Patent Publication Number: US-2021194416-A1

Title: Single axis in-line gearbox modular tracker system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of co-pending U.S. Ser. No. 15/610,532, filed on May 31, 2017, which claims the filing benefit of U.S. Provisional Patent Application Ser. No. 62/392,524, filed on Jun. 3, 2016, now expired, and U.S. Provisional Patent Application Ser. No. 62/495,276, filed on Sep. 8, 2016, now expired, the disclosures of which are hereby incorporated herein by reference in their entireties. 
    
    
     TECHNICAL FIELD 
     This application relates generally to a modular solar tracker. More specifically, this application describes mechanisms and methods for coupling a plurality of solar panels together in a row using a single motor and multiple gearboxes. 
     BACKGROUND 
     Solar trackers rotate long rows and/or columns of solar panels so that the solar panels track the apparent path of the sun, thereby maximizing the amount of sunlight that is absorbed by the solar panels. In this regard, a conventional solar tracker generally uses a motor and a single gearbox to rotate a long stiff torque tube to effectively rotate the solar panels. 
     The desire to reduce the relative cost of the motor per solar panel is dependent on increasing the length of each row of solar panels. Depending on the number of solar panels in the row, the motor may need to generate an extremely high torque to impart sufficient torque to the torque tube to successfully overcome the torque generated by wind loads on the solar panels. In this regard, since a single motor is normally used for a row, or may be used for multiple rows, the torque tubes need to be long, in some cases up to 300 feet or more. Unfortunately, long torque tubes develop large torsional deflections and are vulnerable to premature failure and low frequency vibration due to the torsional loads and thermal expansion axially through the torque tubes. For each table added to a row, the load torque increases along the entire tube requiring a higher total ratio of material per solar panel. This leads to inefficient use of material, as the torque requirements of the long row of solar panels increases towards the point of the torque tube where the drive torque is applied. 
     Additionally, the long torque tube formed as a single structural element sustains the bending loads of the long row of solar panels. From the point of view of bending loads, which are generally even along the entire row, the tube section structural requirement is even along the row. However, from a torsional load point of view, the tube section structural requirement increases towards the point where the driving torque is applied. As such, single torque tube solar trackers are overdesigned in terms of bending loads, resulting in a less than optimal use of material. 
     In addition to single torque tube solar trackers, there are also dual tube solar trackers that use two tubes to transfer the torque from the row of solar panels back to the motor. Dual tube solar trackers generally have shorter rows because it is a less efficient way of transferring torque, but these dual tube solar trackers trade that inefficiency for the simplicity of mounting the solar panels directly to the torque tubes, avoiding the need for mounting rails. In addition, the dual tube solar trackers have another advantage, as they allow the pivot point to be closer to the rotating mass center of gravity, which reduces static torsional loads. However, dual tube solar trackers are overdesigned for the bending loads for the same reasons described above for single torque tube solar trackers. 
     Clearly, a solution that provides the required bending capacity to the structure of long rows, without the significant added cost to transfer torque loads over longer rows, would result in more efficient use of material. Longer rows for a single motor result in a smaller burden per table cost of the motor and microcontroller. In addition to the efficient use of material, a solution that allows long rows to conform to ground undulations, which is not possible with stiff torque tube designs, results in fewer ground preparation requirements at installation sites. 
     Additionally, thermal behavior of long stiff tubes in environments that very often have wide temperature oscillations on a daily cycle create a difficult challenge that is sometimes ignored, with increased risk of failure. A system that includes smaller modular structures connected by flexible members better accommodates the thermal expansion-contraction cycles would solve the problem of thermal deformation without the need for complex compensation mechanisms. 
     Additionally, the dynamic response behavior of a long torque tube, with a very large inertial mass, results in very low natural frequencies. Matching low frequencies may be stimulated by wind effects, requiring expensive and complex dampening systems to prevent failure. A solar tracker that results in breaking up the inertia of the row into smaller sections driven by gear drives (e.g. a non-reversible gear drive) increases the value of resonant frequencies to a safe level not stimulated by wind dynamics, which avoids costly dampening mechanisms. 
