Abstract:
A compacting device ( 40 ) for attachment to an earthmoving machine ( 2 ) to compact a substrate is described. The compacting device ( 40 ) includes a plurality of wheel assemblies ( 41, 42, 43 ) mounted for rotation in bearings ( 46 ). A support is also provided, having a base part ( 48 ) that is adapted to be mounted to the earthmoving machine ( 2 ). One or more bearing support members ( 47 ) extend from the base part ( 48 ) and between the wheel assemblies ( 41, 42, 43 ) to support the bearings ( 46 ). Each wheel assembly ( 41, 42, 43 ) includes a set of ground-contacting feet ( 44 ) secured to and peripherally spaced apart around a rim portion of the wheel assembly ( 41, 42, 43 ). In this arrangement, when the device ( 40 ) is rolled over the substrate a first foot of said set of ground engaging feet ( 44 ) contacts the substrate between axial width limits that differ from axial width limits of a second foot of said set of ground engaging feet ( 44 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority from Australian Provisional Patent Application No 2006902915 filed on 31 May 2006, the contents of which is incorporated herein by reference. 
     FIELD OF THE INVENTION 
     This invention relates to a compacting wheel apparatus of the type fitted to earthmoving machinery for compacting soil, particularly in trenches. 
     BACKGROUND 
     It is a requirement in cable- and pipe laying, and civil engineering in general, to compact soil in a trench, or other confined space, to return the soil to its original grade. For reasons of cost, safety and consistency of results, it is normal to fit a rotatable wheel or drum to a suitable earthmoving machine, the wheel or drum being rolled back and forth over the soil area to be compacted until a suitable level of compaction is obtained. 
       FIG. 1  shows one such arrangement. A wheel-type compacting device  1  is mounted to a backhoe excavator  2  in place of the usual bucket. The device  1  is able to rotate freely about an axis  3  that is parallel to the axes  4  and  5  about which the backhoe&#39;s dipper (sometimes alternatively called stick)  6  and boom  7  rotate. The backhoe operator positions excavator  2  so that axes  4  and  5  are perpendicular to the length of a trench  8 . The operator can then readily position the device  1  at the base of the trench, and by operation of boom  7  and stick  6 , roll the device backwards and forwards along the trench to compact the soil therein. The device  1  is typically provided with radially projecting feet  9  to enhance the compaction effect but may also take the form of a plain-surfaced wheel or drum. 
     In some circumstances vibration devices may be employed with the device  1  for better compaction, and sometimes no vibration capability is provided, reliance being placed simply on repetitive pressing downward of the soil surface by the feet of the wheel. 
     Other types of machines may be used for mounting the compacting devices such as device  1 . For example, device  1  may be mounted to other types of excavators, such as telescopic-boom excavators (sold by Gradall Inc., USA), and to the boom-and-stick backhoe arrangements that are often fitted to the rear of wheeled loaders. With suitable adaptors, front-end loaders of the articulated or skid steer type may also be fitted with compacting devices. 
     Compacting devices that comprise a single drum with feet projecting therefrom and which is supported for rotation between fork arms can lead to difficulties in compacting soil adjacent the walls of a trench. This may be due to the fact that the fork arms are of a size that can prevent the drum accessing the soil at the perimeter of the trench, adjacent the longitudinal walls of the trench. It is therefore known to provide compacting devices, such as device  1 , that employ several individual wheel disks  10  on a common shaft, with supporting members  11  arranged therebetween. In the arrangement as shown in  FIG. 1 , supporting members  11  are secured to a structure  12  releasably attached to the stick  6  and provide support for an axle (not shown) on which are mounted the wheel disks  10 . 
     However, devices of this type, have their own problems. Gaps are needed between some wheel disks  10  to provide clearance for the support members  11  and the ground below such gaps receives no significant compaction. Therefore, to provide adequate and even compaction over the whole width of a trench floor, it may be necessary to shift the device  1  laterally one or more times to ensure that all the soil within the trench is compacted. This can be a time consuming process that requires significant operator skill in manoeuvring the machine. 
