Table of Contents
Table of Contents
Table of Contents
ROCKER-BOGIE
A MAIN PROJECT REPORT
Submitted to
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY, KAKINADA
In partial fulfillment of the requirement for the award of the under graduate degree of
BACHELOR OF TECHNOLOGY
IN
MECHANICAL ENGINEERING
Submitted by
Approved by AICTE
(Affiliated to Jawaharlal Nehru Technological University, Kakinada)
An ISO 90001:2008 Certified Institution
NH 5, Opposite Pratap Industries, Enikepadu, Vijayawada, A.P - 521108
2017-2018
SRK INSTITUTE OF TECHNOLOGY
DEPARTMENT OF MECHANICAL ENGINEERING
CERTIFICATE
This is to certify that the project report entitled “DESIGN AND CONSTRUCTION
OF STEPS CLIMBING ROCKER-BOGIE MECHANISM” being submitted by
EXTERNAL EXAMINER
Page | II
DECLARATION BY THE CANDIDATES
We hereby certify that the work which is being presented in this Project report
entitled ‘DESIGN & CONSTRUCTION OF STEPS CLIMBING ROCKER-BOGIE‘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, S.R.K Institute of
Technology, Enikepadu, Vijayawada (Andhra Pradesh) is an authentic record of our
own work carried out during a period from December 2017 to March 2018 under the
supervision of G.Durga Prasad M.Tech.
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.
Date
Signature of supervisor
Page | III
ACKNOWLEDGEMENT
We are highly grateful to the Hon’ble Chairman Sri.B.S APPA RAO, S.R.K Institute
Of Technology, Enikepadu, Vijayawada for providing us this opportunity to carry out
the present project work.
We would like to express a deep sense of gratitude and thanks profusely to our
Principal, Dr.M.EkKAMBARAM, S.R.K Institute Of Technology, Enikepadu,
Vijayawada. Without his able guidance, it would have been impossible to complete the
project in this manner.
The help rendered by G.DURGA PRASAD M.Tech, Asst. Prof., Project Supervisor,
Department of Mechanical Engineering, S.R.K Institute Of Technology, Enikepadu,
Vijayawada for his wise counsel is greatly acknowledged.
Finally, we are indebted to all whosoever have contributed in this project work.
Project Associates…..
Name Roll. No. Signature
Page | IV
ABSTRACT
Transporting heavy packages while climbing stairs can be a very difficult. So, we
propose a step climbing rover based on the rocker-bogie mechanism. 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. Our concern during
the development of the rocker bogie will be to optimize the speed and CLIMB THE
STEPS on its own and be able to transport material such that the rover do not flip and
may travel a little faster too (20cm/s) and make it cost effective with maximum possible
rigidity and ruggedness. The rocker-bogie suspension system is good at dealing with
obstacles and excellent traversability.
KEYWORDS: Rocker bogie mechanism; optimal design; PVC pipes, Steps climbing.
Page | V
CONTENTS
1.1 INTRODUCTION
1.5 ADVANTAGES
1.6 APPLICATIONS
2.1INTRODUCTION
Page | VI
CHAPER-3 PAST PRESENT & FUTURE ......................................................... 17-23
3.1 INTRODUCTION
Page | VII
4.3.1 Suspension
4.4.1 Mobility
4.4.5 Control
Page | VIII
5.3 LENGTH OF THE LINKS
6.2 LINKAGES
6.3 MOTORS
6.4 CABLES
6.5 CONTROLLER
6.6 ASSEMBLY
Page | IX
CHAPTER-7 CONCLUSIONS .........................................................................57-58
7.1CONCLUSION
9.1 REFERENCES
Page | X
CHAPTER-1
INTRODUCTION
1.1 INTRODUCTION
Over the last decade, mobile robots have been widely used to carry out manifold
tasks such as military, industrial applications, planetary exploration rescue operation
and home/medical services. Therefore, it is not surprising that high mobility on
various environments has been a primary factor among others when evaluating the
performance of the mobile robot. 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 hazardous. In
order to achieve these tasks, any mobile robot needs to have a suitable mobile system
according to each situation.
Page | XI
mechanisms equipped with passive linkages have successfully verified their mobile
performances in real applications, for example, Mars Exploration Rovers (MERs) like
Sojourner, Rocky7, Spirit and Opportunity , ORF-L , CEDRA , SHRIMP , etc.
Among those passive linkages, the rocker-bogie is well known, which consists of two
structural elements called as “rocker” and “bogie”.
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.
Rocker-bogie suspension system 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 similarities in planetary rovers. Issues such as mobility, navigation, and vision,
may differ slightly between missions but are largely the same in most scenarios. There
Page | XII
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 and MAKE IT’S IMPACT IN THE CIVIL SERVICE
APPLICATIONS.
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 visualization 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 visualizing 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.
Page | XIII
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 optimize the speed such that
the rover do not flip and may travel a little faster too and make it cost effective with
maximum possible rigidity and ruggedness. In order to improve the climbing
capability of a wheel-type Rocker-Bogie rover especially against structured terrains
such as steps and stairs, several mechanisms have been developed on the basis of the
rocker-bogie so that a few mobile robots can climb even steps of twice their wheel
diameter.
However, they often suffer from undesired phenomenon that some wheels float
from the ground while climbing steps and stairs, which may cause instability of the
mobile robot. So the main aim of our project is, Based on the rocker-bogie
mechanism, an optimal design of a stair-climbing wheel-type mobile rover is to be
constructed. It can also be used for MATERIAL DELIVERY purposes. This is a
wide field of study and is very less explored. So this gave us the motivation for the
development of this rocker bogie suspension system in a cost effective manner.
