A Proposal by

Jan Henri Cocatre-Zilgien

for the building of a

WALKING MACHINE WITH BACKHOE LEGS

Created April 15, 1997

Edited December 27, 2006


PROPOSAL ABSTRACT

The goal of this Proposal is to initiate the manufacture and sale of versatile legged machines that would complement and expand the existing line of products of a Company primarily manufacturing earth-moving or similar equipment. The specific objectives of the "Sixhoe Project" are to design, build, and evaluate, at a Company plant, a fully operational prototype of such a walking machine, initially using as many Company components as possible.

The main characteristics of the prototype, dubbed "Sixhoe", are described in the Patent Application "Walking Machine with Backhoe Legs" by J.H. Cocatre-Zilgien (1997). It consists of a relatively simple chassis equipped with 6 backhoes as legs. Each backhoe-leg can be fitted quickly with interchangeable feet, buckets, or any other implements specific to a particular trade. The choice of backhoes as legs provides the Sixhoe with decisive advantages over previous walking machines (and over wheeled and tracked vehicles). First, they provide a wide span for its stance, and therefore a great stability of shape that allows it to climb safely on slopes not accessible to other vehicles. Second, because of their reach, they can provide a high ground clearance for its chassis, which allows it to progress over large obstacles in unstructured terrains. The high ground clearance also enables it to carry external underslung payloads, as a walking crane. Third, backhoes have evolved into versatile tools over the years, nearly acting now as manipulators; also using them as legs greatly increases this versatility. The relative lack of strength of the swing of backhoes is compensated for by a walking method that maximizes the use of their powerful boom and dipperstick actuators.

The Sixhoe is envisioned as a relatively slow moving yet agile and forceful machine, for terrains not accessible to wheeled or tracked vehicles. For fast road transport the Sixhoe is either carried on a flatbed trailer or mated to a simple tracked cart that is hydraulically powered by the walking machine it carries. The Sixhoe is to use only statically stable gaits, which are inherently safe for hexapods, and which are not difficult to coordinate by the on-board computers now available.

The multidisciplinary design and construction of the Sixhoe relies on a new combination of well-known technologies, nearly all of which are in the field of expertise of a Company manufacturing hydraulically-powered earth-moving or similar equipment. The prototype is designed to be robust, of relatively low cost, and a fully operational machine, not an experimental research vehicle. Its intended market is the mechanized access to a significant part of the 50% of the land on Earth that is not accessible to wheeled or tracked vehicles, and to do so with minimal environmental impact. Target fields of operation comprise agriculture, sylviculture, oil & mining, transportation, general utility work, military, and many others.

TABLE OF CONTENTS

1. Introduction

2. Problem and background
2.1. Need to access sloped and unstructured environments  
2.2. Walking machines as a solution  
2.2.1. Japanese research  
2.2.2. Review of some significant walking machines  
2.2.2.1. The General Electric "Walking Truck" 
2.2.2.2. The OSU "Adaptive Suspension Vehicle"  
2.2.2.3. The Plustech "Walking Harvester"  
2.3. Problems of walking machines  

3. Project description  
3.1. Project goal  
3.2. Project objectives  
3.3. Project technical justifications  
3.3.1. Choice of legs over wheels  
3.3.2. Choice of wide-span legs  
3.3.3. Choice of backhoes as legs  
3.3.4. Choice of the number of legs  
3.3.5. Choice of sensors  
3.3.6. Choice of control system  
3.3.7. Choice of "no-fall" and other performance objectives  
3.3.8. Choice of actuator control  
3.3.9. Choice of Patent Application  
3.4. Project marketing justifications  
3.4.1. Versatility by design  
3.4.2. Choice of timing  
3.4.3. Choice of Company manufacturing earth-moving or similar equipment 
3.5. An analogy with aircraft design  

4. Work plan  
4.1. Work method and organization  
4.2. Work schedule and evaluation  
4.2.1. Phase 1 - Team constitution  
4.2.2. Phase 2 - Machine design  
4.2.3. Phase 3 - Prototype construction and static testing  
4.2.4. Phase 4 - Mobile two-legged version testing  
4.2.5. Phase 5 - Mobile six-legged version testing  
4.2.6. Phase 6 - Customer evaluations  
4.3. Estimated budget  