     Therefore, there is a need to provide a compacting device that provides improved soil compaction in a relatively simple manner. 
     Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application. 
     SUMMARY OF THE INVENTION 
     In a first aspect, the invention provides a compacting device for attachment to an earthmoving machine to compact a substrate, including: 
     a plurality of wheel assemblies mounted for rotation together in bearings; and 
     a support having a base adapted to be mounted to the earthmoving machine and one or more bearing support members that extend from the base and between the wheel assemblies to support the bearings; 
     wherein each wheel assembly includes a set of ground-contacting feet secured to and peripherally spaced apart around a rim portion of the wheel assembly such when the device is rolled over the substrate a first foot of the set of ground engaging feet contacts the substrate between axial width limits that differ from axial width limits of a second foot of the set of ground engaging feet. 
     In one embodiment, the axial width limits of the first foot partially overlap the axial width limits of the second foot. The first and second feet may be peripherally adjacent members of said set of feet. 
     The first and second feet may be comprised in a multi-foot pad secured to the wheel assembly. The multi-foot pad may comprise two feet only of the set of ground engaging feet. Conveniently, the first and second feet may be integrally formed in said multi-foot pad. 
     The multi-foot pad may be secured to the wheel assembly by at least one of welding, bolting, riveting, and pinning by means of at least one pin. In another form, the multi-foot pad may be formed integrally with the wheel assembly by casting or the like. 
     In another embodiment, for ease of fitting, the multi-foot pad has locating surfaces that, when the multi-foot pad is placed on the wheel assembly for securing thereto, bear against the wheel assembly so as to correctly position the feet radially and/or axially on the rim portion of the wheel assembly. This arrangement may be particularly convenient when the multi-foot pad is to be secured by welding. 
     The multi-foot pad may have a groove within which the rim portion of the wheel assembly is received so as to locate the multi-foot pad on the wheel assembly axially and radially. 
     In another embodiment, when the multi-foot pad is secured to the rim portion of the wheel assembly, the axially leftmost width limit of the first foot is on an opposite side of the rim portion of the wheel assembly from the axially rightmost width limit of the second foot. 
     The first and second feet of the multi-foot pad may have approximately the same shape as each other, save for being oppositely handed in an axial direction, and wherein when the multi-foot pad is secured to the wheel assembly the first and second feet may be approximately equally displaced in opposite axial directions from the rim portion of the wheel assembly. 
     At least one of the wheel assemblies may include an endmost wheel assembly that may be secured to an outermost wheel assembly of the device to increase its working width. 
     In another embodiment, the compaction device or the machine to which it is mounted may be provided with means for vibrating the wheel assemblies to enhance the compaction effect where required. 
     In a further aspect, the invention provides a multi-foot ground engaging pad for a compacting device of the type having a wheel assembly comprising one or more wheels adapted to be rolled over a substrate to be compacted, the pad including a plurality of ground engaging feet integrally formed on a base that is securable to a rim portion of the one or more wheels whereupon said feet are spaced peripherally on said wheel. 
     In an embodiment of this aspect, during rolling of the wheel assembly on the substrate, a first ground engaging foot on the pad contacts the substrate between axial width limits that differ from axial width limits of a second ground engaging foot on the pad. 
     In one form, the axial width limits of the first ground engaging foot may partially overlap the axial width limits of the second ground engaging foot. 
     In one embodiment, the multi-foot pad may comprise two ground engaging feet only. The multi-foot pad may be securable to the wheel by at least one of welding, bolting, riveting, and pinning by means of at least one pin. 
     The multi-foot ground engaging pad may have locating surfaces that, when the pad is placed on the wheel for securing thereto, bear against the wheel so as to correctly position the ground engaging feet radially and/or axially on the wheel. A groove may be provided within which an outer rim of the wheel may be received so as to locate the pad on the wheel axially and radially. 
