area and from deep treads. The large wheel contact area is desired in order

prevent the wheel from sinking into soft soil. Deep treads provide the necessary traction

in soils with low shear strength like sand.


2.1 Lightweight Design The other main effect, which was mentioned earlier, on the energy efficiency of the

wheel is the mass. The torque T needed to turn a wheel without touching the ground is

dependent on the moment of inertia of the wheel J and the angular acceleration ω& .

ω&⋅= JT

The moment of inertia is determined by the mass and the radius from the rotational axis.

For a hollow cylinder the moment of inertia in respect to the rotational symmetric axis is

shown below.

( )2

22oi rrmJ +=

Where ri is the inside radius and ro the outside radius. The wheel moment of inertia can

be calculated, by splitting it up into three hollow cylinders. The three hollow cylinders are

the hub, the core, and the rim with the tread. The moment of inertia is calculated

individually for each cylinder and then added together. In order to keep the required

power for the wheel low, the mass should be small and as close to the axis as possible.

Another reason for the lightweight design is the factor of the cost for sending things to

the planet Mars.

Another reason for the lightweight design is the costs for sending things into space and

further to the planet mars. For example, the Pathfinder mission costs total 265.4M$. A

McDonnell Douglas Delta II 7925 rocket was used as launch vehicle to bring the

Pathfinder spacecraft into earth orbit. The total costs of the launch system are 50.3M$.

The fully fueled spacecraft with the Microrover and the fairing container weighed 894kg.

This flight system costs 135.3M$. The Mars Pathfinder lander weighed 370kg when it

touched the Martian surface. The scientific payload for the Pathfinder mission had total

costs of 38.7M$. This is divided in 25M$ for the Sojourner rover with the alpha proton X-

ray spectrometer and 13.7M$ for the lander’s camera system and atmospheric structure

instrument/meteorology package.[20],[3] According to Prof. Dr. David Miller, the

estimated weight of this science instrumentation was approximately 25kg. The overall

management and operation costs for the Pathfinder mission are 41.1M$.[20] The

transportation hardware consisting of launch vehicle and spacecraft together cost

185.6M$. In principle, the flight hardware for sending one gram to Mars costs 7400$. If

you add the complete management and operation costs to the flight hardware costs, the


price increases for sending one gram to the red planet to around 9000$. The true price

for sending things to Mars lays somewhere in this range.

In addition, the known loading conditions an interplanetary rover will likely encounter, as

well as its limited lifespan, permit a lightweight design. Missions to other planets are

carefully planned and are exactly defined. Usually the highest loads on the components

in a space mission arise from the launch from earth. Missions with a landing on another

planet also suspend the parts and the structure to extreme loads while landing. Many

investigations to determine these loads were accomplished in the last decades.

Therefore the stress and the impact on components can be derived from these

predictions. If the loads are known, then a smaller safety factor can be selected, so long

as it is sufficiently high to guarantee safe operations in all situations. This leads usually

to the decrease of material thickness and thus to the weight reduction. Besides the

length of the application of an interplanetary rover are relatively short. Security against

fatigue failure can be thus set low. This entails also a weight reduction.

2.2 Space Environment Space is a destructive environment for a lot of materials. Parts and units must be

constructed in such a way in order to prevent premature loss during the mission

duration. The space environment is the main factor for the material selection. The author

Bernd Köhler groups the space environment effects into six main categories: Vacuum,

electro-magnetic radiation, plasma, residual gas, micrometeoroid/ orbital debris, and

temperature.[7] These effects vary with the altitude.

Plasma is a gas of ionized atoms. The plasma environment exists mainly near the earth.

Plasma has its highest density at an altitude of 300km. The ions in the plasma charge

surfaces to different potentials. Arcing results when discharging of the surfaces

occurs.[8]

The residual gas decreases with increasing altitude. The residual gas in space, also

called the Neutral environment, causes significant interactions with a spacecraft. The

Author Alan C. Tribble writes in his book ‘The Space Environment’: “The impact of atoms

at these high speeds will give rise to an aerodynamic drag force and physically sputter

material from some surfaces. … The most abundant element in LEO (Low Earth Orbit) is


atomic oxygen which, due to its highly reactive nature, may chemically erode surfaces or

give rise to a visible glow that may interfere with remote sensing observations.”[8]

The universe is full of meteoroids. The frequency of meteoroids is in reverse proportional

to their mass. The average speed of a meteoroid is about 30km/s. The possibility, that a

big meteoroid impacts a spacecraft is very low. Micrometeoroids with diameters in the

micrometer range hit a spacecraft often. They leave microscopic impact craters, which

roughen the surfaces.[7]

The interplanetary rover is stowed as payload in the spacecraft. Therefore the wheels

are mainly affected by three space environment effects, vacuum, temperature, and

radiation, which are covered in the following paragraphs.

2.2.1 Vacuum With increasing altitude the atmospheric pressure drops. At an altitude of 700km the

ambient pressure is twelve orders less than on earth’s surface.[7] This very low pressure

is called vacuum environment. The Author Alan C. Tribble writes in his book ‘The Space

Environment’: “Designing a spacecraft to operate under vacuumlike conditions places

constraints on choices of materials and thermal control. Upon exposure to very low

pressures, many materials will exhibit a mass loss through a process called outgassing.

