DESIGN & FABRICATION OFROCKER-BOGIE MECHANISM MAJOR 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 (JUNE 2016) 1|Page 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, Deenbandhu Chhotu Ram University 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.) 1) Anubhav Kumar (12001004009) 2) Deergha Garg (12001004015) 3) Nitin Verma (12001004037) 4) Rahul Hans (12001004044) Signature This is to certify that the above statement made by the candidate is correct to the best of my knowledge & belief. Signature of Supervisor 2|Page 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 rockerbogie 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. 3|Page ACKNOWLEDGEMENT We are highly grateful to the Hon’ble Vice-Chancellor, Deenbandhu Chhotu Ram University 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. Rajender Singh, Prof. & Chairperson, Dept. of Mechanical Engineering, Deenbandhu Chhotu Ram University 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., Dept. of Mechanical Engineering, Deenbandhu Chhotu Ram University of Science & Technology, Murthal, Sonepat. Without his able guidance, it would have been impossible to complete the project in this manner. The help rendered by Dr. M.S. Narwal B.Tech. Project Coordinator, Department of Mechanical Engineering, Deenbandhu Chhotu Ram University of Science & Technology, Murthal, Sonepat for his wise counsel is greatly acknowledged. We also express our gratitude to other faculty members of Dept. of Mechanical Engineering, Deenbandhu Chhotu Ram University 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. 1) Anubhav 12001004009 2) Deergha Garg 12001004015 3) Nitin Verma 12001004037 4) Rahul Hans 12001004044 Signature 4|Page 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 Figure 10 Step Down Transformer Figure 11 Full Wave Rectifier Figure 12 12-0-12 V Transformer & Rectifier Figure 13 Motors & Linkages Assembly Figure 14 Joystick Figure 15 Rocker Bogie Mechanism 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 5|Page . 1 Introduction 1.2 Related Concepts 3.2 Recent Rovers & their Missions 2.2 Lateral Stability 3.2.1 Traction & Slip 3.4 Static Stability Factor 3.1 Design Requirements & Specification 3. PRESENT & FUTURE 11 2.3 Design Analysis 6|Page .2.3 Longitudinal Stability 3.1 Introduction 2.2.TABLE OF CONTENTS Decleration by the Candidates ii Abstract iii Acknowledgement iv List of Figures & Tables v CHAPTER 1: INTRODUCTION 8 1.3 Objective of the Project CHAPTER 2 : PAST.2 Need & Motivation for the Selection of the Project 1.2.3 Rover Mobility CHAPTER 3: RELATED CONCEPTS &THEORIES 17 3. 5 Track Width CHAPTER 5 : FABRICATION 33 5.3 Length of Links 4.1 Transformer 5.4 Height Calculation 4.1 Diameter of Wheel 4.2 Full Wave Rectifier 5.1.CHAPTER 4: CALCULATIONS 25 4.3 Future Scope References 40 7|Page .2 Linkages 5.3.1.2 Calculation of Wheel Base 4.3.1 Power House 5.2 Budget & Table of Requirements 6.3 Controls 5.1 Joystick 5.2 PCB CHAPTER 6: CONCLUSIONS 38 6.1 Conclusion 6. This is extremely important in soft terrain where excessive ground pressure can result in the vehicle sinking into the driving surface.1 Introduction There is an increasing need for mobile robots which are able to operate in unstructured environments with highly uneven terrain. In order to be able to overcome significantly rough terrain (i. obstacles more than a few percent of wheel radius) without significant risk of flipping the vehicle or damaging the suspension. In order to achieve these tasks. 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. uneven terrain. maximizing the vehicle's motive force capability. any mobile robot needs to have a suitable mobile system according to each situation.e. One of the major shortcomings of current rockerbogie rovers is that they are slow. Among these mobile systems. There are two key advantages to this feature. Exploration rovers take advantage of this configuration by integrating each wheel with a drive actuator. where the rover should increase its speed to arrive faster from point A to point B. 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.. helping to propel the vehicle over the terrain. 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.CHAPTER 1 INTRODUCTION 1. 8|Page . all six wheels will nominally remain in contact with the surface and under load. While performance on rough terrain obstacles is important. The second advantage is that while climbing over hard. The first advantage is that the wheels' pressure on the ground will be equilibrated. These robots are mainly used for tasks which humans cannot do and which are not safe. it should be also considered situations where the surface is flat or it has almost imperceptible obstacles. Our mission is to design. As explained this is a wide field of study and very less 9|Page . and test a rover to serve as a research platform.which is exploring the surrounding to give a visualisation to a person or operator sitting somewhere for carrying the operation. We also hope that the platform developed can be tested and improved upon. may differ slightly between missions but are largely the same in most scenarios.The Rocker bogie Suspension system can be sent for reconnaissance purpose. 