Abstract:
A method and apparatus for transporting heavy machinery, equipment or other heavy loads from one location to another, whereby the apparatus may be constructed as a walking machine including a plurality of lifting assemblies operative to lift the load above the supporting surface and then move the load relative to the supporting surface by transporting the load via rollers or tracks in the walking machines. In one example, the lifting assemblies are provided with separate longitudinal and lateral drive mechanisms independently operative for translating the load in either or both longitudinal and lateral directions.

Description:
RELATED APPLICATION DATA 
       [0001]    This application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Application No. 62/195,466, filed on Jul. 22, 2015, hereby incorporated by reference. 
     
    
     BACKGROUND 
       [0002]    The field of the present invention is related to a class of transportation machines commonly referred to as “walking machines,” which are large, typically non-wheeled power-driven structures operable for transporting massive and heavy loads, upwards of several thousand tons, over a road or other ground surface such as ground, snow, a prepared gravel area, etc. These machines, and the heavy substructures in themselves, are fabricated from steel and other high-strength materials and find particular use in carrying and sequentially transporting large and huge structures such as oil drilling rigs to position, and reposition them, over a drilling well bore in a new field undergoing exploration for oil, or over existing well bores in an old field previously worked, as needed. 
         [0003]    Instead of using ground-contacting wheels to move the heavy loads, these walking machines typically comprise a plurality of lifting assemblies that usually use hydraulic lift cylinders to lift the load above the supporting surface and then move the load relative to the supporting surface by transporting the load via rollers or tracks in the walking machines. 
         [0004]    In order to position the oil rig or other heavy load in a precise position, these walking machines may be provided with a steering mechanism whereby the walking machine unit may be rotated or steered to a desired position. U.S. Pat. No. 6,581,525, hereby incorporated by reference, shows walking machine systems and methods for moving heavy loads, such as oil rig structures. The U.S. Pat. No. 6,581,525 patent also discloses a steering system for a walking machine in which a substructure of the walking unit may be disengaged and rotated relative to its upper structure thus repositioning the substructure for travel at a desired steered angle. Other steering systems for walking machines are disclosed in U.S. Pat. No. 8,573,334 and U.S. Pat. No. 7,806,207. The present inventors have recognized that these steering systems have various limitations and potentially undesirable characteristics, which, depending upon the design, may include: only manual repositioning; complicated rotational position detection and control; complicated or unreliable rotational drive mechanisms; excessively high ground pressures and/or limitations on stroke. 
       SUMMARY 
       [0005]    The present invention is directed to apparatus and methods for transporting heavy machinery, equipment or other heavy load from one location to another, whereby the apparatus is constructed to transport the load in multiple directions in order to move the load in a desired path to a set position. A preferred embodiment is directed to a walking machine comprising a plurality of lifting assemblies operative to lift the load above the supporting surface and then move the load relative to the supporting surface (e.g., the road or other ground surface) by transporting the load via rollers or tracks in the walking machines, the lifting assembly including transport mechanisms operative for transporting the load in multiple directions—in one example both a first direction (e.g., longitudinally) and a second direction (e.g., laterally)—so that lifting assemblies may be driven in a desired walking direction or along a desired path. 
         [0006]    Additional aspects and advantages will be apparent from the following detailed description of preferred embodiments, which proceeds with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a diagrammatic view of an example walking machine system for moving a large support structure shown as an oil rig. 
           [0008]      FIG. 2  is a partial view of the walking machine system of  FIG. 1  with the walking machine units in position connected to the oil rig. 
           [0009]      FIGS. 3-7  are partial views of the walking machine system of  FIG. 1  illustrating the operation of the walking machine units. 
           [0010]      FIG. 8  is a top plan view of a walking machine system according to a preferred embodiment, with four walking machine units, one disposed at each of the four corners of the oil rig. 