Bibliography  

Appendices
1. Patent Application "Walking Machine with Backhoe Legs"  
2. Short Description of Autopod 0.33 (built in 1996)
3. Plustech Advertisement for Walking Harvester

1. Introduction

The Patent Application (P.A.) for a "Walking Machine with Backhoe Legs" is an integral part of this Proposal. It was written with a minimum of legal terminology, as allowed by the U.S. Patent Office, so that it can easily be referred to throughout the Proposal itself. Before proceeding further, the reader is invited to read that Patent Application, except the Claims themselves, as many of its elements will not be addressed again to avoid redundancy.

2. Problem and Background

The problem to be solved can be viewed as what may appear at first as two unrelated issues, the first one from the point of view of backhoes, which is discussed in the beginning of the Patent Application, and the second one from the point of view of legged walking machines, which is discussed later in the Patent Application, and expanded below.

2.1. Need to access sloped and unstructured environments

From a study by the US Army in 1967, it is commonly said that 50% of emerged land on Earth in not accessible to wheeled and tracked vehicles, and yet is accessible to legged animals. It is an inescapable fact that the world population is still increasing in an exponential fashion and yet that the land to support that growing population does not increase. Most of the horizontal arable land of the world is already exploited, and sometimes agriculture is pushed up steep slopes. There are many and varied reasons for humans to go in a mechanized way on slopes and rugged terrain, and to do so with minimal environmental damage. The Patent Application details the installation of a utility pole on a hill as an example of such needs. It is also clear that these needs will only increase in the years to come.

The main problem related to working on slopes is the ability to climb and descend on them, and to do so in a stable and safe manner. The main problem related to progressing in unstructured or rugged environments is the ability to pass obstacles such as boulders, trees, and various gaps, sometimes filled with water.

2.2. Walking machines as a solution

Access of sloped or rugged terrain is possible by the creation of roads, which is justified when repeated or fast access to some destination is necessary, or if the flow of vehicles that will use them warrants it. However, it has long been recognized that walking machines provide a solution for all the many cases where such roads are non-existent, impractical, or too expensive.

2.2.1. Japanese research

SixhoeProposalFig_1.gif

FIG. 1. Survey of the national origin of walking robot US patents.

In a survey conducted in 1996, the number of US Patents related to "walking robots" was plotted against time according to their country of origin. The results (FIG. 1) show that the number of Patents of Japanese origin appear have climbed exponentially since 1990, whereas those of American origin appear stagnant, and those from other countries are practically non-existent. Given the complication of filing patents in both Asia and the United States, this can be interpreted as a will and a readiness of the Japanese industry to "lock on" some of the key technology in preparation for selling Japanese walking machines on US soil. These Patents are indeed the tip of the iceberg, as the Japanese have dynamic research in the field of walking machines, historically led by Shigeo Hirose (1985). Other foreign countries involved in research and development of walking machines comprise Belgium, Canada, England, Finland, France, Germany, and Russia, but except for a very few, they are generally still far from manufacturing an end- product that is useful enough to be commercialized.

2.2.2. Review of some significant walking machines

Quite a number of walking machines and walking robots have been built in the last decades (Todd 1985, special issue 1990, Rosheim 1994). In the field of non-biological walking, the terms "walking machine" and "walking robot" are quite interchangeable, because a computer to control them is required in both cases, at least for leg coordination. An operator can send commands to this computer either while sitting on board the machine, or via remote control. Many small walking machines are electrically powered (Klein et al. 1983, Pfeiffer et al. 1994), some are pneumatically powered (Protobot; Price 1995, Autopod 0.33; Appendix 2), and a few large ones are hydraulically powered (Sutherland 1983, Song & Waldron 1989, Rosheim 1994). Walking machines large enough to carry a human operator and significant payload have to be hydraulically powered, because of mechanical scaling factors. A few representative machines of this latter category will now be presented as a background for the "Sixhoe Project".

2.2.2.1. The General Electric "Walking Truck"

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FIG. 2. Photo of the General Electric Walking Truck (Rosheim 1994).