     The multi-foot pad may be so proportioned that when the pad is secured to the wheel the axially leftmost width limit of the first foot is on an opposite side of a rim portion of the wheel from the axially rightmost width limit of the second foot. The first and second ground engaging feet of the pad may have approximately the same shape as each other save for being oppositely handed in an axial direction. In this regard, when the pad is secured to said wheel the first and second feet may be approximately equally displaced in opposite axial directions from the rim portion of the wheel. 
     In a still further aspect, the invention provides a method for compacting soil including the steps of: 
     securing a compacting device as disclosed herein to an earthmoving machine; and 
     using the machine to roll the device back and forth on a surface of the soil. 
     In one embodiment of this aspect of the invention, the earthmoving machine may include a backhoe mechanism having a boom and a dipper and the device may be secured to a free end of the dipper. 
     According to yet another aspect, the present invention provides a compacting device for attachment to an earthmoving machine to compact a substrate, the compacting device including: 
     a base adapted to be mounted to said earthmoving machine; 
     one or more support members extending from the base; 
     one or more bearings, the or each bearing being mounted to an end of the one or more support members; 
     a shaft rotatably supported within the one or more bearings; and 
     a plurality of wheel assemblies mountable to said shaft such that said one or more support members extend between said wheel assemblies; 
     wherein each wheel assembly includes a plurality of ground-contacting feet spaced apart around the periphery of the wheel assembly, said feet being alternately displaced laterally towards opposing sides of the wheel assembly such that when said wheel assemblies are rolled over a substrate surface said feet contact said substrate surface and compact said substrate. 
     In an embodiment of this aspect of the invention, the wheel assemblies are mountable to the shaft such that the ground contacting feet of adjacent wheel assemblies are circumferentially staggered. 
     In one form, at least two of the wheel assemblies may be directly mounted to the shaft. At least one wheel assembly may be mounted to one of the wheel assemblies directly mounted to the shaft. 
     Each ground contacting foot may be formed integral with at least one adjacent ground contacting foot to form a multi-foot pad attached to a rim portion of each wheel assembly. The multi-foot pad may have two ground contacting feet only. The multi-foot pad may be secured to the rim portion of the wheel assembly by at least one of welding, bolting, riveting, and pinning by means of at least one pin. 
     In one form, the multi-foot pad may have locating surfaces that, when the multi-foot pad is placed on the rim portion of the wheel assembly for securing thereto, bear against he rim portion of the wheel assembly so as to correctly position the ground contacting feet radially and/or axially on the rim portion of the wheel assembly. In another form, the multi-foot pad may have a groove within which the rim portion of the wheel assembly may be received so as to locate the multi-foot pad on the rim portion of the wheel assembly axially and radially. 
     In another embodiment of this aspect of the invention, the first and second feet of the multi-foot pad may have substantially the same shape. In this regard, when the multi-foot pad is secured to the rim portion of the wheel assembly the first and second feet may be approximately equally displaced in opposite lateral directions from the rim portion of the wheel assembly. 
     According to yet another aspect, the present invention provides a compacting device for attachment to an earthmoving machine to compact a substrate, the compacting device including: 
     a base adapted to be mounted to said earthmoving machine; 
     one or more support members extending from the base; 
     one or more bearings, the or each bearing being mounted to an end of the one or more support members; 
     a shaft rotatably supported within the one or more bearings; and 
     a plurality of wheel assemblies mounted on said shaft such that said one or more support members extend between said wheel assemblies, each wheel assembly having a plurality of ground-contacting feet spaced apart around the periphery of the wheel assembly such that when said wheel assemblies are rolled over the substrate surface said feet contact said substrate surface and compact said substrate, 
     wherein, one or more additional wheel assemblies are removably mounted to one or more of the plurality of wheel assemblies mounted on the shaft. 
     In an embodiment of this aspect of the invention, the one or more additional wheel assemblies are removably mounted to an end wheel assembly mounted on the shaft. The one or more additional wheel assemblies may be removably mounted to a hub that is removably mounted to an end wheel assembly mounted on the shaft. 
