DESIGN OF A HOPPING ROBOT

A Project Report submittedIn partial fulfilment Of the completion of internship awarded by

INTERNATIONAL ASSOCIATION FOR EXCHANGE OF STUDENTS FOR TECHNICAL EXPERIENCE (IAESTE)

For

Mechanical & Industrial Engineering

Submitted by

Battula Krishna Chaitanya

Under the guidance of

Dr.Riadh ZaierProfessor,

Department Of Mechanical & Industrial Engineering,College of Engineering, Sultanate of Oman.

ACKNOWLEDGEMENT

I am greatly indebted to our project guide Dr.RIADH ZAIER for providing the required facilities, a conducive working environment and constant support to do my best in the endeavour. His guidance, support and encouragement made this work possible

We had a great experience doing this project work and we would be really grateful to continue such work under your guidance.

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Abstract

The Main Objective of this project is to design a miniature hopping robot that has a knee joint

and with the jumping and balancing capability, and equipped with sensory in order to provide a

suitable platform for advanced research on running biped robot.

Designing a three-link leg with springs and actuators; using spring at the knee/hip joint to store

the gravity energy that will be used to lift off. The actuator will be used to control the motion

only.

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Contents:

1. Introduction. Why Study Leg Robots? -------------------------------------------------------------------------- 5 Back Ground ---------------------------------------------------------------------------------------- 5 Introduction ----------------------------------------------------------------------------------------- 6 Objective --------------------------------------------------------------------------------------------- 7 Scope of Project ------------------------------------------------------------------------------------ 7 Problem Statement -------------------------------------------------------------------------------- 7 What is Hopping ----------------------------------------------------------------------------------- 7

2. Different leg Hoppers.2.1 Monopad --------------------------------------------------------------------------------------- 92.2 Planar one leg-Hopper ---------------------------------------------------------------------- 102.3 3D one leg-Hopper --------------------------------------------------------------------------- 112.4 Uniroo ------------------------------------------------------------------------------------------- 122.5 Robo --------------------------------------------------------------------------------------------- 13

3. Solid Works3.1 Sketch -------------------------------------------------------------------------------------------- 133.2 Parts ---------------------------------------------------------------------------------------------- 143.3 Assemblies -------------------------------------------------------------------------------------- 163.4 Mate ---------------------------------------------------------------------------------------------- 183.5 Simulation --------------------------------------------------------------------------------------- 19

4. Design model4.1 Phases and events ----------------------------------------------------------------------------- 214.2 Dynamics of the model ----------------------------------------------------------------------- 224.3 Control during the stance phase ----------------------------------------------------------- 234.4 Control during the flight phase ------------------------------------------------------------- 23

5. Main Parts

5.1 Thigh ---------------------------------------------------------------------------------------------- 245.2 Shank --------------------------------------------------------------------------------------------- 255.3 Toe ------------------------------------------------------------------------------------------------ 265.4 Bearings ------------------------------------------------------------------------------------------ 275.5 Springs -------------------------------------------------------------------------------------------- 275.6 Body ----------------------------------------------------------------------------------------------- 285.7 Assembling -------------------------------------------------------------------------------------- 29

6. Second Model --------------------------------------------------------------------------------------- 307. Bibliography ------------------------------------------------------------------------------------------- 31

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INTRODUCTION

Why Study Legged Robots?

This report is about the machines that use legs to run. The purpose of these machines is to Study the

principles of legged locomotion. Such principles can help us to understand animal locomotion and to

build useful legged vehicles.

There are three main reasons for exploring the use of legs for locomotion. First reason is the Study of

the mobility in difficult terrain.Today’s vehicles use wheels to move, and wheels can provide motion only

on prepared surfaces, such as rails and roads. However, most of places have not been paved. It seems

possible to build vehicles which use legs like animals for locomotion.

The second reason to study legged machines is to understand human and animal locomotion. The

principles of control which is used in human and animal locomotion is still not understood. One way to

learn more about plausible mechanisms for animal locomotion is to build machines that locomote using

legs.