           [0011]      FIGS. 9-12  are each a top plan view of one side of the walking machine system of  FIG. 8 , illustrating two walking units. In  FIG. 9  the walking units are in a first longitudinal position and central lateral position; in  FIG. 10  the walking units are in a forward extended position and central lateral position; in  FIG. 11  the walking units are in the first (rearward) longitudinal position and right side lateral position; in  FIG. 12  the walking units are in the first (rearward) longitudinal position and left side lateral position. 
           [0012]      FIG. 13  is a top isometric view of the walking machine units of  FIG. 9 . 
           [0013]      FIG. 14  is a top right rear isometric view of a walking machine unit according to an embodiment. 
           [0014]      FIG. 15  is a top left rear isometric view of the walking machine unit of  FIG. 14 . 
           [0015]      FIG. 16  is a right side elevation view of the walking machine unit of  FIG. 14 . 
           [0016]      FIG. 17  is a rear side elevation view of the walking machine unit of  FIG. 14 . 
           [0017]      FIG. 18  is partial cross-sectional view of  FIG. 19  taken along line  18 - 18 . 
           [0018]      FIG. 19  is a top plan view of the walking machine unit of  FIG. 14 . 
           [0019]      FIG. 20  is a detailed view of a portion of  FIG. 18  on an enlarged scale. 
           [0020]      FIG. 21  is a partially exploded isometric view of the walking machine unit in  FIG. 14 . 
           [0021]      FIG. 22  is an isometric view of a foot section of the walking machine unit of  FIG. 14 . 
           [0022]      FIG. 23  is a top plan view of the foot section of  FIG. 22 . 
           [0023]      FIG. 24  is a right side elevation view of the foot section of  FIG. 22 . 
           [0024]      FIG. 25  is a front side elevation view of the foot section of  FIG. 22 . 
           [0025]      FIG. 26  is a top side isometric view of a roller guide section of the walking machine unit of  FIG. 14 . 
           [0026]      FIG. 27  is a top plan view of the roller guide section of  FIG. 26 . 
           [0027]      FIG. 28  is a right side elevation view of the roller guide section of  FIG. 26 . 
           [0028]      FIG. 29  is a front side elevation view of the roller guide section of  FIG. 26 . 
           [0029]      FIG. 30  is a top isometric view of a roller assembly of the walking machine unit of  FIG. 14 . 
           [0030]      FIG. 31  is top plan view of the roller assembly of  FIG. 30 . 
           [0031]      FIG. 32  is a right side elevation view of the roller assembly of  FIG. 30 . 
           [0032]      FIG. 33  is a front side elevation view of the roller assembly of  FIG. 30 . 
           [0033]      FIG. 34  is a cross-sectional view of  FIG. 19  taken along lines  34 - 34 . 
           [0034]      FIGS. 35A, 35B and 35C  illustrate the walking machine unit of  FIG. 14  with the longitudinal drive in the fully retracted position and the lateral drive in the fully extended position,  FIG. 35A  being a top plan view,  FIG. 35B  a front side elevation view, and  FIG. 35C  a partial cross-sectional view of  FIG. 35B  taken along lines  35 C- 35 C. 
           [0035]      FIGS. 36A, 36B and 36C  illustrate the walking machine unit of  FIG. 14  with the longitudinal drive in the fully retracted position and the lateral drive in the fully retracted position,  FIG. 36A  being a top plan view,  FIG. 36B  a front side elevation view, and  FIG. 36C  a partial cross-sectional view of  FIG. 36B  taken along lines  36 C- 36 C. 
           [0036]      FIGS. 37A, 37B and 37C  illustrate the walking machine unit of  FIG. 14  with the longitudinal drive in the fully extended position and the lateral drive in the centered position,  FIG. 37A  being a top plan view,  FIG. 37B  a front side elevation view, and  FIG. 37C  a partial cross-sectional view of  FIG. 37B  taken along lines  37 C- 37 C. 