     The hub may comprise a first mounting disc for mounting said hub to a wheel disc of an end wheel assembly mounted on the shaft and a second mounting disc to which said additional wheel assembly is mounted. The first and second mounting discs may have a plurality of holes formed therethrough to receive one or more fasteners for facilitating mounting of the hub to the end wheel assembly and mounting of the additional wheel assembly to the hub. The plurality of holes may be formed around the periphery of the first and second mounting discs. Corresponding holes formed around the periphery of the first and second mounting discs may be offset such that the plurality of ground-contacting feet spaced apart around the periphery of the additional wheel assembly are circumferentially staggered with respect to the plurality of ground-contacting feet spaced apart around the periphery of the end wheel assembly when the additional wheel assembly is mounted to the end wheel assembly. 
     Other aspects and features will become apparent from the following detailed description. 
     Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       By way of example only, the invention is now described with reference to the accompanying drawings: 
         FIG. 1  is a perspective view of a backhoe excavator fitted with a compacting wheel of known type; 
         FIG. 2  is a schematic diagram showing (upper part) a rear view of a compacting wheel and (lower part) a plan view of areas of a surface compacted by passage of the compacting wheel when rolling over a substrate; 
         FIG. 3  is a schematic diagram showing (upper part) a rear view of a further compacting wheel and (lower part) a plan view of areas of a surface compacted by passage of the compacting wheel when rolling over a substrate; 
         FIG. 4  is an elevation of three-wheel embodiment of the invention; 
         FIG. 5  is an elevation of a two-wheel embodiment of the invention; 
         FIG. 6  is a view from below of the embodiment shown in  FIG. 5 ; 
         FIG. 7  is a perspective view of the embodiment shown in  FIG. 5 ; 
         FIG. 8  is a side view of the embodiment shown in  FIG. 5 ; 
         FIG. 9  is an elevation of a five-wheel embodiment of the invention; 
         FIG. 10  is a cross-sectional view of the embodiment shown in  FIG. 9 , the section being taken at the centre of a shaft mounting wheels of the device; 
         FIG. 11  is a perspective view of the embodiment shown in  FIG. 9 , partially cut away; 
         FIG. 12  is a perspective view of a foot assembly of a compacting device according to the invention; 
         FIG. 13  is a view of the foot assembly shown in  FIG. 12 , looking in the direction of arrow “A”; 
         FIG. 14  is a view of the foot assembly shown in  FIG. 12  looking in the direction of arrow “B”; 
         FIG. 15  is a cross-sectional view of an alternative embodiment of a five-wheel compacting device according to the present invention; 
         FIG. 16  is an isolated perspective view of a mounting hub mounted to a wheel in accordance with the embodiment of the device shown in  FIG. 15 ; 
         FIG. 17  is perspective view of the mounting hub of  FIG. 16 ; 
         FIG. 18  is a plan view of the mounting hub of  FIG. 17 ; 
         FIG. 19  is a plan view of the mounting hub of  FIGS. 16 and 17  connecting adjacent wheels of a compacting device of the present invention; 
         FIG. 20  is a perspective view of a wheel of a compacting device in accordance with one embodiment of the present invention; 
         FIG. 21  is a perspective view of the wheel of  FIG. 20  mounted to a shaft of a compacting device by way of a locating block in accordance with an embodiment of the present invention; and 
         FIGS. 22A-22C  show perspective, plan and cross-sectional views of an embodiment of the locating block of  FIG. 21 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIG. 1  shows a wheel-type compacting device  1  mounted on a backhoe excavator  2  and has been discussed above. The present invention provides an improved compacting device usable in the same way as compacting device  1 . 