The third reason which motivated the study of legged locomotion is the need to build artificial legs for

amputees. For below, knee amputee and above-knee prostheses some practical feet have been built,

but there is still a long way to find appropriate mechanisms which can be substitute the real organs.

Background

Before introducing the main topic, we turn briefly an account of previous work on legged Machines. The

scientific study of legged locomotion began just over a century ago when Muybridge studied the trotting

motion of a horse.His photographic data are still of considerable value and survive as a landmark in

locomotion research.

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During the ninety years that followed, the field viewed that of building walking machines as the task of

designing kinematic linkages that would generate suitable stepping motion. However by the late 1950’s

it had become clear that a linkage providing fixed motion would Not do the trick of walking or running,

and useful walking machines would need control.

Introduction

One approach to control was to harness human. Mosher used this approach in building a four legged

walking truck. Another approach is the use of digital computer for control. McGhee’s group was the first

to use this approach successfully.They built an insect-like Hexaped that could walk with a number of

standard gaits, turn, crab, and negotiate simple obstacles.

Gurnfinkel and his group built a machine quite similar to Mc Ghee’s which used analog computer

(hybrid) for control. Hirose designed clever and unusual mechanisms to simplify The control of

locomotion and improve their efficiency. McGhee, Gurfinkel, and Hirose’s walking machine groups

represent a class called Static Crawlers. Several other machines that fall into this class have been studied

in the intervening years.

Another class turned to the study of dynamic machines that balance actively. Shannon was probably the

first to build a machines that balanced an inverted pendulum in top of a Small powered truck.This study

forwarded by his students to demonstrate controllers for Two pendulums at once, and finally the case

that two pendulums were mounted on top of Each other Later, they extended these techniques to

provide balance for aflexible inverted Pendulum. Miura and Shimoyama built the first walking machine

that really Balanced actively. The control of their biped relied on an inverted pendulum model Matsuoka

was the first to build a machine that was able to hop on one leg. The field of dynamically stable legged

locomotion has made great strides in the past decade, led primarily by Marc Raibert. He built a variety

of running robots, starting with a Planar one legged machine. Followed by a 3D one legged, a two

legged planar robot, and a four, legged quadruped.His latest robots include a 3D two-legged robot.

where each leg has four actuated degrees of freedom. Except for the very first one legged planar

hopper, Which was pneumatically actuated, his subsequent designs are actuated by powerful hydraulic

actuators and rely on pneumatics for the leg spring only. Papantoniou designed an electrically powered

planar robot, capable of operating at maximum speed of 0.3 m/s. In order to obtain that, an original

mechanical design of an articulated leg and leg attitude Control has been realized.

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Objective:

Objective of this project is aim to produce low cost Hopping Robot with one leg that is capable to hope

over uneven terrain.

Scope of project:

This project is to design a simple and build a simple control of the hopping robot that has a single leg so

hopping is only way it can use. The hopping Robot is just like a prototype. The characteristic of this robot

is the leg use spring so that it can be compressed between one step and next to add energy

Problem Statement:When a human learn to walk, there is a long process of trial and error. The baby tries a behavior, and

the result modify further attempts. In developing this robot, a similar procedure takes place. A behavior

is planned and attempts are made, so observation is used to modify the software to achieve the

behavior desire. The human experiments are learning loop for the robot.

What is hopping?

Let Consider what might define hopping. Consider the simplest hopping machine, if ball is

dropped, it will fall to the ground, compress, and spring upward again. If the ball is moving forward, it

will remain moving forward. This can be related that the kinetic energy associated with its forward

velocity is unchanged , if the ball is ideal, there will be no more energy lost, and it will bounce to the

same height from which it was dropped. The chief features of this hopping machine are that the vertical

velocity reverses direction at impact, and that the energy of falling into a potential energy of elastic

deformation and back.