Essentially, volatile materials may escape the attraction to the surface and be released

into the surrounding atmosphere. … In space, outgassing materials may deposit

contaminants onto sensitive surfaces such as thermal control panels, solar arrays, or

optics, thereby altering their thermal or optical properties.”[8] The outgassing of solids is

called sublimation. This effect arises with most metals only at the surface and is

negligibly small. The employment of metals with a higher steam pressure such as

cadmium, zinc or magnesium has to be avoided if possible. Magnesium alloys are

known in machine construction as a light alloy with high weight-strength ratio. The use of

magnesium alloys with protecting film of metal coat is possible. The outgassing rates of

polymers are usually much higher. The vacuum environment in interaction with other

factors such as temperature and radiation also supports the inclination of breaking

macromolecules. This leads to the change of the material properties. Polyamide for

example loses their water content and becomes brittle. Usually polymers are used with a

protection coat of a polymer with a low vapor pressure like PTFE (Teflon) or a metal.[7]


Nevertheless, there is a whole set of polymers available, which are suited for different

space applications.

2.2.2 Radiation The short-wave radiation is nearly completely reflected by the terrestrial atmosphere. In

space, materials are unprotected to exposure to the short-wave spectrum of the sunlight.

The short-wave spectrum consists of UV-radiation (3nm - 300nm), x-ray (0.001nm -

10nm), gamma radiation (0.01pm - 10pm) and cosmic radiation (> 0.01pm). In contrast

to the plasma that only arises on the material surfaces, short-wave radiation penetrates

into material and through it. Alan C. Tribble writes: “Consequently, these particles have

the capacity to cause interactions throughout a spacecraft’s interior. In general, any

energetic particle, (electrons, protons, neutrons, heavier ions), or photon, (gamma rays,

X rays), can be considered radiation. As radiation moves through matter it may displace

and/or ionize the material in its path. The affected matter itself may in turn cause further

disruptions. The result is a reduction in bulk material properties. Radiation damage may

decrease the output power of solar arrays, may create spurious signals in focal planes,

or may induce errors in spacecraft avionics.”[8] The destructive effect from radiation

depends on different factors. The factors are the type of radiation, the radiation energy,

the exposure time, and the absorbing material. UV radiation does not cause damage to

metals. UV radiation causes photochemical reactions in polymers that cause

concatenations and discolorations, which entails solidification and an embrittlement of

the material. Cosmic radiation consists of high-energy protons and electrons. Cosmic

radiation causes a driving out of lattice atoms on interstitial sites. The driving out of

atoms on interstitial sites causes solidifications and embrittlement in metals and the

destruction of the connection mechanisms in polymers. [7]

2.2.3 Temperature Materials are subjected to large variations in temperature in the universe. The heat

transfer in space is based on conduction and radiation. Convective heat transfer does

not exist in a vacuum. The temperature of a part is dependent on the thermal properties

of the surfaces and the conduction head flux to other components. The heat absorbed,

Qin , for a uniform body is calculated by the following equation.


SAQ nin ⋅⋅=α

Where α is the material absorption coefficient, An is the exposed surface normal to the

solar flux, and S is the solar flux per unit area at the distance from the sun. The heat

absorbed, Qin , is in the equilibrium with the radiated head, Qout , of the body. The

radiated head, Qout , is determined by the following equation. 4TAQout ⋅⋅⋅= σε

Where ε is the material emissivity constant, A is the overall surface area, σ is the

Boltzmann constant, and T is the object temperature. Setting this equations equal and

solving them for temperature gives you the equilibrium temperature of the uniform

body.[8] The equation for the equilibrium temperature is determined by equation shown

below.

4ASAT n

⋅⋅⋅⋅

=σε

α

The same conditions apply to a spacecraft or a satellite. The difference is that these

complex systems consist of multiple individual components with different thermal

characteristics. In addition, heat transfer between individual components occurs by

conduction. Therefore thermal control is a very important aspect in spacecraft design.

The web-author C. K. Purvis writes on his website: “In addition to overall temperature

control, it is necessary to consider the effects of thermal expansion of materials. Bonds

between materials with different coefficients of thermal expansion will be placed under

stress as the temperature changes. The thermal cycling which results from repeated

eclipse passage is of particular concern for long term fatigue failure of such bonds (e.g.,

solar cells and circuits on lightweight plastic substrates). Differential expansion can also

result in flexing of large structures.”[9] Bernd Köhler writes: It can come to strong internal

tensions. On the illuminated side the material can loose the strength by superelevated

temperature. On the shadow side it can come by the undercooling to the low-

temperature embrittlement. The result are microcracks and component distortion. In

addition to the changes of the material properties, it can come to malfunctions within

mechanisms.[7] Therefore the surface properties have been chosen in a matter to

maintain the temperature of a component in a safe interval.


2.2.4 Martian Environment The planet Mars is on the average 227.9Mkm away from the earth. Mars possesses a

relatively strong eccentric elliptical trajectory around the sun. In the sun next distance

(Perihelion) it is 206.5Mkm and the furthest (Aphelion) 249,1Mkm away. The smallest

distance between earth and Mars called opposition arises periodically approximately

every 26 months. Mars is about 55Mkm away from the earth during the closest

opposition. One Mars day is 24h and 37min long. The circulation around the sun takes

687 earth days, which corresponds to 669 Martian days. The axis of rotation has a slope

of 25°. Thus seasonal changes occur similar to the seasons on earth. The planet

diameter is 6794km and has equatorial surface gravity of 3.72m/s2. Therefore, the

weight of things on mars is only 38% of that on earth. The average solar constant at

mean Mars distance from the Sun is about 589W/m2. This is 2.3 times less than on

earth. The mean temperature is about –63°C with maximum values of –130°C in the

winter and up to 30°C in the summer. The maximum temperature differences between

day and night can reach up to 100K. The planet Mars has a thin atmosphere with a

mean surface pressure of 610Pa. The atmosphere consists of 95% carbon dioxide

(CO2), 2.7% nitrogen (N2), 1.6% argon (Ar), 0.13% oxygen (CO2), and 0.03% water

vapor. Small portions of carbon monoxide (CO) and ozone as well as the noble gases

neon (Ne), krypton (Kr) and xenon (Xe) are present. Despite the thin atmosphere

weather phenomena arise such as wind, clouds, cloudbanks, storms, and fog banks.

