General Electric Electrical Energy

Design and Fabrication

Six Legged Kinematic Moving

Mechanism

A PROJECT REPORT

Submitted by

Prasanth.L,

Venkatesh.M(211*********)

Prasanth.P,

Vinoth.R

In partial fulfillment for the award of the degree

Of

BACHELOR OF ENGINEERING

IN

MECAHANICAL ENGINEERING

PANIMALAR ENGINEERING COLLEGE, CHENNAI

ANNAUNIVERSITY: CHENNAI 600 025

APRIL 2018

BONAFIDE CERTIFICATE

Certified that this project report “DESIGN AND FABRACATION OF SIX LEGGED KINEMATIC MOVING MECHANISM” is the bonafide work of “Prasanth.L(211415114),Venkatesh.M(211*********),Prasanth.P(211415114),Vinoth.R(211415114)” that carried out the project under my supervision.

SIGNATURE SIGNATURE

Dr. L.Karthikeyan M.Tech., Ph.D Mr. J.GUNASEKHAR M.E,

HEAD OF THE DEPARTMENT SUPERVISOR

ASST.PROFESSOR

Dept. of Mech. Engg., Dept. of Mech. Engg.,

Panimalar Engg.College, Panimalar Engg. College,

Bangalore Trunk Road, Bangalore Trunk Road,

Nazarathpettai, Nazarathpettai,

Poonamallee, Poonamallee,

Chennai-602103. Chennai-602103.

Certified that the candidates were examined in Viva-Voce in the examination held on

INTERNAL EXAMINER EXTERNAL EXAMINER

ACKNOWLEDGEMENT

We wish to express our sincere thanks to Our Founder and Chairman, Thiru.Dr.JEPPIAAR, M.A., B.L., Ph.D., for his endeavor in educating us in his premier institution.

We would like to express deep gratitude to Our Secretary and Correspondent, Thiru.Dr.P.CHINNADURAI, M.A., M.Phil., B.Ed., Ph.D., for his kind words and enthusiastic motivation which inspired us a lot in completing this project.

We express our sincere thank Our Directors Mrs.C.VIJAYA RAJESWARI, and Mr. C.SAKTHI KUMAR, M.E., for providing us with the necessary facilities for completion of this report.

We would like to express our gratitude to Our Principal, Dr.Mani, M.E, Ph.D., for his encouragement and sincere guidance.

We wish to convey our thanks and gratitude to Dr.L.Karthikeyan, M.Tech., Ph.D., HOD, Department of MECHANICAL ENGINEERING and our dedicated guide Mr J.GUNASEKHAR M.E., Asst.Professor, Department of MECHANICAL ENGINEERING for providing us with ample time and encouragement for successful completion of the project.

We also thank All Our Department Staffs who stood by us in every means to finish this project.

We are very much thankful to our beloved PARENTS who helped us financially and supportive for us to finish this project successfully.

ABSTRACT

Mechanical engineering is not more involved in robotics since mechatronics and robotics found a vast application in implementing the concept of running a robot model using servo motors and drives, since it needs more amount of energy to run the robot model. The two six legged walker is linked by using link mechanism and by coupling two kinematic walker with separate motor for each walker. By using separate motor we can run each walker in desired position like front and back, thereby we can able to control the walker

to turn left and griht motion.

This project presents the kinematics of the movement for a six- legged mobile robot, inspired from the living world, as well as the command and control system, which allow the robot to move on different surfaces with different

speeds. For generating the movement, through a command and control system, stepping motors and bars are used. A frame, connecting rod, crank and a lever constitute to obtain the required motion. In this project, the application of simple

four bar mechanism is used. The most important benefit of this mechanism is that, it does not require microprocessor, controller and other actuator mechanisms.

