the invention will now be described in the following detailed description with reference to the drawings , wherein preferred embodiments are described in detail to enable practice of the invention . although the invention is described with reference to these specific preferred embodiments , it will be understood that the invention is not limited to these preferred embodiments . but to the contrary , the invention includes numerous alternatives , modifications and equivalents as will become apparent from consideration of the following detailed description . fig1 is a perspective view and fig2 is a top plan view of the front frame 10 , power train 12 , and track assemblies 14 of a tracked tractor embodying an exemplary embodiment of a multi - axis reaction arm of the present disclosure . many of the illustrated components may be found in the commercially available challenger mt765d tracked tractor , available from agco corporation of duluth , ga . however , the challenger mt765d tractor does not include a reaction arm as described in this disclosure . the illustrated tracked tractor generally has two track assemblies 14 , one on each of the left and right sides of the tractor . a track assembly 14 typically includes a rubber track 16 that forms a loop around a drive wheel 18 , a number of mid - rollers 20 and an idler wheel 22 . during use of the tractor , drive wheel 18 rotates and engages rubber track 16 , thereby causing the rubber track 16 to rotate around a path defined by drive wheel 18 and idler wheel 22 . the rotation of rubber track 16 causes it to engage the ground , thereby propelling the tractor over the ground surface . both drive wheels 18 of the tractor are rotatably attached to the common drive wheel axle 24 extending from a transmission casing 25 of power train 12 ; drive wheel axle 24 has no freedom of movement relative to transmission casing 25 other than this rotational motion . hard bar 26 passes through both track assemblies 14 and oscillates within front frame 10 , thereby providing a suspension function by allowing the undercarriage to move up and down relative to front frame 10 . each drive wheel 18 comprises an inner drive wheel 18 a and an outer drive wheel 18 b , with guide blocks 28 ( visible in fig3 ) of track 16 disposed between inner drive wheel 18 a and an outer drive wheel 18 b . similarly , each idler wheel 22 comprises an inner idler wheel 22 a and an outer idler wheel 22 b , with guide blocks 28 of track 16 disposed between inner idler wheel 22 a and an outer idler wheel 22 b . accordingly , guide blocks 28 prevent track 16 from sliding sideways off of the wheels 18 , 22 and mid - rollers 20 of its respective track assembly 14 . the inner and outer wheel configurations effectively capture guide blocks 28 between them , thereby retaining each track 16 on its respective drive wheel 18 and idler wheel 22 as the tractor moves . fig3 is a perspective view of the left track assembly 14 of fig1 , with the outer drive wheel 18 b and the outer idler wheel 22 b removed . while this discussion will focus on the illustrated left track assembly 14 , it is to be understood that the concepts described herein equally apply to the right track assembly 14 . for proper operation , it is desirable that track 16 be tensioned tautly on its path around drive wheel 18 and idler wheel 22 . in the illustrated tractor , this goal is accomplished with the use of tensioner 30 . a bottom portion 40 of tensioner 30 is attached to track roller frame 42 . a left side of tensioner includes hydraulic cylinder 32 , which may lengthen and shorten , as known in the art . an end of cylinder 32 is pivotally connected to swing link 34 , which carries front hub 36 onto which idler wheel 22 is mounted . as cylinder 32 lengthens , it moves swing link 34 , which in turn moves front hub 36 forward . as a result , a distance between idler wheel 22 and drive wheel 18 increases , thereby tightening track 16 on its path around idler wheel 22 and drive wheel 18 . if track 16 is too tight , cylinder 32 is shortened to decrease the distance between idler wheel 22 and drive wheel 18 , thereby loosening track 16 on its path around idler wheel 22 and drive wheel 18 . mid - rollers 20 help to support the weight of the tractor . a mid - roller 20 is connected by a pivot joint 44 to track roller frame 42 . pivot joints 44 allow mid - rollers 20 to oscillate up and down and serve a suspension function . hard bar 26 ( shown in fig1 and 2 ) is held by bracket 46 of track roller frame 42 and is also connected to front frame 10 ( as shown in fig2 ). hard bar 26 passes through both track assemblies 14 and oscillates within front frame 10 , thereby providing a suspension function by allowing the undercarriage to move up and down relative to front