The cold temperatures in the southern and northern winter cause carbon dioxide to

condense, which occurs at -125°C. Dry ice settles as a consequence on the soil.

Therefore, polar ice caps increase during winter. The hard Martian crust consists mainly

of basalt with a high portion of iron oxide. The iron oxide lends its characteristic red color

to the planet. Rocks with a large range of different sizes occur. A majority of the surface

is covered with a dust like material with a grain size in the micrometer range. The dust

like material interacts with the wind and storms to produce dust storms. These are

usually local, can sometimes occur global and wrap Mars for months.[13]


2.3 Dimensional and Load Constraints The existing rover is designed in American Standard Units. The SI-system is the

standard unit system in science and space technology. Therefore the new wheels were

designed in the metric system. The existing wheels have the following outer dimensions:

Tab. 1: Outer Dimensions of the existing Rover Wheel Design Dimensions Existing wheels design New wheel design Inside diameter outer ring 7.75in 196.85mm 200mm

Wheel width 4.5in 114.3mm 110mm

Hub outside diameter 2.25in 57.15mm 60mm

Even values were selected, which fulfill the design criteria. This is not compellingly

necessary but it makes the work easier. The figure (Fig. 3) shows the existing design of

the wheel attachment to the rover suspension. These dimensional constraints had to be

met in order to mount the wheel on the rover suspension. The wheel is supported by two

radial bearings. The inner radial bearing surfaces are attached to the motor mounting

shaft. The motor mounting shaft is a hollow cylindrical axle, which is connected to the

Fig. 3: Parts and Dimensions of the existing Wheel-Rover Attachment


suspension of the rover. The motor fits in this hole properly. On the end of the motor

mounting shaft a thread is attached. The motor mount screw mounts on this thread. The

motor mount screw is a hollow cylindrical part with a shoulder. The end surface of the

motor where the drive shaft comes out is bolted to the shoulder surface of the motor

mount screw. The motor mount screw also holds the inside ring of the radial bearings in

a fixed axial position. On the drive shaft of the motor is a coupling connection attached.

This coupling connection is bolted to the hubcap. The hubcap transfers the torque of the

motor to the wheel hub. The distance from the coupling surface to outside radial bearing

is about 68mm. The suspension is 48mm away from the inner radial bearing. The inner

radial bearing is from the outer bearing 9.5mm apart. The bearings are 4.76mm thick.

This gives approximately 57.5mm (47.91mm+4.76mm+0.5x9.52mm≈57.5mm) clearance

from the suspension to the centerline between the two bearings. The bearing surfaces in

the hub for the outer bearing rings have a diameter of 47.62mm.

The load, which the wheels have to withstand, is the combined load of the two different

components. The weight of the rover is approximately 60kg. This weight is distributed on

six wheels. The specification requires that one wheel has to be able to support the whole

weight of the rover. This load is based on the gravity and therefore called gravitational

force, Fg. The gravitational force has a maximum magnitude of 588N and is

perpendicular to the ground. The other force on the wheel is generated by the wheel

torque. The direction is tangential to the wheel rim. The result of this force Ft is that in

the contact area between rim and ground developed shear stress. This is the basis for

the movement of the vehicle. This tangential force is determined as follows. The driving

motors produce a nominal torque, TM, of 77.7mNm at a speed of 7070 revolutions per

minute. A planetary gearbox is attached to the motor. The gearing ratio, i , is 86. The

maximum efficiency, η , of the gearbox is given as 70%. Therefore the nominal torque

TG on the gearbox drive shaft is shown by the equation below.

η⋅⋅= iTT MG .

This corresponds to a torque TG = 4.67Nm at a speed 82.2 revolutions per minute in our

case. The wheel diameter is 0.2m. The tangential force, Ft , between the rim and the

contact area to the ground is Ft = 46.7N. These two forces have different directions and

must be added using vectors. These two forces are perpendicular to each other, if the

rover drives on flat terrain. In this case they can be determined by applying the


Pythagoras Theorem. The direction is determined by using the trigonometry. The

magnitude of the force acting on the wheel is 690N and the direction has an angle of 85°

with respect to the ground.

2.4 Previous Wheel Designs Several different wheels have been developed since their invention a few thousand

years ago. Among them are different lightweight wheels available for a number of

applications. For example, lightweight wheels are used in motor racing, bicycle racing,

model airplanes and cars, as well as lightweight wheelchairs. There are different

reasons for the use of lightweight wheels. In racing sports the unsprung weight and the

moment of inertia should be kept as small as possible. In addition the aerodynamic drag

and the weight should be minimized on racing bicycle wheels. Weight reduction is also

the reason for the use in the model construction. The weight of the wheels for

wheelchairs should also be reduced creating easier handling and making transport for

Fig. 4: Lightweight Wheel Designs


example in the car easier. These are in principle similar efforts that also apply to the

FIDO-Rover wheels. Therefore, investigations were employed in order to have a

beginning for the design of lightweight wheels. In the picture (Fig. 4) different design

concepts are shown.

The first wheel (a) is three spoke a bicycle wheel. The spokes and the rim are

manufactured in one piece. The material used is a reinforced carbon fiber epoxy

composite. The aluminum alloy hub is press fitted into the center hole. In the second

illustration, (b) a wheelchair disc wheel construction is shown. Hub and rim consist

alternatively of aluminum or titanium alloys. The disk is a cell structure composite. In the

shown model the cell material consists of aluminum honeycomb. Other manufacturers

use as a core material Nomex® polymer honeycomb or hard foam. The skin layers are

manufactured from epoxy carbon fiber composite. The third wheel (c) is a combination of

a spoke and disc wheel. The disc is mainly added to decrease the aero dynamical drag.