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FIG. 3. Side view of the General Electric Walking Truck (Rosheim 1994).

The Walking Truck was developed by Ralph Mosher at General Electric in the 1960s. This quadruped was quite spectacular (FIG. 2), especially considering it was built using technology that is 40 years old. In particular, it did not use any computer control; its on-board human operator had to directly and simultaneously operate 12 servovalves for the machine to walk. This proved too much of a burden and was enough to cause the termination of the project (Rosheim 1994). The Walking Truck was potentially one of the most agile (FIG. 3) of all the walking machines to follow, and one can only wonder what it could have achieved if the small and powerful computers and servovalves available today existed at the time.

2.2.2.2. The Ohio State University "Adaptive Suspension Vehicle"

SixhoeProposalFig_4.jpg

FIG. 4. Photo of the Adaptive Suspension Vehicle (ASV) (Rosheim 1994).

SixhoeProposalFig_5.gif

FIG. 5. Side and front view drawings of the ASV (Rosheim 1994).

The Adaptive Suspension Vehicle (ASV) was developed by Kenneth Waldron and his team at Ohio State University from the late 1980s to until recently (FIG. 4). Unlike the Walking Truck, the ASV makes heavy use of computers, uses sophisticated vision and scanning systems, and has provided the walking machine community with many insights (Song & Waldron 1989). However, it can also be considered as unnecessarily complex, and expensive. Also, the lateral stability (FIG. 5) is limited by a total width of 5.2'. The pantograph leg design (FIG. 5) does not provide this machine with a clear advantage over, for example, the chassis of a typical front-end loader fitted with oversized tires. As a result, the future of the ASV is uncertain.

2.2.2.3. The Plustech "Walking Harvester"

SixhoeProposalFig_6.jpg

FIG. 6. Photo of the Plustech Walking Harvester (Plustech 1997).

The Walking Harvester (FIG. 6) was recently developed in Finland by Plustech Ltd. and is advertised as the "first working machine application of walking technology in the world" (Appendix 3), which is not far from the truth. The machine does walk and can accomplish a useful marketable work. It is still in its development stage, as technical specifications are not yet officially released, and serial production is still a few years away, according to a representative of that company. However, the Walking Harvester symbolizes the entry of private investment and industry in the field of large civilian walking machines. It may become the first successful expression of an old idea whose time has come.

2.3. Problems of walking machines

The walking machines mentioned above suffer from a problem that in the end restricts their usefulness and therefore hampers their commercialization, as discussed in the Patent Application. Briefly, their legs are designed only as legs and not as tool-carrying manipulators. And, by lacking the associated reach and polyvalence of backhoe-legs used as manipulators, the versatility - and marketability - of such walking machines is compromised from the start.

In many research institutions, there is an overemphasis on the control aspects of walking (adaptive control, fuzzy logic, neural networks, etc.), elaborate classifications of gaits, and the many links with the study of animal intelligence. All are interesting from an academic viewpoint and worth investigating, but the hardware meant to be controlled in such ways just does not measure up to the same levels of effort. The fact is that a hexapod is inherently a stable structure and it can walk with a relatively simple control system. Advanced forms of control are only necessary to improve adaptability, motion smoothness, or energetic efficiency. While worth pursuing, they are only secondary to the act of walking itself.

By convenience, many walking machines are designed to walk first on a flat horizontal surface (where actually they cannot compete with wheeled vehicles), and then tested in more and more sloped and unstructured ones, where sometimes agility problems can reveal themselves to be without solution. In particular, the reaching envelope of their legs is generally too small compared to body dimensions, which defeats the purpose of legs in general. Short legs do not provide enough of a clear advantage over wheeled and tracked vehicles to warrant a new product. The Sixhoe Project expects to follow the opposite process to ensure the compatibility of the machine with its intended rugged environment. Only in its ultimate version is the walking machine of this Project optimized for flat horizontal surfaces (such as roads). This is done by partially reverting to some kind of "wheels", in the form of a removable transporting cart which is hydraulically powered and controlled by the walking machine it carries (see later part of Patent Application).