           [0037]      FIGS. 38A, 38B and 38C  illustrate the walking machine unit of  FIG. 14  with the longitudinal drive in the fully extended position and the lateral drive in the fully retracted position,  FIG. 38A  being a top plan view,  FIG. 38B  a front side elevation view, and  FIG. 38C  a partial cross-sectional view of  FIG. 38B  taken along lines  38 C- 38 C. 
           [0038]      FIGS. 39A, 39B and 39C  illustrate the walking machine unit of  FIG. 14  with the longitudinal drive in the fully extended position and the lateral drive in the fully extended position,  FIG. 39A  being a top plan view,  FIG. 39B  a front side elevation view, and  FIG. 39C  a partial cross-sectional view of  FIG. 39B  taken along lines  39 C- 39 C. 
           [0039]      FIG. 40  is a partial cross-sectional view of the walking machine unit of  FIG. 14  illustrating a lifting device with the lift mechanism in a first (fully) retracted position, with the foot pad lifted off the ground. 
           [0040]      FIG. 41  is a partial cross-sectional view of the walking unit of  FIG. 14  illustrating a lifting device with the lift mechanism in a first partially extended position, with the foot pad in contact with the ground. 
           [0041]      FIG. 42  is a partial cross-sectional view of the walking machine unit of  FIG. 14  illustrating a lifting device with the lift mechanism in a second partially extended position, with the foot pad in contact with the ground. 
           [0042]      FIG. 43  is a partial cross-sectional view of the walking machine unit of  FIG. 14  illustrating a lifting device with the lift mechanism in the fully extended position, in position lifting the load. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0043]    The preferred embodiments will now be described with reference to the drawings. With reference to the above-listed drawings, this section describes particular example embodiments and their detailed construction and operation. To facilitate description, any element numeral representing an element in one figure will be used to represent the same element when used in any other figure. The embodiments described herein are set forth by way of illustration only and not limitation. It should be recognized in light of the teachings herein that there is a range of equivalents to the example embodiments described herein. Notably, other embodiments are possible, variations can be made to the embodiments described herein and there may be equivalents to the components, parts, or steps that make up or augment the described embodiments. 
         [0044]      FIGS. 1-7  are a series of schematic drawings for an example walking machine system for moving a large support structure shown as an oil rig  10  along a ground surface  5 . The oil rig  10  is supported onto the ground surface  5  by a plurality of support legs  55  attached to the bottom support structure  50 . The walking machine system includes a set of four lifting assemblies (or lifting machine units), with a lifting assembly or unit arranged in position proximate each of the corners of the oil rig  10 . Two lifting assemblies  100 ,  102  are visible in  FIGS. 1-7  and the other two lifting assemblies  104 ,  106  are shown in  FIG. 8  described below. The lifting assemblies  100 ,  102 ,  104 ,  106  may be supported via a longitudinal beam (as shown) or other configuration such as via a horizontal beam. Though four lifting assemblies are shown, the system may include additional lifting assemblies. 
         [0045]    Operation of the lifting assemblies  100 - 106  is now described with respect to a first lifting assembly  100 . For initial installation, the lifting assembly  100  is set in position on the ground as in  FIG. 1  with its lifting cylinder retracted. The lifting cylinder is raised partway as in  FIG. 2  and contacts the oil rig support beam/structure  50  and is then connected thereto by bolting (the attachement bolts are visible in  FIG. 2 ) or other suitable attachments. The lifting cylinder is then retracted thereby lifting the lower structure or jack pad of the lifting assembly  100  off the ground (due to its attachment to the support beam  50  of the oil rig  10 ) and then the lifting assembly lower structure and foot pad are driven forward by a first push-pull mechanism to the forward position as in  FIG. 3 . The lifting cylinder is then partially extended, lowering the lifting assembly lower structure and jack pad to the ground as shown in  FIG. 4 . The lifting cylinder is then raised to the extended position thereby lifting the support structure  50  and support legs  55  off the ground as in  FIG. 5 . Once the oil rig  10  is lifted, the lifting assembly lower structure (the foot) is driven rearward by the first push-pull mechanism to the rearward position thereby moving the rig  10  forward as in  FIG. 6 . The lifting cylinder is then retracted, lifting the assembly lower structure as in  FIG. 7 , after which the assembly lower structure may then be driven forward to the position as in  FIG. 3 . The process steps are then repeated. 
