Project Report

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DESIGN & FABRICATION OF
ROCKER-BOGIE MECHANISM
MINOR PROJECT
SUBMITTED IN PARTIAL FULFILLMENT OF REQUIREMENTS FOR THE AWARD
OF THE DEGREE OF
BACHELOR OF TECHNOLOGY
MECHANICAL ENGINEERING
BY
ANUBHAV KUMAR DEERGHA GARG
(12001004009 ) (12001004015 )
NITIN VERMA RAHUL HANS
(12001004037) (12001004044 )
UNDER THE GUIDANCE OF
Dr. AJAY KUMAR
DEPARTMENT OF MECHANICAL ENGINEERING
FACULTY OF ENGINEERING & TECHNOLOGY
D.C.R. UNIVERSITY OF SCIENCE & TECHNOLOGY
MURTHAL, SONEPAT, HARYANA (INDIA) – 131 039
(NOVEMBER 2015)

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DECLARATION BY THE CANDIDATES
We hereby certify that the work which is being presented in this Project report
entitled ‘DESIGN & FABRICATION OF ROCKER-BOGIE MECHANISM’ in partial
fulfillment of requirements for the award of degree of BACHELOR OF TECHNOLOGY
in MECHANICAL ENGINEERING, submitted to the Dept. of Mechanical Engineering,
Faculty of Engg. & Technology, D.C.R. Univ. of Science & Technology, Murthal,
Sonepat (Haryana) is an authentic record of our own work carried out during a period
from July 2015 to May 2016 under the supervision of Dr. AJAY KUMAR The matter
presented in this project work has not been submitted to any other University / Institute
for the award of B.Tech or any other Degree / Diploma.
Name (Roll. No.) Signature
1. Anubhav Kumar (12001004009)
2. Deergha Garg (12001004015)
3. Nitin Verma(12001004037)
4. Rahul Hans(12001004044)
This is to certify that the above statement made by the candidate is correct to the best
of my knowledge & belief.
Signature of Supervisor (s)

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ABSTRACT
The rocker-bogie suspension mechanism it’s currently NASA’s favored design
for wheeled mobile robots, mainly because it has robust capabilities to deal with
obstacles and because it uniformly distributes the payload over its 6 wheels at all
times. Even though it has many advantages when dealing with obstacles, there is one
major shortcoming which is its low average speed of operation, making the rocker-
bogie system not suitable for situations where high-speed traversal over hard-flat
surfaces is needed to cover large areas in short periods of time, mainly due to stability
problems. Our propose is to increase the stability of the rocker-bogie system by
expanding its support polygon, making it more stable and adaptable while moving at
high speed, but keeping its original robustness against obstacles.
The Rocker-Bogie Mobility system was designed to be used at slow speeds. It
is capable of overcoming obstacles that are on the order of the size of a wheel.
However, when surmounting a sizable obstacle, the vehicles motion effectively stops
while the front wheel climbs the obstacle. When operating at low speed (greater than
10cm/second), dynamic shocks are minimized when this happens. For many future
planetary missions, rovers will have to operate at human level speeds (~1m/second).
Shocks resulting from the impact of the front wheel against an obstacle could damage
the payload or the vehicle.We will develop a method of driving a rocker-bogie vehicle
so that it can effectively step over most obstacles rather than impacting and climbing
over them. Most of the benefits of this method can be achieved without any
mechanical modification to existing designs – only a change in control strategy. Some
mechanical changes are suggested to gather the maximum benefit and to greatly
increase the effective operational speed of future rovers.

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ACKNOWLEDGEMENT
We are highly grateful to the Hon’ble Vice-Chancellor, D.C.R. Univ. of Science
& Technology, Murthal, Sonepat for providing us this opportunity to carry out the
present project work.
The constant guidance and encouragement received from Dr. Ajay Kumar ,
Prof. & Chairperson, Dept. of Mechanical Engineering, D.C.R. Univ. of Science &
Technology, Murthal, Sonepat has been of great help in carrying our the present work
and is acknowledged with reverential thanks.
We would like to express a deep sense of gratitude and thanks profusely to our
Project Supervisor, Dr. Ajay Kumar , Asstt. Prof./Associate Prof./Professor, Dept. of
Mechanical Engineering, D.C.R. Univ. of Science & Technology, Murthal, Sonepat.
Without his/her able guidance, it would have been impossible to complete the project in
this manner.
The help rendered by Sh. M.S. Narwal B.Tech. Project Coordinator,
Department of Mechanical Engineering, D.C.R. Univ. of Science & Technology,
Murthal, Sonepat for his/her wise counsel is greatly acknowledged. We also express
our gratitude to other faculty members of Dept. of Mechanical Engineering, D.C.R.
Univ. of Science & Technology, Murthal, Sonepat for their intellectual support
throughout the course of this work.
Finally, We are indebted to all whosoever have contributed in this project work.
Name Roll. No. Signature
1. Anubhav 12001004009
2. Deergha Garg 12001004015
3. Nitin Verma 12001004037
4. Rahul Hans 12001004044