The load is supported by the aluminum alloy rim and the spokes. The rim and the hub

are laminated into the spoke carbon fibers/epoxy composite construction. The fourth

wheel (d) is a wire spoke bicycle wheel. The design principle is similar to usual standard

bicycle wheels. The difference lies in the used materials. The rim is manufactured from a

carbon fiber composite. The spokes consist of a aramid fiber strengthened composite

material. The hub is made of an aluminum alloy. The five spoke wheel (e) is a

motorcycle wheel. Similar designs are also as bicycle and car wheels available. It is

manufactured of magnesium alloy by injection molding. Aluminum alloy can also be

used for this design concept. The aluminum is mainly manufactured in two different

ways. These are casting, forging or a combined process. The whole wheel is therefore

made of the same material and in one part. The finishing operations consist of surface

smoothing and the machining of functional surfaces for bearings and connections. The

last illustration (f) shows a racecar wheel. This is another five spoke wheel. The material

is again a carbon fiber composite.

Additionally wheels from earlier extraterrestrial vehicles were regarded. The wheels of

the lunar rover vehicle (Fig. 5) represent an extremely interesting design. These rovers

have been used in three Apollo missions in 1971 and 1972. The purpose of the lunar

rover vehicle was, to provide the astronauts with a greater mobility to survey different

landmarks on the moon. Two astronauts could travel with this vehicle over the lunar


surface at a top speed of 12km/h. David Baker

writes about the wheel design: “The wheels

consisted of a spun aluminum hub and an

81.8cm diameter, 23cm wide tire made of zinc

coated woven 0.083cm diameter steel strands

attached to the rim and discs of formed

aluminum. Titanium chevrons covered 50% of the

contact area to provide traction. Inside the tire

was a 64.8cm diameter bump stop frame to

protect the hub. Dust guards were mounted

above the wheels.”[15] The author Eric M. Jones

writes in the ‘Apollo Lunar Surface Journal’ over

the wheel performance: “When fully loaded, the

Rover chassis had a clearance of about 14

inches. Rocks bigger than that had to be avoided, of course and, indeed,” the astronaut

“tried to avoid as many rocks as he could to avoid damage to the wheel. Inevitably, he

couldn't avoid all of the six-inch rocks and ran over quite a few and, by the end of the

third EVA, had collected a number of golf-ball-sized dents in the mesh. The dents did not

noticeably degrade the Rover's performance and, indeed, because each of the wheels

was driven by a separate motor and because the vehicle had, as well, both front and

rear steering systems, there was little chance of

a complete Rover breakdown.”[14]

The Web-Author Scot Stride from Mars

Pathfinder Microrover Telecom Team describes

the wheel design (Fig. 6) on their Website as

follows: “The wheels are 13 centimeters (5

inches) in diameter and made of aluminum.

Stainless steel treads and cleats on the wheels

provide traction and each wheel can move up

and down independently of all the others.”[2]

This wheel is a rigid metal design. The wheel

axle has two functions. On one hand the driving

Fig. 5: Lunar Rover Vehicle Wheel (Note: The broken dust guard was fixed with spare maps, tape and lamp clamps.)

Fig. 6: Wheel of the Sojourner Rover


motor is accommodated in the shaft. On the other hand the wheel bearings are attached

to it. This design is similar with the FIDO-Rover.

Finally the existing wheel designs of the FIDO-Rover have been regarded. The wheels

of NASA’s version are similar to design (Fig. 7) of the Sojourner Rover wheels. It is a

solid aluminum wheel with attached studded treads. Contrary to this design the wheels

of the OU’s FIDO-Rover version (Fig. 8) consist of different individual parts. As already

in section 2.2, the hub is supported with two radial bearings at the wheel axle. There are

six parabolic formed spokes bolted to the hub. The free ends of this aluminum spokes

are connected with two rings. The outside diameter of these rings corresponds to the

inside diameter of the rim. The rings are bolted to the rim at a distance of 12mm from the

two front surfaces. The rim is made of an 8 inch PVC pipe. The treads are cut with a 4-

axsis mill into the exterior surface.

2.5 Materials and Structures A lot of effort was made in the last decades to develop more sophisticated materials for

space applications. Today numerous materials for many different applications are

available. For structural components of space vehicles metallic materials and polymers

are used. The primarily requirements are that a favorable strength-mass relationship

exist. The density and the typical tensile strength is shown for different materials in the

table (Tab. 2). The strength-density ratio is calculated by dividing the density thru the

Fig. 7: Wheels of NASA’s FIDO-Rover

Fig. 8: Wheel of OU’s FIDO-Rover

A

te

p

s

w

lig

ti

b

ra

is

ra

s

d

TE

ab. 2: Material Selection (Material Properties adapted from: Callister, W. D.: Materials Science and ngineering: An Introduction, 3. Edition, John Wiley & Sons Inc, New York, 1994).

Material Density [kg/m3]

Typical Tensile Strength [MPa]

Stength-Density-Ratio (x100)

Aluminium 99,8% 2710 60 2,2 Titanium 4510 330 7,3 Beryllium 1840 448 24,3 Nickel 8900 480 5,4

pure

Magnesium 1740 165 9,5 mild strength 7800 1000 12,8

Steel high strength 7800 1500 19,2 Al alloy (7075-T6) 2810 570 20,3 Mg alloy (ZK60A) 1800 350 19,4 Ti alloy (Ti-6Al-4V) 4430 990 22,3