     These problems represent an opportunity for a new design approach that results in functional improvements, assembly simplicity, and cost savings. 
     SUMMARY 
     According to an exemplary embodiment, a modular tracker system is provided which includes at least first and second tables rotatably arranged in a row. Each of the first and second tables includes a support structure including first and second mounting posts that are configured to be mounted in the ground, a frame supported by the support structure, at least one solar panel supported by the frame, and first and second gearboxes. The first gearbox is operatively coupled to the first mounting post. The first gearbox is configured to produce first and second outputs, where the first output has a first rotational speed and the second output has a second rotational speed that is less than the first rotational speed. The second output is operatively coupled to the frame. The second gearbox is operatively coupled to the second mounting post and is concentrically aligned with the first gearbox of the same table. The second gearbox is configured to produce first and second outputs, where the first output has the first rotational speed and the second output has the second rotational speed. The modular tracker system also includes a single motor driving both the first and second tables, a first and second intra-table drive shafts and an inter-table drive shaft. The first intra-table drive shaft connects the first and second gearboxes of the first table. The second intra-table drive shaft connects the first and second gearboxes of the second table. The inter-table drive shaft couples the second gearbox of the first table with the first gearbox of the second table to connect the first and second tables, whereby the first and second tables are rotated synchronously. 
     According to another exemplary embodiment, a modular tracker system is provided which includes at least first and second tables rotatably arranged in a row, a single motor driving both the first and second tables, and an inter-table drive shaft connecting the first and second tables. Each of the first and second tables include a support structure configured to be mounted in the ground, a frame supported by the support structure, at least one solar panel supported by the frame, and at least one gearbox supported by the support structure. The gearbox is configured to produce first and second outputs. The first output has a first rotational speed. The second output has a second rotational speed that is less than the first rotational speed. The second output is operatively coupled to the frame. The inter-table drive shaft couples the first output of the gearbox of the first table with an input of the gearbox of the second table, whereby the first and second tables are rotated synchronously. 
     According to another exemplary embodiment, a modular tracker system is provided which includes a support structure configured to be mounted in the ground, a frame supported by the support structure, a plurality of solar panels supported by the frame, first and second gearboxes, a single motor driving the modular tracker system, and a drive shaft connecting the first and second gearboxes. The first gearbox is supported by the support structure and is configured to produce first and second outputs. The first output has a first rotational speed and the second output has a second rotational speed that is less than the first rotational speed. The second output is operatively coupled to the frame. The second gearbox is supported by the support structure and concentrically aligned with the first gearbox. The second gearbox is configured to produce first and second outputs. The first output has the first rotational speed and the second output has the second rotational speed and is operatively coupled to the frame. The drive shaft couples the first output of the first gearbox with the input of the second gearbox, whereby the plurality of solar panels is rotated synchronously. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various additional features and advantages of the invention will become more apparent to those of ordinary skill in the art upon review of the following detailed description of one or more illustrative embodiments taken in conjunction with the accompanying drawings. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate one or more embodiments of the invention and, together with the general description given above and the detailed description given below, serve to explain the one or more embodiments of the invention. 
         FIG. 1  is a perspective view of a modular tracker system including four tables, each table including solar panels in accordance with an embodiment of the invention. 
         FIG. 2  is a perspective view of the modular tracker system of  FIG. 1  focusing on two tables, with the solar panels of the first table being shown in phantom. 
         FIG. 3  is an enlarged perspective view of the modular tracker system of  FIG. 1 , focusing on a single table with the solar panels of the first table being shown in phantom. 
         FIG. 3A  is a perspective view of a table with a single gearbox in accordance with an alternative embodiment. 
         FIG. 4A  is a detailed perspective view of the encircled portion  4 A of  FIG. 2  showing a universal joint coupling the first inter-table drive shaft to the first gearbox of the second table. 