         [0046]    In one embodiment, a second push-pull mechanism, operating separately or in combination with the first (longitudinal) push-pull mechanism, provides for lateral drive motion. In any event, the second (lateral) push-pull mechanism is operable independently from the first (longitudinal) push-pull mechanism enabling for lateral motion with or without longitudinal motion. 
         [0047]    Further details of the lifting assembly and push-pull mechanisms will now be described.  FIG. 8  illustrates a top plan view of the walking machine system comprised of the four walking machine units  100 ,  102 ,  104 ,  106  with the rig  10  removed and showing substructure  50 . The walking machine units  100 - 106  in  FIG. 8  are illustrated in a first longitudinal (non-extended) travel position, and laterally centered. 
         [0048]      FIGS. 9-13  illustrate one side of the walking machine system and two of the walking machine units  100 ,  102  in various positions. In  FIGS. 9 and 13  the walking machine units  100 ,  102  are illustrated in the first longitudinal, non-extended or rearward, travel position, and laterally centered (similar to  FIG. 8 ). The isometric view of  FIG. 13  further illustrates the forward walking machine unit disposed within the cross beams  52 ,  54  of the substructure  50  and also illustrates the rear lifting assembly with cross beams of the substructure  50  removed. In  FIG. 10  the walking machine units  100 ,  102  are illustrated in the second longitudinal, forward-extended, travel position, and laterally centered. In  FIG. 11  the walking machine units  100 ,  102  are illustrated in the first longitudinal, non-extended or rearward, travel position, and laterally to the right side. In  FIG. 12  the walking machine units  100 ,  102  are illustrated in the first longitudinal, non-extended or rearward, travel position, and laterally to the left side. Though not shown, the walking machine units may be translated into the second longitudinal, forward-extended, travel position, and laterally translated to the left or right. 
         [0049]      FIGS. 14-43  illustrate details of the walking machine unit  100  according to an embodiment. The walking machine unit  100  basically comprises a foot plate assembly or foot section  110 , an upper roller guide assembly  200  (with lateral drive), a longitudinal drive assembly  300 , and a lift assembly  400 . 
         [0050]      FIGS. 14-29  illustrate details of the structure and drive system for the lateral translation mechanism according to an embodiment. The foot section  110  comprises a foot plate  111  which contacts the ground surface during a walking motion of the walking machine unit  100 . The foot section  110  comprises a foot plate  111  of generally rectangular shape with somewhat up-curved ends. Though the foot plate  111  may alternatively be another suitable shape such as oblong or circular, the elongated rectangular structure may enable the walking machine unit  100  to have a longer longitudinal travel stroke with a solid/stable footprint. The foot section  110  includes a plurality of retainer bars secured to and arranged about the upper surface of the foot plate  111 : retainer bars  112   a,    112   b,    112   c  on one lateral side; retainer bars  112   d,    112   e,    112   f  on the opposite side; retainer bars  112   g,    112   h  on the front side; and retainer bars  112   i,    112   j  on the rear side. A slide plate  180 , which may be constructed of stainless steel, is disposed flat on the central portion of the foot plate  111  nesting between the retainer bars  112   a - j.  The slide plate  180  thus remains free-floating, but its lateral and longitudinal position is maintained centrally within and flat against the foot plate  111 . Alternatively the slide plate  180  may be attached to the foot plate  111  such as by welding or connectors (e.g., screws or bolts), but the floating construction may better manage expansion/contraction issues due to different expansion coefficients of the steel types and may also provide for easier construction and/or repair/replacement or allow for expansion of a non-composite plate configuration due to deflection of the foot plate/slide. 