Metals

Alloys

Al-Li-alloy (8090-T6) 2590 600 23,2 Epoxy 1250 (28-90) 59 4,7 PTFE 2200 (14-34) 24 1,1 Polyurthane 1150 (5,5-55) 30 2,6 PMMA 1200 (48-76) 62 5,2

rigid

Nylon 6,6 1140 (76-94) 85 7,4 Low density 30 0,5 1,7

Polymers

foamed High density 600 25 4,2 Carbon fiber 1800 4000 222,2 E-Glas fiber 2500 3500 140,0 Reinforcement Fibers Aramid fiber 1400 3500 250,0

lois Winterholler 18.07.2002

nsile strength. The strength-density ratio gives a rough estimate of which material is

articularly suitable for the application. Beyond strength-mass relationship, the materials

hould have a high rigidity, good shock absorption characteristics, and be able to

ithstand the environment in extraterrestrial space. Preferential metallic materials are

ht weight alloys with a basis of the materials of magnesium, aluminum, beryllium and

tanium. High-strength steel is used for highly stressed structures.[7] As shown

eryllium, aluminum-lithium alloy and titanium alloy have the highest strength-density

tios. The online material database ‘MatWeb’ describes beryllium as follows: “Beryllium

one of the lightest metals and has a high strength-to-weight ratio, stiffness-to-weight

tio, and very high specific heat, thermal conductivity, and heat of fusion. It has

ignificant ductility, and is readily machined and can be rolled, drawn, or extruded.”[16] A

isadvantage of beryllium is the brittle behavior, which comes from the lattice structure.


Berylium is not able to withstand intermittent loads while under tension.[7] Aluminum-

lithium alloys, developed in the 1980’s, are also widely used as structural materials in

aerospace and spacecraft construction. The advantages are lower density than

conventional aluminum alloys and excellent fatigue properties.[17] In a report of the

‘National Academy of Science’ is written: “Moreover, specific aluminum-lithium and

magnesium-aluminum-lithium alloys show markedly increased toughness at cryogenic

temperatures, an important property for liquid oxygen and liquid hydrogen fuel

tanks”.[19] The disadvantages of the high strength aluminum-lithium alloys are reduced

ductility and fracture toughness in comparison with standard aluminum alloys.[17]

Titanium alloys are well known for the high strength in comparison with other metals.

Titanium alloys are 40% lighter than steel and 60% heavier than aluminum. This

combination of high strength and low weight makes titanium a very useful structural

metal. Titanium also features excellent corrosion resistance. A variety of titanium alloys

with different characteristics are available. Titanium alloys are heat treatable and can be

hardened, which means that it can undergo manufacturing while the material is still

ductile and then undergo heat treatment and aging to strengthen the material, which is a

big advantage. Other alloys have good cold formability or are able to be welded.

Examples of current applications include highly stressed airplane and spacecraft parts

such as screws and turbines, sporting equipment, chemical processing equipment and

prosthetic devices.[7],[16]

In the future, trends will lean towards the use of metal matrix materials. These new

reinforced matrix composites are based on magnesium alloy and aluminum alloy matrix

materials. Examples are aluminum-containing silicon carbide ceramic fibers or boron

fibers in a magnesium alloy matrix material. The substantial advantage of metals in

opposite to polymers is their higher temperature stress maximum. Generally polymers

are particularly subjected to the physical influences of space such as pressure,

temperature, radiation and aggressive residual gas. Chemical conversions, destruction,

concatenation and embrittlements are the result.

Presently, the metallic materials are displaced by polymer materials with reinforcement

fibers. The advantage of the fiber reinforced polymers are weight reduction, higher

strength and a low thermal expansion.[7] The reinforcement fibers add high strength and

stiffness to the matrix material. Some fiber-matrix composites have application


temperatures as low as –250°C where the non-strengthened polymer is limited to –

75°C. The Author Ken Easterling writes in his book about fiber reinforced polymer

composites: “These materials are remarkable because they are very strong, posses high

stiffness, and yet are extremely light. As a composite, they combine the enormous

uniaxial strength of, for example, fine carbon fibers and the lightweight but brittle matrix

of polyester or epoxy, or other polymer matrix materials binding the fibers together. They

are used as structural materials in aerospace and spacecraft, and in certain sporting

equipment such as skis and vaulting poles.”[10] The most common materials are glass,

carbon or aramid as reinforcement fibers and epoxy resin as the matrix. The authors M.

Boyle, C. Martin and J. Neuner write over epoxy resins: “Epoxy resins are a class of

thermoset materials used extensively in structural and specialty composite applications

because they offer a unique combination of properties that are unattainable with other

thermoset resins. Available in a wide variety of physical forms from low viscosity liquid to

high-melting solids, they are amenable to a wide range of processes and applications.

Epoxies offer high strength, low shrinkage, excellent adhesion to various substrates,

effective electrical insulation, chemical and solvent resistance, low cost, and low toxicity.

They are easily cured without evolution of volatiles or by-products by a board range of

chemical specie. Epoxy resins are also chemically compatible with most substrates and

tend to wet surfaces easily, making them especially well suited to composites

applications. … Some of their most interesting applications are found in the aerospace

and recreational industries where resins and fibers are combined to produce complex

composite structures. Epoxy technologies satisfy a variety of nonmetallic composite

designs in commercial and military aerospace applications, including flooring panels,

ducting, vertical and horizontal stabilizers, wings, and even the fuselage.”[18]

Polymers are also used as foam materials for space applications. Hard foam is applied

as a stiffening and filling material for gaps and cavities or as insulation material.

Preferential foams are based on PU (polyurethane), PE (polyethylene), PF (phenol

formaldehyde), EP (epoxy) or SI (silicone) basis. These foams should not be exposed to

the direct radiation. The short wave radiation is able to change and destroy the structure.