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LIST OF FIGURES & TABLES
Figure 1 MER (Mars Exploration Rover)
Figure 2 NASA’s Curiosity Rover
Figure 3 Red Rover
Figure 4 Lateral Stability
Figure 5 Longitudinal Stability
Figure 6 Centre Stage Stairs
Figure 7 Calculations at Centre Stage Stairs
Figure 8 Library Stairs
Figure 9 Calculation at Library Stairs
Table 1 Calculation of Wheel Diameters
Table 2 Calculation of Diameter and RPM
Table 3 Hardware to be Purchased
Table 4 Electrical Equipments to be Purchased

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Table of Contents
Decleration by the Candidates
Abstract
Acknowledgement
List of Figures & Tables
CHAPTER 1 INTRODUCTION
1.1 Introduction
1.2 Need & Motivation for the Selection of the Project
1.3 Objective of the Project
CHAPTER 2 PAST, PRESENT & FUTURE
2.1 Introduction
2.2 Recent Rovers & their Missions
2.3 Rover Mobility
CHAPTER 3 RELATED CONCEPTS & THEORIES
3.1 Design Requirements & Specification
3.2 Related Concepts
3.2.1 Traction & Slip
3.2.2 Lateral Stability
3.2.3 Longitudinal Stability
3.2.4 Static Stability Factor
3.3 Design Analysis
CHAPTER 4 CALCULATIONS
1. Diameter of Wheel
2. Calculation of Wheel Base
3. Length of Links
4. Height Calculation
5. Track Width

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CHAPTER 5 CONCLUSIONS
5.1 Conclusion
5.2 Budget & Table of Requirements
5.3 Future Scope
References

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CHAPTER 1
INTRODUCTION
1.1 Introduction
There is an increasing need for mobile robots which are able to operate in
unstructured environments with highly uneven terrain. These robots are mainly
used for tasks which humans cannot do and which are not safe. In order to achieve
these tasks, any mobile robot needs to have a suitable mobile system according to
each situation. Among these mobile systems, it’s the rocker-bogie suspension
system that was first used for the Mars Rover Sojourner and it’s currently NASA’s
favored design for rover wheel suspension. The rocker-bogie suspension is a
mechanism that enables a six-wheeled vehicle to passively keep all six wheels in
contact with a surface even when driving on severely uneven terrain. There are two
key advantages to this feature. The first advantage is that the wheels' pressure on
the ground will be equilibrated. This is extremely important in soft terrain where
excessive ground pressure can result in the vehicle sinking into the driving surface.
The second advantage is that while climbing over hard, uneven terrain, all six
wheels will nominally remain in contact with the surface and under load, helping to
propel the vehicle over the terrain. Exploration rovers take advantage of this
configuration by integrating each wheel with a drive actuator, maximizing the
vehicle's motive force capability. One of the major shortcomings of current rocker-
bogie rovers is that they are slow. In order to be able to overcome significantly
rough terrain (i.e., obstacles more than a few percent of wheel radius) without
significant risk of flipping the vehicle or damaging the suspension, these robots
move slowly and climb over the obstacles by having wheels lift each piece of the
suspension over the obstacle one portion at a time. While performance on rough
terrain obstacles is important, it should be also considered situations where the
surface is flat or it has almost imperceptible obstacles, where the rover should
increase its speed to arrive faster from point A to point B.

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1.2 Need and Motivation for the selection of the project
Rocker-bogie suspension system that was first used for the Mars Rover
Sojourner and it’s currently NASA’s favored design for rover wheel suspension.
This is a very less explored field of study and could be developed into exploration
purpose instrument. The need to develop specialized high-fidelity systems capable
of operating in harsh earth environments typically leads to longer development
timelines and greater expenditures. While specific applications will always require
unique designs, there are many commonalities in planetary rovers. Issues such as
mobility, navigation, and vision, may differ slightly between missions but are largely
the same in most scenarios. Given these fundamental characteristics of many
planetary rovers we believe that a modular and ruggedized system meeting these
basic requirements would aid in the process of developing space-ready technology.
There are currently many mobile research platforms available, yet few are designed
to operate in the harsh earth environments that are often used for planetary surface
rover testing. By creating a rover that is suitable for these types of environments,
our goal is to facilitate the development of rovers and their related technologies, in
addition to lowering development costs. We also hope that the platform developed
can be tested and improved upon, to potentially serve as a model for a rover that
could go to the moon or Mars in the future.
Our mission is to design, develop, and test a rover to serve as a research
platform, suitable for testing planetary surface exploration technologies in harsh
earth environments. The design will focus on incorporating features that are
believed to be essential for most planetary exploration missions.The Rocker bogie
Suspension system can be sent for reconnaissance purpose,which is exploring the
surrounding to give a visualisation to a person or operator sitting somewhere for
carrying the operation, by the help of a video camera. Hence, due to this feature of
the rocker bogie suspension system this can be used in military for visualising the
scenario at a region where a bomb is planted. Not only this, the rocker bogie
suspension system can be developed into a wheel chair too to take the patients
from one place to another climbing the stairs on its own. It can also be used for
material delivery purposes. As explained this is a wide field of study and very less
explored. So this gave the motivation for the development of this suspension
system.