If consider a slightly more complicated machine, we can get an idealized hopper. It consists of mass at

one end of telescoping leg, which is two part leg with sliding joint, which has compressive spring inside

and a toe on the end, if the hopper is dropped straight down, and the toe is directly under the centre of

mass (COM), it will bounce very similarly to the ball, likes the kinetic energy of the body will be absorbed

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by the spring and released, the vertical velocity will have reversed direction, and the horizontal will still

be zero. This assumes a highly ideal operation, with the mass exactly over the toe, since the leg is an

inherently unstable inverted pendulum. If the hopper is moving forward as it fall the horizontal kinetic

energy can be absorbed and released similarly to the ball. For this to work, the leg must be positioned

forward at landing at a position such that it will be at a symmetric position at lit off, which will maintain

from the lift off position, which requires applying torques that will rotates the body. Our solution will

rotates the body. Our solution to this problem is include a tail to counter balance the leg motion.

DIFFERENT LEG HOPPERS1. MONOPAD2. PLANAR ONE LEG-HOPPER3. 3D ONE LEG HOPPER4. UNIROO5. ROBO

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MONOPAD

The Monopod is a planar, single legged robot. The Monopod's distinguishing feature is its use of an

articulated, rather than a telescoping leg found in previous robots. Additionally, the leg terminates in a

leaf spring unlike the air springs of the other running robots. The Monopod was used to investigate the

use of articulated legs that use rotary joints. Ultimately, the Monopod ran at a maximum speed of 2.3

m/s(5.1 mph) averaged over 16 m.

Articulated legs offer mechanical advantages, such as lower moment of inertia, less unsprung mass,

larger range of motion, greater compactness, better ruggedness, and ease of construction. However,

articulated legs also have added kinematic complexity and coupling between degrees of freedom. This

coupling is evident from the fact that displacements of the two joints do not in general cause orthogonal

displacements of the toe or hip.

We believe that articulated legs, those that use rotary joints, can be designed to be stronger, lighter,

faster, and more reliable than the telescoping legs used on previous running machines, one hurdle is to

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incorporate the elastic storage elements vital to good dynamic behavior, without making the leg too

difficult to control. The tests we have done show that it performs quite well as part of a planar hopping

machine, though its asymmetry and high natural frequency pose new locomotion control problems.

PLANAR ONE LEG- HOPPER

The Planar One-Leg Hopper was built to explore active balance and dynamic stability in legged

locomotion. The machine has one leg that changes length and pivots with respect to the body. The body

carries sensors, interface electronics, and the hip actuators. The machine was powered by pneumatics.

Experiments with the Planar One-Leg Hopper showed that balance could be achieved with a simple

control system. The control system has three separate parts: one controlling forward running speed, one

controlling body attitude, and one controlling hopping height. These controllers worked independently,

treating any coupling as disturbances.

The control system for the Planar One-Leg Hopper did not explicitely program a stepping motion, but

allowed the stepping motion to emerge under the constraints of balance and controlled travel. The

Planar One-Leg Hopper hopped in place, travelled at specified rates, and maintained balance when

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disturbed. The simple techniques used for planar one-leg hopper were later generalized for 3D one-leg

hopping, bipedal running, and quadruped trotting, pacing, and bounding.

3D ONE LEG HOPPER

The 3D One-Leg Hopper was built for

experiments on active balance and dynamic in legged locomotion. The machine has a leg that changes

length, a body that carries sensors and interface electronics, and an actuated 2-axis hip. The hip is

powered by hydraulics and the leg by compressed air. The machine has an overall height of 43.5 inches

(l.l0 m) and a mass of 38 lbs. (l7.3 kg).

There were four reasons to build a 3D machine with only one leg. First, it is simpler to study balance a

machine with one leg, because it eliminates the difficult task of coupling the behavior of several legs.

Second, it forces one to focus on balance, because a one legged system has no other way to stand up.

Third, the behavior and control of a one-legged device could be used as the corner-stone for each leg of

multi-legged systems.

Fourth, a one legged system has the minimum equipment. Less equipment means less construction

time, less down time due to mechanical failure, and more reliable operation. Experiments with the 3D

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One-Leg Hopper showed that balance can be achieved with a simple control system. The control system

has three separate parts: one controlling forward running speed, one controlling body attitude, and one

controlling hopping height.

