mechanical spider

INTRODUCTION

GQ64 is not a robotics based machine. It is the simplest form of mechanism which runs with the help of mechanisms like

• gear drive
• belt drive
• motor drive
• chain and sprocket drive

Walking mechanism has been for long a dynamic and fast developing field of mechatronics. This huge interest not only derives from the obvious fact that the usage of legs resembles the way of movement of living animals, but also to its great advantage while moving on a rough, unstructured surface. Due to the possibility to stand on single, well defined points a flexible operation area is achieved.

As a drawback, efficiency and speed are not the strongest qualities of walking mechanism. When it comes to flat, even terrain, moving with wheels turns out to be the faster, more reliable way of locomotion.

The invention provides a walking device which stimulates a gait of a legged animal. The device includes a frame with spaced axial mounts, a leg, axially connected upper and lower rocker arms which limit reciprocating leg motion. The leg is driven by a connecting arm powered by a rotating crank. The position and configuration of the axial connecting sites establish a prescribed orbital path that the foot undertakes with
each revolution of the crank. Both rocker arms and the crank are axially mounted to the frame.
The leg has a hip joint axially connected to the upper rocker arm for limiting hip motion, a foot and a knee joint axially connected to the connecting arm. The connecting arm has three axial connecting sites, one for connecting to the knee, another to the crank, and a third connecting site defined as a centrally disposed elbow joint connecting site which connects onto the lower rocker arm and limits knee joint motion. Under power, crank rotation is transferred to the connecting arm causing the leg to move in an accurate reciprocating movement of a restricted actual pathway which stimulates the gait of the legged animal. The walking device may be manually powered or motorized by applying motorized power to the crank axles.

Klann mechanism is a planar mechanism designed to simulate the giant legged animal and function as a wheel replacement. Here we are using a single leg consists of a six – bar linkage made up entirely of pivot joint that converts rotating motion into linear motion. The linkage consists of the frame, a crank, two grounded rockers, and two couplers all connected by pivot joints. The proportions of each of the links in the mechanism are defined to optimize the linearity of the foot for one-half of the rotation of the crank.

MECHANISMS USED

1. Technical Mechanism

Klann mechanistic mechanism

Klann mechanism is a planar mechanism designed to simulate the giant legged animal and function as a wheel replacement. Here we are using a single leg consists of a six – bar linkage made up entirely of pivot joint that converts rotating motion into linear motion. The linkage consists of the frame, a crank, two grounded rockers, and two couplers all connected by pivot joints. The proportions of each of the links in the mechanism are defined to optimize the linearity of the foot for one-half of the rotation of the crank.

The remaining rotation of the crank allows the foot to be raised to a predetermined height before returning to the starting position and repeating the cycle. Two of these linkages coupled together at the crank and one-half cycle out of phase with each other will allow the frame of a vehicle to travel parallel to the ground. The Klann linkage provides many of the benefits of more advanced walking vehicles without some of their limitations. It can step over curbs, climb stairs, or travel into an area that are currently not accessible with wheels but does not require microprocessor control or multitudes.

TRANSMITTING SYSTEM

Which type of system you need to provide the power into legs for translation motion , in this system crank are the most common part because the main power are transmitted in crank , crank rotates with his own center the leg are joint with the help of pivot .

Main type of transmitting

1. Mechanical spider with gear mechanism
2. Mechanical spider without gear

MOTIVATION

To overcome the previously mentioned problematic a practical solution would be to enable different ways of travelling for one robot, rolling and walking, to adapt it to a changing environment in an easy way. In this bachelor thesis this task is realized by implementing feet equipped with passive skates on a walking robot, deriving a skating trajectory and do first steps into optimization of this movement. One of the main reasons for this choice was that the robot stays in the environment it is geared to. Therefore not the whole robot, but only the feet had to be altered.

Concept Determination

Several concepts for feet giving the robot the opportunity to reach new environ-ments or studying new locomotion concepts were in mind. After reconsidering the potential of different approaches their number could be reduced to the following promising options

A single leg consists of a six-bar linkage made up entirely of pivot joints that converts rotating motion into linear motion. One hundred and eighty degrees of the input crank results in the straight-line portion of the path traced by the foot. The result of two of these linkages coupled together at the crank and one-half cycle out of phase with each other is a device that can replace a wheel and allow the frame of the vehicle to travel relatively parallel to the ground. The remaining rotation of the input crank allows the foot to be raised to a predetermined height before returning to the starting position and repeating the cycle. 