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1.3 Objective of the Project
We will be focusing on eliminating the shortcomings of the rover. one of the
major shortcomings of current rocker-bogie rovers is that they are slow. In order to
be able to overcome significantly rough terrain without significant risk of flipping the
vehicle or damaging the suspension, these robots move slowly and climb over the
obstacles by having wheels lift each piece of the suspension over the obstacle one
portion at a time. While performance on rough terrain obstacles is important, it
should be also considered situations where the surface is flat or it has almost
imperceptible obstacles, where the rover should increase its speed to arrive faster
from point A to point B. The rovers made for the exploration purposes are very
costly too. Due to the high cost of space exploration, most missions to date have
been conducted by NASA and other government-supported organizations.
However, the continually decreasing cost of technology and economic potential in
natural resources has led some private companies to pursue space transportation
and exploration as a core business. For example, Astrobotic Technology, Odyssey
Moon, and Armadillo Aerospace are just a few companies that are developing
rovers and landers for different space missions. While companies like these have
made progress in the commercialization of space exploration, the inherently high
costs continue to hinder economic feasibility. We, in India have not conducted any
mission for the exploration purposes. Not only mars exploration the rocker bogie
can also be used for military and civil purposes but there also it is needed to be a
little cost effective and fast. Thus our concern during the development of the rover
would be to optimise the speed such that the rover do not flip and may travel a litle
faster too and make it cost effective with maximum possible rigidity and
ruggedness.

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CHAPTER 2
PAST PRESENT & FUTURE
2.1 Introduction
This chapter will begin by reviewing some past space exploration rovers as well
as rovers currently in development. It will discuss specific missions along with the
corresponding design features and capabilities, specifically relating to mobility and
navigation, that made these rovers successful in meeting their objectives on the
Martian or lunar surface. Next, specific features of these rovers are discussed in order
to learn more about the types of technologies that are often used on exploration rovers.
Both hardware and software design choices are reviewed, as they relate to the mobility
challenges of ground compliance and hazard avoidance. Lastly, research into analog
testing presents what is currently being done by NASA and others to validate planetary
rovers on Earth. A variety of harsh Earth environments are examined for their suitability
in analog testing based on how well they represent certain aspects of the Martian and
Lunar environments. A few NASA sponsored competitions are also reviewed, as they
can often provide unique opportunities for analog testing at NASA facilities.
2.2 Recent Rovers and their Missions
Much of space exploration can be divided into three categories: a quest to better
understand our universe, interest, and economic potential in using natural resources
outside our planet, and the future colonization of extra-terrestrial bodies. Furthermore,
most interest has been in our moon and Mars, as these planetary bodies are close by,
and have environments that are hospitable enough for rovers, and potentially for future
colonization.
The moon is also very well suited for scientific equipment such as radio observatories
or IR telescopes, as it has no atmosphere, instruments such as these can measure
signals that would otherwise be disturbed or eliminated on Earth. Interest in Mars
mostly relates to expanding our knowledge of the planet, specifically with respect to its

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ability to support a human colony. Learning more about the composition of its
atmosphere and soil can tell us whether Mars could potentially support microbial life.
Since 1976, NASA has been exploring the surface of Mars with rovers, starting
with the dual landing of Viking 1 and Viking 2 landers. In 1997, The Mars Pathfinder
(MPF) lander delivered the Sojourner Rover to the surface successfully. Most recently,
in early 2004, NASA again landed two more rovers on Mars, Spirit and Opportunity. In
November 2011, NASA has launched the Mars Science Laboratory (MSL) with a rover
named Curiosity. Despite the multiple rovers that NASA has sent to Mars, each
mission has similar objectives. Making improvements from past Mars rovers, NASA
has continued to develop autonomous navigation to make it easier and quicker to
control their rovers, given the relatively large time delays in sending commands. To do
this, on-board stereo vision processing was used to develop an image on the
environment, which identified positive and negative obstacles relative to the ground
plane. The other main features of the MERs relate to mobility hardware, which allowed
them to traverse the Martian terrain with relative ease. In continuation of past Mars
rover designs, the rocker-bogie suspension was used. It consists of six wheels and
multiple axles that allow the rover to overcome obstacles larger than its wheel
diameter. The specialized wheels of the rover are approximately 26 centimeters in
diameter and have a unique aluminum flexure structure to connect the hub to the rim
of the wheel. These flexure joints act as shock absorbers which help to reduce the
shock loads on other components of the rover. Each wheel also has small cleats,
which have been found to be effective both for soft sandy terrain and in navigating over
rocks.
Fig. 1 MER Rover