The 3D One-Leg Hopper hopped in place, travelled at a specified rate, followed simple paths, and

maintained balance when disturbed. Top recorded running speed was 2.2 m/sec (4.8 mph). The 3D

control algorithms were generalizations of those used earlier in 2D, with little additional complication.

UNIROOThe Uniroo robot is kinematically similar to a real kangaroo of mass 6.6 kg. The Uniroo consists of a

body, a three-joint (hip, knee, ankle) articulated leg, and a single degree-of-freedom tail. The body is a

bolted framework of aluminum struts, and the leg is composed of welded aluminum tubes. Hydraulic

actuators control each joint. A steel coil spring at the ankle stores elastic energy during stance.

The Uniroo differ from the previous robots in four important respects. The Uniroo is not symmetric, the

leg is articulated instead of telescoping, the hip is offset from the center of mass, and the leg is relatively

heavy (one-third the mass of the body). Because of the asymmetry, the ground forces during stance

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effects the body pitch. A massive leg also affects the body pitch as the leg is swept forward during flight.

Finally, the kinematic redundancy of the leg must be addressed.

Work with the Uniroo showed that it is possible to control the balance of legged robots that have a non-

symmetrical mechanical structure. Regulation of angular momentum allowed the Uniroo robot to hop in

a range of forward velocities from 0 to 1.8m/s for at least a minute. Although nothing proves that a

steadily null angular momentum is part of an optimal hopping strategy, we observed that a small

angular momentum is a characteristic of ``smooth'' hopping and underlies a very natural motion.

ROBOPRobop is a self-stabilizing hopping robot built in 1996. It has no active electronic sensors to use for

feedback. The robot is self-stabilizing in that when the leg is driven in a proper feed-forward periodic

motion, the physics of the robot has inherent dynamic stability. It is stable in hopping height and pitch

and entrains to the driving frequency.

The unique feature which allows Robop to maintain dynamic stability is the curvature in the foot. This

required curvature is a function of the robot's inertial properties and leg spring constant.

Although Robop is now retired from active research, it is still functional and is capable of being

demonstrated.

SOLIDWORKS

SolidWorks is a 3D mechanical CAD (computer-aided design) program that runs on Microsoft Windows

and is being developed by Dassault Systems SolidWorks Corp., a subsidiary of Dassault Systems, S. A.

(Velizy, France). SolidWorks is currently used by over 1.3 million engineers and designers at more than

130,000 companies worldwide

The SolidWorks application is mechanical design automation software that takes advantage of the

familiar Microsoft Windows graphical user interface.

This easy-to-learn tool makes it possible for mechanical designers to quickly sketch ideas, experiment

with features and dimensions, and produce models and detailed drawings.

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Sketch:When you open a new part document, first you create a sketch. The sketch is the basis for a 3D model.

You can create a sketch on any of the default planes (Front Plane, Top Plane, and Right Plane), or a

created plane. You can start by selecting:

Sketch entity tools (line, circle, and so on)

Sketch tool

Planes

Parts:After opening a part document you can create a sketch by using different shapes in different dimensions

as required by selecting the planes in sketch mode. You can start by selecting

Rectangle/Circle as required.

Select the point in the region and draw required shape.

Dimension it.

Extruded Boss/Revolved Boss.

The Extrude Property Manager appears in the Feature Manager design tree (left panel), the view of the sketch changes to trimetric, and a preview of the extrusion appears in the graphics area.

Click ok and save it.

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Assemblies:

You can build complex assemblies consisting of many components, which can be parts or other

assemblies, called sub-assemblies. For most operations, the behaviour of components is the same for

both types. Adding a component to an assembly creates a link between the assembly and the

component. When SolidWorks opens the assembly, it finds the component file to show it in the

assembly. Changes in the component are automatically reflected in the assembly.

The document name extension for assemblies is .sldasm.