These figures show a single linkage in the fully extended, mid-stride, retracted, and lifted positions of the walking cycle. These four figures show the crank (rightmost link in the first figure on the left with the extended pin) in the 0, 90, 180, and 270 degree positions.

SKATING

In this concept the robot travels a flat, unstructured surface by skating. Each leg should be equipped with passive wheels on the feet. By moving the feet in specific way thrust is induced. Designing the specialized feet and deriving a possible trajectory are the emphases of this approach. The goal would be to move faster on the floor than with legged locomotion

Selected Method of Skating, why???

It was decided to further pursuit this way of movement for a couple of reasons:First of all with eight legs on the floor a very stable system is attained. Furthermore, lifting the legs would lead to a dislocation of the robots center of mass.

That means dynamic calculations have to be applied leading to a more complex problem. Aside from that, feet equipped with skating rolls turned out to be quite heavy. When lifted up, high torques in the joints would be generated. That way the motors could be overloaded.

KLANN MECHANISTIC MECHANISM

This mechanism is based on simple kinematic chain, and kinematic chain based on links joint and pivots.

The study of Biological systems and methods has long intrigued Scientists and Engineers in their quest for a greater understanding of the world. Biological systems have managed over thousands of years to evolve many methods for completing tasks that are naturally impossible for humans such as re-growing missing limbs, breathing underwater and even flying. Although humans have managed to mimic some of these abilities through the inventions of submarines and airplanes, there are still many areas of engineering that these biological marvels can be applied to. Biometics, the study of Biological methods and systems and their implications toward robotic systems and engineering problems, is the term applied to this ancient art, and has gained prominence in recent years for its novel solutions.

moter specification

100RPM 12V DC geared motors for robotics applications. It gives a massive torque of 35Kgcm. The motor comes with metal gearbox and off-centered shaft.

Features

• 100RPM 12V DC motors with Metal Gearbox and Metal Gears
• 18000 RPM base motor
• 6mm Dia shaft with M3 thread hole
• Gearbox diameter 37 mm.
• Motor Diameter 28.5 mm
• Length 63 mm without shaft
• Shaft length 30mm
• 180gm weight
• 35kgcm torque
• No-load current =800 mA, Load current = upto 7.5 A(Max)a
• Recommended to be used with DC Motor Driver 20A or Dual DC Motor Driver 20A 

12 Volt Conventional (aka Lead Acid) Type Battery Sizes

12 Volt lead acid or conventional motorcycle batteries can usually be distinguished by a row of plastic stoppers in the top (3 stoppers in a 6 volt battery & 6 stoppers in a 12 volt battery).

Lead acid batteries usually have higher & lower battery acid levels on the front & have a white/clear plastic lower casing.

Conventional motorcycle batteries reference numbers usually start with the letters YB, CB or GB (e.g YB14L-A2) or 12N (e.g 12N24-3).

LIMIT AND FITS

LIMTS - These are two extreme permissible sizes of dimension between which actual size of dimension is contained .The greater of these two is called high limit and the smaller low limit.

FITS - It is the relationship existing between two mating parts with respect to amount of play or interference which is present when they are assembled together.  It is the degree of tightness or looseness between two mating parts to perform a definite function.

TERMINOLOGY-

Zero Line- It is a line along which represents the basic size and zero for measurement of upper or lower deviations.

Basic Size- It is the size with reference to which upper or lower limits of size are defined.

Shaft and Hole- These terms are used to designate all the external and internal features of any shape and not necessarily cylindrical.

Hole Designation - By upper case letters from A, B, … Z, 

Shaft Designation- By lower case letters from a, b, … z, - 25

BASIC DEFINITIONS-

Upper Deviation: The algebraic difference between the maximum limit of and the corresponding basic size.

Lower Deviation: The algebraic difference between the minimum limit of size basic size.

Fundamental Deviation:  It is one of the two deviations which is chosen to define the position of the tolerance zone.  Or nearest from both upper and lower deviations.

Tolerance: The algebraic difference between upper and lower deviations. It is an absolute value.

Limits of Size: There are two permissible sizes for any particular dimension between which the actual size lies, maximum and minimum.

INTERNATIONAL TOLERANCE GRADES
The variation in part size, also called the magnitude of the tolerance zone, and is expressed in grade or IT numbers. Seven grade numbers are used for high-precision parts; these are example
ITOl, ITO, ITl, IT2, IT3, IT4, IT5
The most commonly used grade numbers are IT6 through IT16, and these are based on the Renard R5 geometric series of numbers .For these, the basic equation is calculation of  “i”

LEAF-SPRING

A leaf spring is a simple form of spring commonly used for the suspension in wheeled vehicles. Originally called a laminated or carriage spring, sometimes referred to as a semi-elliptical spring or cart spring, it is one of the oldest forms of spring.