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Curiosity an advantage in terms of its path planning ability. It has a three axis
inertial measurement unit (IMU), enabling the rover to make precise movements while
also monitoring the degree of tilt that the rover is experiencing. To tackle the mobility
challenge, the 900kg rover has a very similar 6 wheel rocker-bogie suspension as
previous Mars exploration rovers have. The larger size combined with the rocker- bogie
suspension allows the rover to go over obstacles 60-75cm higher, which is greater than
its wheel diameter of 50cm. It can also safely traverse slopes up to 45°, but is limited to
30° slopes by software to ensure a factor of safety. Curiosity also has cleated treads
that are similar to the MER rovers, which were found to be an optimal solution for
Martian terrain. With a top speed of 4cm/sec, it was the fastest rover sent to Mars.
Fig 2. NASA’s Curiosity Rover
In reviewing NASA’s rovers for surface exploration on Mars, there were many
similarities in both their mechanical design and software that enable the rovers to
perform on-board path planning. Autonomous planetary navigation combined with
hazard avoidance and other self-preservation autonomy makes these rovers excellent
platforms to reliably transport and position their scientific instruments. The biggest
changes between missions have been the size of the rover and the types of scientific
instruments it supports.

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Astrobotic Technology Inc. is one such company that has founded itself on
making space exploration profitable, by delivering payloads and performing robotic
services on the moon. They are currently in collaboration with Carnegie Mellon
University and others, to develop a rover and lander for their first surface lunar
exploration mission, which if successful will satisfy the X-prize criteria as well as other
objectives. Their robot, called Red Rover, is reviewed here because it is one of the
most developed lunar exploration rovers. Red Rover is designed to be a scout,
exploring places such as polar ice fields or skylights into lunar lava tubes. Its goal is to
determine where the interesting locations are, based on its analysis of chemical
composition and high resolution 3D images. To facilitate roving about the lunar surface,
Red Rover uses a 4 wheel rocker differencing suspension system. This type of passive
suspension is based on the rocker-bogie design but is simplified by reducing the
number of wheels and free-pivoting axles. It drives the two wheels on each side of the
rover together, and thus relies on skid-steering to rotate the rover. For vision, Red
Rover has a stereo camera and flash LIDAR which will allow it to make high-resolution
terrain maps. While it will likely have some form of on-board autonomous hazard
avoidance or path planning it is unclear exactly to what extent, as available information
only suggests that the rover is teleoperated. Figure 3 is a picture of one of the recent
prototypes of Red Rover.
Figure 3 Red Rover

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2.3 Rover Mobility
One of the most challenging aspects of rover operation in planetary
environments is effective mobility. In order for a rover to complete any science tasks, it
first must be able to move confidently in unforgiving terrain. This may include both
challenging surfaces and wider-scale terrain discontinuities. Surface challenges to
rover mobility include fine powders such as lunar regolith, screen fields, and larger
rocks. Topographic features such as craters, hills, gullies, and cliffs present different
forms of challenges. To complicate the problem further, many planetary environments
are not well studied, so rover mobility systems must be flexible to accommodate
unknown factors. Effective rover mobility systems combine robust mechanical
hardware with sensors and programming to detect impassible terrain. The goal of any
rover mobility system is to reduce the impact of variable terrain on the rover’s ability to
traverse a given path. This typically involves a suspension system which allows the
rover to travel over certain obstacles in its path as well as absorb shocks and
unevenness. The most basic mobility system is the wheel, and an effective wheel
design becomes a major part of any rover drive system. Most planetary rovers have
used all-metal wheels for their high strength-to-weight ratio. NASA/JPL’s 10.5 kilogram
Sojourner rover used 13 centimeter one- piece aluminum wheels with sharp stainless
steel cleats to climb obstacles and gain traction in soft soil. Sojourner‟s wheels were
rigidly connected to the drive motors with no suspension elements. It has large billet
aluminum with thin straight spokes and a zigzag aluminum pattern machined into the
outer surface. These 50 centimeter wheels support the 900 kilogram rover over
obstacles up to 75 centimeters in height. Additionally, MSL’s wheels are needed to
support the rover during its final landing, a large shock load. The Mars Science
Laboratory plans to drive about 12 kilometers during its mission, most of it
autonomously. These components are typically articulated to increase the maximum
obstacle the rover is capable of traversing, as well as maintain stability on tilted terrain.
These mobility systems can also incorporate passive or active suspension elements
which help reduce the shock loading experienced by the rover chassis. The two most
common methods of articulating mobility systems include rocker bogie and rocker
differencing. The primary benefit to a rocker-bogie suspension is that a rover is able to
climb an obstacle up to twice the diameter of its wheels while keeping all 6 wheels in
contact with the surface. Because the front and rear wheels can help to push or pull the
free-floating bogie link, it is able to go over relatively large obstacles compare to its
wheel size. As a suspension system, the rocker-bogie contains no spring elements,
and this helps provide stability while going over large obstacles.