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. This is a very less explored field of study and could be developed into exploration purpose instrument. While specific applications will always require unique designs. The design will focus on incorporating features that are believed to be essential for most planetary exploration missions. Hence. and vision. in addition to lowering development costs. Not only this. navigation. yet few are designed to operate in the harsh earth environments that are often used for planetary surface rover testing.1. By creating a rover that is suitable for these types of environments. develop. there are many commonalities in planetary rovers.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. Issues such as mobility. There are currently many mobile research platforms available. to potentially serve as a model for a rover that could go to the moon or Mars in the future. The need to develop specialized high-fidelity systems capable of operating in harsh earth environments typically leads to longer development timelines and greater expenditures. 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. by the help of a video camera. 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. suitable for testing planetary surface exploration technologies in harsh earth environments. our goal is to facilitate the development of rovers and their related technologies. It can also be used for material delivery purposes. However. While performance on rough terrain obstacles is important. While companies like these have made progress in the commercialization of space exploration. it should be also considered situations where the surface is flat or it has almost imperceptible obstacles. 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.3 Objective of the Project We will be focusing on eliminating the shortcomings of the rover. Astrobotic Technology. in India have not conducted any mission for the exploration purposes. where the rover should increase its speed to arrive faster from point A to point B. 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. 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. and Armadillo Aerospace are just a few companies that are developing rovers and landers for different space missions. We. 1. most missions to date have been conducted by NASA and other government-supported organizations. Due to the high cost of space exploration.explored. 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. In order to be able to overcome significantly rough terrain without significant risk of flipping the vehicle or damaging the suspension. 10 | P a g e . The rovers made for the exploration purposes are very costly too. the inherently high costs continue to hinder economic feasibility. For example. Odyssey Moon. one of the major shortcomings of current rocker-bogie rovers is that they are slow. So this gave the motivation for the development of this suspension system. Next. and have environments that are hospitable enough for rovers.1 Introduction This chapter will begin by reviewing some past space exploration rovers as well as rovers currently in development. as they can often provide unique opportunities for analog testing at NASA facilities. Both hardware and software design choices are reviewed. that made these rovers successful in meeting their objectives on the Martian or lunar surface. specific features of these rovers are discussed in order to learn more about the types of technologies that are often used on exploration rovers. as it has no atmosphere. specifically relating to mobility and navigation. 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. and the future colonization of extra-terrestrial bodies. specifically with respect to its 11 | P a g e . most interest has been in our moon and Mars.2 Recent Rovers and their Missions Much of space exploration can be divided into three categories: a quest to better understand our universe. It will discuss specific missions along with the corresponding design features and capabilities. The moon is also very well suited for scientific equipment such as radio observatories or IR telescopes. A few NASA sponsored competitions are also reviewed. 