To create an assembly from a part:

1. Click Make Assembly from Part/Assembly (Standard toolbar) or File, Make Assembly from Part.

An assembly opens with the Insert Component Property Manager active.

8. Click in the graphics area to add the part to the assembly. SolidWorks makes the first component

fixed.

The following topics describe the basics of creating an assembly from components you have already

built and general information about working with assemblies.

Design method

Adding assembly component

Selecting Components

Mates

Working with sub-assemblies

Simplifying large assemblies

Exploding an assembly view

Customizing the appearance of an assembly

Smart Fasteners

Bills of materials in assembly documents

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Fixing the Position of a Component

You can fix the position of a component so that it cannot move with respect to the assembly origin. By

default, the first part in an assembly is fixed; however, you can float it at any time.

It is recommended that at least one assembly component is either fixed, or mated to the assembly

planes or origin. This gives a frame of reference for all other mates, and helps prevent unexpected

movement of components when mates are added.

A fixed component has a (f) before its name in the Feature Manager design tree.

A floating, under defined component has a (-) before its name in the Feature Manager design tree.

A fully defined component does not have a prefix.

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Mate:Mates create geometric relationships between assembly components. As you add mates, you define the

allowable directions of linear or rotational motion of the components. You can move a component

within its degrees of freedom, visualizing the assembly's behaviour.

Some examples include:

A coincident mate forces two planar faces to become coplanar. The faces can move along one another,

but cannot be pulled apart.

A concentric mate forces two cylindrical faces to become concentric. The faces can move along the

common axis, but cannot be moved away from this axis.

Mates are solved together as a system. The order in which you add mates does not matter; all mates are

solved at the same time. You can suppress mates just as you can suppress features.

Other topics about mates include:

Adding Mates

Mate Property Manager

Smart Mates

Best Practices for Mates

Solving Mate Problems

Advanced mates, including:

Limit Mates

Path

Linear/Linear Coupler

Symmetric

Width

Mechanical mates, including:

Cam

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Gear

Hinge

Rack and Pinion

Screw

Universal Joint

Types of Mates * Angle Mate

* Coincident Mate

* Concentric Mate

* Distance Mate

* Lock Mate

* Parallel and Perpendicular Mates

* Tangent Mate

* Advanced Mates

* Mechanical Mates

Simulation: SolidWorks Simulation is a design analysis system fully integrated with SolidWorks.

SolidWorks Simulation provides one screen solution for stress, frequency, buckling, thermal, and

optimization analyses. Powered by fast solvers, SolidWorks Simulation enables you to solve large

problems quickly using your personal computer. SolidWorks Simulation comes in several bundles to

satisfy your analysis needs.

SolidWorks Simulation shortens time to market by saving time and effort in searching for the optimum.

The Simulation toolbar provides you with shortcuts to frequently used operations. You can customize

the toolbar by adding buttons, hiding them, or moving them around. The behaviour is identical to

SolidWorks toolbars.

Additionally you can use the Simulation Command Manager. The program makes buttons available

based on the status and type of analysis study. For example, Thermal is available in the Result Tools

flyout toolbar only after running a thermal study.

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The Simulation toolbar includes the following categories:

Main

Fixtures/External Loads

Thermal Loads

Result Tools

List Results Tools

Fatigue

Trend Tracker

Dynamics

Design Model:The several design solutions needed to make an articulated leg springy and attaching a spring to each

joint is good option.

The two active joints are the hip and shank. The main important thing of this

model is the arrangement of the leg spring, it is attached between thigh and shank which is inclined to

the shank. The springs can be replaced by hydraulic servo between thigh and heel.

The most distinctive feature of this model is the arrangement of the leg spring. The leg spring is attached

between the thigh and shank inclined to the shank.

The two important effects during hopping are :

During Stance

During Flight

During stance holding the shank enables the leg spring to absorb a large impulse at

touch down and to transfer its kinetic energy to potential energy for the next stride.

