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Manual Animal traction in Africa (GTZ-Publikationen)

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Plough or plow; draught or draft? All four spellings have been used in the English language for several hundred years and there are numerous ancient and recent precedents for the shorter, simpler versions. Current North American stand arcs arose from the adoption of the simpler variations of the alternative spellings that were in use in English-speaking countries two to three hundred years ago. Although the "ugh" spellings have predominated in British publications for the last century, it would simplify terminology greatly if international publications used one spelling.

Since the simpler alternatives have been used and accepted many times in the past, there seems little justification for maintaining the "ugh" spellings. Thus, in a continuation of the precedent set by other books in this series, "plow" and "draft" have been adopted here.

Introduction 1. It is important to people from diverse backgrounds with different levels of experience and education. Programme planners, extension workers, farmers, researchers, lecturers and students all have need for information on the subject, but while some need to start with very basic information, others require concise yet detailed technical content.

Ideally there should be many different texts to meet these diverse requirements, ranging from simple extension manuals, filled with drawings of how to use and adjust animal-drawn implements, to specialist papers on implement working parameters or construction details. Luckily such an "ideal" situation does exist, the problem is that few people are aware of it!

As should become apparent, there are very many useful documents, some widely disseminated and others little known, which together cover all the required levels of complexity. This book is not designed to replace these, but to lead people to them. In past years there has been insufficient liaison between people working on harnessing and animal-drawn implements.

As a result, there has been much unnecessary repetition of similar work, and limited opportunity to build on the experiences of others. Many misconceptions have arisen as to which equipment and techniques farmers have used successfully, and which implements farmers have found inappropriate. For this reason this book is intended to lead readers not only to printed sources, but to people and organizations with experience of the various topics discussed. It should be clear that this book has not been conceived as a technical manual, for this would have inevitably fallen into the trap of being too simple, too complex, too general or too specific to be of wide-ranging value.

Rather this book is intended as a resource document that can stimulate greater exchange of information between workers of many different levels and backgrounds.

The objective has been to provide a thorough yet readable "state of the art" review, that informs people not only of further appropriate reading, but also makes them aware of organizations that may have relevant experience in the various subjects discussed. Nevertheless it must be remembered that these books were the product of their times, and some of the emphases and approaches may be less applicable today than when they were written.

These have proved to have little application for smallholder farmers in tropical Africa. The previous GTZ animal traction book also illustrated some of these applications, and went on to emphasize more recent designs of equipment developed by researchers in Africa. As it transpired several of the illustrated designs such as the TAMTU harrows and double plows subsequently proved unacceptable to farmers, often because they were too heavy, too complicated or too expensive Kjpirby, It is also intended to provide ideas on future options.

It is a specific intention to counteract the tendencies of many of those involved in animal traction development to present over-optimistic and rather euphoric views of the application of draft animal power, and various wonderful "new" techniques and designs. The problems of development are seldom that simple. The strong element of caution considered by the author as "realism" may well be interpreted by some as pessimism.


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This is certainly not the intention as the author himself is both optimistic and enthusiastic about the potential for draft animal power. However in the past decade excessive optimism has often given way to great frustration among policy makers, researchers, extension workers and farmers. Such damaging disappointments could often have been avoided had a more realistic approach been adopted, based on existing knowledge and previous experiences.

This background whereby unguarded optimism has led to disappointments should be borne in mind in the interpretation of each of the following chapters.


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  • It is not intended to dampen existing enthusiasm, but it is hoped that, by highlighting the potential problems, the resources and human energy available will be channelled in more constructive ways. Should anyone read this book from cover to cover, they Will inevitably be aware of repetitious themes. In practice few people read resource books so comprehensively: most people gather a general impression from the illustrations and captions, and then read only those sections of particular interest.

    For this reason key points and key references have sometimes had to be included in several sections. One recurrent theme will inevitably be that technical excellence is only one of many criteria to be used when assessing equipment and harnessing; farmers require materials and techniques that are affordable, sustainable and usable within the realities of their farming systems.

    Finally, in the following chapters and appendices some implements have been referred to by trade names and mention has sometimes been made of specific manufacturers. However it cannot be too strongly stressed that the mention of names should not be interpreted as approval or endorsement of any specific manufacturer or any particular implement design. Similarly no significance whatsoever should be drawn from the lack of mention of any manufacturer or design. Some mechanical principles 2.

    It is therefore not intended to present any detailed analyses of the dynamics of animal traction equipment, with impressive combinations of arrows, cosines, integration signs and Greek letters. For such technical details readers are referred to Devnani , Viebig , Crossley and Kilgour , Goe and Matthews Nevertheless there are a few basic principles, which may-be combined with common sense to provide a useful approach to animal traction equipment for people who would not consider grappling with the more complex theories of mechanics.

    Thus this brief section is intended to remind people of basic principles already known to them, and give some examples of the type of context in which they can be applied. In many cases, even a vague recollection of mathematical concepts learnt long ago, can help in interpreting and understanding different features of harnesses and equipment.