         FIG. 4B  is an exploded perspective view of  FIG. 4A  showing details of the universal joint. 
         FIG. 5A  is an exploded perspective view showing the universal joint of  FIG. 4A . 
         FIG. 5B  is a top plan view partially broken away of the universal joint of  FIG. 4A  showing movement of the gearbox shaft in a first orthogonal direction. 
         FIG. 5C  is a side cross-sectional view of the universal joint of  FIG. 4A  showing movement of the gearbox shaft a second orthogonal direction. 
         FIG. 6  is a detailed perspective view of the encircled portion  6  of  FIG. 2  showing a rigid joint coupling a first intra-table drive shaft to a second gearbox of the first table. 
         FIG. 7A  is an exploded perspective view of the rigid joint of  FIG. 6 . 
         FIG. 7B  is a cross-sectional perspective view of  FIG. 7A . 
         FIG. 8  is a bottom perspective view of two universal joints. 
         FIG. 9  is a side view of a flexible drive shaft coupling the first and second tables together. 
         FIG. 9A  is an enlarged view of the first table of  FIG. 9 . 
         FIG. 10A  is a front perspective view of a gearbox system according to another exemplary embodiment, removed from the modular tracker system  10  of  FIG. 2 . 
         FIG. 10B  is a front perspective view of a gearbox system according to another exemplary embodiment. 
         FIG. 10C  is a front perspective view according to another exemplary embodiment, where the first output of the first gearbox is connected to the input of a second gearbox using a drive shaft. 
         FIG. 11  is a perspective view of a modular tracker system including five tables, with the solar panels being omitted, in accordance with another embodiment of the invention. 
         FIG. 12A  is a perspective view of an exemplary gearbox for use with the modular tracker system. 
         FIG. 12B  is perspective view of the gearbox of  FIG. 12A  taken from another angle. 
         FIG. 13A  is an exploded perspective view showing the internal components gearbox of  FIG. 12A . 
         FIG. 13B  is an exploded perspective view of the gearbox of  FIG. 12B . 
     
    
    
     DETAILED DESCRIPTION 
     With reference to  FIG. 1 , a modular tracker system  10  includes multiple tables (with first, second, third, and fourth tables  12   a - d  being shown in  FIG. 1 ), a single motor  14  driving the tables, and inter-table drive shafts connecting adjacent tables (with first, second, and third inter-table drive shafts  16   a - c  being shown in  FIG. 1 ). The inter-table drive shafts  16   a - c  and/or associated joints (e.g. universal joint) allow for misalignment (e.g. misalignment caused by uneven ground surfaces), which is problematic with a single stiff torque tube. 
     With continued reference to  FIG. 1 , the tables  12   a - d  respectively include first, second, third, and fourth support structures  18   a - d . As shown, the support structures  18   a - d  each respectively include a first mounting post  20   a - d  and a second mounting post  22   a - d , each configured to be mounted into the ground  24  or which may include a structure (not shown). Additionally, each table  12   a - d  respectively includes a frame  26   a - d  supported by the support structure  18   a - d , at least one solar panel  28  supported by the frame  26   a - d , and first and second gearboxes (with first, second, third, and fourth gearboxes  30   a - d  being shown in  FIG. 2  with respect to the first and second tables  12   a - b ). Additional details and aspects of the gearboxes  30   a - d  are described below with reference to  FIGS. 12A-13B . 
     The modular tracker system  10  enables the solar panels  28  to follow (i.e. track) the apparent path of the sun, thereby maximizing the amount of sunlight that is absorbed by the solar panels  28  for collection and/or distribution. While each table  12   a - d  shown in  FIGS. 1 and 2  includes eight solar panels  28 , more or less solar panels are also envisioned. The solar panels  28 , also known as photo-voltaic panels, are shown in phantom in  FIGS. 2 and 3  to better illustrate the relevant structures. Each solar panel is made up of an array of photo-voltaic cells, and the most common sizes are known as 60-cell modules and 72-cell modules. A variety of solar panels  28  may be used, 60-cell modules and 72-cell module versions, among others. 