TABLE OF CONTENTS

Chapter Title Page No:

ABSTRACT i

LIST OF FIGURES v

LIST OF TABLES vi

LIST OF SYMBOLS vii

1. INTRODUCTION 01

1.1Introduction 01

1.2 Legged Mechanism 02

2. LITERATURE REVIEW 05

2.1 History of Legged Mechanism 05

2.2 Literature Review 07

2.3 Project Summary 07

3. PROBLEM STATEMENT AND METHODOLOGY 14

3.1 Problem Statement 14

3.2 Methodology 14

4. DEVELOPMENT OF THE SIX LEGGED 22

KINEMATIC MOVING MECHANISM

4.1 Main components 22

4.2 Aluminium Bars 23

4.3 Supporting Bars 24

4.4 Leg Linkage 25

4.5 Legs 25

4.6 Connector between the connecting rod and legs 27

4.7 Motor 27

4.8 Chain and sprocket

4.9 Threaded rod

5. DESIGN PROCEDURE 28

5.1 Construction 28

5.2 Working of Legged Mechanism 32

5.3 Design Calculation 34

5.3.1 CALCULATION OF

DEGREES OF FREEDOM

5.3.2 CALCULATION OF GEARS

5.3.3 DESIGN CALCULATION

6. DISCUSSION 45

6.1 Obstacle Clearance 46

6.2 Applications 49

6.3 Advantages 50

7. CONCULSION 59

FUTURE SCOPE OF WORK 60

REFERENCES 62

PHOTOGRAPHS

LIST OF FIGURES

Figure No Title Page No

1.1 Methodology 03

2.1 Six Legged Robot 06

2.2 Simplified frontal view of the mechanism 06

2.3 Parallel Flow & Counter Flow Arrangements 08

2.4 Flat Aluminium Bars 09

5.1 Supporting Bars 28

5.2 Motor 30

5.3 Chain and Sprocket 33

6.1 Chain 45

LIST OF SYMBOLS

n Degree of freedom

l Number of links

j Number of binary joints

d1 Pitch Diameter

DP Diametric Pitch

Do Outside Diameter

a Addendum

d Dedendum

l Length

b Breath

t Thickness

d Depth

CHAPTER 1

1.1 INTRODUCTION

Generally the walking mechanisms are developed by imitating natures like insects movement. The nature inspired the researchers and new innovative ideas come in mind but sometimes they are simple and effective, sometimes cumbersome and critical. One of the first walking machines was developed in about 1870 by Russian Mathematician Chebyshev. This walking machine had four legs arranged into pairs. Legged machine have been used for at least a hundred years and are superior to wheels. Legged locomotion should be mechanically superior to wheeled or to tracked locomotion over a variety of soil conditions and certainly superior for crossing obstacles. US army investigation reports that about half the earth surface is inaccessible to wheeled tracked vehicles, whereas this terrain is mostly exploited by legged animals. Wheeled robots are the simplest and cheapest also tracked robots are very good for moving, but not over almost all kinds of terrain. There are different types of legged walking robots. They are roughly divided into groups according to the number of legs they possess. Bipeds have two legs, quadrupeds four, hexapods six and octopods have eight legs. Bipeds robots are dynamically stable, but statically unstable, such robots are harder to balance, and dynamic balance can only be achieved during walking. Hexapods are six legged robots, on the other hand, have advantages of being statically stable. During walking they can move three legs at a time, thus leaving three other legs always on the ground forming a triangle.

1.2 Legged mechanism

The main advantage of legged robots is their ability to access places impossible for wheeled robots. By copying to the physical structure of legged animals, it may be possible to improve the performance of mobile robots. To provide more stable and faster walking, scientists and engineers can implement the relevant biological concepts in their design. The most forceful motivation for studying legged robots is

To give access to places which are dirty

To give access to places those are dangerous

Job which are highly difficult

Legged robots can be used for rescue work after earthquakes and in hazardous places such as the inside of a nuclear reaction, giving biologically inspired autonomous legged robots great potential. Low power consumption and weight are further advantages of walking robots, so it is import ants to use the minimum number of actuators. In this context, an objectives is set in this project to develop a six- legged mobile robot whose structure is based on the biomechanics of insects

CHAPTER 2

2.1 History of Legged Mechanism

The scientific study of legged locomotion began just very a century ago when Leland Stanford, then governor of California, commissioned Edward Muyridge to find out whether or not a trotting horse left the ground with all four feet at the same time. Stanford had wagered that it never did. The study of machines that walk also had its origin in Muybridge’s time. An early walking model appeared in about. It used a linkage to move the body along a straight horizontal path while the feet moved up and down to exchange support during stepping. The linkage was originally designed by the famous Russian mathematician Chebyshevsome years earlier. During the 80 or 90 years that followed, workers viewed the task of building walking machines as the task of designing linkages that would generate suitable stepping motions when driven by a source of power.

