DESIGN AND FABRICATION OF ROCKER BOGIE 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
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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. 3
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. 4
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.
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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 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 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 8 the interaction of two surfaces
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 9
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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
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)
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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
Diamete r M
cm
10
0.153
20
10cm/s
Velocity
Diamete r m
cm
15.277
10
0.191
0.076
7.638
20
30
0.051
5.092
40
0.038
50
12cm/s
Diamete r m
cm
19.096
10
0.229
22.915
0.095
9.548
20
0.115
11.458
30
0.064
6.365
30
0.076
7.638
3.819
40
0.048
4.774
40
0.057
5.729
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
RPM
RPM
RPM
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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. 17
DESIGN AND FABRICATION OF ROCKER BOGIE MECHANISM
Calculation-1
1. Diameter of Wheel 100 = πDN/60 DN=1909.86 D 10 20
Selected DN combination: 190.99 D = 70 mm 95.49 N = 27.28 rpm N
30
63.66
40
47.75
50
38.2
60
31.83
70
27.28
80
23.87
90
21.22
100
19.1
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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
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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 =2(165)2 =54450 Therefore, BC = 233.33mm
… (1)
Rounding off to 230mm. BC = 230mm 21
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 + MN2 = 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 – 162.632)1/2 = 162.639 mm Net Height = height + radius = 162.639 + 35 = 197.639 mm 5. Track Width
Tw = 513.86 23
DESIGN AND FABRICATION OF ROCKER BOGIE MECHANISM Calculation - 2
θ = 25.016 Wheelbase = 300 – 2(35) = 230mm
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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 Budget and Table of Requirements S. 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. 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
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DESIGN AND FABRICATION OF ROCKER BOGIE MECHANISM
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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