frame 10 . as hard bar 26 moves , track roller frame 42 moves along with it . thus , track roller frame 42 is allowed to slightly twist and shift from side to side in use as the tractor travels over uneven terrain . however , no oscillating or up / down movement is accommodated at drive wheel axle 24 . accordingly , a multi - axis reaction arm 50 of the present disclosure is provided between track roller frame 42 and drive wheel axle 24 to take up the load forces created by the movement of track roller frame 42 relative to drive wheel axle 24 ( such load forces typically being created by the tractor traversing uneven terrain ). fig4 is a perspective view of an exemplary embodiment of the multi - axis reaction arm 50 of the present disclosure . fig5 is a top view of reaction arm of 50 . fig6 is a cross - sectional view of reaction arm 50 , taken along the line 6 - 6 of fig5 . fig7 is a cross - sectional view of reaction arm 50 , taken along the line 7 - 7 of fig4 . reaction arm 50 comprises arm portion 52 , yoke 54 , bearing housing 56 ( see fig5 - 7 ), bearing assembly 58 , collet 60 and drive wheel hubs 72 . arm portion 52 is mounted by fasteners ( not shown ) via flange 62 to track roller frame 42 ( such as shown in assembled form , e . g ., in fig3 ). on the opposite end of reaction arm 50 , collet 60 is secured by fasteners , such as bolts , to drive wheel axle 24 ( again , as illustrated , for example , in fig3 ). thus , collet 60 rotates with drive wheel axle 24 . inner and outer drive wheels 18 a , 18 b are fastened , such as by bolts , to drive wheel hubs 72 ( see again , e . g ., fig3 ). in an exemplary embodiment , drive wheel hubs 72 are fixed to collet 60 , such as by integral formation or by fasteners , so that drive wheel hubs 72 rotate with drive wheel axle 24 . as shown in fig7 , bearing assembly 58 is disposed between collet 60 and bearing housing 56 to allow bearing housing 56 to remain relatively stationary even while collet 60 rotates with drive wheel axle 24 . moreover , bearing assembly 58 extends between drive wheel hubs 72 and bearing housing 56 to allow bearing housing 56 to remain relatively stationary even while drive wheel hubs 72 rotate with drive wheel axle 24 . in an exemplary embodiment , bearing assembly 58 comprises a plurality of roller bearings 59 . referring to fig6 and 7 , bearing housing 56 is connected by pins 64 to yoke 54 in a manner that allows bearing housing 56 to pivot about pivot axis 66 , which is substantially vertical when the tractor is disposed upright on a substantially horizontal ground surface . in an exemplary embodiment , pivot axis 66 corresponds to a longitudinal axis of pins 64 . thrust washers 74 are disposed between bearing housing 56 and yoke 54 and around pins 64 . thrust washers 74 are used to control vertical axial forces from the tractor &# 39 ; s weight . a thrust washer is a type of bearing that provides a bearing surface for forces acting axial to the corresponding pin 64 . yoke 54 is connected by shaft 68 to arm portion 52 in a manner that allows yoke 54 to pivot about pivot axis 70 , which is substantially horizontal when the tractor is disposed upright on a substantially horizontal ground surface . in an exemplary embodiment , pivot axis 70 corresponds to a longitudinal axis of shaft 68 . in an exemplary embodiment , the two pivot axes 66 , 70 are substantially orthogonal to each other . thus , the present disclosure describes a multi - axis reaction arm 50 that is able to resolve both the horizontal force from the track tension ( the direction of which is illustrated by arrow 76 in fig5 and 8 ) and the vertical force from the weight of the tractor ( the direction of which is illustrated by arrow 78 in fig6 and 7 ). this is accomplished by attaching drive wheel hubs 72 and drive wheel axle 24 to track roller frame 42 in a manner that allows track roller frame 42 to pivot about both horizontal pivot axis 70 and vertical pivot axis 66 . thus , all twisting and side - to - side motions of track roller frame 42 relative to drive wheel hubs 72 and drive wheel axle 24 are accommodated by the two degrees of freedom provided by multi - axis reaction arm 50 . the foregoing has broadly outlined some of the more pertinent aspects and features of the present invention . these should be construed to be merely illustrative of some of the more prominent features and applications of the invention . other beneficial results can be obtained by applying the disclosed information in a different manner or by modifying the disclosed embodiments . accordingly , other aspects and a more comprehensive understanding of the invention may be obtained by referring to the detailed description of the exemplary embodiments taken in conjunction with the accompanying drawings .