Many designs were proposed but the performance of such machines was limited by their fixed patterns of motion, since they could not adjust to variations in the terrain by placing the feet on the best footholds. By the late 1950 s, it had become clear that linkages providing fixed motion would not suffice and that useful walking machines would need control. One approach to control was to harness a human. Ralph Mosher used this approach in building a four-legged walking truck at General Electric in the mid-1960s.The project was part of a

decade-long campaign to build advanced operators, capable of providing better dexterity through high-fidelity force feedback. The machine Mosher built stood 11 feet tall, weighed 3000 pounds, and was powered hydraulically. Each of the driver s limbs was connected to a handle or pedal that controlled one of the truck s four legs. Whenever the driver caused a truck leg to push against an obstacle, force feedback let the driver feel the obstacle as though it were his or her own arm or leg doing the pushing. After about 20 hours of training, Mosher was able to handle the machine with surprising agility. Films of the machine operating under his control show it ambling along at about 5 MPH, climbing a stack of railroad ties, pushing a foundered jeep out of the mud, and maneuvering a large drum onto some hooks. Despite its dependence on a well-trained human for control, this walking machine was a landmark in legged technology.

Computer control became an alternative to human control of legged vehicles in the 1970s. Robert McGhee s group at the Ohio State University was the first to use this approach successfully. In 1977 they built an insect like hexapod that could walk with a number of standard gaits, turn, walk sideways, and negotiate simple obstacles. The computer s primary task was to solve kinematic equations in order to coordinate the 18 electric motors driving the legs. This coordination ensured that the machine s center of mass stayed over the polygon of support provided by the feet while allowing the legs to sequence through a gait. The machine traveled quite slowly, covering several yards per minute. Force and visual sensing provide a measure of terrain accommodation in later developments.

The hexapod provided McGhee with an excellent opportunity to pursue his earlier theoretical findings on the combinatorics and selection of gait .The group at Ohio State is currently building a much larger hexapod (about 3 tons), which is intended to operate on rough terrain with a high degree of autonomy . Gurfinkel and his co-workers in the USSR built a machine with characteristics and performance quite similar to McGhee s at about the same time .It used a hybrid computer for control,

with heavy use of analog computation for low-level functions. Hirose realized that linkage design and computer control were not mutually exclusive. His experience with clever and unusual mechanisms he had built seven kinds of mechanical snakes-led to a special leg that simplified the control of locomotion and could improve efficiency. The leg was a three dimensional pantograph that translated the motion of each actuator into a pure Cartesian translation of the foot.

With the ability to generate x, y, and z translations of each foot by merely choosing an actuator, the control computer was freed from the arduous task of performing kinematic solutions. The mechanical linkage was actually helping to perform the calculations needed for locomotion. The linkage was efficient because the actuators performed only positive work in moving the body forward. Hirose used this leg design to build a small quadruped, about one yard long. It was equipped with touch sensors on each foot and an oil-damped pendulum attached to the body. Simple algorithms used the sensors to control the actions of the feet. For cleared the obstacle, the cycle would repeat.

The use instance, if a touch sensor indicated contact while of several simple algorithms like this one permitted the foot was moving forward, the leg would move Hirose s machine to climb up and down stairs and to backward a little bit, move upward a little bit, then negotiate other obstacles without human intervention resume its forward motion, if the foot had motion. These three walking machines, McGhee s, Gurfinkel s, and Hirose s, represent a class called static crawlers. Each differs in the details of construction and in the computing technology used for control, but shares a common approach to balance and stability. Enough feet are kept on the ground to guarantee a broad base of support at all times, and the body and legs move to keep the center of mass over this broad support base. The forward velocity is kept sufficiently low so that stored energy need not be figured into the stability calculation. Each of these machines has been used to study rough terrain locomotion in the laboratory through experiments on terrain sensing, gait selection and selection of foothold sequences.