     With respect to  FIG. 2 , the gearboxes of a respective table (e.g. the first and second gearboxes  30   a - b  with respect to the first table  12   a ) are concentrically aligned to define an axis of rotation (“GA”) that coincides with the axis of the rotation of each respective table (e.g. the first table  12   a ). While the axis of rotation (“GA”) shown in  FIG. 2  is along a single common linear axis for both the first and second tables  12   a - b , the modular tracker system  10  allows for concentrically aligned first and second gearboxes of each table  12   a - d  to have a unique axis of rotation, which may be different for adjacent tables (as shown in  FIG. 11 ) with respect to the modular tracker system  10   b . As such, any pair of gearboxes (e.g. the first and second gearboxes  30   a - b ) connected to the rotating frame are concentrically aligned to define the axis of rotation of the table, independently of the alignment of the first and second mounting posts  20   a - d ,  22   a - d  that support the gearboxes  30   a - d . As shown, spherical bearings  124   a - b  (described with respect to the first table of  FIG. 9A ) may allow the first and second gearboxes  30   a - b  of the first table  12   a  to align with each other and the first and second gearboxes  30   c - d  of the second table  12   b  to align with each other and define the axis of rotation for a respective table. As shown in  FIG. 9A , two gearboxes  30   a - b  of the first table  12   a  are connected with an intra-table drive shaft  42   a  (e.g. a rigid tube) coaxially aligned to the shafts of the two gearboxes  30   a - b . Any misalignment “D” (shown in  FIG. 9A ) in the vertical direction between the first and second posts  20   a ,  22   a  of a single table is accommodated by the spherical bearings  124   a - b . A similar self-alignment mechanism would accommodate a horizontal misalignment perpendicular to the axis of rotation. A third direction of misalignment, along the axis of rotation, is accommodated by elongate slots  112  ( FIG. 7A ) in the gearbox shafts. 
     This facilitates alignment of each table with gearboxes  30   a - b  and makes the construction of each table  12   a - d  easier by allowing for loose tolerances and no alignment procedure. The result is that consecutive tables of the modular tracker system  10  are not likely aligned with respect to a single common linear axis of rotation, but rather, the gearboxes of each respective table are aligned (as shown in  FIG. 9A ). Since the torque load carried by the inter-table drive shaft (e.g. first inter-table drive shaft  16   a ) is very small compared to the torque capacity of the gearboxes, the inter-table drive shaft may deflect and accommodate misalignment without generating large bending stresses, while still being able to carry the required torque. 
     Specific aspects of the modular tracker system  10  will now be described in relation to the figures, however, persons skilled in the art would appreciate that these principles may also apply to other tables and to a continuous modular tracker system, which is not separated into distinct tables. 
     As shown in  FIG. 3 , the frame  26   a  may include cross beams  32   a - b  and support beams  34   a - b . In the exemplary embodiment shown, the first cross beam  32   a  is generally parallel to the second cross beam  32   b , and the first support beam  34   a  is generally parallel to the second support beam  34   b , however, other arrangements of cross beams  32   a - b  and support beams  34   a - b  are also envisioned. The cross beams  32   a - b  and support beams  34   a - b  may be attached to each other using an attachment structure, for example a fastener  40 , such as a nut and bolt. The solar panels  28  may be attached to frame  26   a , such as the first and second support beams  34   a - b , using a variety of attachment structures, such as using clips  36 , bolts, screws, or other suitable attachment structures. 