       FIG. 2  shows a compacting device  20  such as that shown in the prior art device of  FIG. 1 . In the upper part of  FIG. 2 , a rear elevation of a compacting device  20  is shown, rolling on a substrate  21 . Device  20  comprises three wheels  22 ,  23  and  24 , that are mounted on a single shaft (not shown) so as to rotate together rather than independently. The shaft is in turn supported for rotation in bearing assemblies  39  mounted to a pair of support members  38  located between wheels  22  and  23 , and  23  and  24  respectively. Wheel assemblies  22 ,  23  and  24  each have compacting feet  29  whose outer surfaces  30  (all shown shaded) contact substrate  21  as the device  20  is rolled over the substrate  21 . No other constructional details of wheel assemblies  22 ,  23  and  24  are shown. The lower part of  FIG. 2  shows, in plan view, a portion of substrate  21  after the device  20  has been rolled over the substrate in a single rolling pass, with the areas  31  that are contacted by surfaces  30  indicated by shading. 
     It is apparent from  FIG. 2  that a rolling pass of device  20  over substrate  21  provides compaction in three strips  32 ,  33  and  34 , but does not directly compact substrate  21  in the two intervening strips  35  and  36 . These strips are not directly compacted by the device due to the support members  38  (similar to members  11  in  FIG. 1 ) being provided between adjacent pairs of wheel assemblies  22 ,  23  and  24  to support bearing assemblies  39 . 
     In practice, to compact the whole area of substrate  21  (which could be the floor of a trench) adequately and evenly, device  20  would need to be moved axially (i.e. in the direction of rotation axis  37  of device  20 ) from time to time and multiple rolling passes would need to be made at each axial position. This process also allows compaction to be carried out at the edges of a trench, despite the fact that the device  20  would in general be narrower than the trench width. As will be appreciated, in order to achieve effective soil compaction using such a process, significant operator skill and time is required. 
     According to the present invention, it has been found that, in at least some ground conditions, the performance of a device, such as device  20 , can be enhanced by making the individual feet on each wheel assembly narrower (in the axial direction) while maintaining the width of the strip contacted by each wheel assembly by offsetting some feet axially from others. One embodiment of such an arrangement is shown in  FIG. 3 . In order to facilitate direct comparison of the device of the present invention as shown in  FIG. 3 , and that of the prior art, as shown in  FIG. 2 , the same item numbers with the suffix ‘a’ have been used for equivalent items. The effectiveness of the device  20   a , as shown in  FIG. 3 , is thought to arise because the total area of the device  20   a  in contact with the substrate  21   a  is decreased, so leading to a higher level of compaction for a given downward force on the device  20   a . In successive passes of the device  20   a  over the substrate  21   a , particularly if the device  20   a  is lifted clear of the substrate  21   a  at the end of each pass, the feet  29   a  will not in general touch the substrate at identical positions as in previous passes, so that strips  32   a ,  33   a  and  34   a  of the same width as strips  32 ,  33  and  34  can be compacted, thereby providing improved compaction of the soil in these regions. 
       FIG. 4  shows a compacting device  40  in accordance with an embodiment of the present invention. The device  40  is shown as having three individual wheels  41 ,  42  and  43 , each with feet  44  that are staggered in essentially the same way as the feet  29   a  of the embodiment as shown in  FIG. 3 . Wheels  41 - 43  are mounted to a single shaft (not shown) so as to rotate together as a unit, about a transverse axis  45 . Bearing assemblies  46  support the shaft and are themselves held by support members  47 . Support members  47  extend from a base  48  that is able to be secured (for example via a quick-hitch arrangement of known type, not shown) to an excavator stick in a similar manner to that shown for device  1  in  FIG. 1 . 
     It will be appreciated that compacting devices according to the present invention may employ any number of individual wheels, and are not limited to having three wheels. Different numbers of individual wheels may be used to suit different work conditions, different trench widths and different supporting machinery.  FIGS. 5 to 8  show a compacting device  50  having two wheels  51  and  52  and only one supporting member  53  positioned therebetween. Device  50  is otherwise similar to device  40 , especially in relation to the arrangement of the feet  54  provided on wheels  51  and  52 , and in this embodiment the wheels  51  and  52  also rotate together. 