During Flight, the spring constitutes a member of the parallel four-bar linkage,

compressive force to the spring is not so large at the duration consequently, it enables passive retraction

and extension of the leg, provided the inertia of the links is chosen approximately.

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Phases and events:

In general, legged robots are event-driven intermittent dynamical systems. The change dynamical

characteristics depending on leg conditions, whether or not legs are on the ground. For instance, legged

robots are often modeled as a manipulator when one leg is on the ground, a closed- chain mechanism

when more than one leg is on the ground. Those conditions are called phases in the field of legged

locomotion. Stance phase is a phase in which at least one leg is on the ground and the leg supports the

body and propels the body to keep the locomotion. Some researchers call it double –stance phase if two

legs of a multi legged robot are simultaneously on the ground. In the field of physiology, some

researchers call it ground contact phase, instead. Flight phase is a phase that no leg is on the ground and

the whole body is in the air. Some call it aerial phase, instead.

In the case of our one-legged hopping robot, there are only two conditions for state change: either the

leg is on the ground or it is not. If the leg is on the ground, it is called stance phase. If the leg is off the

ground , it is called flight phase. The phase transitions are driven by two events touchdown and lift-off.

Touchdown happens as an event from flight into stance. Lift-off occurs from stance into flight. The robot

repeats the cycle of shifting phases and keeps it as long as it is stable. As a result, a one-legged hopping

robot must be in either of these two phases, and its phase determines the dynamical characteristics of

the robot.

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The figure shows the cycle of the two phases with the two phase transition events. It is seen that phases

shift through events. This is the simplest state machine and is used as the locomotion control scheme for

simulation and experiment.

Dynamics of the Model:The Controlled Variables are (x,z,pi) the forward speed, vertical speed and attitude of the body in the

sagittal plane. The virtual leg length r and angle theta, which are used in the control at flight, are also

defined in the figure. Control inputs i1 and i2, the input currents to the hip actuator and knee actuator

respectively.

Firstly Passive dynamics of free fall are investigated. The robot is set to the nominal configuration in

which the foot is below the CM, and the both control inputs are set to zero(i1=0, i2=0). Then the

following behaviour was observed

(a) At the instant of touchdown, a large impulsive ground force makes the body pitch forward

suddenly.

(b) From touchdown to the bottom, the body pitches forward (pi<0) because of the negative

reaction moment.

(c) After maximum extension of the leg spring, the body pitches backward (pi>0).

(d) When the vertical reaction force becomes zero, the robot lifts off with positive angular

momentum.

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Next, actuated dynamics were investigated because these are the basis for control actions, which are

selected according to the system state. Here , the robot is set to the nominal configuration, with its foot

contacting the ground. Then, the constant inputs are fed to one actuator.

(e) If extending the hip actuator with the knee fixed (i1>0 and i2=0), the leg spring is extended and

backward body pitching (pi>0) occurs.

(f) If extending the knee actuator with the hip fixed (i2>0 and i1=0), the leg spring is extended and

forward pitching (pi<0) occurs.

(g) If shortening the hip actuator with the knee fixed( i1<0 and i2=0), the spring buckles(of course

this is not allowed).

(h) If shortening the knee actuator with the hip fixed (i2<0 and i1=0), undesirable oscillation and

chattering occurs.

Although there are some quantitative differences from the initial configuration and the amount

of the inputs, the qualitative behaviour is identical.

Control during the stance phase:The hip actuator controls body pitch by a feedback law, which is executed ‘only when’ the pitch angle is

lower than the specified value, while the knee actuator controls vertical speed and also suppresses the

backward body pitch by giving a constant input, which is exerted ‘only when’ maximum spring extension

occurs.

Control during the flight phase:During flight, the robot swings the leg to prepare for the next touchdown. It also retracts and extends

the leg to reduce inertia for fast leg swinging and prevent stubbing against the ground. Note that the

touch down angle (foot placement) of the leg is critical to gait stability for robots that cannot change

their leg lengths arbitrarily and have no actuator at their foot.

