This document describes the design and fabrication of a rocker bogie mechanism. The rocker bogie system is a suspension used on Mars rovers to allow independent wheel movement over obstacles. The design includes two rocker arms that allow the left and right wheels to climb obstacles individually. Calculations are shown for tilt angle, wheel base, link lengths, and motor specifications. Components include shafts, links, wheels, bearings, and motors. The advantages of the rocker bogie system include its ability to climb obstacles twice the wheel diameter and distribute load evenly across independently moving wheels.
1. DEPARTMENT OF MECHANICAL ENGINEERING
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
DrDr. M.PUVI YARASAN M.E Ph.D (Assistant Professor)
BATCH NUMBER: 76
2. ABSTRACT:
• 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:
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:
•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.
9. VELOCITY 8cm/s VELOCITY 10cm/s VELOCITY 12cm/s
RPM(N) DIA(D) RPM(N) DIA (D) RPM(N) DIA (D)
cm cm cm
10 15.277 10 19.096 10 22.915
20 7.638 20 9.548 20 11.458
30 5.092 30 6.365 30 7.638
40 3.819 40 4.774 40 5.729
50 3.055 50 3.819 50 4.583
60 2.546 60 3.183 60 3.819
70 2.182 70 2.728 70 3.274
80 1.910 80 2.387 80 2.864
We have chosen 30rpm motor.
From the table for 10cm/s ; the wheel diameter is
63.6mm(70mm approx)
Velocity, V =(∏DN)/60
10. CALCULATION OF TILT ANGLE & WHEEL BASE:
Θ=tan-1
(y/x)
Θ=tan-1
(12/40)=16.69⁰
Tilt angle:
Wheel base:
To deduce the wheel base,
Wheel base=Total length - (radius of front wheel + radius of rear wheel)
b=40-(3+3)
b=34cm
11. CALCULATION OF LENGTH OF LINKS:
Length of link AC: Length of link DB:
BC2
=AB2
+AC2
BE2
=DB2
+ED2
402
=2(AB2
) 202
=2(DB2
)
AB=AC=28.2cm(28cm approx) DB=DE=14.1cm(14cm approx)
13. PROCESS INVOLVED:
• Design of bogie
• Welding of links
• Drilling
• Fastening of shaft with links
• Assembly of wheels and motors
• Testing of rig
14. COURTESY: MARS CURIOSITY ROVER
ON ROCKER BOGIE SUSPENSIONCuriosity 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
15. ADVANTAGES:
• 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
16. CONCLUSION:
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. Our concern
during the development of the rover will be to optimize the
speed such that the rover do not flip and may travel a little
faster too and make it cost effective with maximum possible
rigidity and ruggedness. With certain developments the bogie
system can be used for defense related operations and also in
wheelchairs for climbing stairs.