       FIGS. 9 ,  10  and  11  show another embodiment of a compacting device  60  according to the present invention. Device  60  has a total of five wheels,  61 ,  62 ,  63 ,  64  and  65 , similar in their arrangement of feet  66  to wheels  41 - 43  of device  40 . Device  60  has only two support members  66  and  67 , having bearing assemblies  68  and  69  mounted respectively thereto. Support members  66 ,  67  and bearing assemblies  68 ,  69  are located between, firstly, wheels  62  and  63 , and, secondly,  63  and  64 . As can be seen in the sectional views of  FIGS. 10 and 11 , wheels  62 ,  63  and  64  are mounted to a single shaft  70  to rotate together. The outer wheels  61  and  65  are not mounted directly to shaft  70  but to hubs  71  and  72 , that are in turn bolted to wheel discs  73  and  74  respectively of wheels  62  and  64 . With this arrangement, outer wheels  61  and  65  are readily detachable so that device  60  is convertible to the narrower three-wheel device  40 , as required. This feature allows a narrow trench to be accommodated, or higher compaction with a given supporting machine weight, using three wheels  62 - 64  only when required or, alternatively, a wider trench can be accommodated using all five wheels  61 - 65 . 
       FIG. 15  shows an alternative embodiment of a compacting device  100  according to the present invention. As described the embodiment shown in  FIGS. 9-11 , device  100  has a total of five wheels  101 - 105 . End wheels  101  and  105  are removable to enable the device  100  to be readily converted between a wide five-wheeled device and a narrow three-wheeled device, according to the requirements of the job to be performed. In this regard, device  100  also has two support members  106 ,  107  having bearing assemblies  108 ,  109  respectively mounted to an end thereof. A shaft  110  extends through the bearing assemblies  108 ,  109 , and wheels  102 ,  103  and  104  are mounted to the shaft  110  to rotate about the axis of the shaft  110 . 
     The end wheels  101  and  105  are respectively mounted to the shaft mounted wheels  102  and  104  by way of mounting hubs  115 . The mounting hubs  115  are mounted to the wheel discs of the wheels by appropriate bolts which allow ready attachment/detachment of the end wheels  101  and  105 , when required. This is shown in  FIG. 16  wherein mounting hub  115  is mounted to the wheel disc  104   a  of wheel  104 , in readiness to receive wheel  105 . 
     Mounting hub  115  is shown in more detail in  FIGS. 17 and 18  and comprises a pair of mounting cups/discs  116 ,  118  separated by a central core  117 . Each mounting cup/disc  116 ,  118  is mounted to a wheel disc of the corresponding wheel pairs  104 / 105  and  101 / 102  such that rotation of the shaft mounted wheel  102 ,  104  is transferred to the corresponding end wheel  101 ,  105 . To facilitate mounting of the cups/discs  116 ,  118  to the wheel discs, a plurality of holes  119  are formed around the periphery of each cup/disc to receive a fastener such as a bolt or the like. Holes  119  align with holes formed in the wheel discs of the wheels such that the fastener can pass through the wheel discs and cups  116 ,  118 . 
     As shown more clearly in  FIG. 18 , the holes  119  provided around the periphery of the cup/disc  116  are offset with respect to corresponding holes  119  provided around the periphery of cup/disc  118 . In the embodiment as shown the corresponding holes  119  are offset an angle θ with respect to the central axis of the mounting hub  118 . This offset angle θ is preferably between around 10° and 20°, more preferably 15°. 
     Such an offset angle between corresponding holes  119  formed in the periphery of the cups/discs  116 ,  118 , ensures that when wheels  101 / 102  and wheels  104 / 105  are mounted together by way of the mounting hub  115 , the contacting feet of adjacent wheels are arranged in a circumferentially staggered manner. As discussed above, such a circumferentially staggered arrangement of contacting feet between adjacent wheels aids in facilitating improved soil compaction as the device  100  is rolled over the soil surface in multiple passes. 