3. Project Description

3.1. Project goal

The goal of the Sixhoe Project is to initiate the manufacture and sale of versatile walking legged machines that would complement and expand the existing line of products of a Company manufacturing hydraulically-powered earth-moving or similar equipment.

3.2. Project objectives

The objectives of the Sixhoe Project are to design, build, and evaluate, at a Company plant, a prototype of a versatile walking machine with backhoe legs, using as many pre-existing Company components as possible. It is envisioned as a relatively slow moving yet agile and forceful machine, for terrains not accessible to wheeled and tracked vehicles. The prototype is to be a fully capable and marketable machine, not a research platform with functional afterthoughts, although it would provide invaluable know-how for subsequent models. This walking machine, tentatively named "Sixhoe", has its hardware described in the Patent Application (Appendix 1). Some topics that were not relevant in the Patent Application itself, such as control system and marketing issues, will be presented below.

3.3. Project technical justifications

One of the important features of the Sixhoe Project is that it does not rest on untested or unproven technology, but on the new combination of existing and well-known ones, many of which are already in the field of expertise of the Company. The project is essentially the combination of old elements into a new entity, as will be shown.

3.3.1. Choice of legs over wheels

The reasons behind walking machines have been discussed above and in the Patent Application. The relatively new availability of powerful on-board computers and associated hardware is one of the time-dependent factors that makes walking machines currently possible.

3.3.2. Choice of wide-span legs

The Sixhoe uses a leg arrangement that is intermediary between a mammalian model (femur and tibia projecting straight down from the body) and an insect/spider model (femur projecting mostly up and then tibia down), and follows essentially a reptilian model (femur horizontal and tibia down). This choice results in two significant advantages. First, the Sixhoe can have a wide span between footholds, which provides a large stability of shape, as opposed to stability of weight. This is indispensable on slopes, and for roll-over safety in general. Second, the Sixhoe has a large adjustable body height above the ground, and yet retains large stability. This not only allows it to tackle large obstacles in the walking path, but opens the new possibility of carrying payloads slung under its body (P.A. Claim 5), and that of mating to a wheeled or tracked cart to be carried itself as a payload (P.A.).

3.3.3. Choice of backhoes as legs

The advantages of using backhoes as legs have been discussed at length in the Patent Application, as they are at the core of the design of the Sixhoe. Very briefly, these advantages are lower manufacturing and operational costs, simplicity, robustness, wide stability base, high ground clearance, and most importantly, ability to fit to them a wide variety of tools, apart from feet.

Selecting a backhoe for a leg may also be viewed as a voluntary constraint to get a useful end-product. The disadvantage of this choice is that backhoe-legs are generally not strong enough to bear the stresses of lateral swings, but this is compensated for by the way the control system employs them (see P.A. and section 3.3.6 below). The same limitation was actually encountered in Autopod 0.33 (Appendix 2). Offsprings of the Sixhoe Project may optimize the design of future backhoes made by the Company so that these are better suited to their double purpose of backhoe and leg.

3.3.4. Choice of the number of legs

A number of Japanese researchers study anthropomorphic bipeds, which generally need a solid ground to stay upright. However, in the context of large hydraulically powered machines, using fewer than 4 legs would be an invitation to disaster, as stability is then marginal and a fall more likely to cause damage than for a smaller machine. It has long been recognized that 6 legs is one of the best compromises of agility and stability, although 8 legs can also be an option in the present case. Publications never mention falls and the fact that walking machines, even if not damaged, are unable to get up on their feet again on their own after falling. In 1994 even the 8-legged robot Dante II tipped over (by overcompensation of suddenly yielding soil) while climbing out of the crater of Mount Spurr in Alaska. Although it occurred in very difficult conditions, this well-publicized fall has unfortunately been a source of sarcasm since the accident.