    Simple principles rather than learned rules can also be useful when it comes to assessing the advantages and disadvantages of various designs, and the significance of any modifications and adjustments. The day-to-day application of such units is not essential because comparative performances are more relevant than absolute values in the majority of field situations: farmers are more concerned with whether a particular combination of animals and implement can achieve acceptable work in a reasonable time, than with numbers illustrating weights, draft and power.

    Nevertheless there are great advantages in using standard units of measurement since this facilitates exchange of information between people in different countries, in the past meaningful exchange has been hampered by the wide range of different units that have been used when assessing animal drawn implements horsepower, kilowatts, kilogram force, pound force, newtons, joules, miles per hour, kilometres per hour, metres per second, square metres per hour, hours per hectare, acres per day, etc. Whenever practicable, internationally accepted standard units have been used in this book.

    Such units are merely convenient measures of magnitude, and do not convey any information as to the authority or reliability of numbers. While measurements obtained under accepted standard and repeatable test conditions can be widely applicable, there are very few standard measurements relating to animal draft, other than implement and animal weight and physical dimensions.

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    When draft animals work pulling implements in a farmer's field or at a research station there are so many highly specific variables influencing the situation that the actual figures may have little relevance away from the conditions in which they were obtained. Thus although the use of international units is to be encouraged, these should not be confused with international test standards, and great care should be taken when interpreting data obtained in different circumstances Similarly, because local conditions are so variable, it is generally unwise to ascribe "typical" values to agricultural operations.

    Nevertheless in order to make readers more familiar with the units that will be used in subsequent chapters, a few illustrative values of force, work and power will be given, merely as examples. Some people may even remember that Newton's first law was that a body will remain at rest or in straight-line motion unless acted upon by a force.

    His second related to changes in momentum and direction of movement as a result of forces, while his third was that actions and reactions are equal in magnitude and opposite in direction. The standard unit of force is a newton symbol N. The definition of a newton is based on the force resulting from acceleration acting on a mass of one kilogram. Since the acceleration due to the Earth's gravity is about 9. Thus although some purists may object, for all practical purposes a newton can be simply considered as a unit of force equivalent to grams weight.

    Thus 10 N is equivalent to one kilogram 1 kg or 2. Newton units are used in this book as these are the accepted international standard, and will be found in other references.

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    Some authors have used decanewtons dN which are broadly equivalent to kilograms and some have used kilonewtons kN equivalent to kg force. However for most people it should be sufficient to remember that dividing the newton figure by 1 0 will give the kilogram equivalent. By way of illustration, a low-draft implement such as a light seeder might impose a draft resistance force of about N; a small mouldboard plow in light soils might require a tractive force of N while a double mouldboard plow in heavy soils might require a force of N.

    In scientific terms "weight" is actually a force, since it depends on the acceleration of gravity. A body can appear "weightless" in space, even though its "mass" does not change. The standard units of mass are grams and kilograms while it has been noted that the units of force are newtons.

    A spring balance, even one calibrated in kilograms, actually measures weight not mass, and will give slightly different readings at different altitudes. Purists would calibrate spring balances in newtons, whether they are to be used as weighing instruments or as dynamometers for measuring draft forces.

    However for those concerned mainly with tilling the earth's surface, gravity can be considered approximately constant, and the interchange of the words "mass" and "weight" is unlikely to be a source of confusion. For this reason, the word "weight" will often be used in this book in the loose, colloquial sense, in which weight is measured in kilograms, rather than newtons.

    Forces have direction as well as magnitude, and the concept of vectors is useful in studying them. Forces can be analysed in terms of three axes at right angles to each other, although many can be considered more simply and conveniently as acting in just one plane. In such cases a "diagonal" force such as the pull on a traction chain , can be thought of in terms of vertical and horizontal components Fig.

    Such a pull has an upward component and a forward component. One means of achieving a more effective horizontal force would be the use of a very long traction chain, and another would be to lower the point from which it were pulled. In terms of horizontal pull, short-legged oxen with a low-hitched harness and a very long traction chain would be more efficient than long-legged camels with a high hump harness and short chain. This exaggerated example illustrates two points: firstly that agriculturalists do not have to be engineers to be able to consider in a very simple but useful way the forces involved in the application of harnesses and equipment, and that such consideration may well lead to ideas for improving field adjustments or overall designs; secondly what may be theoretically optimal in terms of one aspect of efficiency may not be appropriate in terms of operational convenience or animal availability.

    Over-long chains make turning very difficult and short legged mini-beasts may not have sufficient 12 power, speed or endurance. In practice, design considerations such as convenience, cost, availability and even appearance may outweigh technical refinements. Some readers may have seen comparable diagrams with arrows going in other directions. This can be explained with reference to Newton's third law, since all the forces cited will have opposing forces the pull of the animals is opposed by the draft of the implement; the downward force of the yoke due to gravity and the vertical component of the draft is opposed by the body of the animal as it stands and pulls.