The multi terrain hexapod works on the principle of bogie-rocker mechanism. It is a very hot topic of research and offers a wide range for engineering and research in this space rober field. it can find its use in domestic purpose as well.

1. DEPARTMENT OF MECHANICAL ENGINEERING
DESIGNAND FABRICATION OF ALLTERRAIN HEXAPOD
(USING ROCKER-BOGIE MECHANISM)
PRESENTED BY:
NIRANJAN KUMAR (BE/6054/14)
ASHISH KUMAR (BE/6053/14)
MUKESH KUMAR (BE/6055/14)
ANUJ KUMAR (BE/6059/14)
ANIMESHGAUTAM(BE/6051/14)
UNDERTHE GUIDANCE OF: Dr. ABHISHEK KUMAR SINGH
BIRLA INSTITUTE OFTECHNOLOGY, MESRA

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 45deg without tipping over the
sideways.
 The rocker-bogie suspension system is NASA’s favored
design for wheeled mobile robot mainly because it has
robust capabilities to deal with obstacles and because it
uniformly distributes the payload over its six wheels.

3. INTRODUCTION
 The Rocker-bogie system is the suspension
arrangement used in Mars rover introduced for
Mars Pathfinder.The primary mechanical
feature of this arrangement is it’s drive train
simplicity, which is accomplished by its two
rocker arms.

4. OBJECTIVE
The objective of this project is to design a small,
robust and easy to steer and handle rover robot.
It will be designed for working on different
platforms like rough terrains, smooth surfaces,
overcoming obstacles in its path and climbing
over obstacles of certain height.

5. WORKING 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 wheels then lifts the front of the vehicle up and
over the obstacle.
 The middle wheel is 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 wheels 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
obstacles one portion at a time.

6. 2D CAD MODEL

7. RELATED CONCEPT AND THEORIES
Traction and Slip
 The rover must maintain good wheel traction in overcoming rough terrains.
 If traction is too high, the vehicle will consume lot of power in order to overcome the
force and move.
 If traction is too low, the rover will not be 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 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 difficult to determine the precise friction coefficient μ for the interaction
of two surfaces.

8. Lateral stability
 The rover is said to be stable when it is in quasi-static
state in which it does not tilt over.
 The lateral stability of rover ensures that the rover
does not tilt sideways.
 Lateral stability is computed by finding the
minimum allowed angle on the slope before the
rover tips over.
 Lateral stability of rover is ensured if the overall
stability angle
θstab ≥ α
∴ min(θr, θl) ≥ α

9. Lateral stability

10. Longitudinal stability
 Longitudinal stability of the vehicle is given
when all wheels have ground contact and the
condition Ni > 0 is satisfied, where Ni is normal
force at wheel i.
 Even though this condition is necessary for ideal
model to work, a physical rover does not
necessarily tip if a wheel loses contact to the
ground however it is less steerable.

11. Static Stability Factor(SSF)
 The static stability factor(SSF) of a vehicle is one
half the track width divided by height of the
center of gravity above the road.
 The inertial force which causes a vehicle to sway
on its suspension and rollover in extreme cases
in response to conditions such as cornering,
rapid steering reversals when sliding laterally
may be thought of as a force acting at the CoG
to pull the vehicle body laterally.
SSF=TW/(2*h)

16. PHYSICAL MODEL FOR STUDY PURPOSE

17. THE END