2. as they relate to the mobility challenges of ground compliance and hazard avoidance. research into analog testing presents what is currently being done by NASA and others to validate planetary rovers on Earth. Interest in Mars mostly relates to expanding our knowledge of the planet. as these planetary bodies are close by. and potentially for future colonization. Lastly. and economic potential in using natural resources outside our planet.CHAPTER 2 PAST PRESENT & FUTURE 2. instruments such as these can measure signals that would otherwise be disturbed or eliminated on Earth. Furthermore. interest. which identified positive and negative obstacles relative to the ground plane. in early 2004. the rocker-bogie suspension was used. Each wheel also has small cleats. It consists of six wheels and multiple axles that allow the rover to overcome obstacles larger than its wheel diameter. To do this. NASA has been exploring the surface of Mars with rovers. NASA has launched the Mars Science Laboratory (MSL) with a rover named Curiosity. The Mars Pathfinder (MPF) lander delivered the Sojourner Rover to the surface successfully. Most recently. NASA again landed two more rovers on Mars. on-board stereo vision processing was used to develop an image on the environment. Learning more about the composition of its atmosphere and soil can tell us whether Mars could potentially support microbial life. which have been found to be effective both for soft sandy terrain and in navigating over rocks. Making improvements from past Mars rovers. Since 1976. In 1997. These flexure joints act as shock absorbers which help to reduce the shock loads on other components of the rover. which allowed them to traverse the Martian terrain with relative ease. starting with the dual landing of Viking 1 and Viking 2 landers. 1 MER Rover 12 | P a g e . Fig. Despite the multiple rovers that NASA has sent to Mars. given the relatively large time delays in sending commands. 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. Spirit and Opportunity. In November 2011. each mission has similar objectives. In continuation of past Mars rover designs. NASA has continued to develop autonomous navigation to make it easier and quicker to control their rovers.ability to support a human colony. The other main features of the MERs relate to mobility hardware. the 900kg rover has a very similar 6 wheel rocker-bogie suspension as previous Mars exploration rovers have. Fig 2.Curiosity an advantage in terms of its path planning ability. With a top speed of 4cm/sec. NASA’s Curiosity Rover In reviewing NASA’s rovers for surface exploration on Mars. Curiosity also has cleated treads that are similar to the MER rovers. there were many similarities in both their mechanical design and software that enable the rovers to perform on-board path planning.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°. To tackle the mobility challenge. The larger size combined with the rocker. which were found to be an optimal solution for Martian terrain. it was the fastest rover sent to Mars. enabling the rover to make precise movements while also monitoring the degree of tilt that the rover is experiencing. Autonomous planetary navigation combined with hazard avoidance and other self-preservation autonomy makes these rovers excellent 13 | P a g e . but is limited to 30° slopes by software to ensure a factor of safety. It has a three axis inertial measurement unit (IMU). The biggest changes between missions have been the size of the rover and the types of scientific instruments it supports. Red Rover uses a 4 wheel rocker differencing suspension system. which if successful will satisfy the X-prize criteria as well as other objectives.platforms to reliably transport and position their scientific instruments. based on its analysis of chemical composition and high resolution 3D images. called Red Rover. is one such company that has founded itself on making space exploration profitable. Fig 3. Red Rover is designed to be a scout. Its goal is to determine where the interesting locations are. Astrobotic Technology Inc. exploring places such as polar ice fields or skylights into lunar lava tubes. To facilitate roving about the lunar surface. Red Rover has a stereo camera and flash LIDAR which will allow it to make high-resolution terrain maps. Their robot. For vision. 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. While it will likely have some form of on-board autonomous hazard avoidance or path planning it is unclear exactly to what extent. and thus relies on skid-steering to rotate the rover. is reviewed here because it is one of the most developed lunar exploration rovers. as available information only suggests that the rover is teleoperated. They are currently in collaboration with Carnegie Mellon University and others. It drives the two wheels on each side of the rover together. to develop a rover and lander for their first surface lunar exploration mission. Figure 3 is a picture of one of the recent prototypes of Red Rover. Red Rover 14 | P a g e . by delivering payloads and performing robotic services on the moon. 2. it is able to go over relatively large obstacles compare to its 15 | P a g e . The most basic mobility system is the wheel. Surface challenges to rover mobility include fine powders such as lunar regolith. Topographic features such as craters. The Mars Science Laboratory plans to drive about 12 kilometers during its mission. 