     As shown in  FIGS. 2 and 3 , the gearboxes  30   a - d  of the first and second tables  12   a - b  may be respectively supported by the first and second support structure  18   a - b  of the first and second tables  12   a - b . More specifically, the gearboxes  30   a - d  may be operatively coupled to the first mounting post  20   a - b  and the second mounting post  22   a - b  of each of the first and second tables  12   a - b . For example, as shown in  FIG. 3 , the first gearbox  30   a  may be coupled to the first mounting post  20   a  using a lever arm  38   a  and a first mounting bracket  116   c  (shown in  FIG. 8 ), and the second gearbox  30   b  may be coupled to the second mounting post  22   a  using a lever arm  38   b  and a second mounting bracket  116   b  (shown in  FIG. 9A ). The mounting brackets  116   a - b  locate the spherical bearings  124   a - b  that mount the rotatable gearbox housings (i.e. the second outputs  50   a - b ), and the lever arms  38   a - b  prevent the non-rotatable gearbox housings  54   a - b  from rotating. 
     With continued reference to  FIGS. 2 and 3 , the modular tracker system  10  includes first and second intra-table drive shafts  42   a - b . The first intra-table drive shaft  42   a  connects the first and second gearboxes  30   a - b  of the first table  12   a  to the frame  26   a  of the first table  12   a , and the second intra-table drive shaft  42   b  connects the first and second gearboxes  30   c - d  of the second table  12   b  to the frame  26   b  of the second table  12   b . As alignment within each of the first and second tables  12   a - b  is established by self-aligning the axes of the gearboxes  30   a - b  with the axis of rotation established by the centers of the spherical bearings mounting the two gearboxes  30   a - b , using the first and second intra-table drive shafts  42   a - b  to coaxially connect the shafts of the two gearboxes  30   a - b , alignment between the adjacent first and second tables  14   a - b  is corrected using the first inter-table drive shaft  16   a  using two universal joints  44  at the ends of the inter-table drive shaft  16   a  or by making the inter-table drive shaft  16   a  flexible enough (e.g. using flexible shaft  122 ) to deflect without inducing high bending loads. This is because the torque required to drive the gearboxes is very low, due to the very high gear ratio of the gearboxes  30   a - b.    
     The modular tracker system  10  may be powered by a single motor  14 . The single motor  14 , as shown in  FIG. 2 , may be rotatably connected to the input of the first gearbox  30   a , with the single motor  14  for imparting rotational motion to the first gearbox  30   a , thereby causing the gearbox shaft to rotate within the gearbox  30   a . The single motor  14  may be, for example, any type of device or method, either automatic or manual, for supplying rotational energy, such as: an electric, gas, solar or other type of energy powered motor, a manually operated crank, or any combination of these devices. For example, a 24 Volt DC geared motor having a max torque of 92 Newton meters, a rated torque of 46 Newton meters, and a rated speed of 10.3 rotations/minute may be used, however, a variety of other suitable motors  14  are also suitable. The coupling of the single motor  14  to the modular tracker system  10  is simplified since the transmitted torque is relatively small. Concurrently, the torque carried by the drive shafts should never be higher than the torque provided by the motor  14 , requiring a relatively light section to provide the required torque capacity. 
     For the solar panel platform  382  to effectively track the apparent path of the sun, a microcontroller (not shown) in electronic connection with the single motor  14 . The microcontroller may be programmed to vary the angular velocity of the gearbox shaft  64  as needed, which in turn varies the angular velocity of the solar panel platform  382 . Microcontrollers are well understood in the art, and as a result, are not described in detail below. 
       FIGS. 4A and 4B  show detailed perspective views of the third gearbox  30   c  of the second table  12   b  operatively coupled to the frame  26   b . While the third gearbox  30   c  is described in detail, these principles apply equally to other gearboxes of other tables  12   a - d , such as the first gearbox  30   a , and the second gearboxes  30   b ,  30   d , and subsequent gearboxes (not shown) for the third and fourth tables  12   c - d . Description below is with respect to the third gearbox  30   c  and not the first gearbox  30   a , since the first gearbox  30   a , according to this exemplary embodiment, is coupled to the single motor  14  and not to an adjacent table. 