         [0051]    A low friction plate  190  comprising a flat bushing is disposed on the lower surface of the roller guide assembly  200  to provide for a low friction slide surface between the roller guide assembly  200  and the slide plate  180 . The low friction plate  190  may be made of nylon (e.g., a lubricant filled plastic such as Nylatron® plastic available from Quadrant EPP USA, Inc. of Reading, Pa.), PTFE, bronze or other metal, or other suitable plate/sheet material or coated plate. In other embodiments, a lubrication, e.g., grease, may be applied to the slide plate  180 . Alternately, the positions of the slide plate  180  and the low friction plate  190  may be reversed. Alternately, instead of a low friction slide surface configuration, roller bearings or other suitable bearing or roller assembly system may be employed to provide for low friction lateral movement. 
         [0052]    The roller guide assembly  200 , details of which are shown in  FIGS. 26-29 , comprises a main or bottom plate  210  and first and second roller support sides. The first roller support side comprises a top plate  230  and a vertical wall  234  forming a generally I-beam cross-section with the bottom plate  210 . The top plate  230 , vertical wall  234  and bottom plate  210  form a channel  235 . The top plate  230  is secured to the vertical wall  234  and the bottom plate  210  via a series of eight stiffening ribs, two of which are designated by element numerals  232   a  and  232   b.  Similarly, the second roller support side comprises a top plate  220  and a vertical wall  224  forming a generally I-beam cross-section with the bottom plate  210 . The top plate  220 , vertical wall  224  and bottom plate  210  form a channel  225 . The top plate  220  is secured to the vertical wall  224  and the bottom plate  210  via a series of eight stiffening ribs, two of which are designated by element numerals  222   a  and  222   b.    
         [0053]    Guide tubes  160 ,  170  are attached to the bottom plate  210  on opposite longitudinal sides. The guide tube  160  includes an attachment bracket  164 , and the guide tube  170  includes an attachment bracket  174 . The roller guide assembly  200  is mounted to the foot plate  111  via the guide tubes  160 ,  170  to allow lateral movement. Guide bars  161 ,  171  are disposed on opposite longitudinal sides of the foot plate  111 . Guide bar  161  is secured to the foot plate  111  via brackets  162 ,  166 , and guide bar  171  is secured to the foot plate  111  by brackets  172 ,  176 . Brackets  144 ,  154  are also secured onto the foot plate  111  for attachment to the lateral drive cylinders  140 ,  150 . A cylindrical sleeve or bushing  160   a  of low friction material (e.g., nylon or other suitable material) may be installed within the guide tube  160  and around the guide bar  161 , and a cylindrical sleeve or bushing  170   a  of low friction material is similarly installed within the guide tube  170  and around the guide bar  171 . 
         [0054]    The lateral drive force is provided by lateral drive cylinders  140  and  150  attached between the roller guide assembly  200  and the foot plate  111 . The drive cylinder  140  is connected at one end  141  to the bracket  164  via a pin  149 , and at its second end  145  on piston shaft  142  to the bracket  144  on foot plate  111  via pin  146 . Similarly on the other side, the drive cylinder  150  is connected at one end  151  to the bracket  174  via a pin  159 , and at its second end  155  on piston shaft  152  to the bracket  154  on foot plate  111  via pin  156 . Alternate lateral drive force may be provided by any suitable drive mechanism including the piston/cylinder drive (as illustrated), jack screw drive, rack and pinion assembly, chain and sprocket drive, gear drive, electric motor, or other drive systems. 