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. and cliffs present different forms of challenges.3 Rover Mobility One of the most challenging aspects of rover operation in planetary environments is effective mobility. Sojourner‟s wheels were rigidly connected to the drive motors with no suspension elements. it first must be able to move confidently in unforgiving terrain. Additionally. screen fields. Because the front and rear wheels can help to push or pull the free-floating bogie link.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. as well as maintain stability on tilted terrain. 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. so rover mobility systems must be flexible to accommodate unknown factors. a large shock load. most of it autonomously. 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. This may include both challenging surfaces and wider-scale terrain discontinuities. gullies. To complicate the problem further. and larger rocks. NASA/JPL’s 10. many planetary environments are not well studied. These components are typically articulated to increase the maximum obstacle the rover is capable of traversing. These 50 centimeter wheels support the 900 kilogram rover over obstacles up to 75 centimeters in height. It has large billet aluminum with thin straight spokes and a zigzag aluminum pattern machined into the outer surface. The two most common methods of articulating mobility systems include rocker bogie and rocker differencing. In order for a rover to complete any science tasks. MSL’s wheels are needed to support the rover during its final landing. and an effective wheel design becomes a major part of any rover drive system. hills. These mobility systems can also incorporate passive or active suspension elements which help reduce the shock loading experienced by the rover chassis. Effective rover mobility systems combine robust mechanical hardware with sensors and programming to detect impassible terrain. Most planetary rovers have used all-metal wheels for their high strength-to-weight ratio. the rocker-bogie contains no spring elements. As a suspension system. and this helps provide stability while going over large obstacles. 16 | P a g e .wheel size. the rover needs to easily integrate new hardware and software as part of its payloads.CHAPTER 3 RELATED CONCEPTS & THEORIES 3. the rover will aim to recognize the size and weight constraints that all space bound vehicles face. our design goals for our rover have been made into these categories: 1. to be useful for other users both in academia or industry. Mobility and navigation 2. Given what we have learned about existing rovers and the types of missions they aim to accomplish. and thus one of our central requirements. Given sufficient mobility in planetary environments. In formulating the design specifications relating to mobility we wanted to ensure that the rover could traverse a wide variety of harsh Earth environments. on terrain similar to that of our moon and Mars. 17 | P a g e . and test a rover to serve as a mobility platform. sand dunes. Such terrain includes deserts.1 Design Reqiurement & Specifications Our main goal is to design. 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. Size and weight restrictions While our rover will not be travelling to space. While there are many resource constraints that prohibit us from designing a space-ready rover. the rover should prove useful to anyone interested in testing rover related technologies or conducting research in the field of space exploration.if possible. Additionally. rock fields. and mountainous areas in many different climates. By providing a robust mobility platform that can accommodate a wide range of payloads. gravel pits. Transporting sensitive scientific instruments across rough terrain is the main goal for nearly all exploration rovers. develop. Lastly. the rover must also be able to accommodate payloads. the design will attempt to accommodate space considerations when possible. suitable for testing planetary surface exploration technologies in harsh earth environments. it is our goal to make a robust and ruggedized platform that will be suitable for testing in harsh earth environments. and speeds that the rover must achieve. Lateral stability is ensured if this angle is smaller 18 | P a g e . the vehicle consumes a lot of power in order to overcome the force and move. In reality it is very challenging to determine the precise friction coefficient μ for the interaction of two surfaces. no slip occurs if the condition Ti ≤ μNi is satisfied. inclines. The lateral stability of the rover ensures that the rover does not tip sideways. a more advanced approach is using a static model.2 Related Concepts 3. Hence.1 Traction and Slip The rover must maintain good wheel traction in challenging rough terrains. 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. As the asymmetric suspension system of the passively articulated rover has a great influence on the vehicle’s effective stability. 3. 3. both positive and negative to the ground plane.2.In examining these terrains we will make design criterias relating to the size of obstacles. which is commonly referred to as stability margin. 