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CHAPTER 3
RELATED CONCEPTS & THEORIES
3.1 Design Reqiurement & Specifications
Our main goal is to design, develop, and test a rover to serve as a mobility
platform, suitable for testing planetary surface exploration technologies in harsh earth
environments. The design will focus on incorporating features that are believed to be
essential for most planetary exploration missions based on research of past and
current rovers. Given what we have learned about existing rovers and the types of
missions they aim to accomplish, our design goals for our rover have been made into
these categories:
1. Mobility and navigation
2. Size and weight restrictions
While our rover will not be travelling to space, it is our goal to make a robust
and ruggedized platform that will be suitable for testing in harsh earth environments, on
terrain similar to that of our moon and Mars. Given sufficient mobility in planetary
environments, the rover must also be able to accommodate payloads,if possible.
Transporting sensitive scientific instruments across rough terrain is the main goal for
nearly all exploration rovers, and thus one of our central requirements. Additionally, to
be useful for other users both in academia or industry, the rover needs to easily
integrate new hardware and software as part of its payloads. By providing a robust
mobility platform that can accommodate a wide range of payloads, the rover should
prove useful to anyone interested in testing rover related technologies or conducting
research in the field of space exploration. Lastly, the rover will aim to recognize the
size and weight constraints that all space bound vehicles face. While there are many
resource constraints that prohibit us from designing a space-ready rover, the design
will attempt to accommodate space considerations when possible. In formulating the
design specifications relating to mobility we wanted to ensure that the rover could
traverse a wide variety of harsh Earth environments. Such terrain includes deserts,
rock fields, gravel pits, sand dunes, and mountainous areas in many different climates.
In examining these terrains we will make design criterias relating to the size of
obstacles, inclines, and speeds that the rover must achieve, in order to ensure that it
could maneuver in many different environments. in most scenarios the ability to go
over larger obstacles always increases mobility potential. For our rover we set the goal
of being able to traverse obstacles, both positive and negative to the ground plane.

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3.2 Related Concepts
3.2.1 Traction and Slip
The rover must maintain good wheel traction in challenging rough terrains. If traction
is too high, the vehicle consumes a lot of power in order to overcome the force and
move. If traction is too low, the rover is not able to climb over obstacles or inclined
surfaces. Slip occurs when the traction force at a wheel-terrain contact point is larger
than the product of the normal force at the same wheel and the friction coefficient.
Hence, no slip occurs if the condition
Ti ≤ μNi
is satisfied. In reality it is very challenging to determine the precise friction coefficient μ
for the interaction of two surfaces.
3.2.2 Lateral Stability
The rover is said to be stable when it is in a quasi-static state in which it does not tilt
over. The simplest approach to find the static stability is using the geometric model,
which is commonly referred to as stability margin. As the asymmetric suspension
system of the passively articulated rover has a great influence on the vehicle’s effective
stability, a more advanced approach is using a static model.
The lateral stability of the rover ensures that the rover does not tip sideways. As the
rover has two symmetric sides, the geometric model is used to find the lateral stability
of the vehicle. Lateral stability is computed by finding the minimum allowed angle on
the slope before the rover tips over. Lateral stability is ensured if this angle is smaller
than the maximum angle of incline α on the slope at the wheel-terrain contact points.
The angles θl and θr are obtained geometrically. The overall stability angle θstab can
be computed by
θstab = min(θr,θl)
Lateral stability of the rover is ensured if the overall stability angle
θstab ≥ α
.:. min(θr,θl) ≥ α