A leaf spring can either be attached directly to the frame at both ends or attached directly at one end, usually the front, with the other end attached through a shackle, a short swinging arm. The shackle takes up the tendency of the leaf spring to elongate when compressed and thus makes for softer springiness. Some springs terminated in a concave end, called a spoon end (seldom used now), to carry a swivelling member.

Historical Background

Leaf springs were very common on automobiles, right up to the 1970s in Europe and Japan and late 1970s in America when the move to front-wheel drive, and more sophisticated suspension designs saw automobile manufacturers use coil springs instead. Today leaf springs are still used in heavy commercial vehicles such as vans and trucks, SUVs, and railway carriages. For heavy vehicles, they have the advantage of spreading the load more widely over the vehicle's chassis, whereas coil springs transfer it to a single point. Unlike coil springs, leaf springs also locate the rear axle, eliminating the need for trailing arms and a Pan hard rod, thereby saving cost and weight in a simple live axle rear suspension. A further advantage of a leaf spring over a helical spring is that the end of the leaf spring may be guided along a definite path. Typically when used in automobile suspension the leaf both supports an axle and locates/ partially locates the axle. This can lead to handling issues (such as 'axle tramp'), as the flexible nature of the spring makes precise control of the unsprung mass of the axle difficult. Some suspension designs use a Watts link (or a Pan hard rod) and radius arms to locate the axle and do not have this drawback. Such designs can use softer springs, resulting in better ride. The various Austin-Healey 3000's and Fiat 128's rear suspension are examples.

Explanation of Diagrams

Diagram shows a laminated semi- elliptic spring. The top leaf is known as the master leaf. The eye is provided for attaching the spring with another machine member. The amount of bend that is given to the spring from the central line, passing through the eyes, is known as camber. The camber is provided so that even at the maximum load the deflected spring should not touch the machine member to which it is attached. The camber shown in the figure is known as positive camber. The central clamp is required to hold the leaves of the spring. However, the bolt holes required to engage the bolts to clamp the leaves weaken the spring to some extent. Rebound clips help to share the load from the master leaf to the graduated lea Design Features When the springs are manufactured, each leaf is curved or given a camber set. The smallest leaf receives the maximum set, which is progressively reduced with the increase of the span of the leaf, so that the main leaf has the least set.

A centre bolt is used to align and clamp the various leaves together. For holding the leaves together along their span, they are clamped with steel clamps (sometimes rubber-lined) at about halfway between the centre bolt and the spring eyes. During multi-leaf spring deflection, the upper side of each leaf tip slides or rubs against the underside of the blade above it.

 This inter-leafs action creates friction, which may be useful under certain conditions, as it reduces the amount of bounce, but normally it does not match the ride characteristics required and it makes the suspension too stiff, so that harsh riding over light road irregularities is experienced. Inter-leaf rubbing in the presence of moisture causes fretting corrosion, which decreases the fatigue strength, so that the oscillating life of the spring is also reduced. This problem can be reduced to some extent by applying phosphate paint between the blades.

 Also by fitting a thin layer of lead or an anti-friction disc between the blades, the fiction in the interference and hence fretting can be reduced. The top surface of each leaf is shot-peened or work-har­dened to prolong its life. This process changes the stresses on the upper side of the blade from a normal tensile to a compres­sive state so that the fatigue life of spring-blade is greatly improved. Rounding the edges of the blades also reduces risk of fatigue failure. Further by changing from a straight cropping of the blade ends to a tapering of the leaves near their ends, the stresses within the blade are more evenly distributed along each blade span. This reduces the peaking of stress level so that spring life is increased. At present, leaf springs are mostly made from silicon manganese steel

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MECHANICAL MEASUREMENT

The essential purpose and basic function of all branches of engineering is to design.

Design begins with the recognition of a need and the conception of an idea to meet

that need. One may then proceed to design equipment and processes of all varieties

to meet the required needs. Testing and experimental design are now considered a

necessary design step integrated into other rational procedures. Experimentation is

often the only practical way of accomplishing some design tasks, and this requires

measurement as a source of important and necessary information.  

Valid data are defined as those data which support measurement of the most representative value of the desired quantity and its associated precision or uncertainty. When calculated quantities employ measured parameter.