The result is a decrease of the compression strength. For protection they are covered

with steady foils and on outside use with additional thermal insulation.[7]


Another way to build lightweight structures is the sandwich material. This composite

material consists of a cellular core with thin skin layers. The advantage is that the

continuous supporting of the skin layers eliminates the structural buckling. The function

is that the bending stress is divided, whereby the surface layers experience the tensile

and the pressure stress and the core supports the shear force. The core structure is

made of different materials. The materials include aluminum, polymers, paper, or even

balsa wood. The most common form is a hexagonal cell form, the so-called honeycomb.

Sheet metal or fiber reinforced composite materials used for the outside layers. The

Hexcel company writes in their 1997 annual report about the honeycomb material:

“Advanced structural materials are strong and lightweight, they tolerate extremes in

temperatures, they are highly resistant to corrosion and they help reduce the life-cycle

costs of operating the aircraft. That is why they have become an essential material for

the commercial aerospace, space and defense industries. … Used for aircraft

components, automotive components, high speed and mass transit trains, energy

absorption, athletic shoes and many other components. … Honeycomb cores are

manufactured from aluminum, Nomex®, fiberglass, carbon and other materials, and

supplied directly to customers. These honeycomb cores can be sandwiched between

metallic or prepreg skins to form lightweight and exceptionally strong honeycomb

sandwich panels. Honeycomb and panels can also be shaped and tailored into any

number of forms to meet customer’s specifications.”[11]

Adhesives: Epoxy-Phenol, Vinyl-Phenol, Nitril-Phenol

This are the glues used in space applications. I have to find more detailed information.

2.6 Design Decision After reviewing and evaluating the collected information and data the principle design

ideas were developed. These ideas include four different designs. In the figure (Fig. 9)

the first sketches are shown. The names given to the different designs represent the

main structural material between the hub and rim. The principle design concepts are

explained in the following paragraphs.


1. This wheel has a cellular

hexagonal core between the hub

and rim. The cells of the

honeycomb core are

perpendicular to the wheel axle.

2. The design for the second wheel

includes a carbon fiber reinforced

composite material with epoxy

resin as the matrix material. The

connection between the hub and

rim should be implemented by

three spokes.

3. The third design idea possesses

hard foam as the connecting

element. This is like the other sandwich construction used in the first wheel. The

difference lies in the irregular cell structure of the hard foam. Polyurethane was the

foam that was used.

4. The last design concept was a wheel with six spokes of sheet metal. The selected

material is aluminum alloy.

In the figures (Fig. 9 and Fig. 10) different

sketches for wheel treads are shown. The basic

idea was to integrate the tread into the wheel

rim. Therefore, no other connections like screws

or rivets are needed to mount the studs on the

wheel. Another thought was to keep the

manufacturing time low. The wheel treads were

formed by pressing the tread pattern into a

formable material like aluminum alloy or

titanium alloy.

The design of the wheel hub

I have to write here a few sentences.

Fig. 9: Wheel design ideas

Fig. 10: Pressed wheel thread


A list of needed material and equipment was worked out for the four wheel designs. The

decision was made to carry out three of these concepts after consulting with my advisor,

Dr. David Miller. The three designs that were chosen are the honeycomb wheel, the

carbon fiber wheel, and the hard foam wheel. The aluminum wheel design was

abandoned for the following reasons. The time frame for the execution of the diploma

thesis should be kept. Also, there are already similar wheels for the rover available,

which can be used to accomplish the tests and the comparison.

3 Wheel Design and Manufacturing Three different wheel prototypes should be designed and manufactured.

As mentioned before, the wheels are designed in the metric system. The threads are an

exception. Since metric screws are not very common in the USA, all bolt connections

were selected in the American standard system.

Besides was also the thought, to select simple available materials.

3.1 Honeycomb Honeycomb is a common building method in the

aircraft industry. The production of laminar aluminum

Honeycomb (Fig. 11) is explained in the following

sentences. On a thin sheet metal with thicknesses

between 0.03mm to 0.15mm (typical 0.08mm)

adhesive strips are applied. A heat curing adhesive

tape is usually used. A certain number of sheet metal

layers, depending upon size of the plates and the cell

size to be manufactured, are put down one above

another. Afterwards the prepared piles are pressed

and cured into a hot-press. The adhesive hardens at the zones where the cells connect.

The manufactured material is cut with a sheet metal shear in strips. The strip width

determines the Honeycomb thickness (cell height). In the zones that were not attached

by the adhesive of the outside layers are intervenes with combs. The fingers of the

combs are adjustable in the distance. The combs are pulled apart and honeycomb cells

Fig. 11: Honeycomb manufacturing


form. The length of the metal strips is reduced. To not obstruct the cell forming process

the distance between comb fingers have to be reduced accordingly. honeycomb cells

form. The length of the metal strips is reduced. To not obstruct the cell forming process

the distance between comb fingers have to be reduced accordingly.

The same principle should be used for the Honeycomb core of the first prototype. The

fundamental idea was to manufacture a cylindrical closed core. In order to achieve a

certain rigidity, the cells should run perpendicularly to the wheel axle. First it had to be

determined if whether this possible by the geometrical conditions. Therefore, the

following considerations must be employed. As layer circular closed rings must be used.

The dimensions have to be selected in such a way, that the cells form out evenly on the

entire core. This was reached by the following computations. The outer dimensions of

the cylindrical Honeycomb core, which

had to be manufactured, are known.

These are in detail the outside diameter,

d1, the internal diameter, d2, and the

thickness, t. The number of layers nL is

selected from this data. From this the half

cell width h is computed by dividing the

core thickness, t , thru the number of

layers, nL. In addition the number of cells

per layer, nC ,and a value for the length of the adhesive surfaces edge a must be

specified.

First, with these parameters, the half cell length, s ,is determined as follows.

Cnds⋅⋅=

2π

The length of the bent cell edge, l ,can be computed with the following relationship and

the known data.

( ) 222 hasl +−=

The diameter of the raw layer dL is determined using the bent cell edge, l .

