The document describes the design and fabrication of a rocker bogie mechanism. It discusses: 1) The introduction of the rocker bogie suspension system used on Mars rovers and its ability to maintain contact over uneven terrain. 2) The objectives of the project to optimize speed while preventing flipping and increase cost effectiveness for exploration and other applications. 3) The related concepts of traction, stability, and mobility required for the rover to traverse rough terrain and obstacles. Wheel diameter and RPM calculations are provided to design wheels that can achieve various speeds over different terrains. The requirements, applications, and future scope of the rocker bogie mechanism are also summarized.

1. Anubhav Kumar Deergha Garg
12001004009 12001004015
Nitin Verma Rahul Hans
12001004037 12001004044
Under the Guidance of
Dr. Ajay Kumar
Mechanical Engineering Department
Deenbandhu Chhotu Ram University of Sc. &Tech. Murthal
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DESIGN AND FABRICATION OF ROCKER BOGIE MECHANISM

2. 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

3. 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.
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DESIGN AND FABRICATION OF ROCKER BOGIE MECHANISM

4. 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

5. 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

6. 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

7. 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
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DESIGN AND FABRICATION OF ROCKER BOGIE MECHANISM

8. 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

9. 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
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DESIGN AND FABRICATION OF ROCKER BOGIE MECHANISM

10. 10

11. 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
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DESIGN AND FABRICATION OF ROCKER BOGIE MECHANISM

12. 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

13. 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

14. 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

15. Wheel Design
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
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DESIGN AND FABRICATION OF ROCKER BOGIE MECHANISM

16. 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

17. 17
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

18. 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
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DESIGN AND FABRICATION OF ROCKER BOGIE MECHANISM

19. 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

20. 3. Length of Links
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DESIGN AND FABRICATION OF ROCKER BOGIE MECHANISM

21. 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
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DESIGN AND FABRICATION OF ROCKER BOGIE MECHANISM

22. 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
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DESIGN AND FABRICATION OF ROCKER BOGIE MECHANISM

23. 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
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DESIGN AND FABRICATION OF ROCKER BOGIE MECHANISM

24. 24
Calculation - 2
θ = 25.016
Wheelbase = 300 – 2(35)
= 230mm
DESIGN AND FABRICATION OF ROCKER BOGIE MECHANISM

25. 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

26. 26
Budget and Table of Requirements
S. No Item Qty Material Budget
1 Link 4 Acrylic/Wood 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

27. 27
Dimensions
Wheel Thickness 40mm
Wheel Diameter 70 mm
Height 185mm
Wheel Base 360mm
Track Width 400mm
SSF 1.08
Bogie Dimensions 140mm
Rocker Dimensions260mm
DESIGN AND FABRICATION OF ROCKER BOGIE MECHANISM

28. 28
Structure Without the assembly of motors and wheels
DESIGN AND FABRICATION OF ROCKER BOGIE MECHANISM

29. 29
Structure with assembly of all required equipments
DESIGN AND FABRICATION OF ROCKER BOGIE MECHANISM

30. 30
Initial Working of the Mechanism
DESIGN AND FABRICATION OF ROCKER BOGIE MECHANISM

31. 31
Working on a Complex Trackl
DESIGN AND FABRICATION OF ROCKER BOGIE MECHANISM