2.2Literaturereview

Normally six bar mechanism is chosen for moving leg robot because of its superior force-transmission angle and bigger oscillating angle in comparison with other types such as the four-bar mechanism. Force transmission is very important for leg mechanisms, because of the point contact with the ground. The leg mechanism itself has one DOF for lifting, whilst the base of mechanism has another DOF for swinging. The body size and link dimensions are determined from the maximum swing and lift angles. Each link is created by entering its shape and reference coordinates. To mate the contact surfaces of the parts, the assembly bar of the assembly mating menu is used. Then the component is rotated around an axis, specifying the desired axis and rotation for the selected surfaces [1]. Yoseph Bar-Cohen, in his report named -Biomimetics: mimicking and inspired-by biology, discussed that how the evolution of nature led to the introduction of highly effective and power efficient biological mechanisms. Imitating these mechanisms offers enormous potentials for the improvement of our life and the tools we use [2]. Shibendu Shekhar Roy, Ajay Kumar Singh, and Dilip Kumar Pratihar, in their paper, highlighted the analysis of Six-legged Walking Robots and the attempt made to carry out kinematic and dynamic analysis of a six-legged robot. A three-revolute (3R) kinematic chain has been chosen for each leg mechanism in order to mimic the leg structure of an insect [3]. Patil Sammed Arinjay and Khotin developed Bio-Mimic Hexapod and explained Dynamic Modeling and Control in Operational Space of a Hexapod Robot and comments the real times application of hexapod robot for control. Based on an operational trajectory planner, a computed torque control for the leg of hexapod robot is presented. This approach takes into account the real time force distribution on the robot legs and the dynamic model of the hexapod. First, Kinematic and

dynamic modeling are presented. Then, a methodology for the optimal force distribution is given. The force distribution problem is formulated in terms of a nonlinear programming problem under equality and in equality

on straits. The friction on strains is transformed from nonlinear inequalities into a combination of linear equalities and linear inequalities. Simulations are given in order to show the effectiveness of the proposed approach [4].

Gabriel Martin Nelson, in his report titled Learning about Control of Legged Locomotion using a Hexapod Robot with Compliant Pneumatic actuators; he describes efforts to get a biologically-inspired hexapod robot, Robot III, to walk. Robot III is a pneumatically actuated robot that is a scaled-up model of the Blaberus discoidalis (cockroach). It uses three-way solenoid valves, driven with Pulse- Width-Modulation, and off-the shelf pneumatic cylinders to actuate its 24 degrees of freedom. Single-turn potentiometers and strain gage load cells provide joint angle and three axis foot force sensing respectively.

2.3 Project summary

Literature review reveals that legged robots have ability to access places which are impossible for wheeled robots. By copying to the physical structure of legged animals, it may be possible to improve the performance of the mobile robots. By implementing relevant biological concepts in the design, more stable and faster walking robots could be developed. Based on the results of literature review, an attempt is made in this project to develop a six- legged mobile robot.

CHAPTER 3

PROBLEM STATEMENT AND METHODOLOGY

3.1 Problem Statement

Literature review reveals that the main concern with the moving leg mechanism is the number of links involved in the design of the structure, since the numbers of links are more it is very tedious to design and operate. For the machine to move in a smooth manner the dimensions of the pieces should precise. More priority should be given to the position of the holes to be drilled since the movement depends on the amount of power or motion which is transferred to the locomotive parts respective to the position of the drills. The key to success for this mechanism is for the designer to make it locomotive even in the roughest of terrains thus the legs form an integral part and should be designed more cautiously. An objective is set to develop a six- legged mobile robot in this project.

3.2 Methodology

Fig.1 Methodology

CHAPTER 4

DEVELOPMENT OF THE SIX LEGGED

KINEMATIC MOVING MECHANISM

The six legged robot developed in this project is shown in Figure.1 below.

Fig.2 Six Legged Robot

Consists of flat aluminium bars, a chain and sprocket arrangement, motor connected to give the required motion. This figure shows the simplified diagram of the project drawn using AutoCAD.

4.1 Main components

Details of the major components used in the six legged kinematic moving robot are listed below. Aluminium bar, Supporting bars, Leg Linkage, Leg Connector between the connecting rod and leg, Motor, Chain, Sprocket, Threaded rod.