Page | XIV
Fig.1.1 Projected 3-d view of our project
The rover consists of several joints. By adjusting its joints the rover is capable of
locomotion over various uneven terrains. The rocker bogie structure has six
independently driven wheels which are mounted on an articulated passive suspension
system. The four corner wheels are steerable. The suspension system consists of two
rocker arms connected to the rover body. Each rocker has a rear wheel connected to
one end and a bogie connected to the other end. The bogie is connected to the rocker
with a free pivoting joint. At each end of the bogie there is a drive wheel. The rockers
are connected to the rover body with the differential joint.
Page | XV
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 the lift the front of the vehicle
up and over the obstacle.
The middle wheel is 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 traversal of the obstacle, forward progress of the vehicle
slowed or completely halted.
1.5 ADVANTAGES
One of the most important and useful feature of autonomous mobile robots is their
ability to adopt themselves to operate in unstructured environment.
The mechanism allows climbing obstacles twice the size of the wheel diameter.
Does not employ springs and sub axles.
Equal distribution of load on all wheels.
The design is simple and reliable.
Independent movement of rocker on either side of the bogie.
The front and back wheels have individual drives for climbing.
1.6 APPLICATIONS
By the development of a bigger model it can be used for transporting man and
material through a rough terrain or obstacles containing regions like stairs.
We could develop it into a Wheel Chair too. It can be sent to valleys, jungles
or such places where humans may face some danger.
Military purposes
Mining
Bomb Inspections
Mobile robots in artificial Intelligence.
Page | XVI
CHAPTER-2
LITERATURE REVIEW
2.1 INTRODUCTION
Mankind has long sought improved methods of land transport. Over the centuries,
these land locomotion methods have included travelling on foot, riding on the backs
of horses or other animals, using carts and wagons drawn by both humans and
animals and using a variety of vehicles powered by steam, internal combustion, or
other engines. With the advent of automation and robots in 20th century, a new level
of sophistication has been added to these methods, namely, the development of
automated vehicles, or mobile robots, which can be sent to perform these tasks with
little or no human intervention.
In recent years, practical mobile rovers have been successfully used in controlled
environments such as factories, offices, and hospitals, as well as outdoors on prepared
surfaces and terrain with minor irregularities. However, thus far, the operation of
mobile robots in extremely rough, uneven terrain has been impossible or unreliable at
best. Nevertheless, many benefits would result if robotic mobility “in the field” were
made practical (Whittaker, 1993).
Hence, the study of field robotics has become an active area of research. Several
previous publications ,including papers by McGhee(1985), Fitcher and
Albright(1987), Bares and Whittaker(1989), and Oral (1994) have noted that
approximately 50% of the earth’s total land surface is inaccessible to wheeled or
tracked vehicles, but that in contrast, most animals can cross rough terrain in an
efficient and fairly rapid fashion.
Thus, it is desirable to create legged mechanisms that will imitate the excellent
mobility of animals. Reliable mobility on extremely uneven terrain remains an elusive
goal for man-made devices.
In year 1995 Shigeo Hirose et al. [1] outlined the fundamental considerations for a
planetary rover. They compared the wheeled, legged and articulated body shapes, and
it was found that the wheel type is currently the optimum for a planetary rover. Next
Page | XVII
they studied specific methods for configuring a planetary rover with one, two, three
and four wheels.
Pedersen et al. [3] at NASA have done a survey on space robotics and determine
the state-of-the-art and future scenario in space robotics. They described the various
issues like human-robot collaboration, planetary surface access, and surface
investigation in the field of space robotics.
Miller and Lee [5] at NASA described a method of driving a rocker-bogie vehicle
that can effectively step over most obstacles rather than impacting and climbing over
them. They suggested some mechanical changes to gather the maximum benefit and
to greatly increase the effective operational speed of future rovers. Most of the
benefits of this method can be achieved without any mechanical modification to
existing designs but a change in control strategy.
In year 2002 Yoshida and Hamano [6] investigated kinetic behavior of a planetary
rover with attention to tire-soil traction mechanics and articulated body dynamics, and
thereby studies the control when the rover travels over natural rough terrain. They
carried out experiments with a rover test bed using the tire slip ratio as a state variable
to observe the physical phenomena of soils and to model the traction mechanics.
In year 2004 Lamon et al. [7] described quasi-static modeling considering the
system constraints: maximal and minimal torques, positive normal forces of a six-
wheeled robot with a passive suspension mechanism together with a method for
Page | XVIII
selecting the optimal torques. The method is used to limit wheel slip and to improve
climbing capabilities.
In year 2005 Tarokh and Dermott [8] described a general approach to the
kinematics modeling and analyses of articulated rovers traversing uneven terrain for
6-DOF motion. Differential kinematics is derived for the individual wheel motions in
contact with the terrain and then combined to form the composite equation for the
rover motion. Three types of kinematics navigation, actuation, and slip kinematics are
identified, and the equations and application of each are discussed.
In year 2005 Mann and Shiller [9] described the stability considering both static
equilibrium and dynamic effects of a Rocker Bogie vehicle that accounts for the
tendency to slide, tip over, or lose contact with the ground. The measure of stability is
computed by solving for the range of acceptable velocities and accelerations that
satisfy a set of dynamic constraints and the maximum acceptable velocity serves as a
dynamic stability measure, whereas the maximum acceptable acceleration at zero
velocity serves as a static stability measure.