( )π

22 ⋅⋅+= CL

nald

The following calculations are valid for both the inside and outside diameter.

Fig. 12: Honeycomb cell dimensions


The results are afflicted with a slight error. To simplify the computations direct distances

instead of the lengths of curves were used in the calculations. This is especially helpful

for the surfaces of the cells that are not perpendicular to the honeycomb axis. They

represent a non-perpendicular cut thru a cylinder and have thus as delimitations elliptical

curves. To have an order of magnitude for the error the following consideration was

made. The perimeter of a circle with 200mm diameter is 628.32mm. For a regular

polygon with 64 segments and 200mm width between parallel sides the perimeter is

628.82mm. The difference is 0.5mm or around 0.08%.

A simple Honeycomb model was made of paper after the computations were

accomplished,. The model consisted of seven layers with 16 cells per layer. The

honeycomb cells had a width of 8mm. The finished honeycomb ring should have an

internal diameter of 80mm and an outside diameter of 160mm. The layers were drawn

with a CAD program, printed and cut out of paper. Sticking them together was

accomplished with simple paper adhesive. For pulling the layers apart pencils were

used. The result agreed with the desired predictions. The manufacturing with paper

layers produced a good result. The model had already had a certain stiffness. Therefore

it was decided to produce the honeycomb core for the prototype out of paper.

The design of a functional prototype began after the feasibility was determined by the

production of a model. The established geometrical relations have to be processed in a

spreadsheet program to accelerate the computation work. A further reason besides this

was to facilitated the selection of suitable dimensions. The illustration (Fig. 13)

represents this spreadsheet. Index 1 stands for the outside dimensions and index 2 for

inside dimensions. In the top section the given and selected parameter are entered. For

the selected value of outside adhesion width a1 was always selected a whole interval of

values (usually 10 values). In the middle part of the spreadsheets the cell form

dimensions are calculated. This computed data include adhesive surfaces lengths, the

diameters of the layer and the cell angle. The number of columns in the middle and

lower part corresponds to the number of selected outside adhesion width a1 values.

Through the possibility of direct comparison of the computed dimensions, a better

overview the of geometric tendencies is provided. In the lower part of the spreadsheet

values are determined, which are processed with a CAD program.


For the prototype which should be manufactured different values were tried out with the

spread-sheet. The decision fell on a core with a thickness t of 100mm, 20 layers and 16

cells per layer. For outside adhesion width a1 8.4mm was selected. The appropriate

column in calculation sheet (Fig. 13) is yellow underlaid. This corresponds to an angle

between the connecting surfaces of the cells of 120°. A further reason for this choice

were the dimensions of the adhesive surface. The internal total length of the adhesive

surface is 3.06mm. This sufficiently ensured a safe bonded connection between the

layers.

Calculation Sheet Honeycomb Geometry (Prototype) all dimensions in mm Given Honeycomb Dimensions outer diameter Honeycomb [d1] = 200,0 inner diameter Honeycomb [d2] = 60,0 thickness Honeycomb [t] = 100,0 number of layers [nL] = 20 number of cells per layer [nC] = 16 calculated half cell width [h] = 5,00 outside adhesion width [a1] = 8,2 8,4 8,6 Calculated Dimensions half outside cell length [s1] = 19,63 19,63 19,63 half outer curve length layer [b1] = 22,36 22,55 22,76 outer diameter layer [dL1] = 227,7 229,7 231,8 cell angle [alpha] = 57° 60° 64° half inside cell length [s2] = 5,89 5,89 5,89 half inner curve length layer [b2] = 8,61 8,80 9,02 inner diameter layer [dL2] = 87,7 89,7 91,8 inside adhesion width [a2] = 1,33 1,53 1,73 CAD Layer Dimensions angle increment (compl. Cell) = 22,5° 22,5° 22,5° angle increment (half Cell) = 11,25° 11,25° 11,25° angle increment (quarter Cell) = 5,625° 5,625° 5,625° angle increment (adh L out) = 4,127° 4,091° 4,053° angle increment (adh L in) = 1,735° 1,952° 2,156° Fig. 13: Spreadsheet for the Honeycomb calculation


In a CAD-program the calculated values were

converted into a drawing for the layers (Fig. 14).

The shaded squares represent the adhesive

surfaces. In addition triangular markings were

attached. They are needed for sticking of the

layers together. These markings are a half cell

length apart and symmetrically to the center line

of an adhesive surface. This drawing was twenty

times printed out with a computer printer. Five

expressions on a thicker paper were made

additionally. These thicker layers were used as

masks for the adhesive applying process. Therefore the shaded squares were cut out

with a razor knife. For cutting out of the layer templates were manufactured (Fig. 15).

The template for the internal circle is a conical ring. This ring served also as centers for

coaxial alignment when the layers were glued together. For the outside circle a template

was made of sheet metal. When cutting out the layers, alternating two of the four

markings on circle were cut off. The layers had to be stuck together in an order, that the

position of the adhesive surface shifts at each layer a half cell length. After all layer and

masks were cut out, the sticking than together began. As glue spraying adhesive in

spray can of the brand 3M was used. Therefore the mask was put down on the Layer in

such a way, that the hatched adhesive surfaces could be seen. To prevent from

Fig. 14: Layer drawing

Fig. 15: Layer assembling


underflow with adhesive, pieces of metal were put down on the mask. After the spraying

the adhesive on the layer, the mask was carefully removed. After this the layers put

down on each other and pressed. For the axial centering the conical ring served. The

markings ensure the adjustment in the correct angle. This was repeated until all layer

had been stuck together. The five prepared masks have been changed through to allow

them to dry between the uses. The so stuck together piles were a little expanded with

sheet metals pieces. Thus made a better air flow for faster drying possible. In addition

the alignment markings were cut off with a razor knife.