         [0055]    The entire lift assembly  400  and roller guide assembly  200  thus are able to be translated laterally, driven by the hydraulic drive cylinders  140 ,  150 , via sliding support surfaces. Further details of the sliding support surface combination are best shown in  FIGS. 18-21 . The slide plate  180  is disposed on the top surface of the foot plate  111 , nesting within the frame established by the retainer bars  112   a - j.  The low friction plate  190 , which may be about 1.5 inches thick (about 3.8 cm), is retained in position between the bottom plate  210  and the slide plate  180  via a retaining frame  192  arranged around the low friction plate  190 . The retaining frame  192  may be made of steel and welded to the roller guide plate  210 . The retaining frame  192  may be continuous and surround the low friction plate  190  on all sides, or may just be on two lateral sides. The retaining frame  192  may alternatively be intermittent, akin to the structure of the retainer bars  112   a - j.  The retainer bars  112   a - j  (see, for example, retainer bar  112   b  in  FIG. 20 ) may have the same height as the slide plate  180 . The retainer frame  192  has a lower height than the low friction plate  190  such that even with any compression of the low friction plate  190 , a gap G is maintained between the retaining frame  192  and the slide plate  180 , thus preventing or inhibiting metal-to-metal contact between the retaining frame  192  and the slide plate  180 . Alternately, the low friction plate  190  may be mounted onto the foot plate  11  by a retaining frame secured to the foot plate  111  in essentially a reverse configuration to that illustrated. 
         [0056]    A wiper  194  is provided along the outside perimeter of the retaining frame  192  and serves to span and cover the gap G, sliding along the upper surface of the slide plate  180  to inhibit debris from getting onto the surface of the slide plate  180  and/or between the slide plate  180  and the low friction plate  190 . 
         [0057]    The low friction plate  190  may be attached to the lower surface of the roller guide plate  210 , or it may merely be free-floating, kept in position by the retainer frame  192  disposed about its outer perimeter. Alternately, instead of the low friction plate  190  and slide plate  180 , a roller system may be provided to provide for low friction movement between the foot section  110  and the upper roller guide assembly  200 . 
         [0058]    The longitudinal drive assembly  300  comprises a roller assembly  305  and drive cylinder  310 . The roller assembly  305  includes a roller housing section  320  of generally rectangular box shape formed with two internal channels  331 ,  335  for accommodating the rollers  334 ,  336 . The first internal channel  331  is formed by side walls  326   a,    326   b,  with roller plate  334  attached to the side walls  326   a,    326   b.  The second internal channel  335  is formed by side walls  324   a,    324   b,  with roller plate  336  attached to the side walls  324   a,    324   b.  The rollers  334 ,  336  may comprise chain roller bearings such as available from Hilman Incorporated of Marlboro, N.J. Other low friction or reduced friction systems may be employed for the longitudinal drive assembly  300  in place of the roller assembly  305 , such as other types of bearings, slide surfaces (e.g., a plate bushing), or other suitable construction. 
         [0059]    The roller assembly  305  includes centering springs  360 ,  350  disposed on its lateral sides. Centering spring  360  is connected along side wall  326   a,  and centering spring  350  is connected along side wall  324   a.  Rollers  362 ,  364  are disposed on the ends of the centering spring  360  and travel along the channel  225  in the roller guide assembly  200 . Rollers  352 ,  354  are disposed on the ends of the centering spring  350  and travel along the channel  235  in the roller guide assembly  200 . A slide pad  366  is attached along a center outside portion of the spring  360  for providing a low friction sliding surface against the vertical wall  224 . A slide pad  356  is attached along a center portion of the centering spring  350  for providing a low friction sliding surface against the vertical wall  234 . The centering springs  350 ,  360  comprise leaf springs that allow for some lateral movement to accommodate for some misalignment during the drive operation when moving the load, and then serve to re-center the roller assembly  305  when the load is released. 
         [0060]    The roller assembly  305  includes a drive connection bracket assembly including a U-shaped upper bracket  370  and a U-shaped lower bracket  380 . An attachment bracket  374  is disposed on the end of the upper bracket  370 . A hole  372  is disposed in the end of the upper bracket  370  for connection to the longitudinal drive cylinder  310 . 