3.3.5. Choice of sensors

Unlike the ASV (section 2.2.2.2.), the Sixhoe does not use any vision or landscape scanning system, and does not construct any formal representation of the 3-D ground on which it is to tread. It directly uses local information from its legs, some of it tactile (foot contact), most of it proprioceptive (joint angles, cylinder pressures), and eventually, from body attitude indicators (gyroscopic or simpler tilt indicators). Many insects walk successfully on very complex ground with tactile and proprioceptive information from their legs, in total darkness. Also, relying on vision and spatial representation is unnecessary for a machine that is piloted by a human operator; this operator selects the trajectory to be followed that is most suitable. Reliable tactile information is a difficult problem, both in the robotics literature and in from personal experience. In the Sixhoe, the proprioceptive sensors are privileged relative to tactile sensors, because they are generally more reliable and less exposed to damage - and erroneous readings. As a result, the Sixhoe will be able to walk safely irrespective of darkness, smoke, dust, standing and moving liquids, because it relies mostly on inner perceptions, not easily misunderstood external perceptions (even with analytical help from powerful computers).

Given the importance of the sensors of the Sixhoe, for safety purposes production machines may use redundant parallel sensory systems, with error reporting to the operator on a diagnostic screen. This could be a double system with automatic stopping or freezing if two readings do not agree, or a triple system with polling and rejection of any value not agreeing with the two others, as used in the aerospace industry.

Sensory input comprises about 62 analog channels, namely 6x1 foot "contacts", 6x3 joint angles, 6x6 actuator pressures, and 2 body attitudes (pitch & roll). Some of these inputs can be preprocessed by dedicated microcontrollers. Several fast analog- to-digital boards with 64 analog inputs and Direct Memory Access (DMA) are currently available to convert that information into a form directly usable by the controlling computer system.

3.3.6. Choice of control system

The on-board control system envisioned for the Sixhoe is based on a single centralized computer, not a distributed system. This computer collects sensory information as described above. The operator's input is provided by a pair of joysticks (forward- backwards, left-right crab, left-right turn, up-down pitch), a few discrete potentiometers (up-down elevation, left-right tilt), a few push-buttons (emergency freeze, emergency kill), and a keyboard to select different walking and different backhoe or tool operation modes. The computer, in turn, sends appropriate servo-valve commands. The choice of computer should be based on ubiquity, easy maintenance, well-known performance, and the availability of a wide array of interfaces. Supplemental computers may perform specific watchdog functions in parallel.

As said earlier, the Sixhoe is envisioned as a "slow moving yet agile and forceful" machine. The relatively slow speed allows a statically stable walk, compared to what would be required for the dynamic stability of a biped. It not only minimizes the energy consumption for the acceleration and deceleration of the legs, but provides ample time for sensor data acquisition and for the actual "thinking" necessary to coordinate walking. Significantly, the motion of the legs is slow enough relative to computing speed that simple proportional control schemes can be used without risk of feedback instability and mismatched response times. In other words, the control, at least in initial implementations, is of a very conservative nature. The primary reason for this choice is that stability is the first duty of the control system, for safety reasons discussed later.

The algorithm is based on an endless loop of sequenced sensory, thinking, and motor phases as used in Autopod 0.33 (Appendix 2). Such a cycle would repeat at about 50 Hz, although the similarly slow Autopod 0.33 uses a 12 Hz refresh rate without problem. During the sensory phase, the computer collects all the data from the sensors and collects the commands from the operator. It may also display relevant information in a multimode synoptic way for the operator on a computer screen. During the thinking phase, the computer first analyzes the current forces and stability margins, and then, as a function of the commands of the operator, draws itself in a virtual "phantom" position and attitude in space in the immediate future, and re- analyzes what the new stability margins would then be. At that stage it would refuse motions that would narrow stability margins beyond prespecified safety thresholds. The algorithm then focuses on where the body-leg "hips" are desired to be positioned relative to the ground in the immediate future. This determines how each backhoe-leg is to be employed, that is either as an outrigger or as a propulsive unit, as explained in the Patent Application. Essentially, the algorithm would activate the actuators of a leg bearing weight (on the ground) so that it pushes or pulls its associated hip towards its desired phantom position, and those of a leg not bearing weight (off the ground) so that it positions its foot in a favorable location for the time it will bear weight again. During the motor phase, the computer sends off appropriate commands to servo-valves or variable-displacement hydraulic pumps used to control flow and pressure in the actuators.