In year 2005 Lindemann [10] described the Mars exploration rovers named Spirit
and Opportunity which were landed on the mars surface in January 2004. In order to
assess the mobility characteristics of the rovers in the Mars environment, an
engineering model vehicle was tested before the mission launches in a representative
environment of slopes, rock obstacles, and soft soil. In addition, to gain better insight
into the rovers' capabilities, a dynamic model of the rovers was created in the software
package ADAMS. The rover model was then used to simulate many of the test cases,
which provided a means for model correction and correlation.
In year 2006 Randel et al. [11] described the Mars Exploration Rover (MER)
Project launched in mid-2000 to land on the Mars, and discussed the mission
requirements, design architecture, mechanical mobility, hardware design,
development and testing.
Page | XIX
velocities and steering angles from the desired forward velocity and turning rate of the
robot. By comparing information from onboard sensors and wheel velocities traction
control is also developed to improve traction to minimize wheel slip. Simulation is
done with a rover has rocker bogie in two conditions of surfaces including climbing
slope and travel over a ditch.
In year 2006 Xinyi Yu et al. [13] analyzed the motion of articulated lunar rover
with six cylinder-conical wheels and force acting to wheels, according to the
mechanical configuration of rover, operations pattern of wheel, and principle of speed
matching of wheels they presented a control algorithm which can fit various uneven
terrains and merge it into the whole locomotion control system.
In year 2007 Deng et al. [14] discussed the optimum control model of the motion,
they done motion control of a lunar rover, the power optimum control was carried out
for a lunar rover prototype with six cylinder-conical wheels in wheel walking motion
mode in order to minimize the power consumption. The kinematics model of wheel-
walking motion was built up and the simulation model was constituted based on
Simulink.
In year 2007 Bai-chao et. al. [15] analyzed the structure of the new suspension and
the kinematics of the levers, and to know the distortion capability of the suspension,
relational equations of the suspension levers are established. In order to test the
capability of suspension, they design a prototype rover with the new suspension and
take a test of climbing obstacles, and the prototype rover with new type of suspension
had excellent capability to climb .up obstacles with keeping cab smooth in the results.
In year 2007 Kanfeng et. al. [16] analyzed the external disturbances cause the
lunar rover's unexpected move because rover may run on the uneven surface of the
moon. They investigate the effects of external disturbance. The six wheeled- rocker-
bogie lunar rover is considered as a six-wheeled vehicle with four steering wheels and
the steering dynamic equation is built based on automotive theory. External
disturbance is expressed as a force acted on the mass center of the rover and the
Laplace transform is introduced. The research results show that the travel changes of
the rovers will be different distinctly when the rovers with different steering
characteristics are disturbed simultaneously.
Page | XX
In year 2007 Thueer et al. [17] presented the performance optimization tool
(POT). The POT enables the comparison and optimization of a rover chassis in a
quick and efficient way. The tool is based on a static approach including optimization
of the wheel torques in order to maximize traction. Tests with real hardware were
performed to validate the POT. Two different rovers, CRAB and RCL-E, were
assessed in simulation and hardware with respect to specific, well defined metrics. In
simulation, their performances were compared to the rocker-bogie-type rover MER.
In 2008 Thueer and Siegwart [19] analyzed three different rovers from a
kinematic point of view. The optimal velocities at the actual position were calculated
for all wheels based on a kinematic model and used for characterization of the
suspension of the different rovers. Simulation results show significant differences
between the rovers and thus, the utility of the chosen metric. It is found that by
integrating kinematics in a model-based velocity controller a substantial reduction of
slip can be achieved.
In year 2008 Yuan et al. [20] presented a wheel-ground contact angle and slip
estimation scheme for skid-steered lunar rover by combining drive and guidance
system to form a closed control system, in which an observer will work out the slip
values and wheel-terrain contact angle by using the measured datum of passed route
of lunar rover's mass center. Simulation and experiment results show that the terrain
and control parameters algorithms can accurately and efficiently be identified for
loose sand.
In year 2008 Younse et al. [21] at the Jet Propulsion Laboratory used the Mars
technology rover Sample Return Rover 2000 (SRR2K) for their experiment. They
presented the Mars sample return missions technology to robotically acquire and
cache multiple samples for delivery back to Earth. To prevent cross-contamination,
Page | XXI
individual detachable scoops and caching boxes were designed for use with a rover.
They used a robotic arm on the rover to open and close the cache boxes. A clamping
mechanism designed for the end effecter of the robotic arm attached and detached
individual scoops and performed the scooping for sample collection.
In year 2008 Pathak et al. [22] presented the bond graph model of an autonomous
vehicle, called RobuCar, with four independently driven wheels and two
independently adjustable steering angles. The system bond graph is constructed for
generating the Analytical Redundancy Relations (ARRs) which are evaluated with
actual measurements to generate residuals and to perform structural fault isolation.
The system is reconfigured to achieve given control objectives.
In year 2008 Suojun et al. [23] build the mobility performance indexes .based on
work conditions by summarizing the lunar surface terrain characteristics. The
performance of overturning stability, load equalization of the wheels and trafficability
are analyzed and established an optimization mathematical model of suspension
parameters of rocker-bogie rover.
In 2009 Yongming et al. [24] presented a model based on force analysis of the
differential joints and force analysis between the wheels and the ground; they
established the quasi-static mathematical model of the 6-wheel mobile system of
planetary exploration rover with rocker-bogie structure. Using the method of finding
the wheels friction force solution space feasible region, obstacle-climbing capability
of the mobile mechanism was analyzed by considering the constraint conditions. The
simulation is done by giving the same obstacle heights and contact angles of wheel-
ground.
Page | XXII
Hacot [26] at Massachusetts Institute of Technology presented the models of
mechanics and method for solving the inverse kinematics of the rocker-bogie rover.