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Fig 4 Lateral Stability
Let N1 be the reaction on the right wheel and N2 be the reaction on the left wheel.
Let α be the slope of the inclination, θr & θl be the angle that the point of contact
makes with the Centre of Gravity on the left and right wheels respectively.Z be the
height of the centre of gravity. And yl and yr be the perpendicular between the point of
contact and the Centre of Gravity.
In this condition to ensure the stability the rover should not tip off the inclined. And
hence the normal reaction on any of the wheel should not be 0. Taking moment at the
left wheel.
Mg z sin α + Mg yl cos α = N1 (yl+yr)
Dividing the equation by z
Mg sin α + Mg yl/z cos α = N1 (yl+yr)/z
From the figure above the yl/z = tan θl and yr/z =tan θr
Mg sin α + Mg tan θl cos α = N1 (tan θl + tan θr)
Let θl θr and α be very small then
Mg α + Mg θl = N1 (θl + θr)
Mg( α + θl ) = N1 (θl +θr)
Mg > N1
( α + θl ) < (θl +θr)
α < θr
Hence to ensure stability this condition should be fulfilled.

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3.2.3 Longitudinal Stability
The computation of the longitudinal stability of the rover makes use of a statical model
as it is not symmetric in longitudinal direction. Using a statical model, the mechanical
properties of the suspension system are taken into account. According to , longitudinal
stability of the vehicle is given when all wheels have ground contact and the condition
Ni > 0 is satisﬁed, where Ni is the normal force at wheel i. It should be noted that even
though this condition is compulsory for the statical model to work, a physical rover does
not necessarily tip if a wheel looses contact to the ground. However, it is less
steerable.
Figure 5 Longitudinal Stability
3.2.4 Static Stability Factor
The Static Stability Factor (SSF) of a vehicle is one half the track width, TW, divided by
h, the height of the center of gravity above the road. The inertial force which causes a
vehicle to sway on its suspension (and roll over in extreme cases) in response to
cornering, rapid steering reversals or striking a tripping mechanism, when sliding
laterally may be thought of as a force acting at the CoG to pull the vehicle body
laterally. A reduction in CoG height increases the lateral inertial force necessary to
cause rollover by reducing its leverage, and the advantage is represented by an
increase in the computed value of SSF. A wider track width also increases the lateral
force necessary to cause rollover by increasing the leverage of the vehicle's weight in
resisting rollover, and that advantage also increases the computed value of SSF. The
factor of two in the computation "TW over 2h" makes SSF equal to the lateral
acceleration in g's (g-force) at which rollover begins in the most simplified rollover
analysis of a vehicle represented by a rigid body without suspension movement or tire
deflections

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3.3 Design & Analysis
Under this section we will discuss our complete rover design and discuss how
our key design decisions were made in order to meet the requirements and goals
presented in the previous sections. Each one of these is related to meeting
fundamental requirements.
Mobility
Mobility relates to the rover’s capacity to traverse varying terrains, slopes, and
obstacles. In beginning the process of formulating the drive architecture we reviewed
current and past rovers in consideration of chassis design, suspension methods, wheel
design, and power requirements. Since nearly all rover hardware is related to mobility,
this section will review most of the mechanical design including the chassis,
suspension, and wheel components. These rovers move slowly and climb over the
obstacles by having wheels lift each piece of the suspension over the obstacle one
portion at a time. NASA’s currently favored design, the rocker-bogie, uses a two
wheeled rocker arm on a passive pivot attached to a main bogie that is connected
differentially to the main bogie on the other side. The ride is further smoothed by the
rocker which only passes on a portion of a wheel’s displacement to the main bogie.
Each wheel is independently driven. The maximum speed of the robots operated in this
way is limited to eliminate as many dynamic effects as possible, and so that the motors
can be geared down so that the wheels can individually lift a large portion of the entire
vehicle’s mass.
In order to go over an obstacle, the front wheels are forced against the obstacle
by the rear wheels. The rotation of the front wheel then lifts the front of the vehicle up
and over the obstacle. The middle wheel is the pressed against the obstacle by the
rear wheel and pulled against the obstacle by the front, until it is lifted up and over.
Finally, the rear wheel is pulled over the obstacle by the front two wheels. During each
wheel’s traversal of the obstacle, forward progress of the vehicle is slowed or
completely halted. We will be using the same mechanism the six wheel independent
drive to cross the obstacles but without any differential. To further simplify the design
we choose to use one motor to directly drive each wheel. Since it is a skid steering
rover an alternative solution could be to have one motor drive two wheels on either
side, resulting in fewer motors and less mass. However, having one motor for each
wheel reduces the need for a complex power transfer system, which is often done with
belts, gears, or drive shafts. The material used for the links should be cheap as well as
light in weight thats why we will use the Acrylic material which has the required
properties of light weight and rigidity.