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FIG. 7. Maximum weight-bearing ability of a CAT 426C backhoe modified by replacement of its bucket by a foot, as a function of boom and dipper stick angles. Surface is saddle-like with a diagonal "cliff" (see text).

A double action cylinder actuator exerts more "pushing" force than "pulling" force, because of the presence of a rod on its extension side. This has consequences when using such actuators in multi-segment articulated legs. The weight-bearing force available, for example, to a CAT 426C backhoe as a function of boom and dipper stick angles is shown in FIG. 7. A clear "cliff" is apparent in that figure, delineating the combinations of angles beyond which the stick has to be pulled instead of pushed to bear weight. One of the tasks of the controlling system is to remain in a volume bound by the surface depicted in FIG. 7, both for the current positions and for the virtual positions of the immediate future, with appropriate safety margins to allow for perturbations.

A series of watchdog features would monitor the progress of the legs as a function of hydraulic pressures to detect slippery or sticky conditions without tactile information. The algorithm would have the ability to branch out in insect-like reflexes such as trial and error methods to step a leg over an obstacle, for example. For the prevention of falls, the control system would possess a "bracing reflex" (Appendix 2) that pressurizes actuators in a predetermined way if too few of the sensors that should reveal a load are stimulated, a condition that most likely anticipates a fall. Originally, the algorithm would lift only one leg at a time, the most convenient way to progress safely in a very rugged environment, but it would ultimately lift three at a time in the classic alternating tripod gait, which is the fastest on easy terrains. Computer control enables completely different methods of walking by merely changing software. Only as a complementary option, further avenues for control (fuzzy logic, neural networks, genetic programs) can be explored. Eventually this can be done by collaboration with academic research institutions, which undoubtedly will be interested in the machine as a support for their own investigations. Advanced control methods are not necessary for statically stable hexapods, unlike for dynamically stable bipeds, where they are actually required.

3.3.7. Choice of "no-fall" and other performance objectives

The Sixhoe is a large and therefore heavy machine. Its first "performance" objective is to stay upright on its feet no matter what unfavorable conditions are encountered. This may be a truism for a walking machine designed to walk on relatively flat and horizontal terrains, but the Sixhoe is to tackle quite unstructured terrains by design. A fall, potentially injuring operator or bystanders and damaging the machine, is not acceptable (and even less so if it results from shortcuts or unproven or experimental methods in the field of stability control). Also, falls - like plane crashes - are not acceptable because the bad publicity they generate can signify the end of an otherwise perfectly worthy project. Only secondary to this crucial "no-fall" performance objective, in very general terms, the Sixhoe should be able to climb and descend at least 30deg slopes of most textures in any direction and to step over obstacles equal in height to its "body" height on unstructured terrain, while carrying a useful load of tool implements.

3.3.8. Choice of actuator control

By its very nature, a fluid tends to follow a path of least resistance. This has been a problem when simultaneously operating several actuators of a standard backhoe, and special banks of valves have had to be designed to solve it. This is also a problem for a hydraulically powered walking machine, if operating one leg robs pressure from another. It will change the load-bearing and propulsive ability of the latter in generally unpredictable ways. In a worst-case scenario, it can even lead to a collapse of that leg, for example by jumping out without warning through the "cliff" of FIG. 7. Several approaches around this problem are possible for a hexapod walking machine: using a single hydraulic pump and advanced flow-controlling valves for all actuators, using six pumps (one per leg) and servoed backhoe- type controls, or using 18 variable-displacement pumps under servo control (as used in the ASV, section 2.2.2.2). As of this writing, the choice of actuator control has not been made.

3.3.9. Choice of Patent Application

The walking machine described in the Patent Application (Appendix 1) is the best compromise between all different factors to reach the status of a marketable machine as defined in the Project Goals and Project Objectives (stated at the beginning of section 3). The design, construction, and evaluation process will also generate invaluable know-how not only for this kind of walking machine, but for its marketing, as it is to create and fill a totally new market.