     This circumferential staggered arrangement of the contacting feet of adjacent wheels can be seen more clearly in the isolated view of  FIG. 19 . As shown, end wheel  105  is mounted to wheel  104  by way of mounting hub  115  in the manner as discussed above. When mounted in this manner, the contacting feet  120   a  of end wheel  105  are circumferentially offset with respect to the contacting feet  120   b  of wheel  104 . In this regard, when the device  100  is rolled over the soil to be compacted such that the adjacent wheels rotate together, the corresponding feet  120   a  and  120   b  on adjacent wheels do not contact and pass over the soil at the same time. This avoids the formation of a common path or plane of soil compaction extending orthogonal to the direction in which the device travels, which can cause corrugation in the compacted soil and inconsistent compaction. 
     One embodiment of the construction of the wheels of the compacting devices according to the present invention will now be described. This construction can be best seen in the sectioned views of  FIGS. 10 and 11  that show wheels  61 - 65 . However, it is to be understood that essentially the same construction can be used in the wheels  41 - 43  of device  40 , wheels  51 ,  52  of device  50 , and wheels  101 - 105  of device  100 . 
     Wheel  64  will be described by way of illustration. Wheel  64  has a hub  80  that is secured (by any suitable means known in the art such as a key or pin, not shown) to shaft  70 . A wheel disc  74  is then secured to hub  80 . This could be achieved by welding or bolting the wheel disc  74  to the hub  80  or by any other suitable manner known in the art. Alternatively, hub  80  and wheel disc  74  could be integrally formed, for example by casting. Secured to the outer edge of wheel disc  74  are foot assemblies  82 , each of which includes two feet  66 . The feet  66  of each foot assembly  82  are offset from each other in an axial direction (i.e. a direction parallel to shaft  70  in device  60 ).  FIGS. 12 ,  13  and  14  show one embodiment of the foot assembly  82 . 
     Foot assembly  82  is advantageously a single casting and has a base  83  that connects feet  66  and has an arc that which generally conforms to the arc of the circumference of the wheel disc  74 . Formed within base  83  is a groove  84  that is shaped and sized to snugly receive an outer peripheral part of wheel disc  74 . Foot assembly  82  can be secured to wheel disc  74  by positioning it on disc  74  so that the disc  74  is received in groove  84  with the outer circumferential edge of disc  74  abutting surface  85  of groove  84 , and then welding assembly  82  to disc  74 . This process is repeated for each of the assemblies  82  required to be secured around the periphery of wheel disc  74 . Assembly  82  is shown in use in devices  40 ,  50  and  60 . 
     It will be apparent to persons skilled in the art that, as an alternative, an assembly similar to assembly  82 , namely having two offset feet  66 , could be made that would be able to be secured to wheel disc  74  by bolting therethrough or by pinning, rather than welding. The assemblies  82  may also be formed integral with the wheel disc  74 , by casting or other such methods. It will also be apparent that different numbers of feet than the two feet  66  could be incorporated in an alternative design of foot assembly (not shown) if required. 
     It will also be apparent that if the depth of groove  84  is suitably chosen, a foot assembly such as assembly  82  could be mounted to a range of diameters of wheel disc  74 . 
     An alternative wheel construction is shown in  FIG. 20  as wheel  120 . Wheel  120  is cast as a single unit and includes an integral hub  122  that is adapted to be secured to a shaft of the device in a manner discussed below. A wheel disc  125  is formed about the hub  122  and has a plurality of holes  126  formed therethrough for mounting a mounting hub  115  in the manner as described above. A plurality of radial spoke elements  127  extend from the wheel disc  125  and hub  122  and terminate in an external rim  128 . A plurality of contacting feet  129  extend from the outer surface of the rim  28 , and each of the feet  129  are offset from each other in an axial direction (i.e. in a direction parallel to a shaft extending through the hub  122 ). The feet  129  function in the same manner as the feet  66  discussed above and have the same general shape characteristics. 