     The first inter-table drive shaft  16   a  is connected to the third gearbox  30   c  of the second table  12   b  using a universal joint  44 , shown in greater detail with reference to  FIGS. 5A-5C , and the second intra-table drive shaft  42   b  is connected to the first gearbox  30   c  using a rigid joint  46 , shown in greater detail with reference to  FIGS. 6, 7A and 7B . While universal joints  44  are shown as being used between tables (e.g. the first and second tables  12   a - b ) and rigid joints are shown as being used within a table (e.g. the first table  12   a ), a universal joint  44  may be used both within and between tables for simplicity (as shown in  FIGS. 10A-B ), and a rigid joint  46  may be used both within and between tables when a flexible inter-table drive shaft  122  (shown in  FIG. 9 ) is used to accommodate misalignment. 
     As will be described in greater detail below, but introduced here for greater clarity, the third gearbox  30   c  includes a rotatable input housing  54   c  ( FIG. 4A  and  FIG. 4B ), a gearbox shaft  64   c  having an input  66   c  and a first output  68   c , and a second output  50   c , which is shown as a rotatable output housing. The input  66   c  of the gearbox shaft  64   c  may have cutout portions  77 , and the first output  68   c  may have cutout portions  69 . Once again, the principles described with respect to the third gearbox  30   c , also apply to the other gearboxes  30   a - d  etc. 
     More specifically, the third gearbox  30   c  may provide two separate output rotational motions that are generated from imparting an input rotational motion from the single motor  14  to the input  66   c  of the gearbox shaft  64   c : a rotational motion of the first output  68   c  of the gearbox shaft  64   c , and a rotational motion of the second output  50   c . The rotational motion of the first output  68   c  of the gearbox shaft  64   c  is generated due to the structural features of the gearbox, which enables the gearbox shaft  64   c , which is disposed within the third gearbox  30   c , to extend from the input  66   c  of the gearbox shaft  64   c , positioned outside of the third gearbox  30   c , to the first output  68   c  of the gearbox shaft  64   c , also positioned outside of the third gearbox  30   c . In short, the gearbox shaft  64   c  may extend all the way through the third gearbox  30   c , preferably with the input  66   c  and the first output  68   c  of the gearbox shaft  64   c  extending outside of the third gearbox  30   c  as shown. 
     Instead of, or into addition to, the gearboxes  30   a - d  being coupled to the support structure  18   a - b , the gearboxes  30   a - d  may also be respectively coupled to the first and second frame  26   a - b . As shown, the first gearbox  30   a  may be attached to cross beam  32   a  of the frame  26   a . As shown in  FIGS. 4A and 4B , regarding the coupling of the third gearbox  30   c  to the frame  26   c , the flange portion  48  of the second output  50   c  is operatively coupled to the cross-beam  32   c  using any suitable attachment structure, such as fastener  52 , for example a nut and bolt. More specifically, the input  66   c  of gearbox shaft  64   c  extends away from the table  12   c  and the second output  50   c  of gearbox shaft  64   c  extends through an opening (not shown) within the cross beam  32   c  and into an open space within the table  12   c  formed by the cross beam  32   c  and the first mounting post  20   b.    
     Similarly, the non-rotatable housing  54   c  may be coupled to an upper portion  56  of the first lever arm  38   c  of the second table  12   b , using any suitable attachment structure, such as a fastener  58 , for example a nut and bolt. Additionally, a lower end  60  of the first lever arm  38   c  is operatively coupled to the first mounting post  20   b  of the second table  12   b  using any suitable attachment structure, such as a fastener  62 , for example a nut and bolt. As shown, the first lever arm  38   c  may have a bent shape to better accommodate the structure of the first mounting post  20   b  and first gearbox  30   c  and to provide greater flexibility for installation and operation. 