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. The simplest approach to find the static stability is using the geometric model. in order to ensure that it could maneuver in many different environments. As the rover has two symmetric sides. For our rover we set the goal of being able to traverse obstacles. If traction is too low.2. the rover is not able to climb over obstacles or inclined surfaces. in most scenarios the ability to go over larger obstacles always increases mobility potential.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. If traction is too high. θr & θl be the angle that the point of contact makes with the Centre of Gravity on the left and right wheels respectively.than the maximum angle of incline α on the slope at the wheel-terrain contact points.θl) Lateral stability of the rover is ensured if the overall stability angle θstab ≥ α .Z be the height of the centre of gravity. 19 | P a g e . And hence the normal reaction on any of the wheel should not be 0. min(θr. The overall stability angle θstab can be computed by θstab = min(θr.:. And yl and yr be the perpendicular between the point of contact and the Centre of Gravity. Taking moment at the left wheel. Let α be the slope of the inclination. The angles θl and θr are obtained geometrically. In this condition to ensure the stability the rover should not tip off the inclined.θl) ≥ α Fig 4 Lateral Stability Let N1 be the reaction on the right wheel and N2 be the reaction on the left wheel. 3. it is less steerable. According to . a physical rover does not necessarily tip if a wheel looses contact to the ground. where Ni is the normal force at wheel i. the mechanical properties of the suspension system are taken into account. It should be noted that even though this condition is compulsory for the statical model to work. Using a statical model. However.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. longitudinal stability of the vehicle is given when all wheels have ground contact and the condition Ni > 0 is satisfied. Figure 5 Longitudinal Stability 20 | P a g e .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.2. rapid steering reversals or striking a tripping mechanism. Since nearly all rover hardware is related to mobility. TW.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. In beginning the process of formulating the drive architecture we reviewed current and past rovers in consideration of chassis design. and the advantage is represented by an increase in the computed value of SSF. The inertial force which causes a vehicle to sway on its suspension (and roll over in extreme cases) in response to cornering. slopes.3.3. suspension methods. divided by h. uses a two 21 | P a g e . the rocker-bogie. when sliding laterally may be thought of as a force acting at the CoG to pull the vehicle body laterally.2. suspension. 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. Each one of these is related to meeting fundamental requirements. and wheel components.4 Static Stability Factor The Static Stability Factor (SSF) of a vehicle is one half the track width. and obstacles. 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. this section will review most of the mechanical design including the chassis. NASA’s currently favored design. wheel design. and that advantage also increases the computed value of SSF.1 Mobility Mobility relates to the rover’s capacity to traverse varying terrains. 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 3. 3. A reduction in CoG height increases the lateral inertial force necessary to cause rollover by reducing its leverage. the height of the center of gravity above the road. and power requirements. Since it is a skid steering rover an alternative solution could be to have one motor drive two wheels on either side. And their diameter depend upon the availability and amount of speed required. which is often done with belts. Finally. 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. having one motor for each wheel reduces the need for a complex power transfer system. the front wheels are forced against the obstacle by the rear wheels. Each wheel is independently driven. resulting in fewer motors and less mass. forward progress of the vehicle is slowed or completely halted. or drive shafts. until it is lifted up and over. 22 | P a g e . The maximum speed of the robots operated in this way is limited to eliminate as many dynamic effects as possible.3. However.2 Wheel Design The wheels are needed to be wider for increasing the traction to traverse upon the obstacles.wheeled rocker arm on a passive pivot attached to a main bogie that is connected differentially to the main bogie on the other side. gears.The main problem during the selection of the wheels is light weight consideration and the distribution of load on the wheels. 