Suspension system which can handle the harsh environment of Mars.

1. DESIGN AND FABRICATION OF
ROCKER BOGIE MECHANISM
BY
DINESH CM (211414114087)
GIRIDHARAN TS (211414114100)
HANIROOTH C (211414114115)
HARISH T (211414114123)
Under the guidance ofUnder the guidance of
Department of Mechanical engineering
Panimalar Engineering College, Chennai-123
BATCH NUMBER: 76

2. ABSTRACT:
2
• The need to develop a highly stable suspension system
capable of operating in multi terrain surfaces while keeping all
the wheels in contact with the ground.
• To design a mechanism that can traverse terrains where the left
and right rockers individually climb different obstacles.
• To sustain a tilt of over 50deg without tipping over the
sideways.

3. INTRODUCTION:
3
• The Rocker bogie system is the suspension arrangement
used in Mars rovers introduced for Mars Pathfinder and
also used on Mars Exploration Rover(MER) and
Mars Science Laboratory(MSL) missions
• This bogie can resist mechanical failures caused by the
harsh environment on MARS
• The primary mechanical feature of
the Rocker Bogie design is it’s drive train simplicity, which is
accomplished by two rocker arms

4. PRINCIPLE:
4
•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.

5. 5

6. ADVANTAGES:
6
• This mechanism allows climbing obstacles twice the size of
wheel diameter
• Does not employ springs and stub axles
• Equal distribution of load on all wheels
• Independent movement of rocker on either sides of the bogie
• The front and back wheels have individual drives for
climbing, enabling the rover to traverse obstacle without
slip
• The design is simple and reliable

7. WORKING OF ROCKER BOGIE MECHANISM:
7

8. COURTESY: MARS CURIOSITY ROVER
ON ROCKER BOGIE SUSPENSION
8
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

9. 9
APPLICATIONS
•RBM was employed in Viking 1 & Viking 2 space landers of NASA in 1996.
•In 1997, The Mars Pathfinder (MPF) lander delivered the Sojourner Rover
to the surface successfully which was mounted on this bogie system.
•Two other Mars rovers namely Spirit and Opportunity launched by NASA in
early 2004 was also built on RBM.
•Most Recently in 2011, RBM was used in NASA’s Mars Science Laboratory
(MSL) with a rover named Curiosity rover.

10. COMPONENTS REQUIRED:
COMPONENT NAME QUANTITY
SHAFT 1
LINK 4
WHEEL 6
BEARING 2
MOTOR 6
BEARING BUSH 4
10

11. PROCESS INVOLVED:
11
• Design of bogie
• Cutting of links
• Welding of links and bushes
• Drilling
• Facing and turning of shaft
• Assembly of wheels, motor, bearing, shaft,
pin.
• Soldering in power distribution circuit
• Testing of Rig

12. VELOCITY 80mm/s VELOCITY 100mm/s VELOCITY 120mm/s
SPEED(N) DIA(D) SPEED(N) DIA (D) SPEED(N) DIA (D)
rpm mm rpm mm rpm mm
10 152.77 10 190.96 10 229.15
20 76.38 20 95.48 20 114.58
30 50.92 30 63.65 30 76.38
40 38.19 40 47.74 40 57.29
50 30.55 50 38.19 50 45.83
60 25.46 60 31.83 60 38.19
70 21.82 70 27.28 70 32.74
80 19.10 80 23.87 80 28.64
We have chosen 30rpm motor.
From the above table for 100mm/s ; the wheel diameter is
63.6mm(70mm approx)
Velocity, V =(πDN)/60
12

13. CALCULATION OF TILT ANGLE & WHEEL BASE:
Θ=tan-1
(y/x)
Θ=tan-1
(120/400)=16.69⁰
Tilt angle:
Wheel base:
To deduce the wheel base,
Wheel base=Total length - (radius of front wheel + radius of rear wheel)
b=400-(35+35)
b=330mm
13

14. CALCULATION OF LENGTH OF LINKS:
Length of link AC: Length of link DB:
BC2
=AB2
+AC2
BE2
=DB2
+ED2
4002
=2(AB2
) 202
=2(DB2
)
AB=AC=282mm DB=DE=141mm
14

15. HEIGHT AND TRACK WIDTH CALCULATION
 HEIGHT CALCULATION
Height2
= AC2
– EC2
(2802
– 2002
)1/2
= 195.95mm
Net Height = height + radius
= 195.95 + 35
= 230.95mm.
TRACK WIDTH CALCULATION
SSF = Tw/(2h)
0.5= Tw/ (2*230.95)
Tw= 230.95mm
15

16. GROSS WEIGHT CALCULATION
 MASS = VOLUME X DENSITY
DENSITY OF MILD STEEL = 0.00785 g/mm3
1)Weight of rocker arms = 2[(320*25*3*0.00785) +
(200*25*3*0.00785)] = 612.3gm
2)Weight of bogies = 2[2*(180*25*3*0.00785)] = 423.9gm
3)Weight of shaft = [(π/4)*9*9*230*0.00785) = 114.8gm
4)Weight of pin = 2*[2((π/4)*8*8*7*0.00785) +
((π/4)*9*9*7*0.00785)] = 18.02gm
5)Weight of bearings = 4*10 = 40gm
6)Weight of bush = 4*28.7 = 114.8gm
 Total weight = 612.3+423.9+114.8+18.02+40+114.8
=1323.82gm
16
GROSS WEIGHT OF THE MECHANISM IS 1.323Kg