To ensure an evenly expanding of the core a device had to be designed and built. This

tool must fulfill certain conditions. It must have the same number of fingers like the core

has cells. The fingers must be radially adjustable to be able to position it before

expanding and removed than after the expanding process is completed. The diameter of

the core is reduced the further it is pulled apart. The device may not obstruct this. The

core before the expansion is relatively flat. Therefore the highest and lowest layer of the

pile are near each other. The fingers must be able to be slid into this position. Besides a

mounting support for the hub should be present in the center.

3.2 Carbon Fiber

3.3 Hardfaom

3.4 Wheel Tread

4 Wheel Comparison and Evaluation

4.1 Cost and Manufacture Comparison

4.2 Weight and Stability Comparison

Building and test of the autonomous solar rover in April to June 2002.

Travel long distances to survey different geological landmarks


5 List of Illustrations Fig. 1: Mars-Panorama-Picture taken at the Pathfinder-Mission

Fig. 2: Field Integrated Design and Operations Rover (FIDO)

Fig. 3: Parts and Dimensions of the existing Wheel-Rover Attachment

Fig. 4: Lightweight Wheel Designs

Fig. 5: Lunar Rover Vehicle Wheel

Fig. 6: Wheel of the Sojourner Rover

Fig. 7: Wheels of NASA’s FIDO-Rover

Fig. 8: Wheel of OU’s FIDO-Rover

Fig. 9: Wheel design ideas

Fig. 10: Pressed wheel thread

Fig. 11: Honeycomb manufacturing

Fig. 12: Honeycomb cell dimensions

Fig. 13: Spreadsheet for the Honeycomb calculation

Fig. 14: Layer drawing

Fig. 15: Layer assembling

6 List of Tables Tab. 1: Outer Dimensions of the existing Rover Wheel Design

Tab. 2: Material Selection


7 Reference [1] Ellery, Alex: An Introduction to space robotics. Book

1.Title, Berlin, Heidelberg, New York, Springer Verlag, 2000.

ISBN 1-85233-164-X

[2] NASA: Overview of the Mars Pathfinder Mission. (Ref: JPL 96-207 p.32) Internet

Web-Author: Scot Stride, NASA-JPL, Telecommunications Hardware Section 336.

http://mars.jpl.nasa.gov/MPF/rovercom/rovintro.html

[3] NASA Facts: Mars Pathfinder Report

Jet Propulsion Laboratory, California Institute of Technology,

Pasadena, CA 91109.

http://www.jpl.nasa.gov/news/fact_sheets/mpf.pdf

[4] NASA: Pathfinder Mission. Internet

http://mars.jpl.nasa.gov/missions/past/pathfinder.html

[5] NASA: Field Integrated Design and Operation Rover. Internet

Contact: Dr. Eric Baumgartner, FIDO Testing Task Manager.

http://fido.jpl.nasa.gov/description.html

[6] Miller, Prof. Dr. David: Assignment Letter for the Diploma Thesis Letter

Date: Monday, August 27th, 2001

[7] Hallmann, Willi; Ley, Wilfried: Handbuch der Raumfahrttechnik Book

Author: Bernd Köhler, Chapter: 6.Werkstoffe

2. Edition, München, Wien, Karl Hanser Verlag, 1999.

ISBN 3-446-21035-0

[8] Tribble, Alan C.: The space environment: Implications for Spacecraft Design Book

Princeton New Jersey, Princeton University Press, 1995.

ISBN 0-691-03454-0

[9] Purvis, C. K.: The Space Environment: Sunlight and Earthshine Internet

http://powerweb.grc.nasa.gov/pvsee/publications/seeov/sunerfshin.html

[10] Easterling, Ken: Tomorrow’s Materials Book

2. Edition, London, The Institute of Metals, 1990.

ISBN 0-901462-83-7

[11] Hexcel Company Annual Report 1997: Chapter Honeycomb Material Internet

http://www.corporate-ir.net/media_files/nys/hxl/annual/annual97.pdf


[12] Bekker, Mieczyslaw G.: Introduction to Terrain-Vehicle Systems Book

The University of Michigan Press, 1969.

[13] Heuseler, Holger; Jaumann, Ralf; Neukum, Gerhard: Book

Die Mars-Mission: Pathfinder, Sojourner und die Eroberung des roten Planeten.

München, BLV Verlagsgesellschaft, 1998

ISBN 3-405-15461-8

[14] Jones, Eric M.: Apollo Lunar Surface Journal: The Lunar Rover Internet

http://www.hq.nasa.gov/office/pao/History/alsj/apollo.engin.html

[15] Baker, David: Lunar Roving Vehicle: Design Report Internet

Spaceflight, 13, 234-240, July1971.

http://nssdc.gsfc.nasa.gov/planetary/lunar/apollo_lrv.html

[16] MatWeb: Material Property Data: Beryllium I-220H Grade 1 Internet

http://www.matweb.com/search/SpecificMaterial.asp?bassnum=MBEI21

[17] James, Richard S.: Aluminum-Lithium Alloys Book

Metals Handbook, Volume 2, 10. Edition, ASM International, 1990.

ISBN 0-87170-378-5

[18] Boyle, Maureen A., Martin, Cary J., Neuner, John D.: Epoxy Resins Book

ASM Handbook, Volume 21, Composites, ASM International, 2001.

ISBN 0-87170-703-9

[19] National Academy of Science: Technology for small Spacecraft Book

Washington D.C., National Academy Press, 1994.

ISBN 0-309-05075-8

[20] McCrudy, Howard E.: Faster, Better, Cheaper: Low-cost innovation Book

in the U.S. space programm

Baltimore, The John Hopkins University Press, 2001.

ISBN 0-8018-6720-7

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