3. The rotation of the front wheel then lifts the front of the vehicle up and over the obstacle. We will be using the same mechanism the six wheel independent drive to cross the obstacles but without any differential. During each wheel’s traversal of the obstacle. The middle wheel is the pressed against the obstacle by the rear wheel and pulled against the obstacle by the front. The actual rover uses billet wheels. the rear wheel is pulled over the obstacle by the front two wheels. and machine the wheel and tread from one piece of round aluminum stock. 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. The ride is further smoothed by the rocker which only passes on a portion of a wheel’s displacement to the main bogie. In order to go over an obstacle. To further simplify the design we choose to use one motor to directly drive each wheel. 096 9.864 2.022 0.728 2.021 0. it will result in a cost effective solution with minimal manufacturing time.637 .018 0.819 3.092 3.774 3.389 1.915 11.083 1.011 Velocity RPM Cm 15.038 0.014 0.364 10 20 30 40 50 60 70 80 90 100 110 120 130 140 12cm/s Diameter M 0.095 0.365 4.3 Drive motor Selection Since the rover consists of six indepently drive wheels hence the drive motor is needed for every wheel.076 0.591 1.387 2.458 7.638 5. We will be using a 30 rpm motor with 12V DC because it is well suited depending upon the requirements and calculations.016 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.736 1.763 1.046 0.273 1. 23 | P a g e cm 22.910 1. 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.091 10 20 30 40 50 60 70 80 90 100 110 120 130 140 10cm/s Diameter M 0.013 0.910 1.038 0.051 0.528 1.032 0.292 2.024 0.057 0.583 3.819 3.017 0. We will try to design the rover for a speed of 10 cm/s and will choose the parameters based upon it.546 2.175 1.277 7.183 2.076 0.819 3.038 0.153 0.182 1.025 0.548 6.017 0. 3.029 0.064 0. While our wheel design may not be optimized in terms of strength and weight reduction.469 1.019 0.910 1.019 0.012 0.048 0.729 4.016 0.229 0.015 0.638 5.015 0.274 2.025 0.122 1.546 2.191 0. The Selection of drive motor depends upon the speed of the rover that is desired.019 0.023 0. and a wheel that should meet all design goals.055 2.697 1.014 Velocity RPM cm 19.3.021 0.Velocity RPM 10 20 30 40 50 60 70 80 90 100 110 120 130 140 8cm/s Diameter M 0.033 0.115 0.031 0.027 0. 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. 24 | P a g e . It will be helpful while taking a turn. 3. 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.4 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.5 Control The Control of the rover will be manual with the help of a joysticks for driving each side of the rover separately.3.3.3. 1 Table 2 Calculation of Diameter and RPM So the selected D-N combination isD = 70 mm N = 27.75 38.1 Diameter of Wheel ?= πDN 60 Assumed speed be 10 cm/s i.49 63.e.66 47.2 31. 100mm/s Therefore.CHAPTER 4 CALCULATIONS Calculation 1 4. 100 = πDN 60 DN=1909.87 21.22 19.86 D 10 20 30 40 50 60 70 80 90 100 N 190.99 95.28 23.83 27.28 rpm 25 | P a g e . To deduce the wheel base.4. y x 160 400 θ = 21. Total length – (radius of front wheel + radius of rear wheel) =400-(35+35) =330 mm 26 | P a g e .2 Calculation of Wheel Base Fig 6 Centre Stage Stairs θ = tan−1 θ = tan−1 Therefore. width of the stairs is 400 mm. So the maximum length of the rover can be 400mm.80˚ Now. 4. NC = NB NC2 + NB2 = BC2 … (Pythagporas Theorem) BC2 = 2(NC)2 … (1) =2(165)2 =54450 Therefore. BC = 233.3 Length of Links Figure 7 Calculations at Centre Stage Stairs Total Wheel base = 330 mm Let us assume.33mm Rounding off to 230mm. angle BNC = 90˚ Angle NBC = Angle NCB = 45˚ Therefore. Θ=45˚ In Triangle BNC. BC = 230mm 27 | P a g e . 639 mm 28 | P a g e .639 + 35 … (net ht = ht + radius) = 197.99 =115 mm Now. due to symmetry.63 2 AM = 114.4 Height Calculation: Height2 = BC2 – NC2 (2302 – 162.Substituting to eqn (1) we get. AM = MN = 115 mm BM = AB – AM =230 – 115 =115 mm Therefore. angle AMN = 90 AM2 + MN2 = AN2 … (Pythagoras Theorem) 2AM2 = AN2 2AM2 = 162.632)1/2 = 162. 2302 = 2(NC) 2 NC = 162.639 mm Net Height = 162. BM = 115 4. AN = NC = 162.63 Also.63 In triangle AMN. 29 | P a g e .86 Calculation-2 4.3 = ?? 2ℎ ?? 2 × 197. y x 140 300 θ = 25. width of the stairs is 300 mm.4.5 Track Width ??? = 1. So the maximum length of the rover can be 300mm.016˚ Now.6 Calculation of Wheel Base Figure 8 Library Stairs θ = tan−1 θ = tan−1 Therefore.639 Tw = 513. angle BNC = 90˚ Angle NBC = Angle NCB = 45˚ Therefore.To deduce the wheel base.7 Length of Links Figure 9 Calculation at Library Stairs Total Wheel base = 230 mm Let us assume. Total length – (radius of front wheel + radius of rear wheel) =300-(35+35) =230 mm 4. Θ=45˚ In Triangle BNC. NC = NB NC2 + NB2 = BC2 … (Pythagporas Theorem) 30 | P a g e . 55 In triangle AMN. 1622 = 2(NC) 2 NC = 114.BC2 = 2(NC)2 … (1) =2(115)2 =26450 Therefore. BC = 162.63 mm Rounding off to 162 mm.55 2 AM = 80.55 Also. BM = 8 31 | P a g e . AN = NC = 114. BC = 162mm Substituting to eqn (1) we get. AM = MN = 81 mm BM = AB – AM =162 – 81 =81 mm Therefore.999 =81 mm Now. due to symmetry. angle AMN = 90 AM2 + MN2 = AN2 … (Pythagoras Theorem) 2AM2 = AN2 2AM2 = 114. 3 = ?? 2ℎ ?? 