One must naturally ask how the precision or uncertainty is propagated to any calculated quantity. Use of appropriate propagation-of-uncertainty equations can yield a final result and its associated precision or uncertainty. Thus the generalized measurement problem requires consideration of the measuring system and its characteristics as well as the statistical analysis necessary to place confidence in the resulting measured quantity. The considerations necessary to accomplish this task  

STANDARDS OF MEASUREMENT  

The defined standards which currently exist are a result of historical development,
current practice, and international agreement. The System International d'Unites (or SI system) is an example of such a system that has been developed through international agreement and subscribed to by the standard laboratories throughout the world, including the National Institute of Standards and Technology of the United States. The SI system of units consists of seven base units, two supplemental units, a series of derived units consistent with the base and supplementary units, and a series of prefixes for the

formation of multiples and sub multiples of the various units  

CALIBRATION  

The process of calibration is comparison of the reading or output of a measuring system to the value of known inputs to the measuring system. A complete calibration of
a measuring system would consist of comparing the output of the system to known
input values over the complete range of operation of the measuring device. For
example, the calibration of pressure gauges is often accomplished by means of a
device called a dead-weight tester where known pressures are applied to the input of
the pressure gauge and the output reading of the pressure gauge is compared to the
known input over the complete operating range of the gauge.  

Sensitivity  

The sensitivity is defined as the change in the output signal relative to the change in

the input signal at an operating point k. Sensitivity S is given by

                                                                                                                                              Resolution

       

The resolution of a measuring system is defined as the smallest change in the input
signal that will yield an interpretable change in the output of the measuring system

at some operating point. Resolution R is given by  

     

Response  

When time-varying signals are to be measured, the dynamic response of the measuring system is of crucial importance. The components of the measuring system must be
selected and/or designed such that they can respond to the time-varying input signals
in such a manner that the input information is not lost in the measurement process 

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SHAFT- Power transmission

A shaft is a rotating machine element, usually circular in cross section, which is used to transmit power from one part to another, or from a machine which produces power to a machine which absorbs power. The various members such as pulleys and gears are mounted on it.

A shaft is a rotating machine element, usually circular in cross section, which is used to transmit power from one part to another, or from a machine which produces power to a machine which absorbs power. The various members such as pulleys and gears are mounted on it.

As torque carriers, drive shafts are subject to torsion and shear stress, equivalent to the difference between the input torque and the load. They must therefore be strong enough to bear the stress, whilst avoiding too much additional weight that would in turn increase their inertia.

Historical Background

The term drive shaft first appeared during the mid19th century. In 1861 Storer's patent reissue for a planning and matching machine, the term is used to refer to the belt-driven shaft by which the machine is driven, the term is not used in original patent.
Another early use of the term occurs in the 1861 patent reissue for the Watkins and Bryson horse-drawn mowing machine. Here, the term refers to the shaft transmitting power from the machine's wheels to the gear train that works the cutting mechanism.

Terminology

·        In machinery, the general term “shaft” refers to a member, usually of circular cross-section, which supports gears, sprockets, wheels, rotors, etc., and which is subjected to torsion and to transverse or axial loads acting singly or in combination.

·        An “axle” is a non-rotating member that supports wheels, pulleys, and carries no torque.

·        A “spindle” is a short shaft. Terms such as line-shaft, head-shaft, stub shaft, transmission shaft, countershaft, and flexible shaft are names associated with special usage

 Steps of Shaft Design

·        Material selection

·        Geometric layout

·        Stress and strength

·        Static strength

·        Fatigue strength

·        Deflection and rigidity

·        Bending deflection

·        Torsional deflection

·        Vibration due to natural frequency

Possible Shaft Materials 

1.     Shafts can be made from low carbon, cold-drawn or hot-rolled steel,  

such as ANSI 1020-1050 steels.

2.     A good practice is to start with an inexpensive, low or medium carbon steel for the first time through the design calculations.

3.     Typical alloy steels for heat treatment include ANSI 1340-50, 3140-

50, 4140, 4340, 5140, and 8650. 

     4. Typical material choices for surface hardening include carburizing

          grades of ANSI 1020, 4320, 4820, and 8620.

5.     Cast iron may be specified if the production quantity is high, and the gears are to be integrally cast with the shaft.

          DESIGN OF SHAFTS SUBJECTED TO TWISTING MOMENT / TORQUE ONLY:

We have the general Torsion equation as   T / J = Ƭ / r - 

Where, T = Torsional moment / Twisting Moment / Torque - N-mm

            J = Polar Moment Inertia of cross sectional area about the axis of rotation

                  - mm⁴

            Ƭ = Torsional Shear stress of the shaft – MN / mm²

             r = Radius of the outer most fabric from the axis of the rotation

               = d/2, where d = dia. of the shaft.

               Also J = πd⁴ / 32

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