Rocker Bogie Ppt

Anubhav Kumar Deergha Garg

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Nitin Verma

Rahul Hans

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Under the Guidance of

Dr. Ajay Kumar

Mechanical Engineering Department

Deenbandhu Chhotu Ram University of Sc. &Tech. Murthal

DESIGN AND FABRICATION OF ROCKER

BOGIE MECHANISM

CONTENTS TO 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

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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.

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.

•The need to develop specialized high-fidelity systems capable of operating in harsh earth environments typically leads to longer development timelines and greater expenditures.

•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. This is a wide field of study and is very less explored. So this gave us the motivation for the development of this rocker bogie suspension system in a cost effective manner.

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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.

•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.

•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.

• 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.

DESIGN AND FABRICATION OF ROCKER

BOGIE MECHANISM

Past, Present and Future

• 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.

•In early 2004, NASA again landed two more rovers on Mars, Spirit and Opportunity.

•Most Recently in 2011, NASA has launched the Mars Science Laboratory (MSL) with a rover named Curiosity.

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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.

Launch date: November 26, 2011 Rocket: Atlas V

Manufacturer: NASA Operator: NASA

Mission Type :- Mars Exploration Rover

Launch Mass:- 900 Kg Max Speed:- 50mm/s

Average Speed :- 10mm/s

DESIGN AND FABRICATION OF ROCKER

BOGIE MECHANISM

Related Concepts and Theories

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 8

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.

•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 of the rover is ensured if the overall stability angle θstab ≥ α

.:. min(θr,θl) ≥ α

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

DESIGN AND FABRICATION OF ROCKER

BOGIE MECHANISM

Related Concepts & Theories

Longitudinal Stability

•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.

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DESIGN AND FABRICATION OF ROCKER

BOGIE MECHANISM

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.

• 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 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.

SSF= TW/(2*h)

DESIGN AND FABRICATION OF ROCKER

BOGIE MECHANISM

Mobility

• 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.

•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.

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DESIGN AND FABRICATION OF ROCKER

BOGIE MECHANISM

Wheel Design

Velocity 8cm/s Velocity 10cm/s Velocity 12cm/s

RPM Diamete r   RPM Diamete r   RPM Diamete r     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

DESIGN AND FABRICATION OF ROCKER

BOGIE MECHANISM

Requirements

Power Supply :- 12-0-12 Step Down transformer

Drive Motor :- Depends upon Availability & Calculation We have chosen 30 rpm motor

Controls :- Joysticks will be used for each halves Other

Requirements :- Full Wave Rectifier for the conversion of A.C. To D.C.

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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.

• By the development of a bigger model it can be used for transporting man and material through a rough terrain or obstacles containing regions like stairs.

• We could develop it into a Wheel Chair too. It can be send in valleys, jungles or such places where humans may face some danger.

• It can also be developed into Suspension System for the automobile vehicles through proper research.

DESIGN AND FABRICATION OF ROCKER

BOGIE MECHANISM

Calculation-1

1. Diameter of Wheel 100 = πDN/60 DN=1909.86 Selected DN combination: D = 70 mm N = 27.28 rpm 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 18

DESIGN AND FABRICATION OF ROCKER

BOGIE MECHANISM

2. Calculation of Wheel base

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

DESIGN AND FABRICATION OF ROCKER

BOGIE MECHANISM

3. Length of Links

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DESIGN AND FABRICATION OF ROCKER

BOGIE MECHANISM

3. Length of Links

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 BC2 _{= 2(NC)}2 _{… (1)} =2(165)2 =54450 Therefore, BC = 233.33mm Rounding off to 230mm. BC = 230mm

DESIGN AND FABRICATION OF ROCKER

BOGIE MECHANISM

3. Length of Links (Contd)

Substituting to eqn (1) we get, 2302 = 2(NC) 2

NC = 162.63

Also, AN = NC = 162.63

In triangle AMN, angle AMN = 90 AM2 _{+ MN}2 _{= AN}

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 22

DESIGN AND FABRICATION OF ROCKER

BOGIE MECHANISM

4. Height Calculation: Height2 = BC2 – NC2

(2302 _{– 162.63}2₎1/2 _{= 162.639 mm}

Net Height = height + radius = 162.639 + 35 = 197.639 mm 5. Track Width   Tw = 513.86

DESIGN AND FABRICATION OF ROCKER

BOGIE MECHANISM

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Calculation - 2

θ = 25.016

Wheelbase = 300 – 2(35) = 230mm

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.

DESIGN AND FABRICATION OF ROCKER

BOGIE MECHANISM

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Budget and Table of Requirements

S. No Item Qty Material Budget

1 Link 4

Acrylic/Woo

d 500/100

2 Shaft 1 SS 100

3 Nut Bolts /Washers 4/8 SS 50

4 Wheel 6 Plastic 35

5 Motor 6 Alloy 150

       

Electrical

purchase        

S. No Item Qty Budget

1 Transformer 1 150

2 Rectifier 1 20

3 Joystick 2 80

4 PCB 2 50

5 Wires and Cables   150

     

DESIGN AND FABRICATION OF ROCKER

BOGIE MECHANISM

DESIGN AND FABRICATION OF ROCKER

BOGIE MECHANISM

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Structure Without the assembly of motors and wheels

DESIGN AND FABRICATION OF ROCKER

BOGIE MECHANISM

Structure with assembly of all required equipments

DESIGN AND FABRICATION OF ROCKER

BOGIE MECHANISM

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Initial Working of the Mechanism

DESIGN AND FABRICATION OF ROCKER

BOGIE MECHANISM

Working on a Complex Trackl

DESIGN AND FABRICATION OF ROCKER

BOGIE MECHANISM