The quasi-static force analysis was described for the rover. The simulation of the
rover was done and compared with experimental results.
Nitin Yadav at. Al .[28],The place, where the value of gravity remain lower than
earth’s own gravitational coefficient, at that place the existing suspension system fails
to fullfil desired results as the amount and mode of shock absorbing changes. To
counter anti gravity impact, NASA and Jet Propulsion Laboratory have jointly
developed a suspension system called the rocker-bogie Suspension system. It is
basically a suspension arrangement used in mechanical robotic vehicles used
specifically for space exploration. The rocker-bogie suspension based rovers has been
successfully introduced for the Mars Pathfinder and Mars Exploration Rover (MER)
and Mars Science Laboratory (MSL) missions conducted by apex space exploration
agencies throughout the world. The proposed suspension system is currently the most
favored design for every space exploration company indulges in the business of space
research. The motive of this research initiation is to understand mechanical design and
its advantages of Rocker- bogie suspension system in order to find suitability to
implement it in conventional loading vehicles to enhance their efficiency and also to
cut down the maintenance related expenses of conventional suspension systems.
Dongkyu Choi at.al [29], To verify whether the rocker bogie, with certain lengths
of the linkages and radii of the wheels, could climb up a target stair or not, a
kinematic analysis and its posture are determined. The trace of the center of mass of
the rocker bogie was considered and the situation that three wheels contact the front
Page | XXIII
side of the stair is analyzed. With this two analyses, the stair climb ability graph
(SCG) determined with the length and the height of a stair was drawn.
Hong-an Yang at.al [30], 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. This paper proposes 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: One
rocker-bogie system, two modes of operation.
Brian D. Harrington and Chris Voorhees [31], over the past decade, the rocker-
bogie suspension design has become a proven mobility application known for its
superior vehicle stability and obstacle-climbing capability. Following several
technology and research rover implementations, the system was successfully flown as
part of Mars Pathfinder’s Sojourner rover. When the Mars Exploration Rover (MER)
Project was first proposed, the use of a rocker-bogie suspension was the obvious
choice due to its extensive heritage. The challenge posed by MER was to design a
lightweight rocker-bogie suspension that would permit the mobility to stow within the
limited space available and deploy into a configuration that the rover could then
safely use to egress from the lander and explore the Martian surface. This paper will
describe how the MER rocker-bogie suspension subsystem was able to meet these
conflicting design requirements while highlighting the variety of deployment and
latch mechanisms employed in the design.
Page | XXIV
damping for low force transmission to vehicle frame, whereas high damping is
desired for fast decay of oscillations.
S. Madhavarao [33], in his paper discussed that vehicle ride comfort is one of the
most important performances of vehicle; the research of automotive ride comfort is
getting more and more important. He said this paper is to design and develop a system
that is “Automatic ground clearance adjustment system” to overcome this problem by
adjusting the ground clearance over this particular time period.
Paul W.Bartlett [34], designed a scarab rover for mobility and drilling in the lunar
cold traps. The vehicle design employs a passive kinematic suspension with an active
adjustability to lower for drilling and aid in driving. He explained that Scarab was
designed and built in 2007 and is currently in lab and field testing and further
development. In the laboratory, drawbar pull tests characterized the strength and
traction of the rover. With the rubber skid loader tires in place, Scarab pulled 2,000 N
in mixed grain sized sand, which is approximately 0.7 x vehicle weight, and 2,700 N
on concrete pavement, which is approximately equal to vehicle weight. Similar tests
are planned where lunar gravity is simulated with an off-loading system.
Page | XXV
2.3 GAP IDENTIFICATION FROM LITERATURE
The existing literature shows that researchers have attempted kinematic analysis of
rocker bogie rover and studied the behavior of the rover. This has been done with the
assumption that rover moves with a very slow speed.
This work presents the construction of dynamic model of step climbing rocker-
bogie mechanism and makes it useful in the civil purpose applications. In order to
improve the climbing capability of a wheel-type mobile rover especially against
structured terrains such as steps and stairs, several mechanisms have been developed
on the basis of the rocker-bogie so that a few mobile robots can climb even steps of
twice their wheel diameter. However, they often suffer from undesired phenomenon
that some wheels float from the ground while climbing steps and stairs, which may
cause instability of the mobile robot. It is worthwhile to note that a trajectory of center
of mass (CM) may serve as a tool for effectively predicting such undesirable
phenomenon which is likely to occur at the moment the trajectory of CM drastically
or discontinuously changes. Therefore, it is highly required to make the trajectory of
CM as smooth as possible, which implies that the trajectory of CM must be close to a
straight line whose slope is determined by a step or a stair. Since this requirement on
the trajectory of CM minimizes the required motor power, the possibility is increased
that the mobile robot can efficiently climb a step or a stair even for the relatively low
friction coefficient
Page | XXVI
CHAPTER-3
3.1 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. 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.
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 ability to support a human colony. Learning more about the composition
Page | XXVII
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.
Page | XXVIII
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.
Rocket : Atlas V
Manufacturer : NASA
Operator : NASA
Page | XXIX
Max Speed : 50mm/s
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 created treats 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.
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.
NASA’s most modern rover, the Mars Rover Curiosity (MRC), gives us proven
information that demonstrates the efficiency of rocker-bogie systems dealing with
obstacles the size of the diameter of its wheels, but moving at an average speed below
2 cm/s to ensure stability against overturning due to sudden changes in the position of
the center of gravity. Similarly, studies obtained with the MRC show that the
maximum speed on hard, flat ground is 4 cm/s, also having as main limiting condition
the position of the CoG and its influence on the stability margin of the system.
