DESIGN AND FABRICATION OF ROCKERBOGIE MECHANISM Anubhav Kumar 12001004009 Nitin Verma 12001004037 Deergha Garg 12001004015 Rahul Hans 12001004044 Under the Guidance of Dr. Ajay Kumar Mechanical Engineering Department Deenbandhu Chhotu Ram University of Sc. &Tech. Murthal 1 DESIGN AND FABRICATION OF ROCKER BOGIETO MECHANISM CONTENTS BE COVERED • Introduction • Need and Motivation for the Project • Objective of the Project work • Past Present & Future of the Project • Related Concepts & Theories • Wheel Design • Requirements • Calculations • Budget & Table of Requirements 2 DESIGN AND FABRICATION OF ROCKER BOGIE MECHANISM INTRODUCTION • The rocker-bogie suspension system was first used for the Mars Rover and is currently NASA’s favoured design for rover wheel suspension. The intelligently designed wheel suspension allows the vehicle to traverse over very uneven or rough terrain and even climb over obstacles. • 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. • 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. • These robots are mainly used for tasks which humans cannot do and which are not safe. 3 This is a wide field of study and is very less explored. •Not only this. •It can also be used for material delivery purposes. So this gave us the motivation for the development of this rocker bogie suspension system in a cost effective manner. •The need to develop specialized high-fidelity systems capable of operating in harsh earth environments typically leads to longer development timelines and greater expenditures.DESIGN AND FABRICATION OF ROCKER BOGIE MECHANISM Need and Motivation for the selection of 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. 4 . 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. •The rovers made for the exploration purposes are very costly too. 5 . Due to the high cost of space exploration. 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.DESIGN AND FABRICATION OF ROCKER BOGIE MECHANISM Objective of Project Work •We will be focusing on eliminating the shortcomings of the rover that is the current rocker-bogie rovers is that they are slow. • Our concern during the development of the rover will 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. •We. most missions to date have been conducted by NASA and other government-supported organizations. in India have not conducted any mission for the exploration purposes. NASA has been exploring the surface of Mars with rovers. •Most Recently in 2011.DESIGN AND FABRICATION OF ROCKER BOGIE MECHANISM Past. NASA again landed two more rovers on Mars. •In early 2004. Present and Future • Since 1976. 6 . • In 1997. NASA has launched the Mars Science Laboratory (MSL) with a rover named Curiosity. starting with the dual landing of Viking 1 and Viking 2 landers. Spirit and Opportunity. The Mars Pathfinder (MPF) lander delivered the Sojourner Rover to the surface successfully. Launch date: November 26.DESIGN AND FABRICATION OF ROCKER BOGIE MECHANISM Curiosity Rover Curiosity is a car-sized robotic rover exploring Mars as part of NASA's Mars Science Laboratory(MSL) mission. 2011 Rocket: Atlas V Manufacturer: NASA Operator: NASA Mission Type :.50mm/s Average Speed :.Mars Exploration Rover Launch Mass:.900 Kg Max Speed:.10mm/s 7 . DESIGN AND FABRICATION OF ROCKER Related Concepts and TheoriesBOGIE MECHANISM Traction and Slip •The rover must maintain good wheel traction in challenging rough terrains. • If traction is too low. •If traction is too high. the vehicle consumes a lot of power in order to overcome the force and move. the rover is not able to climb over obstacles or inclined surfaces. Hence. •In reality it is very challenging to determine the precise friction coefficient μ for 8 the interaction of two surfaces . no slip occurs if the condition Ti ≤ μNi is satisfied. •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. • Lateral stability is computed by finding the minimum allowed angle on the slope before the rover tips over. •The lateral stability of the rover ensures that the rover does not tip sideways. min(θr. •Lateral stability of the rover is ensured if the overall stability angle θstab ≥ α . As the rover has two symmetric sides. the geometric model is used to find the lateral stability of the vehicle.θl) ≥ α 9 .:.DESIGN AND FABRICATION OF ROCKER BOGIE MECHANISM Related Concepts & Theories Lateral Stability •The rover is said to be stable when it is in a quasi-static state in which it does not tilt over. 10 . DESIGN AND FABRICATION OF ROCKER BOGIE MECHANISM 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 11 . •It should be noted that even though this condition is compulsory for the statical model to work. it is less steerable.DESIGN AND FABRICATION OF ROCKER BOGIE MECHANISM Related Concepts & Theories Longitudinal Stability •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. However. 