     The hub  122  has a pair of opposing recess portions  124  formed therein to facilitate mounting of the wheel  120  to a shaft  123 . As shown in  FIG. 21 , each recess portion  124  is shaped to receive a locating block  130 . The locating block  130  is shown in more detail in  FIGS. 22A-22C  and is generally in the form of a wedge or insert having a head portion  132  and a body portion  134 . The body portion  134  is shaped to fit into the recess portion  124  such that the distal end of the body portion  134  abuts the shaft  123 , as shown in  FIG. 21 . The head portion  122  is shaped to abut the surface of the hub  122  and has a pair of V-shaped wings  131  which are snugly received in a pair of V-shaped grooves formed in the surface of the hub  122 . Such an arrangement provides a snug fit between the locating block  130  and the hub  122 , such that the locating block  130  is able to be simply aligned into the recess portion  124 . 
     In order to secure the wheels  120  to the shaft  123 , holes  123   a  are provided through the shaft  123 , as shown in  FIG. 21 . The holes  123   a  are provided at desired positions along the length of the shaft  123  and orientated in the same manner, for ease of construction. As shown in  FIG. 22C , each locating block  130  has a hole  135  formed therethrough. 
     To assemble the device, the wheels  120  are positioned on the shaft  123  and the locating blocks are inserted into the recess portions  122  such that the hole  135  formed in the locating blocks aligns with the hole  123   a  formed in the shaft  123 . A suitable pin or key may then be inserted through the aligned holes  135  and  123   a  to secure the wheel  120  in position on the shaft  123 . 
     Such an arrangement overcomes the need to drill precise holes through the hub  122 , which can be difficult due to the orientation and size of the hub  122  and the tolerances required. Further, in order to orientate adjacent wheels  120  of the device such that the feet  129  of adjacent wheels  120  are arranged in a circumferentially staggered manner, it would be necessary to drill holes through the hub at different positions for each wheel  120 , such that when the wheels are secured to the shaft  123  they are correctly orientated with respect to neighbouring wheels. 
     By employing the locating blocks  130  of the present invention adjacent wheels can be relatively easily positioned and secured in place such that the contacting feet  29  of adjacent wheels are circumferentially staggered, in the manner as shown in  FIG. 19 . This is achieved through forming the holes  135  in the locating block  130  at an angle β to the vertical axis, as shown in  FIG. 22C . Such an orientation of the holes  135  provides a relatively simple way in which to control the orientation of adjacent wheels  120  when secured to the shaft  123 . The angle β can vary to provide a variety of circumferentially staggered arrangements. In a preferred form, in order to ensure that there is a constant  150  stagger between wheels, the angle β may be 7.5°. Therefore by inserting the locating blocks  130  within the recess portion  124  of the hubs  122  of adjacent wheels in opposite orientations, adjacent wheels  120  will have their contacting feet  129  circumferentially staggered by 15°. Such an arrangement enables a single type of wheel  120  and locating block  130  to be supplied for assembling the compacting devices to a variety of needs. 
     Plain bearings may be used to mount devices such as  40 ,  50 ,  60 ,  100 , and  120  to their support members  47 ,  53 ,  66 ,  67 ,  106 , and  107 . These may use suitable plastics bushes. Alternatively, rolling element bearings may be used. 
     Although for each of the devices  40 ,  50 ,  60 ,  100  and  120  the wheels  41 - 42 ,  51 - 53 ,  61 - 65 , and  101 - 105  have been described as rotating together, it is possible as an alternative to arrange for some or all of the wheels to be allowed to rotate separately. 
     The present invention provides various embodiments of a soil compacting device that can be readily attachable to a variety of machines to achieve improved soil compaction through greater distribution of soil compacting forces to the soil being compacted. The devices are constructed in a manner that enables the compacting wheels to be relatively easily attached/detached from the device. This facilitates conversion of the device between a narrow device suitable for compacting narrow soil regions, and a wider device suitable for compacting larger surface areas, depending on the type and nature of the task to be performed. 
     It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.