Page | XXX
Fig.3.3 NASA’S Curiosity Mars Rover
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
Page | XXXI
autonomous hazard avoidance or path planning it is unclear exactly to what extent, as
available information only suggests that the rover is tele operated. Below is a picture
of one of the recent prototypes of Red Rover.
Page | XXXII
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.
Page | XXXIII
CHAPTER-4
RELATED CONCEPTS & THEORIES
Our main goal is to design, develop, and test a rover to serve as a mobility
platform, suitable for climbing steps and overcome obstacles. The design will focus
on incorporating features that are believed to be essential for most planetary
exploration missions and it’s capability to overcome the obstacles 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:
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 and be able to climb steps. 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 criteria’s relating to the size
Page | XXXIV
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.
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.
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
Page | XXXV
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 ≥ α
Thus, min (θr,θl) ≥ α
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.
Page | XXXVI
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.
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.
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
Page | XXXVII
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.
SSF = TW / 2h →Equation 1
Page | XXXVIII
the convex hull of the polygon formed by wheel–terrain contact points projected onto
a horizontal plane. An early geometric measure defined stable vehicle configurations
as those where the horizontal projection of the vehicle CoG lies within this polygon.
A stability margin was then defined based on the shortest distance from the projected
CoG to a side of the polygon
After an analysis, the authors introduce a possible solution that meets the
conditions laid down, which is based on adding a rotation axis over the Y-plane of the
bogie system, varying the yaw orientation of the bogie, thereby altering the position
of the outer support polygon points and increasing the size of the area in contact with
the ground.The below figure gives us an idea about the dynamic bogie modifications
during it’s transversal.
Page | XXXIX
Fig.4.5 Dynamic Bogie Modifications
The proposed system includes rotation motors for each wheel that are in charge of
the translation of the rover, also, it uses an extra motor on each wheel to change its
orientation and therefore change the orientation of the rover. In addition it controls the
added bogie rotation axis with a motor that allows the movement of each bogie when
it’s needed.
Using Equation1, different rotation angles about the new axis are analyzed,
seeking to find a suitable value in which the suspension provided by the rocker-bogie
system is not compromised and the expansion of the contact polygon is expanded
achieving an optimal SSF (see Table 1).
Initially, we assume 45 degrees as the optimal rotation factor in the dynamic bogie
design because the criteria in Equation 1 shows a favorable increase in the SSF,
considering this rotation angle as the maximum possible without altering the original
rocker-bogie performance.
10 1.34
20 1.40
35 1.54
Page | XL
45 1.55
The rocker bogie suspension system, which was specifically designed for space
exploration vehicles have deep history embedded in its development. The term
“rocker” describes the rocking aspect of the larger links present each side of the
suspension system and balance the bogie as these rockers are connected to each other
and the vehicle chassis through a selectively modified differential.
As accordance with the motion to maintain centre of gravity of entire vehicle, when
one rocker moves up-word, the other goes down. The chassis plays vital role to maintain
the average pitch angle of both rockers by allowing both rockers to move as per the
situation. As per the acute design, one end of a rocker is fitted with a drive wheel and
the other end is pivoted to a bogie which provides required motion and degree of
freedom.
Fig.4.6 Line Diagram of Rocker Bogie Suspension System and its Mobile Joints
In the system, “bogie” refers to the conjoining links that have a drive wheel
attached at each end. Bogies were commonly used to bare loading as tracks of army
tanks as idlers distributing the load over the terrain. Bogies were also quite commonly
used on the trailers of semi trailer trucks as that very time the trucks will have to carry
much heavier load.
4.3.1 Suspension
Page | XLI
As simple and lightweight as possible
Distribute load equally to each wheel for most of the orientation possibilities to
prevent from slipping
Rocker-Bogie suspension has been developed for first Mars rover Sojourner by
NASA.
This suspension has 6 wheels with symmetric structure for both sides. Each side
has 3 wheels which are connected to each other with two links. Main linkage called
rocker has two joints. While first joint connected to front wheel, other joint assembled
to another linkage called bogie, which is similar to train wagon suspension member.
In later design of articulated suspension system, called rocker-bogie with small
changes.
Page | XLII
Fig.4.8 Kinematic Diagram of Rocker Bogie Suspension
A rover’s obstacle limit generally compared with robot’s wheel size. In four wheel
drive off-road vehicles, limit is nearly half of their wheel diameter. It is possible to
pass over more than this height by pushing driving wheel to obstacle which can be
called as climbing. Step or stair climbing is the maximum limit of obstacles. The
contact point of wheel and obstacle is at the same height with wheel center for this
condition.
Field tests show that Mars mobile robots should be able to overcome at least 1.5
times height of its wheel diameter. This limitation narrows the mobile robot selection
Page | XLIII
alternatives and forces scientists to improve their current designs and study on new
rovers.
While driving on a flat surface, if there is no slipping, wheel center will move on a
line parallel to the surface with constant velocity. Although, obstacle geometries can
be different, most difficult geometry which be can climbed by wheel is stair type
rectangular obstacle.
From the above figure, same wheel diameter (a) and more than half wheel diameter
(b) height obstacle.
In figure 4.10 (a), height of the obstacle is same or less than the half diameter of the
wheel. For this condition, the wheel’s instant center of rotation (IC1) is located at the
contact point of the obstacle and wheel. Trajectory of the wheel centers’ during
motion generates a soft curve, thus, horizontal motion of the wheel center does not
break.