12 . longitudinal stability of the vehicle is given when all wheels have ground contact and the condition Ni > 0 is satisfied. SSF= TW/(2*h) 13 . when sliding laterally may be thought of as a force acting at the CoG to pull the vehicle body laterally. TW. divided by h. and that advantage also increases 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. the height of the center of gravity above the road. rapid steering reversals or striking a tripping mechanism. • The inertial force which causes a vehicle to sway on its suspension (and roll over in extreme cases) in response to cornering. • A reduction in CoG height increases the lateral inertial force necessary to cause rollover by reducing its leverage.DESIGN AND FABRICATION OF ROCKER BOGIE MECHANISM Static Stability Factor • The Static Stability Factor (SSF) of a vehicle is one half the track width. and the advantage is represented by an increase in the computed value of SSF. •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. During each wheel’s traversal of the obstacle. the rear wheel is pulled over the obstacle by the front two wheels. 14 . until it is lifted up and over. •Finally. forward progress of the vehicle is slowed or completely halted. 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. the front wheels are forced against the obstacle by the rear wheels.DESIGN AND FABRICATION OF ROCKER BOGIE MECHANISM Mobility • In order to go over an obstacle. 458 30 0.637 RPM RPM RPM 15 .546 60 0.021 2.910 80 0.064 6.915 0.055 50 0.728 70 0.638 20 30 0.910 130 0.017 1.031 3.191 0.095 9.122 90 0.365 30 0.019 1.229 22.012 1.469 130 0.015 1.115 11.016 1.638 3.389 110 0.076 7.038 50 12cm/s Diamete r m cm 19.076 7.183 60 0.014 1.027 2.292 110 0.774 40 0.019 1.021 2.018 1.057 5.548 20 0.387 80 0.910 100 0.083 120 0.023 2.046 4.153 20 10cm/s Velocity Diamete r m cm 15.274 80 0.697 90 0.819 40 0.011 1.819 70 0.048 4.091 140 0.032 3.022 2.038 3.025 2.546 100 0.051 5.583 60 0.029 2.273 120 0.015 1.819 50 0.024 2.016 1.182 70 0.DESIGN AND FABRICATION OF ROCKER BOGIE MECHANISM Wheel Design Velocity 8cm/s Velocity Diamete r M cm 10 0.033 3.591 120 0.092 40 0.175 130 0.013 1.025 2.528 100 0.864 90 0.017 1.736 110 0.364 140 0.014 1.019 1.729 0.096 10 0.763 140 0.038 3.277 10 0. Joysticks will be used for each halves Other Requirements :- Full Wave Rectifier for the conversion of A. To D.12-0-12 Step Down transformer Drive Motor :. 16 .C.C.Depends upon Availability & Calculation We have chosen 30 rpm motor Controls :.DESIGN AND FABRICATION OF ROCKER BOGIE MECHANISM Requirements Power Supply :. • We could develop it into a Wheel Chair too. 17 . jungles or such places where humans may face some danger.DESIGN AND FABRICATION OF ROCKER BOGIE MECHANISM Application & Future Scope • With the development in technology the rover can be used for reconnaissance purposes with the cameras installed on the rover and minimizing 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. It can be send in valleys. • 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. • It can also be developed into Suspension System for the automobile vehicles through proper research. 49 N = 27.86 D 10 20 Selected DN combination: 190.2 60 31.28 80 23.66 40 47.28 rpm N 30 63. Diameter of Wheel 100 = πDN/60 DN=1909.75 50 38.DESIGN AND FABRICATION OF ROCKER BOGIE MECHANISM Calculation-1 1.83 70 27.87 90 21.22 100 19.99 D = 70 mm 95.1 18 . DESIGN AND FABRICATION OF ROCKER BOGIE MECHANISM 2. Calculation of Wheel base Θ = 21. Total length – (radius of front wheel + radius of rear wheel) =400-(35+35) =330 mm 19 . To deduce the wheel base. So the maximum length of the rover can be 400mm. width of the stairs is 400 mm.80 Now. Length of Links 20 .DESIGN AND FABRICATION OF ROCKER BOGIE MECHANISM 3. BC = 233. BC = 230mm 21 . Length of Links Total Wheel base = 330 mm Let us assume.DESIGN AND FABRICATION OF ROCKER BOGIE MECHANISM 3.33mm … (1) Rounding off to 230mm. angle BNC = 90˚ Angle NBC = Angle NCB = 45˚ Therefore. Θ=45˚ In Triangle BNC. NC = NB NC2 + NB2 = BC2 BC2 = 2(NC)2 =2(165)2 =54450 Therefore. 63 Also. Length of Links (Contd) Substituting to eqn (1) we get. AM = MN = 115 mm BM = AB – AM =230 – 115 =115 mm Therefore.DESIGN AND FABRICATION OF ROCKER BOGIE MECHANISM 3. BM = 115 22 .99 =115 mm Now. 2302 = 2(NC) 2 NC = 162.63 In triangle AMN. angle AMN = 90 AM2 + MN2 = AN 2AM2 = AN2 2AM2 = 162. AN = NC = 162. due to symmetry.63 2 AM = 114. DESIGN AND FABRICATION OF ROCKER BOGIE MECHANISM 4.86 23 .632)1/2 = 162.639 mm 5.639 mm Net Height = height + radius = 162. Height Calculation: Height2 = BC2 – NC2 (2302 – 162. Track Width Tw = 513.639 + 35 = 197. DESIGN AND FABRICATION OF ROCKER BOGIE MECHANISM Calculation .2 θ = 25.016 Wheelbase = 300 – 2(35) = 230mm 24 . .DESIGN AND FABRICATION OF ROCKER BOGIE MECHANISM Calculation -2 Using same method used earlier dimension of the links is calculated for the stair shown in previous slide. No Item Qty 1 Link 4 Material Acrylic/Woo d 2 Shaft 1 SS 100 3 Nut Bolts /Washers 4/8 SS 50 4 Wheel 6 Plastic 35 Motor 6 Alloy 5 Electrical purchase Budget 500/100 150 S.DESIGN AND FABRICATION OF ROCKER BOGIE MECHANISM Budget and Table of Requirements S. No Item Qty 1 Transformer 1 150 2 Rectifier 1 20 3 Joystick 2 80 4 PCB 2 50 5 Wires and Cables 150 Budget 26 . DESIGN AND FABRICATION OF ROCKER BOGIE MECHANISM 27 . DESIGN AND FABRICATION OF ROCKER BOGIE MECHANISM Structure Without the assembly of motors and wheels 28 . DESIGN AND FABRICATION OF ROCKER BOGIE MECHANISM Structure with assembly of all required equipments 29 . DESIGN AND FABRICATION OF ROCKER BOGIE MECHANISM Initial Working of the Mechanism 30 . DESIGN AND FABRICATION OF ROCKER BOGIE MECHANISM Working on a Complex Trackl 31 .