         [0061]    The longitudinal drive cylinder  310  is disposed within a central channel or opening between the (inner) side walls  326   b,    324   b  and extends into the open inner portion of the U-shaped brackets  370 ,  380 . The longitudinal drive cylinder  310  is connected at one end (the shaft end)  312  to bracket  240  on the upper roller guide assembly  200  via a pin  313  and on the other end  314  to upper and lower brackets  370 ,  380  via a pin  315  through the hole  372  in the upper bracket  370  and a corresponding hole in the lower bracket  380 . 
         [0062]    The walking machine system includes a control system for controlling the operation of the walking machine units  100 ,  102 ,  104 ,  106 . Each walking machine unit, for example walking machine unit  100 , is provided with a hydraulic control system for operating the lift mechanism  120 , the longitudinal drive mechanism (longitudinal drive cylinder  310 ) and the lateral drive mechanism (lateral drive cylinders  140 ,  150 ). The longitudinal drive system may operate independently or in combination (i.e., simultaneously) with the operation of the lateral drive system. Thus the lifting mechanism and load may be controlled/operated to transport the lifting assembly and load in any direction: forward, backward, sideward (left or right), or diagonally at any desired angle or direction. In addition, by operating the front walking machine units  102 ,  106  in one lateral direction (such as left or diagonally left) and the rear walking units  100 ,  104  in another lateral direction (such as right or diagonally right) the oil rig  10  may be rotated. 
         [0063]    Though the longitudinal drive mechanism is shown for example as a hydraulic drive system comprising the longitudinal drive cylinder  310 , other types of longitudinal drive mechanisms may be employed such as the piston/cylinder drive (as illustrated), jack screw drive, rack and pinion assembly, chain and sprocket drive, gear drive, electric motor, or other drive systems. 
         [0064]      FIGS. 34-39  illustrate various longitudinal and lateral drive positions for the walking machine unit  100 . 
         [0065]      FIG. 34 , in combination with  FIGS. 17 and 19 , illustrates the walking machine unit  100  with the longitudinal drive in the fully retracted position and the lateral drive in a centered position,  FIG. 17  being a front side elevation view,  FIG. 19  being a top side plan view, and  FIG. 34  being a partial cross-sectional view of  FIG. 19 . 
         [0066]      FIGS. 35A, 35B and 35C  illustrate the walking machine unit  100  with the longitudinal drive in the fully retracted position and the lateral drive in the fully extended position,  FIG. 35A  being a top plan view,  FIG. 35B  a front side elevation view, and  FIG. 35C  a partial cross-sectional view of  FIG. 35B . 
         [0067]      FIGS. 36A, 36B and 36C  illustrate the walking machine unit  100  with the longitudinal drive in the fully retracted position and the lateral drive in the fully retracted position,  FIG. 36A  being a top plan view,  FIG. 36B  a front side elevation view, and  FIG. 36C  a partial cross-sectional view of  FIG. 36B . 
         [0068]      FIGS. 37A, 37B and 37C  illustrate the walking machine unit  100  with the longitudinal drive in the fully extended position and the lateral drive in the centered position,  FIG. 37A  being a top plan view,  FIG. 37B  a front side elevation view, and  FIG. 37C  a partial cross-sectional view of  FIG. 37B . 
         [0069]      FIGS. 38A, 38B and 38C  illustrate the walking machine unit with the longitudinal drive in the fully extended position and the lateral drive in the fully retracted position,  FIG. 38A  being a top plan view,  FIG. 38B  a front side elevation view, and  FIG. 38C  a partial cross-sectional view of  FIG. 38B . 
         [0070]      FIGS. 39A, 39B and 39C  illustrate the walking machine unit  100  with the longitudinal drive in the fully extended position and the lateral drive in the fully extended position,  FIG. 39A  being a top plan view,  FIG. 39B  a front side elevation view, and  FIG. 39C  a partial cross-sectional view of  FIG. 39B . 