Since in figure 4.10 (b), height of the obstacle is more than the half diameter of wheel,
this condition can be classified as climbing. Climbing motion consist of two sub
motions. First one is a vertical motion, which causes a horizontal reaction force on
wheel center. This vertical motion’s instant center (IC2) is at infinity. Second one is a
soft rotation similar to figure 4.10 (a) with instant center of rotation (IC3) at the
corner.
Page | XLIV
4.4 DESIGN AND ANALYSIS
Under this section we will discuss our complete STEP CLIMBING ROCKER-
BOGIE 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.
4.4.1 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
Page | XLV
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 that’s why we will use the Acrylic material (PVC PIPES) which has
the required properties of light weight and rigidity.
The wheels are needed to be wider for increasing the traction to traverse upon the
obstacles. And their diameter depends 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.
Page | XLVI
VELOCITY 8m/s VELOCITY 10m/s VELOCITY 12m/s
m cm m cm m cm
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.
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 20cm/s and will
Page | XLVII
choose the parameters based upon it. The rover is designed to cross the obstacle and
hence need more traction thus the motor chose 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.
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 for climbing of
steps, rather than the power source so we will be using the cheapest possible
alternative that is the 12v Dc power supply lead acid battery, to supply the adequate
power to all motors in connection.
4.4.5 Control
The Control of the rover will be manual with the help of a joystick 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. Here we are using DPDT (DOUBLE POLE DOUBLE THROW RELAY)
switch to control the rover movements.
We also made a wireless arrangement also, so that it can be operated with ease. We
are using RF 2.4 GHz receiver and 20A (motor drive) control unit, along with RF
2.4GHz play station 2 remote control with receiver.
Page | XLVIII
CHAPTER-5
CALCULATIONS
From velocity,
(𝝅𝑫𝑵)
𝑽=
𝟔𝟎
Assumed speed of the rover to be 20cm/s i.e. 200mm/s.
(𝝅𝑫𝑵)
𝟐𝟎𝟎 =
𝟔𝟎
𝟐𝟎𝟎 ∗ 𝟔𝟎
𝑫𝑵 =
(𝝅)
𝑫𝑵 = 𝟑𝟖𝟏𝟗. 𝟕𝟏
From the below table we can come to estimation of the diameter of the wheel, (or)
since we have taken the rpm of the motor as 30, we can substitute and get the required
diameter.
DIAMETER RPM
20 190.9
40 95.49
60 63.66
80 47.74
100 38.197
120 31.830
125 30.55
140 27.28
Page | XLIX
D=125mm
N=30rpm
𝒀
𝜽 = 𝐭𝐚𝐧−𝟏
𝑿
𝟏𝟒𝟎
𝜽 = 𝐭𝐚𝐧−𝟏
𝟔𝟎𝟎
Therefore,
𝜽 = 𝟏𝟑. 𝟏𝟑°
Now, width of the stair is 600mm.So the maximum length of the rover can be 600mm.
=600 – (62.5+62.5)
=475mm
Page | L
5.3 LENGTH OF THE LINKS
Let us assume,
Ɵ=45˚
Therefore,
Page | LI
NC = NB
NC2 + NB2=BC2
BC = 2(NC)2 (1)
=2(230)2
=105800
Therefore,
BC=325.26mm
BC=320mm
3202=2(NC)2
NC=226.27
NC =230mm
Also,
AN = NC = 230mm
In triangle AMN,
2AM2 = AN2
2AM2= 2302
AM = 162.63
Page | LII
AM= 160mm
AM = MN =160mm
BM = AB – AM
= 320-160
=160mm
Therefore,
BM = 160mm
= (320)2 – (230)2
= 222.48mm
HEIGHT = 220mm
=282.5mm
Page | LIII
5.5 TRACK WIDTH
𝑻𝑾
𝑺𝑺𝑭 =
𝟐𝒉
On substituting the values, from the table 1, based on the rotation degree the SSF is
chosen.
𝑻𝑾
𝟏. 𝟑 =
𝟐 ∗ 𝟐𝟖𝟐. 𝟓
𝑻𝑾 = 𝟕𝟑𝟒. 𝟓𝒎𝒎
Thus, the required calculations are done, and the lengths of links are noted down for
the construction of the step climbing rocker bogie. The below figure depicts the
overview of all the dimensions of the rocker bogie rover.
Page | LIV
Fig.5.5 2-d view of Rocker Bogie Rover with all Dimensions
Page | LV
CHAPTER-6
FABRICATION
To give power supply to the motors, dc power supply lead acid battery is
connected. The specifications of the battery include 12v,4Ah.such that, adequate
power supply is given to the motors. The lead–acid battery was invented in 1859 by
French physicist Gaston Planté and is the oldest type of rechargeable battery. Despite
having a very low energy-to-weight ratio and a low energy-to-volume ratio, its ability
to supply high surge currents means that the cells have a relatively large power-to-
weight ratio. These features, along with their low cost, make them attractive for use in
motor vehicles to provide the high current required by automobile starter motors.
There is no need for the step up or step down transformer, since the motors are dc
gear motors
6.2 LINKAGES
The Linkages used are made up of PVC generally; PVC pipes are used as links. It
provides flexibility as well as good stiffness. The Linkages are connected in a way to
form the rocker as well as the bogie. With holes of appropriate sizes for the
connection of motors as well as the wheels of required specifications. And there is a
provision for the connection of screws to connect the rocker to the bogie. The term
Page | LVI
“rocker” comes from the rocking aspect of the larger links on each side of the
suspension system. The term “bogie” refers to the links that have a drive wheel at
each end.The considerations are listed below
List of materials
1. PVC pipe
Length: 6 feet, size: 1’’ (25mm)
4. PVC cap
Quantity: 2 pieces, size: 1" (25mm)
These are assembled together to form the required rocker bogie mechanism.