     Each gearbox  30   a - d , with the second and third gearboxes  30   b - c  being shown and described for representative purposes, is configured to produce a first output  68   b - c  and a second output  50   b - c . The first output  68   b - c  has a first rotational speed and the second output  50   b - c  has a second rotational speed that is less than the first rotational speed. The first output may have a first rotational speed equal to the input rotational speed. According to an exemplary embodiment, the first output  68   b - c  may have a speed ratio of about 1:1 and the second output  50   b - c  may have a speed ratio of about 1:60 or less. According to an embodiment, the gearbox reduction ratio is 1/361, and the row driven by one motor is 160 solar panels  28  long, resulting in the torque sustained by the gearbox lever arm being equal to the maximum torque load on four solar panels  28 . The torque on the single motor  14  is 160/(4×361) or 1/9th of the torque already designed for which is the wind load from four solar panels  28 . For example, there is no specific requirement to provide an additional rotational anchoring support for the single motor  14  when the first lever arm  38   a  is designed with a 10% capacity margin. The second outputs  50   b - c  of the second and third gearboxes  30   b - c  are operatively coupled to the respective frame  26   b - c . The input  66   b - c  of the second and third gearboxes  30   b - c  may be formed on a common shaft as the first output  68   b - c , resulting in the input  66   b - c  having the same speed ratio as the first output  68   b - c.    
     Regarding the rotation of the frame  26   c , the single motor  14  supplies rotational energy to the first table  12   a  and causes the first inter-table drive shaft  16   a  rotatably coupled to input  66   c  of the gearbox shaft  64   c . The gearbox shaft  64   c  imparts rotational motion to the first output  68   c , such that the rotational motion may be utilized to provide the rotational motion to other tables. Also, the second output  50   c  will rotate around corresponding drive shafts that are integral with a corresponding pair of gearboxes  30   c - d , and due to the connection of the second output  50   c  to corresponding cross beams  32   c - d , the frame  26   b  may rotate at the same angular velocity as the second output  50   c . More specifically, due to the connection of the second output  50   c  to the frame  26   c  (e.g. cross beam  32   c ), the frame  26   c  may rotate around first and second mounting posts  20   b ,  22   b  at the same angular velocity as the second output  50   c  of the third gearbox  30   c.    
     Now with reference to the universal joint  44  shown in greater detail with respect to  FIGS. 5A-5C . According to an exemplary embodiment, the universal joint  44  includes a yoke  70  having first and second portions  72   a - b . An alignment structure  74   a - b  is disposed on the connecting portion  76   a - b  to suitably align the first and second portions  72   a - b . However, a yoke  70  integrally formed as a unitary piece is also envisioned. The first and second portions  72   a - b  each respectively include a cutout portion  78   a - b  sized to accommodate the input  66  extending therethrough. The first and second portions  72   a - b  each respectively include a through hole  80   a - b  disposed on an end surface  82   a - b . The end surfaces  82   a - b  of the first and second portions  72   a - b  may be arcuately shaped, as will be discussed below. 
     With continued reference to  FIGS. 5A-5C , the yoke  70  allows for connection between two shafts with an attachment structure. As shown, a fastener  84 , such as a bolt, extends through the first through hole  86   a  of the first output arm  88   a  of the first inter-table drive shaft  16   a , the first through hole  80   a  of the first portion  72   a , the elongate slot  90  of the input  66  of the third gearbox  30   c , the second through hole  80   b  of the second portion  72   b , and the second through hole  86   b  of the second output arm  88   b  of the first inter-table drive shaft  16   a . The fastener  84  may then be threadably coupled with a nut  92 . 
     As shown in  FIGS. 4A and 4B , the universal joint  44  may include a bracket  93  to couple the first inter-table drive shaft  16   a  with the input  66   c  of the third gearbox  30   c . The bracket  93  may be reversible according to an exemplary embodiment. Using a reversible bracket  93  allows for fewer distinct parts, which may make installation simpler and cheaper. The bracket  93  includes first and second ends  95   a - b . The first end  95   a  includes first and second legs  97   a - b , with the first leg  97   a  including a first through hole  99   a , and the second leg  97   b  including a second through hole  99   b . The bracket  93  may be secured using an attachment structure, such as fasteners  101 , for example nuts and bolts, in a flange portion of the bracket  93 . 