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Wheel Design
The wheels are needed to be wider for increasing the traction to traverse upon
the obstacles. And their diameter depend upon the availability and amount of speed
required. The actual rover uses billet wheels, and machine the wheel and tread from
one piece of round aluminum stock.The main problem during the selection of the
wheels is light weight consideration and the distribution of load on the wheels.
Velocity 8cm/s Velocity 10cm/s Velocity 12cm/s
RPM Diameter RPM Diameter RPM Diameter
M cm m cm M cm
10 0.153 15.277 10 0.191 19.096 10 0.229 22.915
20 0.076 7.638 20 0.095 9.548 20 0.115 11.458
30 0.051 5.092 30 0.064 6.365 30 0.076 7.638
40 0.038 3.819 40 0.048 4.774 40 0.057 5.729
50 0.031 3.055 50 0.038 3.819 50 0.046 4.583
60 0.025 2.546 60 0.032 3.183 60 0.038 3.819
70 0.022 2.182 70 0.027 2.728 70 0.033 3.274
80 0.019 1.910 80 0.024 2.387 80 0.029 2.864
90 0.017 1.697 90 0.021 2.122 90 0.025 2.546
100 0.015 1.528 100 0.019 1.910 100 0.023 2.292
110 0.014 1.389 110 0.017 1.736 110 0.021 2.083
120 0.013 1.273 120 0.016 1.591 120 0.019 1.910
130 0.012 1.175 130 0.015 1.469 130 0.018 1.763
140 0.011 1.091 140 0.014 1.364 140 0.016 1.637
Table 1 Calculation of Wheel Diameters
Hence for the light weight and cost effectiveness of the rover we will choose plastic
wheels with rubber treads available in the market depending upon the calculations.
While our wheel design may not be optimized in terms of strength and weight
reduction, it will result in a cost effective solution with minimal manufacturing time, and
a wheel that should meet all design goals.

22 | P a g e
Drive motor Selection
Since the rover consists of six indepently drive wheels hence the drive motor is
needed for every wheel. The Selection of drive motor depends upon the speed of the
rover that is desired. We will try to design the rover for a speed of 10 cm/s and will
choose the parameters based upon it. The rover is designed to cross the obstacle and
hence need more traction thus the motor choosed should be of low rpm but the rpm
cannot be very low because to maintain the speed the diameter of the wheel will have
to be increased thus an optimum rpm motor is needed to be selected. We will be using
a 30 rpm motor with 12V DC because it is well suited depending upon the
requirements and calculations.
Power Supply
The MER has to travel the surface of mars where there is no availability of
power source thus it used solar cell to charge the battery and derive the power from
the battery for the motors and other equipments. But since we are using the rover on
the earth surface and our main focus is the development of mechanism rather than the
power source so we will be using the cheapest possible alternative that is the 12 0 12
Step down Transformer and a Full wave Rectifier for converting the AC into DC to
supply the adequate power to all motors in connection.
Control
The Control of the rover will be manual with the help of a joysticks for driving
each side of the rover separately. It will be helpful while taking a turn. All the
connections will be wired and no wireless means will be used because we need to
simulate the mechanism and not the actual rover and to make it cost effective in all
possible manners.

23 | P a g e
CHAPTER 4
CALCULATIONS
Calculation 1
1. Diameter of Wheel
𝑉 =
πDN
60
Assumed speed be 10 cm/s i.e. 100mm/s
Therefore,
100 =
πDN
60
DN=1909.86
D N
10 190.99
20 95.49
30 63.66
40 47.75
50 38.2
60 31.83
70 27.28
80 23.87
90 21.22
100 19.1
Table 2 Calculation of Diameter and RPM
So the selected D-N combination is-
D = 70 mm
N = 27.28 rpm

24 | P a g e
Figure 6 Centre Stage Stairs
θ = tan−1
y
x
θ = tan−1
160
400
Therefore, θ = 21.80˚
Now, width of the stairs is 400 mm. So the maximum length of the rover can be
400mm.
To deduce the wheel base,
Total length – (radius of front wheel + radius of rear wheel)
=400-(35+35)
=330 mm

25 | P a g e
3. Length of Links
Figure 7 Calculations at Centre Stage Stairs
Total Wheel base = 330 mm
Let us assume, Θ=45˚
In Triangle BNC, angle BNC = 90˚
Angle NBC = Angle NCB = 45˚
Therefore, NC = NB
NC2
+ NB2
= BC2
… (Pythagporas Theorem)
BC2
= 2(NC)2
… (1)
=2(165)2
=54450
Therefore, BC = 233.33mm
Rounding off to 230mm.
BC = 230mm
Substituting to eqn (1) we get,

