DESIGN AND FABRICATION OFROCKER BOGIE MECHANISM

BYDINESH CM (211414114087)GIRIDHARAN TS (211414114100)HANIROOTH C (211414114115)HARISH T (211414114123)

Under the guidance ofUnder the guidance of

Department of Mechanical engineeringPanimalar Engineering College, Chennai-123

BATCH NUMBER: 76

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.

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) andMars 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

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

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

WORKING OF ROCKER BOGIE MECHANISM:

7

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, 2011Rocket: Atlas VManufacturer: NASAOperator: NASAMission Type :- Mars Exploration

Rover

Launch Mass:- 900 Kg

Max Speed:- 50mm/s

Average Speed :- 10mm/s

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.

COMPONENTS REQUIRED:COMPONENT NAME QUANTITY

SHAFT 1LINK 4

WHEEL 6BEARING 2MOTOR 6

BEARING BUSH 410

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

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 is63.6mm(70mm approx)

Velocity, V =(πDN)/60

12

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

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

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

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

16GROSS WEIGHT OF THE MECHANISM IS 1.323Kg

DIMENSIONS AND MATERIAL SPECIFICATIONS

17

DESCRIPTION DIMENSIONSWheel 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 MATERIALSFrames Mild steel

Shaft Mild steel

Bearings Hardened carbon steel

Bearing housing(bush) Stainless steel EN8

COMPONENTS DIMENSIONShaft 9mm dia.,

400mm length

Frames 1250*25*3mm

Bush 26mm dia.,

100mm length

PART MODEL WITH DIMENSIONS

BEARING BUSH BEARING BUSH

PIN LENGTH PIN DIAMETERPIN LENGTH PIN DIAMETER 18

PART MODEL WITH DIMENSIONS CONTD.

19

ROCKER BOGIEROCKER BOGIE

SHAFT

PART MODEL

20

BEARING ROCKER PINBEARING ROCKER PIN

BOGIE BUSHBOGIE BUSH

SHAFTSHAFT

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.

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 twosupport pins; in general practice, one of the support pinis left unconnected

(contd.)

COST ESTIMATION

23

MATERIAL/COMPONENT NOs COST/UNIT COSTMS Frame 2 Rs.25 Rs.50MS Shaft 1 Rs.30 Rs.30Ball bearing 4 Rs.300 Rs.1200MS Bush rod 1 Rs.30 Rs.30DC Motor 6 Rs.300 Rs.180012V Battery 1 Rs.800 Rs.800Wheels 6 Rs.35 Rs.210PCB 1 Rs.40 Rs.40Wire plug 6 Rs.15 Rs.90Connecting wires 5m Rs.40 Rs.40SPDT switch 3 Rs.5 Rs.15Battery cap 2 Rs.2 Rs.4

COST ESTIMATION

24

PROCESS COST

Frame cutting Rs.50Bush machining Rs.250Welding Rs.100Lathe operation Rs.100Drilling Rs.50

Labor cost:Labor cost:

TOTAL COST ESTIMATION IS Rs.4859

(contd.)

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

FAILURES

26

During the assembly of shaft and the bearing an 8mmDuring the assembly of shaft and the bearing an 8mmMS 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 the of 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.)

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.

FUTURE SCOPE

28

• With the development in technology the rover can be used forreconnaissance 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

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.

Thank you