6.3 MOTORS
Page | LVII
DC motors were the first type widely used, since they could be powered from
existing direct-current lighting power distribution systems. A DC motor's speed can
be controlled over a wide range, using either a variable supply voltage or by changing
the strength of current in its field windings. Small DC motors are used in tools, toys,
and appliances. The universal motor can operate on direct current but is a lightweight
motor used for portable power tools and appliances. Larger DC motors are used in
propulsion of electric vehicles, elevator and hoists, or in drives for steel rolling mills.
From the calculations chapter, we concluded that 30rpmmotor is required for the
project. We need 6 dc geared motors. 30RPM high quality industrial grade metal
Gearbox Motor with offset shaft 12VDC. Below are the specifications of the dc
geared 30rpm motor.
Specifications:
125gm weight
10kgcm torque
Every motor we use have the same specifications. Here rpm is the measure of
frequency of rotation. Whereas torque is the measure of turning force of an object.rpm
and torque are inversely proportional to each other, i.e. if rpm increases torque
decreases and vice-versa.
Page | LVIII
Fig.6.2 Side Shaft DC geared motor
6.4 CABLES
Generally, for the connection of motors to the power supply cables are essential.
Here we are using telephonic cables to avoid the confusion during connection.These
cables are soldered to the motor terminals. A wire is a single, usually cylindrical,
flexible strand or rod of metal. Wires are used to bear mechanical loads or electricity
and telecommunications signals. Wire is commonly formed by drawing the metal
through a hole in a die or draw plate. Wire gauges come in various standard sizes, as
expressed in terms of a gauge number. The term wire is also used more loosely to
refer to a bundle of such strands, as in "multi stranded wire", which is more correctly
termed a wire rope in mechanics, or a cable in electricity.
6.5 CONTROLLER
We need a controller to control the motors assembled rocker bogie,so we are trying
both types of transmission. wireless and wired transmission. For controlling the
Page | LIX
motion of the Rocker Bogie Mechanism we have provided joysticks which will
control the forward and backward motion of each part of the rocker bogie i.e the left
and the right part individually.
For many applications the medium of choice is RF since it does not require line of
sight. RF communications incorporate a transmitter and a receiver. They are of
various types and ranges. Some can transmit up to 500 feet. RF modules are widely
used in electronic design owing to the difficulty of designing radio circuitry.
Page | LX
Fig.6.5 Functions of Remote Control
By using this we can control the rover easily, and make it move in the required
direction, The below figure depicts the joystick controls.
In the wired connection we are using DPDT switches(double pole double throw),
In electrical engineering, a switch is an electrical component that can "make" or
"break" an electrical circuit, interrupting the current or diverting it from one conductor
Page | LXI
to another. The mechanism of a switch removes or restores the conducting path in a
circuit when it is operated. It may be operated manually, for example, a light switch or
a keyboard button, may be operated by a moving object such as a door, or may be
operated by some sensing element for pressure, temperature or flow.
A switch will have one or more sets of contacts, which may operate
simultaneously, sequentially, or alternately. Switches in high-powered circuits must
operate rapidly to prevent destructive arcing, and may include special features to
assist in rapidly interrupting a heavy current. Multiple forms of actuators are used for
operation by hand or to sense position, level, temperature or flow. Special types are
used, for example, for control of machinery, to reverse electric motors, or to sense
liquid level. Many specialized forms exist. A common use is control of lighting,
where multiple switches may be wired into one circuit to allow convenient control of
light fixtures.
Below is the connection of the four motors to a dpdt switch, in the similar way
connect the remainining motors in parallel connection.
Page | LXII
Fig.6.8 Parallel Connection of motors
This switch is equal to two SPDT switches; it means two separate circuits, connecting
two inputs of each circuit to one of two outputs. The switch position controls the
number of ways and from the two contacts each contact can be routed. When it is in
ON-ON mode or ON-OFF-ON mode they works like two discrete SPDT switches
worked by the similar actuator. At a time only two loads can be ON. A DPDT switch
can be used in any application that needs an open & closed wiring system.
6.6 ASSEMBLY
The following steps are to be followed for the construction of Steps climbing rocker
bogie rover.
STEP.1 Initially, the PVC pipes are cut into the desired lengths using a cutter. The
dimensions should be accurate.
STEP.2 Secondly, 90˚ and 45˚ PVC elbow joints and cap are used to connect the PVC
pipes together to form a rocker bogie mechanism half section.
STEP.3 Motors are connected to the sections using hose clips, which are connected to
wheels of diameter 125mm.6 wheels are connected to the six ends of rover. The
motors are connected using couplers to the wheels; the internal diameter of the
coupler should 6mm
Page | LXIII
STEP.4 we need a frame i.e. differential to connect the two rocker bogie sections.The
dimensions are already illustrated in the calculation part. So, it is to be placed using
wooden pieces and the two rocker sections are joined together using bolts and nuts.
STEP.5 The rocker and bogie parts are connected using metal plates.
STEP.6 Later, cables are soldered to the motor terminals and the motors are
connected in parallel connection.
Page | LXIV
STEP.7 Battery is mounted on the differential, such that it should not intervene the
movement of rover.
STEP.8 finally, wire-less or wired controller is connected to the power supply. Such
that it controls the movement of rover.
STEP.9 The mounted battery is placed into a plastic box, such that its weight is
concentrated on the differential.
Page | LXV
STEP.10 finally, stickering is done to have a better look.stickering doesn’t have any
impact on its movement.
Thus, the STEP CLIMBING ROCKER BOGIE ROVER is ready to climb the steps.