26 | P a g e
2302
= 2(NC) 2
NC = 162.63
Also, AN = NC = 162.63
In triangle AMN, angle AMN = 90
AM2
+ MN2
= AN2
… (Pythagoras Theorem)
2AM2 = AN2
2AM2
= 162.63 2
AM = 114.99
=115 mm
Now, due to symmetry,
AM = MN = 115 mm
BM = AB – AM
=230 – 115
=115 mm
Therefore, BM = 115
4. Height Calculation:
Height2
= BC2
– NC2
(2302
– 162.632
)1/2
= 162.639 mm
Net Height = 162.639 + 35 … (net ht = ht + radius)
= 197.639 mm

27 | P a g e
5. Track Width
𝑆𝑆𝐹 =
𝑇𝑤
2ℎ
1.3 =
𝑇𝑤
2 × 197.639
Tw = 513.86
Calculation-2
Figure 8 Library Stairs
θ = tan−1
y
x
θ = tan−1
140
300
Therefore, θ = 25.016˚
Now, width of the stairs is 300 mm. So the maximum length of the rover can be
300mm.
To deduce the wheel base,
Total length – (radius of front wheel + radius of rear wheel)

28 | P a g e
=300-(35+35)
=230 mm
7. Length of Links
Figure 9 Calculation at Library Stairs
Total Wheel base = 230 mm
Let us assume, Θ=45˚
In Triangle BNC, angle BNC = 90˚
Angle NBC = Angle NCB = 45˚
Therefore, NC = NB
NC2
+ NB2
= BC2
… (Pythagporas Theorem)
BC2
= 2(NC)2
… (1)
=2(115)2

29 | P a g e
=26450
Therefore, BC = 162.63 mm
Rounding off to 162 mm.
BC = 162mm
Substituting to eqn (1) we get,
1622
= 2(NC) 2
NC = 114.55
Also, AN = NC = 114.55
In triangle AMN, angle AMN = 90
AM2
+ MN2
= AN2
… (Pythagoras Theorem)
2AM2 = AN2
2AM2
= 114.55 2
AM = 80.999
=81 mm
Now, due to symmetry,
AM = MN = 81 mm
BM = AB – AM
=162 – 81
=81 mm
Therefore, BM = 8
8. Height Calculation:
Height2
= BC2
– NC2
(1622
–1152
)1/2
= 114.101 mm
Net height = Height + Radius of wheel

30 | P a g e
= 114.101 + 35
= 149.101 mm
9. Track Width
𝑆𝑆𝐹 =
𝑇𝑤
2ℎ
1.3 =
𝑇𝑤
2 × 149.101
Tw = 387.66 mm

31 | P a g e
CHAPTER 5
CONCLUSIONS
5.1 Conclusion
This project will try reaching nearly all of our design requirements, and in many
respects exceeding original design goals. Furthermore all components, mechanical
and electrical, will be thoroughly tested as a completed system in real-world field
testing conditions to validate their success. Overall, preliminary estimates for the
general scope, budget, and timeline, for the project will be closely followed; with the
exception if the project goes moderately over budget.
5.2 Budget and Table of Requirements
S. No Item Qty Material Budget Net
1 Link 4 Acrylic 50 200
2 Shaft 1 SS 50 50
3 Bearing 4 SS 20 80
4 Wheel 6 Plastic 15 90
5 Motor 6 Alloy 150 900
Total 1320
Table 3 Hardware to be Purchased
Electrical
purchase
S. No Item Qty Budget Net
1 Transformer 1 500 500
2 Rectifier 1 30 30
3 Joystick 2 30 60
4 PCB 2 25 50
5 Wires and Cables 150 150
Total 790
Table 4 Electrical Equipments to be Purchased

32 | P a g e
With the total of Electrical and Hardware Purchases the rover will cost around Rs. 2110
or a little more.
5.3 Future Scope
As modular research platform the rover developed by this project is designed
specifically to facilitate future work. With the development in technology the rover can
be used for reconnaissance purposes with the cameras installed on the rover and
minimising the size of rover. With some developments like attaching arms to the rover
it can be made useful for the Bomb Diffusing Squad such that it can be able to cut the
wires for diffusing the bomb. By the development of a bigger model it can be used for
transporting man and material through a rough terrain or obstacle containg regions like
stairs.We could develop it into a wheel chair too. It can be send in valleys, jungles or
such places where humans may face some danger. It can also be developed into low
cost exploration rover that could be send for collecting information about the
environment of some celestial bodies.

33 | P a g e
REFERENCES
 mars.nasa.gov/mer/home
 robots.mit.edu/publications/papers/1998_07_Hac_Dub_Bid
 https://www.youtube.com/watch?v=bP7p5Bd2d50
 https://en.wikipedia.org/wiki/Longitudinal_static_stability
 www.nhtsa.gov/cars/rules/regrev/evaluate/809868/pages/IntroBack
 www.esmats.eu/amspapers/pastpapers/pdfs/2004/harrington

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