2 × 149.4.101 mm Net height = Height + Radius of wheel = 114.9 Track Width ??? = 1.101 Tw = 387.66 mm 32 | P a g e .101 mm 4.8 Height Calculation: Height2 = BC2 – NC2 (1622 –1152)1/2 = 114.101 + 35 = 149. 1. Step Down Transformer 33 | P a g e . This kind of transformer “steps down” the voltage applied to it. As a step-down unit. high-current power. the transformer converts high-voltage.CHAPTER 5 FABRICATION 5. may be made of smaller-gauge wire. The primary winding. The power is supplied to the Step Down Transformer of 12-0-12 V. The larger-gauge wire used in the secondary winding is necessary due to the increase in current. It is designed to reduce the voltage from the primary winding to the secondary winding. which doesn’t have to conduct as much current. The AC is Converted to DC by a Full Wave Rectifier. Fig 10.1 Power House The Power House of the Mechanism is a collection of some electrical equipments equipped to Supply DC Power to the rocker bogie. And there is a provision of 2 way switch for supplying 12V Supply and 24V Supply according to the requirements.1 Transformer A Step down transformer is one whose secondary voltage is less than its primary voltage. 5. lowcurrent power into low-voltage. which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage.5. 12-0-12 V Transformer & Rectifier 34 | P a g e . It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage. Full Wave Rectifier Fig 12.2 Full wave rectifier A Full Wave Rectifier is a circuit. Fig 11.1. It provides flexibility as well as good stiffness. Fig 13.e the left and the right part individually. Motors & Linkages Assembly 5. The Linkages are connected in a way to form the rocker as well as the bogie. And there is a provision for the connection of screws to connect the rocker to the bogie. The term “bogie” refers to the links that have a drive wheel at each end.3 Controls For controlling the 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. With holes of appropriate sizes for the connection of motors as well as the wheels of required specifications.2 Linkages The Linkages used are made up of fibre. The term “rocker” comes from the rocking aspect of the larger links on each side of the suspension system. 35 | P a g e .5. pads and other features etched from copper sheets laminated onto a non-conductive substrate. Fig 14.1 Joysticks A joystick is an input device consisting of a stick that pivots on a base and reports its angle or direction to the device it is controlling.5. Joystick 36 | P a g e .3. The connections are done by soldering. The structure of circuit is laid on the PCB.3. There are two joysticks for each portion the left portion as well as the right portion of the mechanism. 5.2 PCB A printed circuit board (PCB) mechanically supports and electrically connects electronic components using conductive tracks. Fig 15. Rocker Bogie Mechanism 37 | P a g e . 1 Conclusion This project will try reaching nearly all of our design requirements.2 Budget and Table of Requirements S. and timeline.CHAPTER 6 CONCLUSIONS 6. No Item Qty Material Budget 1 Link 4 Acrylic 50 200 2 Shaft 1 SS 50 50 3 Bearing 2 SS 20 40 4 Wheel 6 Plastic 40 240 5 Motor 6 Alloy 150 900 Total Net 1430 Table 3 Hardware to be Purchased Electrical purchase S. and in many respects exceeding original design goals. with the exception if the project goes moderately over budget. 6. will be thoroughly tested as a completed system in real-world field testing conditions to validate their success. mechanical and electrical. No Item Qty Budget 1 Transformer 1 150 150 2 Rectifier 1 30 30 3 Joystick 2 30 60 4 PCB 2 25 50 5 Wires and Cables 150 150 Total Net 440 Table 4 Electrical Equipments to be Purchased 38 | P a g e . budget. Overall. for the project will be closely followed. Furthermore all components. preliminary estimates for the general scope. 39 | P a g e . 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. It can be send in valleys.We could develop it into a wheel chair too. 1770 or a little more. The Electrical equipments are purchased from the Lajpat Rai Market Near Red Fort New Delhi and the Material for the links is purchased from Sonepat rest bearings and other nut bolts type material are from Junk Yard at Murthal and hardware stores. jungles or such places where humans may face some danger.With the total of Electrical and Hardware Purchases the rover will cost around Rs. 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.3 Future Scope As modular research platform the rover developed by this project is designed specifically to facilitate future work. 6. 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. It can also be developed into low cost exploration rover that could be send for collecting information about the environment of some celestial bodies. esmats.org/wiki/Longitudinal_static_stability www.com/watch?v=bP7p5Bd2d50 https://en.eu/amspapers/pastpapers/pdfs/2004/harrington 40 | P a g e .edu/publications/papers/1998_07_Hac_Dub_Bid https://www.REFERENCES mars.wikipedia.nhtsa.nasa.gov/mer/home robots.youtube.gov/cars/rules/regrev/evaluate/809868/pages/IntroBack www.mit.