4.2 Aluminium bars

Aluminium is a silvery white, soft, non-magnetic, ductile metal. Aluminium is the third most abundant element (after oxygen and silicon), and the most abundant metal in the Earth's crust. It makes up about 8% by weight of the Earth's solid surface. Aluminium is remarkable for the metal's low density and for its ability to resist corrosion due to the phenomenon of passivation. Corrosion resistance can be excellent due to a thin surface layer of aluminium oxide that forms when the metal is exposed to air, effectively preventing further oxidation. The strongest aluminium alloys are less corrosion resistant due to galvanic reactions with alloyed copper. This corrosion resistance is also often greatly reduced by aqueous salts, particularly in the presence of dissimilar metals. Aluminium is usually alloyed – it is used as pure metal only when corrosion resistance and/or workability are more important than strength or hardness. The strength and durability of aluminium alloys vary widely, not only as a result of the components of the specific alloy, but also as a result of heat treatments and manufacturing processes. The main reason for choosing aluminium is that it is light in weight and light weight ultimately increases the efficiency of the machine. The low density of aluminium accounts for it being lightweight but this does not affect its strength.

Fig.4 Flat Aluminium Bars

4.3 Supporting Bars

The supporting bars are usually aluminium bars of length 25cm and width 2cm.The mechanism usually consists of a four supporting rods of suitable gaps. They determine the overall width of the mechanism. They act as a support for the entire arrangement comprising of connecting rod, legs and motor. Drills are made at suitable areas in coherence with the position of the holes in the connecting rod and the legs. The thickness of these bars is usually less to increase the ease of drilling and to reduce the weight.

Fig.5 Supporting Bars

4.4 Leg linkage

In a reciprocating piston engine, the connecting rod connects the piston to the crank or crankshaft. Together with the crank, they form a simple mechanism that converts reciprocating motion into rotating motion. In the same way it transfers the motion or power from the threaded stud to the legs. Connecting rods are used to convert rotating motion into reciprocating motion. The entire mechanism consists of six connecting rods connected between the stud and the leg. The length of the connecting rod is varied with respect to the dimensions of the leg. The ends need not be well polished like the legs since it does not involve any contact with the ground. Here the stud acts as the crank which receives power from the motor. Holes are made at both the ends of the connecting rod.

4.5 Legs

A mobile robot needs locomotion mechanisms to make it enable to move through its environment. There are several mechanisms to accomplish this aim; for example one, four, and six legged locomotion and many configurations of wheeled locomotion. The focus of this elaboration is legged and wheeled locomotion. Legged robot locomotion mechanisms are often inspired by biological systems, which are very successful in moving through a wide area of harsh environments. To make a legged robot mobile each leg must have at least two degrees of freedom. It is very difficult to copy these mechanisms for several reasons. The main problems are the mechanical complexity of legs, stability and power consumption. For each loco motion concept, doesn t matter if it is

wheeled, leg or a different concept, there are three core issues: stability, the characteristics of ground contact and the type of environment. When the surface becomes soft wheeled locomotion offers some inefficiency, due

to increasing rolling friction more motor power is required to move. It is proven that legged locomotion is more power efficient on soft ground than wheeled locomotion, because legged locomotion consists only of point

contacts with the ground and the leg is moved through the air. This means that only a single set of point contacts is required, so the quality of the ground does not matter, as long as the robot is able to handle the ground. But

exactly the single set of point contacts offers one of the most complex problems in legged locomotion, the stability problem. Stability is of course a very important issue of a robot, because it should not overturn. Stability can be divided into the static and dynamic stability criterion. Static stability means that the robot is stable, with no need of motion at every moment of time. To achieve statically stable walking a robot must have a minimum number of four legs, because during walking at least one leg is in the air. Statically stable walking means that all robots motion can be stopped at every moment in the gait cycle without overturning. Most robots which are able to walk static stable have six

legs, because walking static stable with four legs means that just one leg can be lifted at the same time (lifting more legs will reduce the support polygon to a line), so walking becomes slowly. To move a leg forward at least two degrees of freedom are required, one for lifting and one for swinging. Most legs have three

degrees of freedom; this makes the robot able to travel in rougher terrain and to do more complex maneuvers. But adding degrees of freedom causes also some disadvantages, because for moving additional joints and more servos are required, this increases the power consumption and the weight of the robot. Furthermore controlling the robot becomes more complex, because more motors have to be controlled and actuated at the same time. Six legged locomotion is the most popular legged locomotion concept because of the ability of static stable walking.