3.4. Project marketing justifications

Until now, the great majority of walking machine projects have been undertaken by research institutions and universities, generally with public funds (NSF, DARPA, NASA). A few were funded privately, and were actually among the most accomplished (General Electric's Walking Truck, Plustech's Walking Harvester), presumably because they were intended from the start to execute a useful task, and not just to walk about in various environments.

3.4.1. Versatility by design

One of the key attributes of the Sixhoe, as explained in the Patent Application, is its versatility. First, it is a new platform for an unlimited array of specific applications, just like the chassis of a car or truck can support a wide variety of vehicles. The difference is that the Sixhoe can go where wheeled vehicles cannot go, which is half of the land on Earth. Second, it possesses legs that are essentially manipulators equipped with quick-changing tools. These tools can be the ones specific to any particular trade, as shown in the following non-exhaustive list of examples.

In agriculture, a Sixhoe can walk above the top of corn, shrubs and small fruit trees, on sloped and disorganized terrain. In sylviculture, the Sixhoe can perform logging tasks similar to those of the Plustech Walking Harvester (Appendix 3). In mining and road construction, a Sixhoe can be a rock drilling platform prior to blasting of obstacles. In precision demolition work, a sixhoe can support simultaneously a hydraulic hammer and scooping bucket feet. A Sixhoe can erect utility poles in forbidding terrains, as described in detail in the Patent Application. A Sixhoe can progress on loose debris for post-earthquake or post-explosion cleanup work. A Sixhoe can walk in standing water for rice and cranberry culture. In shoreline maintenance, a sixhoe can wade in surf with its body above the waves. As described in Patent Application, a Sixhoe can act as a walking crane in warehouses and harbors. It can also simply act as a walking excavator. It can be used for plain patrol or reconnaissance in difficult terrains (including volcano craters). However, planetary exploration, of Mars in particular, which is often brought forward as justification for walking machines, is currently too narrow and restricted a field to be part of this list. It is important to realize that standard market studies are likely to ignore many of these specific trades because of the very novelty of the product. This is why versatility (mostly conferred by the multi-functional role of backhoes) is such an important attribute of the Sixhoe. It can be adapted to any specific task.

The target acquisition cost of a Sixhoe should be of the same order of that of a standard wheeled loader-backhoe. This is important as this walking machine will be called to work in countries with much less wealth per capita than in the United States. Low cost is here part of versatility.

It is worth noting at this point that the human appeal for walking machines is very real. This was witnessed at the University of Illinois Engineering Open House exhibiting Protobot (Price 1995), and for Autopod 0.33 (1996). Depending on their size, they are regarded as pets, horses, or elephants. As a consequence, the recreational use of a Sixhoe just carrying a couple of passengers is not to be underestimated. It is a fact that US manufacturers shunned the building of All Terrain Vehicles (ATVs). They usually carry only one person and a very limited payload, and yet they were a huge commercial success in the USA (incidentally for mostly Japanese companies). The Sixhoe can be envisioned as an "artificial horse" of the future. This human appeal can also capitalized on for self-advertising of the product (section 4.2.6.).

3.4.2. Choice of timing

One may wonder why successful walking machines have not been built yet, and why they should be built now. Apart from the general needs stated above (section 2.1), one reason is the recent availability of computers small enough to be on-board the machine and powerful enough to control it in real time. Another reason is that fluid power motion control has also made progress in recent years. Most importantly, using backhoes as legs open possibilities unheard of before for walking machines. Also, the number of teams dedicated to the design and construction of walking machines and robots is increasing, in several countries. There is already a competitor in the Walking Harvester made by Plustech. Waiting too long at this stage can make one lose the edge in a global market, and lose to others new technologies that will emerge from the completion of the project.

3.4.3. Choice of Company

A Company with experience of hydraulically-powered earth-moving implements is ideally suited to support the Sixhoe Project.

Human beings are said to evolve in a 3-D space; however, they usually roam on a 2-D surface, and all man-built structures include flat horizontal surfaces on purpose, including roads. Most, if not all, companies manufacturing backhoes, for eaxample, happen to be located in "flat" locations, so the need for the machine described in these pages may not be initially recognized. The same applies to the potential purchasers of Sixhoes; the sale of such walking machines in Illinois or in the Netherlands will be minimal; they are not intended for such lands, but nearly all the others.