Although it has a knee actuator at its foot, it has a knee actuator that can be used to control its leg

length. However, the knee actuator has already been used for vertical speed control. Hence, the

touchdown leg angle was used for forward speed control.

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Main Parts:The Design of hopping robot mainly includes different parts to assemble

They are:

1. Thigh

2. Shank

3. Foot

4. Bearings

5. Springs

6. Body.

These are the main parts include in this design of leg

Thigh: It is one of the important part of the system which connects the system body and knee to the edges of

the thigh. The length of the thigh is of 25 cm’s, width is 4cm’s and depth is 50 cm’s and it has some

spherical connecting position at the edges of the thigh to fit the bearings in as shown in the figure.

To move the slider there is a path of 20 cm’s to slide down the link over the way which connects the

thigh and shank to control over the system. A damper is fixed at one end of the thigh so that the link can

enter into the damper and it can enable the smooth stoppage of the system

Locking system

The main importance of the usage of spring lock mechanism is to store energy for a while and to release

the energy with respect to spring .The main components involved in this system are link, Dumper and

locking system.

When the force exerted on the spring through the body the spring start compress and in the mean while

link gets expanded to the max extent and get locked at the locking point.

Now the spring is at the position of compression and the link is locked at maximum point to retrieve the

energy from the spring the link is unlocked at max extent and comes to minimum point in the sliding link

mechanism. When the link is unlocked it slowly releases the position of locking to unlocking and

transfers energy through spring from shank to thighs.

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The length of the spring compression should be equal to the length of the minimum point of link to the

maximum point so that it can equalizes the momentum in the body. Damper will be linked at the locking

position to smooth stoppage of shank force to the link and spring.

The design of thigh is as shown in the figure.

Shank:Shank is also designed in the same module of thigh to assemble with thigh and there is a holder at one

end of the shank to connect the slider to thigh. Length of the shank is same as thigh is around 25 cm’s

and the width is 4 cm’s and depth is 30cm’s. The two cylindrical rods are extended at side thigh contact

with bearings.

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Foot:

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The foot is designed in the view of humanoid foot so that it is divided into two parts front part and back

part. The back part is connected to the shank directly it has some elongation produced towards front

part as it maintains the stress on the foot. The spring was placed in middle of the two parts so that it can

balance and smoothen the foot.

Bearings:

Bearings play key role in the moment of the system. They are placed between the links of shank & thigh,

shank & ankle and body & thigh. Same type of bearings was used in the three places and the dimensions

of the system are as radius of the bearing is around 14.5 cm’s and minimum radius is around 4.5cm’s.

Springs:Springs play the main role in the system. The leg spring was the key for the whole structure and its

spring constant value cannot be easily specified if only the maximum and minimum boundaries are

known.

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Body:It was connected on the top of the thigh end through bearings and connector

Assembling: The whole parts get at their positions and assemble them by aligning and mating

them simulate it to determine the momentum of the system.

As Shown in figure above the slider moves the thigh in the axis of the link and the body connects on the

one end of the thigh and we can find a spring connected at the toe is to regulate the force acting on the

toe. Two bearings was connected at the joint to have a smooth condition of the toe moment because

they don’t have a actuator to control over there.

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Second Model:The second model was also same to the first but there is a difference in the designing of the damper and

sliding momentum. There were two cylinders which one can move into another so that one can damper

into another there was a damper at the end with locking system and having a small orifice let to go off

air at that position. The spring was covered on the outside of the two cylinders so that it can engage

through the expansion and contraction of the system. When the system is at expansion it takes air from

atmosphere and it releases air from orifices, it get damp at the end of the way to smooth stoppage of

the system.

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Bibliography:1. Department of Mechatronics and Precision

Engineering, Graduate School of Engineering, Tohoku University,

Aramaki-Aza-Aobo 01, Aobaku, Sendai 980-8579, Japan

2. Modified Raibert controller (http://www.cim.mcgill.ca/arlweb/).

3. Faculty of Electrical Engineering University technical Malaysia Melaka.

4. IEEE International Conference on Robotics and Automation, 1999, pp. 1689–1694.

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