         [0071]    Prior walking units that required rotation of the lower walking mechanism in order to allow for lateral movement/steering had limitation on the length of the foot pad thus limiting longitudinal travel stroke. Since the walking machine unit  100  does not require rotation of the foot pad  110 , it may be constructed with a longer foot pad  110  and thus produce a longer longitudinal stroke. In comparison to earlier units of comparable size and lift capability that have a typical stroke (in any direction) of about 15 inches (38 cm), the walking machine unit  100  may be constructed with a longitudinal stroke on the order of 48 inches (120 cm). The lateral stroke would still have the same structural limitations and would thus be on the order of 12 inches (30 cm). Moreover, since both lateral and longitudinal motion may be implemented in the same push-pull cycle, and steering rotation (and the time it takes to rotate the drive system) is not required, the walking unit  100  may travel at a much faster rate because of reduced reset times and due to the considerably longer longitudinal travel stroke. 
         [0072]    It is noted that in  FIGS. 8-39  the lift mechanism  120  is shown in the retracted condition.  FIGS. 21 and 40-43  illustrate details of the lifting device and its operation according to an embodiment. 
         [0073]      FIG. 40  illustrates the walking machine unit  100  with the lift mechanism  120  in the fully retracted position (with no gap between the piston  126  and the lift cylinder  125 ), with the foot pad  110  being lifted off the ground by a gap A. The two-part lifting plate  121  is secured by bolts  122 , through spacers  123  to the top plate  322  of the roller assembly  305 . The bottom face of the piston cylinder  126  comprises a spherical concave surface  129  (see also  FIG. 34 ) for engaging the corresponding convex dome surface of the dome plate  323 . The piston cylinder  126  (and its concave bottom surface) is separated by a gap B from the dome plate  323  of the lifting plate  121 , and the shoulder  127  of the piston  126  is in contact with the lifting plate  121 . As the piston  126  is retracted, the shoulder  127  comes in contact with the lifting plate  121  to lift the foot section  110  off the ground surface  5 . There is a gap B between the piston  126  and the dome plate  323  when retracting/lifting the foot section  110  as shown. 
         [0074]      FIG. 41  illustrates the walking machine unit  100  with the lift mechanism  120  in a first partially extended position (with a gap A 1  between the piston  126  and the lift cylinder  125 ), with the foot plate  111  just touching the ground surface  5 . There is still the gap B between the piston  126  and the dome plate  323  when retracting/lifting the foot section  110  is in the position as shown. 
         [0075]      FIG. 42  is illustrates the walking machine unit  100  with the lift mechanism  120  in a second partially extended position (with a gap A 2  between the piston  126  and the lift cylinder  125 ), with no gap between the piston  126  and the dome plate  323 , but there is a gap C between the lifting plate  121  and the shoulder  127 . 
         [0076]      FIG. 43  illustrates the walking machine unit  100  with the lift mechanism  120  in a fully extended position with a gap A 3  between the piston  126  and the lift cylinder  125  and with the load lifted off the ground surface  5 . As in  FIG. 42 , there is no gap between the piston  126  and the dome plate  323 , but there is a gap C between the lifting plate  121  and the shoulder  127 . 
         [0077]    Other embodiments are envisioned. Although the description above contains certain specific details, these details should not be construed as limiting the scope of the invention, but as merely providing illustrations of some embodiments/examples. It should be understood that subject matter disclosed in one portion herein can be combined with the subject matter of one or more of other portions herein as long as such combinations are not mutually exclusive or inoperable. 
         [0078]    The terms and descriptions used herein are set forth by way of illustration only and not meant as limitations. It will be obvious to those having skill in the art that many changes may be made to the details of the above-described embodiments without departing from the underlying principles of the invention.