Page | LXVI
CHAPTER-7
CONCLUSIONS
7.1 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.
3 Plates 2 METAL 20 40
4 Bolts 8 METAL 10 80
5 Plates 2 WOOD 10 20
TOTAL 940
5 Cables 8 25 200
TOTAL 11000
Page | LXVII
7.3 FUTURE SCOPE
Page | LXVIII
CHAPTER-8
RECOMMENDATIONS
Page | LXIX
A rigid wheel sinks on the soft terrain as in figure 8.2. sh distance is called sinkage
height. Geometry of wheel, material and ground stiffness affects sinkage height.
Depending on the geophysical properties of soil, different reaction and resistance
forcesact on wheel.
The towed wheel carries some part of body weight (Ww). The force P which tries
to move the wheel, acts from vehicle axis to center point of the wheel. These two
forces are balanced by vertical ground reaction force (Rv) and resistance force of soil
R. In towed wheel, resistance force has to be as small as possible. Motion resistance
force is resultant of soil compaction resistance, bulldozing resistance, rolling
resistance, gravitational resistance and obstacle resistance.
On the driven wheel, additional traction force F acts to the contact point with the
same direction of motion. Traction force tries to pull the chassis of robot.
As we discuss in wheel forces, there are several forces act on wheel on x axis. If
the surface friction of an obstacle is not enough to climb, obstacle force (Fobs) can
reach high values. This problem can also occur while middle wheel actuator failure.
Driving velocity is also restricted by bogie overturn problem. Bogie pitch angle can
be adjusted by active control methods .An easy solution method for this problem can
be a linear motion suspension usage where obstacle reaction force cannot create any
moment.
Page | LXX
CHAPTER-9
BIBLIYOGRAPHY
9.1 REFERENCES
[2] Y. Xu, C. Lee and H. B. Brown, "A Separable Combination of Wheeled Rover
and Arm Mechanism: (DM)2", Proceedings of the IEEE International Conference on
Robotics and Automation, Minneapolis, Minnesota, pp. 2383-2388, April 1996.
[5] D. P. Miller and Tze-Liang Lee, "High-Speed Traversal of Rough Terrain Using a
Rocker-Bogie Mobility System ", In the Proceedings of Robotics 2002: The 5th
International Conference and Exposition on Robotics for Challenging Situations and
Environments, Albuquerque, New Mexico, March 2002.
[10] R. Lindemann, "Dynamic testing and simulation of the Mars Exploration Rover",
Proceedings of the ASME International Design Engineering Technical Conference
and Computers and Information in Engineering Conference, Long Beach, California,
USA, September 24-28, 2005.
[13] X. Yu, Z. Deng, H. Fang and J. Tao, "Research on Locomotion Control of Lunar
Rover with Six Cylinder-conical Wheels ", Proceedings of the IEEE International
Conference on Robotics and Biomimetics, Kuming, China, pp. 919-923, December
2006.
[16] K. Gu, H. Wang and M. Zhao, "The Analyse of the Influence of External
Disturbance on the Motion of a Six-Wheeled Lunar Rover", Proceedings of the IEEE
International Conference on Mechatronics and Automation, Harbin, China, pp. 393-
398, August 2007.
Page | LXXII
[17] T. Thueer, A. Krebs, R. Siegwart and P. Lamon, "Performance Comparison of
Rough-Terrain Robots-Simulation and Hardware", International Journal of Field
Robotics, vol. 24, pp. 251-271, 2007.
[23] S. Li, H. Gao, and Z. Deng, "Mobility Performance Evaluation of Lunar Rover
and Optimization of Rocker-bogie Suspension Parameters ", IEEE 2nd International
Symposium on Systems and Control in Aerospace and Astronautics, Shenzhen,
December 2008.
Page | LXXIII
[26] H. Hacot, S. Dubowsky, and P. Bidaud, "Analysis and Simulation of a Rocker-
Bogie Exploration Rover", Proceedings of the Twelfth Symposium on Theory and
Practice of Robots and Manipulators, Paris, France, July 1998.
[28] Nitin Yadav, BalRam Bhardwaj , Suresh Bhardwaj “Design analysis of Rocker
Bogie Suspension System and Access the possibility to implement in Front Loading
Vehicles” IOSR Journal of Mechanical and Civil Engineering e-ISSN: 2278-1684,p-
ISSN: 2320-334X, Volume 12, Issue 3 Ver. III (May. - Jun. 2015), PP 64-67
[29] Dongkyu Choi, Jongkyun Oh and Jongwon Kim, Analysis method of climbing
stairs with the rocker-bogie mechanism Journal of Mechanical Science and
Technology 27 (9) (2013) 2783~2788
[30] Hong-an Yang, Luis Carlos Velasco Rojas, Changkai Xia, Qiang Guo, Dynamic
Rocker-Bogie: A Stability Enhancement for High-Speed Traversal International
Journal of Robotics and Automation (IJRA) Vol. 3, No. 3, September 2014, pp.
212~220 ISSN: 2089-4856
[31] Brian D. Harrington and Chris Voorhees, The Challenges of Designing the
Rocker-Bogie Suspension for the Mars Exploration Rover, Proceedings of the 37th
Aerospace Mechanisms Symposium, Johnson Space Center, May 19-21, 2004
[33] Paul W.Bartlett, David wattergreen, William Whittaker, “Design of scarab rover
for mobility and drilling in lunar cold traps” [11] Wesley B.Williams and Eric
J.Schaus, “Design and Implementation of Rocker Bogie Suspension for a Mining
robot”, 2015 ASEE Southeast Section Conference
Page | LXXIV
Page | LXXV