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DESIGN & FABRICATION OF
ROCKER-BOGIE MECHANISM
MINOR PROJECT
SUBMITTED IN PARTIAL FULFILLMENT OF REQUIREMENTS ...
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DECLARATION BY THE CANDIDATES
We hereby certify that the work which is being presented in this Project report
...
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ABSTRACT
The rocker-bogie suspension mechanism it’s currently NASA’s favored design
for wheeled mobile robots,...
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ACKNOWLEDGEMENT
We are highly grateful to the Hon’ble Vice-Chancellor, D.C.R. Univ. of Science
& Technology, M...
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LIST OF FIGURES & TABLES
Figure 1 MER (Mars Exploration Rover)
Figure 2 NASA’s Curiosity Rover
Figure 3 Red Ro...
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Table of Contents
Decleration by the Candidates
Abstract
Acknowledgement
List of Figures & Tables
CHAPTER 1 IN...
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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 operat...
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1.2 Need and Motivation for the selection of the project
Rocker-bogie suspension system that was first used fo...
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1.3 Objective of the Project
We will be focusing on eliminating the shortcomings of the rover. one of the
maj...
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CHAPTER 2
PAST PRESENT & FUTURE
2.1 Introduction
This chapter will begin by reviewing some past space explora...
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ability to support a human colony. Learning more about the composition of its
atmosphere and soil can tell us...
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Curiosity an advantage in terms of its path planning ability. It has a three axis
inertial measurement unit (...
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Astrobotic Technology Inc. is one such company that has founded itself on
making space exploration profitable...
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2.3 Rover Mobility
One of the most challenging aspects of rover operation in planetary
environments is effect...
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CHAPTER 3
RELATED CONCEPTS & THEORIES
3.1 Design Reqiurement & Specifications
Our main goal is to design, dev...
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3.2 Related Concepts
3.2.1 Traction and Slip
The rover must maintain good wheel traction in challenging rough...
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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.
L...
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3.2.3 Longitudinal Stability
The computation of the longitudinal stability of the rover makes use of a static...
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3.3 Design & Analysis
Under this section we will discuss our complete rover design and discuss how
our key de...
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Wheel Design
The wheels are needed to be wider for increasing the traction to traverse upon
the obstacles. An...
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Drive motor Selection
Since the rover consists of six indepently drive wheels hence the drive motor is
needed...
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CHAPTER 4
CALCULATIONS
Calculation 1
1. Diameter of Wheel
𝑉 =
πDN
60
Assumed speed be 10 cm/s i.e. 100mm/s
Th...
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2. Calculation of Wheel Base
Figure 6 Centre Stage Stairs
θ = tan−1
y
x
θ = tan−1
160
400
Therefore, θ = 21.8...
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3. Length of Links
Figure 7 Calculations at Centre Stage Stairs
Total Wheel base = 330 mm
Let us assume, Θ=45...
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2302
= 2(NC) 2
NC = 162.63
Also, AN = NC = 162.63
In triangle AMN, angle AMN = 90
AM2
+ MN2
= AN2
… (Pythagor...
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5. Track Width
𝑆𝑆𝐹 =
𝑇𝑤
2ℎ
1.3 =
𝑇𝑤
2 × 197.639
Tw = 513.86
Calculation-2
6. Calculation of Wheel Base
Figure...
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=300-(35+35)
=230 mm
7. Length of Links
Figure 9 Calculation at Library Stairs
Total Wheel base = 230 mm
Let ...
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=26450
Therefore, BC = 162.63 mm
Rounding off to 162 mm.
BC = 162mm
Substituting to eqn (1) we get,
1622
= 2(...
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= 114.101 + 35
= 149.101 mm
9. Track Width
𝑆𝑆𝐹 =
𝑇𝑤
2ℎ
1.3 =
𝑇𝑤
2 × 149.101
Tw = 387.66 mm
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CHAPTER 5
CONCLUSIONS
5.1 Conclusion
This project will try reaching nearly all of our design requirements, an...
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With the total of Electrical and Hardware Purchases the rover will cost around Rs. 2110
or a little more.
5.3...
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REFERENCES
 mars.nasa.gov/mer/home
 robots.mit.edu/publications/papers/1998_07_Hac_Dub_Bid
 https://www.yo...
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Project Report

  1. 1. 1 | P a g e 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)
  2. 2. 2 | P a g e 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)
  3. 3. 3 | P a g e 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.
  4. 4. 4 | P a g e 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
  5. 5. 5 | P a g e 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
  6. 6. 6 | P a g e 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
  7. 7. 7 | P a g e CHAPTER 5 CONCLUSIONS 5.1 Conclusion 5.2 Budget & Table of Requirements 5.3 Future Scope References
  8. 8. 8 | P a g e 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.
  9. 9. 9 | P a g e 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.
  10. 10. 10 | P a g e 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.
  11. 11. 11 | P a g e 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
  12. 12. 12 | P a g e 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
  13. 13. 13 | P a g e 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.
  14. 14. 14 | P a g e 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
  15. 15. 15 | P a g e 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.
  16. 16. 16 | P a g e 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.
  17. 17. 17 | P a g e 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
  18. 18. 18 | P a g e 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.
  19. 19. 19 | P a g e 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
  20. 20. 20 | P a g e 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.
  21. 21. 21 | P a g e 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. 22. 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. 23. 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. 24. 24 | P a g e 2. Calculation of Wheel Base 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. 25. 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. 26. 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. 27. 27 | P a g e 5. Track Width 𝑆𝑆𝐹 = 𝑇𝑤 2ℎ 1.3 = 𝑇𝑤 2 × 197.639 Tw = 513.86 Calculation-2 6. Calculation of Wheel Base 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. 28. 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. 29. 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. 30. 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. 31. 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. 32. 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. 33. 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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