17. DIMENSIONS AND MATERIAL SPECIFICATIONS
17
DESCRIPTION DIMENSIONS
Wheel Thickness 20mm
Wheel Diameter 70mm
Height 230mm
Wheel Base 340mm
Track Width 231mm
Bogie length 141mm
Rocker length 282mm, 141mm
Bearing ID 8mm OD 22mm
Bearing bush ID 22mm OD 26mm
Shaft diameter 9mm
Shaft length 230mm, 18mm
COMPONENTS MATERIALS
Frames Mild steel
Shaft Mild steel
Bearings Hardened carbon steel
Bearing housing(bush) Stainless steel EN8
COMPONENTS DIMENSION
Shaft 9mm dia.,
400mm length
Frames 1250*25*3mm
Bush 26mm dia.,
100mm length

18. PART MODEL WITH DIMENSIONS
BEARING BUSHBEARING BUSH
PIN LENGTH PIN DIAMETERPIN LENGTH PIN DIAMETER 18

19. PART MODEL WITH DIMENSIONS CONTD.
19
ROCKER BOGIEROCKER BOGIE
SHAFT

20. PART MODEL
20
BEARING ROCKER PINBEARING ROCKER PIN
BOGIE BUSHBOGIE BUSH
SHAFTSHAFT

21. POWER DISTRIBUTION CIRCUIT
21
• The power from the battery is equally distributed to all the six
motors through the power distribution circuit
• Negative terminals make 1 solder joint; positive terminals from 3
motors from both side make 2 solder joints with 3 SPDT switches
• The direction of the motor rotation is reversed by changing the
input poles from the battery
• Drawback of this circuit is the heating of the connecting wires due
to the failure in calculating the resistance of the wires for 12V.

22. POWER DISTRIBUTION
CIRCUIT
22
• Most common SPDT slide switch is used
• A Single Pole Double Throw(SPDT) individually controls a
single circuit as for single throw and has two positions(ON/OFF)
as for double throw
• SPDT switch has 3 terminals one common pin and two
support pins; in general practice, one of the support pin
is left unconnected
(contd.)

23. COST ESTIMATION
23
MATERIAL/COMPONENT NOs COST/UNIT COST
MS Frame 2 Rs.25 Rs.50
MS Shaft 1 Rs.30 Rs.30
Ball bearing 4 Rs.300 Rs.1200
MS Bush rod 1 Rs.30 Rs.30
DC Motor 6 Rs.300 Rs.1800
12V Battery 1 Rs.800 Rs.800
Wheels 6 Rs.35 Rs.210
PCB 1 Rs.40 Rs.40
Wire plug 6 Rs.15 Rs.90
Connecting wires 5m Rs.40 Rs.40
SPDT switch 3 Rs.5 Rs.15
Battery cap 2 Rs.2 Rs.4

24. COST ESTIMATION
24
PROCESS COST
Frame cutting Rs.50
Bush machining Rs.250
Welding Rs.100
Lathe operation Rs.100
Drilling Rs.50
Labor cost:Labor cost:
TOTAL COST ESTIMATION IS Rs.4859
(contd.)

25. FAILURES
25
Initially the rocker and bogie link are
made from 1mm thickness stainless
Steel sheets; Which resulted in failure
due to bending of the links which was
the effect of drilling operation and
excessive load condition.
A bearing was lost due to the
uneven and irregular fitting of the
Shaft and bush. The bearing was
Broke to disassemble the bearing
bush and the shaft

26. FAILURES
26
During the assembly of shaft and the bearing an 8mmDuring the assembly of shaft and the bearing an 8mm
MS rod was found to be a loose fit with a 8mm ID bearing.MS rod was found to be a loose fit with a 8mm ID bearing.
This was a failure due to error in measuring the diameterThis was a failure due to error in measuring the diameter
of the rod during purchase. Due to presence of chip at theof the rod during purchase. Due to presence of chip at the
tip of the rod; it was wrongly measured as 8mm;tip of the rod; it was wrongly measured as 8mm;
but was actually 7.5mm.but was actually 7.5mm.
(contd.)

27. CONCLUSION:
27
• The various components of the rocker bogie is assembled and the
total weight of the frames and shaft is calculated to be 1.3Kg.
• In reference to the specification of the DC motor, the allowable net
reaction on the motor is 1.5Kg. Hence the design is safe.
• This is a wide field of study which is very less explored. So this gave us
the motivation for the development of this rocker bogie suspension
system in a cost effective manner.
• In future rocker bogie mechanism can be used in defense related
operations and also in wheelchairs for climbing stairs.

28. FUTURE SCOPE
28
• 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
• By the development of a bigger model it can be used for
transporting humans and material through a rough terrain
or obstacles containing regions like stairs
• It can also be used for geological mapping of unknown terrains
as it can even provide live video feed and images of the
terrains being explored

29. REFERENCES
29
• "NASA Patent Abstracts Bibliography, Section 1. Abstracts”
June 1990: 19. ARTICULATED SUSPENSION SYSTEM
• IOSR Journal of Mechanical and Civil Engineering (IOSR-JMCE)
e-ISSN:2278-1684, p-ISSN:2320-334X, Vol. 12,
Issue 3 Ver. III (May-June 2015) , PP64-67
• Synge J L and B A Griffiths : Principles of Mechanics,
Section 6.3, McGraw-Hill Kogakusha Ltd,3rd Edition, 1970.

30. Thank you