Rocker Bogie Mechanism Study Guide

DEPARTMENT OF MECHANICAL
ENGINEERING
STUDY OF ROCKER BOGIE MECHANISM
GUIDE:
Mr. DAYAKAR.M
BATCH 10B:
K.PRAVEEN REDDY
(147Y1A0376)
N.SUJITH RANA
(147Y1A0388)
RAGAVENDHRA
(147Y1A0377)

OBJECTIVE :-
Your objective is to study and over come the limitations of rover and use the
mec

INTRODUCTION
• The rocker-bogie system is the suspension arrangement used in the mars rover which was
ﬁrst introduced in the Mars pathfinder rover .
•Its is currently NASA’s samedesign for rover wheel suspension. The intelligently designed
wheel suspension allows the vehicle to travel over 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.
• These mechanism are used in the robots mainly used for tasks which humans cannot do
and which are not safe like space exploration , surveillance in military operation
Bogie

• The term “rocker” comes from the aspect
of the larger links on each side of the
suspension system.
• The term “bogie ” refers to the links that have
a drive wheel at each end. Bogies were commonly
used as load wheels in the tracks of
army tanks as idlers distributing the load over
the terrain.
• These rockers are connected to each other
and the vehicle chassis through a differential

The differential will prevents the rover body from tipping all the way forward and backward.
when one rocker goes up, the other goes down. The chassis maintains the average pitch angle
of both rockers . One end of a rocker is fitted with a drive wheel and the other end is pivoted to
a bogie.

HISTORY
• In 1997, The Mars Pathfinder Sojourner Rover was the first rover ever built with rocker-
bogie mechanism due to terrain surface on the mars.
•In early 2004, NASA again landed two more rovers on Mars, Spirit and Opportunity
which have the same mechanism.
•Most Recently in 2011, NASA has launched the Mars Science Laboratory (MSL) with a
rover named Curiosity.

Curiosity Rover
Curiosity is a car-sized robotic
rover exploring Mars as part of
NASA’ 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

Concepts and Theories

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 and slip will occur.
•In reality it is very challenging to determine the precise friction coefﬁcient μ for
the interaction of two surfaces

Related Concepts & Theories:
Lateral Stability
•The rover is said to be stable when it is in a unbalance 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

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.

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.

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
13

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

KINEMATICS LINKS

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

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

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

ADVANTAGES:-
• The design is simple and reliable.
• Load on each wheel is nearly similar.
• The mechanism allows climbing obstacles twice the size of wheel diameter
• It has no axles and springs which helps to maintain equal traction force on all the wheels.
DISADVANTAGES:-
• 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.

Application & Future Scope
• 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.

CONCLUSION:-
This work shows how rocker bogie system works on different surfaces. As per the
different weight acting on link determines torque applied on it. By assuming accurate
stair dimensions, accurately dimensioned rocker bogie can climb the stair with great
stability. The design and manufactured model can climb the angle up to 45˚.
.

23

Rocker Bogie Mechanism Study Guide

Rocker Bogie Mechanism Study Guide

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