3.5. An analogy with aircraft design

For analogy purposes and as a form of conclusion, it is useful to compare flying machines and walking machines. A model project could be found in the creation of the Douglas DC-3 aircraft in the 1930s, which did not introduce any revolutionary technology, but combined existing ones in a result that certainly was revolutionary, and created an entire market in the process. It also had a determinant effect on the long-term success of that company. At present, the development of new aircraft is certainly limited by technology and not by imagination or design, but the opposite is true for walking machines, which are limited much more by imagination than by technology. A clear paradox appears from this analogy. On one hand the largest (now extinct) flying animal weighed in the order of tens of pounds, but man- made airplanes weighing half-a-million pounds can cross oceans. On the other hand, an elephant weighing three tons can walk miles on the energy from grass and leaves, but no man-made walking machine can match it. This is all the more surprising, when such a machine is now readily possible, unlike at the times of Ralph Mosher and his Walking Truck. The company seizing this opportunity can potentially repeat the success of a DC-3, and do that with a low investment risk.

4. Work Plan

4.1. Work method and organization

[deleted]

4.2. Work schedule and evaluation

The Sixhoe Project is organized in 6 phases separated in time but not especially in content. Evaluation will take place at the end of each phase.

4.2.1. Phase 1 - Team constitution

[deleted]

4.2.2. Phase 2 - Machine design

After a thorough survey of available means in the company by each team member, Phase 2 consists in the identification and choice of backhoes, power plants, number and type of hydraulic pumps, type of valves, sensors, computer, and in the engineering design of body chassis and feet. Phase 2 leads to a precise time-frame for parts acquisition, new parts manufacture, assembly, and testing, as well as a precise cost estimate for the prototype.

4.2.3. Phase 3 - Prototype construction and static testing

The chassis is built and bolted down to a flatbed trailer or to the ground. Two backhoes are modified to act as front legs and are connected to it. All systems are tested for control response and performance. Brackets are designed for the addition of removable axle and wheels from a loader, for example. Phase 3 leads to the gathering of the first actual data. Those are compared with initial estimates and used for performance estimation of the completed machine. The last significant hardware or design changes are made during this phase.

4.2.4. Phase 4 - Mobile two-legged version testing

The chassis with two front legs is fitted with temporary shock absorbers of adjustable height in the front, and to the axle and wheels in the back. The resulting appearance is similar to that of Autopod 0.33 (Appendix 3), except that the two front legs project forward as described in the Patent Application (Appendix 2) instead of laterally. The Sixhoe will make its first steps, not only on the factory floor, but on actual unstructured terrains. During that time a simple tracked cart is designed. Phase 4 leads to the first analysis of the performance of backhoes used as legs. The last significant software changes for leg control are made during this phase.

4.2.5. Phase 5 - Mobile six-legged version testing

Four supplemental modified backhoes are fitted to the chassis to create the final hexapod. The chassis is either equipped with an array of adjustable shock absorbers on its periphery, or mated to a tracked cart. The Sixhoe takes its first legs-only steps, again first on the factory floor for initial debugging, but quickly on the sloped and unstructured terrains it is designed for. All testing will be videotaped from several points of view for further analysis (dynamics replay). The hybrid legged and tracked version is tested. Phase 5 leads to the official public release of the Sixhoe.

4.2.6. Phase 6 - Customer evaluations

This last phase will be centered on the adaptation of the Sixhoe to the specific trades it was envisioned to perform a task for, and to unsuspected new ones that may not yet be apparent at the beginning of the project, as it is the case for novel products of this kind. This phase will be very active in the field of public relations, with especially careful listening to the needs of potential customers. To use the potentially self- advertising qualities of the Sixhoe beyond copyright-free footage for the media, the machine could also be made available to the movie industry.

4.3. Estimated budget

[deleted]

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Appendices

1. Patent Application "Walking Machine with Backhoe Legs", 1997, 34 pages, 196 kB

2. Description of Autopod 0.33, built in 1996, 26 pages, 258 kB

3. Plustech Advertisement for Walking Harvester, 1997, 1 page, 29 kB