The most used static stable gait is the tripod gait, where each times the two exterior legs on the one side and the inner leg of the other side are moved together.

4.6 Connector between the connecting rod and leg

It is a flat aluminium bar of length 4cm, it provides a contact between the supporting bar, connecting rod and the leg .It ensures that the motion is transmitted in the correct manner. Holes are drilled at both the sides of the bar and one end is bolted with the frame and the other end with the leg and connecting rod. The size of this part should precise because any small alternation in length may lead to improper motion transfer resulting in malfunction of the machine and also unwanted interference between the moving parts.

4.7 Motor

An electric motor is an electrical machine that converts electrical energy into mechanical energy. A fractional horsepower motor (FHP) is an electric motor with a rated output power of 746 Watts or less. There is no defined minimum output, however, it is generally accepted that a motor with a frame size of less than 35mm square can be referred to as a 'micro-motor'. Servo motors and stepper motors are specialist types of fractional horsepower electric motors usually intended for high-precision or robotics applications. Electric motors are used to produce linear or rotary force (torque), and should be distinguished from devices such as magnetic solenoids and loudspeakers that convert electricity into motion but do not generate usable mechanical powers. A motor is selected with respect to the mass of the entire setup. In normal motoring mode, most electric motors operate through the interaction between an electric motor's magnetic field and winding currents to generate force within the motor. In certain applications, such as in the transportation industry with traction motors, electric motors can

operate in both motoring and generating or braking modes to also produce electrical energy from mechanical energy.

Fig.6 Motor

4.8 Chain and sprocket

A sprocket or sprocket-wheel is a profiled wheel with teeth, cogs, or even sprockets that mesh with a chain, track or other perforated or indented material. The name 'sprocket' applies generally to any wheel upon which radial projections engage a chain passing over it. It is distinguished from a gear in that sprockets are never meshed together directly, and differs from a pulley in that sprockets have teeth and pulleys are smooth. Sprockets are of various designs, a maximum of efficiency being claimed for each by its originator. Sprockets typically do not have a flange. Some sprockets used with timing belts have flanges to keep the timing belt centered. Sprockets and chains are also used for power transmission from one shaft to another where slippage is not admissible, sprocket chains being used instead of belts or ropes and sprocket-wheels instead of pulleys. They can be run at high speed and some forms of chain are so constructed as to be noiseless even at high speed.

Roller chain or bush roller chain is the type of chain drive most commonly used for transmission of mechanical power. It is driven by a toothed wheel called a sprocket. It is a simple, reliable, and efficient means of power transmission. There are actually two types of links alternating in the bush roller chain. The first type is inner links, having two inner plates held together by two sleeves or bushings upon which rotate two rollers. Inner links alternate with the second type, the outer links, consisting of two outer plates held together by pins passing through the bushings of the inner links. The "bushing less" roller chain is similar in operation though not in construction; instead of separate bushings or sleeves holding the inner plates together, the plate has a tube stamped into it protruding from the hole which serves the same purpose. This has the advantage of removing one step in assembly of the chain. The roller chain design reduces friction compared to simpler designs, resulting in higher efficiency and less wear. The original power transmission chain varieties lacked rollers and bushings, with both the inner and outer plates held by pins which directly contacted the sprocket teeth; however this configuration exhibited extremely rapid wear of both the sprocket teeth, and the plates where they pivoted on the pins. This problem was partially solved by the development of bushed chains, with the pins holding the outer plates passing through bushings or sleeves connecting the inner plates. This distributed the wear over a greater area; however the teeth of the sprockets still wore more rapidly than is desirable, from the sliding friction against the bushings. The addition of rollers surrounding the bushing sleeves of the chain and provided rolling contact with the teeth of the

sprockets resulting in excellent resistance to wear of both sprockets and chain as well. There is even very low friction, as long as the chain is sufficiently lubricated. Continuous, clean, lubrication of roller chains is of primary importance for efficient operation as well as correct tensioning.

Fig.7Chainandsprocket

The effect of wear on a roller chain is to increase the pitch (spacing of the links), causing the chain to grow longer. Note that this is due to wear at the pivoting pins and bushes, not from actual stretching of the metal (as does happen to some flexible steel components

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