     The fastener  84  may extend through the first through hole  99   a  of the first end  95   a  of the bracket  93 , through the first through hole  86   a  of the first inter-table drive shaft  16   a , through the hole of the yoke  70   a - b , the elongate slot  90  of the gearbox shaft  64   c , the second through hole  99   b  of the first inter-table drive shaft  16   a , and through the second through hole  99   b  of the first end  95   a  of the bracket  93 . 
     As shown, the bracket  93  may be reversible allowing the bracket  93  to be used for both the universal joint  44 , shown in greater detail with reference to  FIGS. 5A-5C , and the rigid joint  46 , shown in greater detail with reference to  FIGS. 6, 7A and 7B . More specifically, a first end  95   a  of the bracket  93  may be used for coupling the universal joint  44  to the respective structures, and a second end  95   b  may be used for coupling the rigid joint  46  to the respective structures. As shown, for example, the bracket  93  may be rotated 180° to couple the first output  68   c  of the third gearbox  30   c  to the second intra-table drive shaft  42   b . The second end  95   b  of the bracket  93  includes first and second through holes  103   a - b.    
     This arrangement allows torque to be suitably transferred, while the input  66  of the first gearbox  30   c  is free to rotate about two axes orthogonal to the axis of rotation of the first inter-table drive shaft  16   a . As shown in the top view of  FIG. 5B , the fastener  84  allows for the input  66  (e.g. the input connecting end) of the first gearbox  30   c  to rotate about first orthogonal plane, as shown by arrow  94 . Additionally, the oppositely disposed end surfaces  82   a - b  of the first and second portions  72   a - b  being arcuately shaped allow for the end surfaces  82   a - b  to pivot on the first and second output arms  88   a - b  allowing for a range of rotation about a second orthogonal plane, that is perpendicular to the first orthogonal plane. Additionally, the elongate slot  90  of the input  66  allows for rotation, shown by arrow  96  in  FIG. 5C , in both the first and second orthogonal planes and a range of axial motion, due to the elongate nature of the elongate slot  90 , generally along the axis of rotation for accommodation of assembly tolerances and thermal displacements. The outwardly tapering walls  98   a - b  of the first and second through holes  80   a - b  allows for the yoke  70  to pivot about the fastener  84  for added flexibility. 
     As such, the universal joint  44  allows for accommodation of substantial misalignment between axes of adjacent tables (e.g. between the first and second tables  12   a - b  or between the second and third tables  12   b - c ) while also transmitting torque between two adjacent shafts that are not aligned. To accommodate uneven ground locations, it is desirable to have the universal joint  44  accommodate as much as 10 degrees of axial misalignment and a vertical misalignment of 12 inches, according to an exemplary embodiment. This allows the first inter-table drive shaft  16   a  to be in an angled orientation relative to the first and second tables  12   a - b . In this manner, the first and second tables  12   a - b  may be secured in uneven ground or other surfaces, without impacting the operation of the modular tracker system  10  as described above. Other universal joints are also envisioned. 
       FIGS. 6, 7A and 7B  show a detailed view of  FIG. 2 , where the second intra-table drive shaft  42   b  is connected to the second gearbox  30   b  using a rigid joint  46 . The rigid joint  46  includes a spacer  100  that allows a hollow shaft, such as the second intra-table drive shaft  42   b , to connect to a smaller shaft, such as the first output  68   b  of the second gearbox  30   b  for coaxial torque transfer. While the spacer  100  is shown as being integrally formed as a unitary piece, persons skilled in the art would appreciate that the spacer  100  may be collectively formed from distinct components. 
     With the rotating frame integrated self-aligning bearings mounting the gearbox to the mounting bracket, there is flexibility to accommodate position tolerances between the two mounting points of each gearbox (such as the second gearbox  30   b ), facilitating the tracker assembly process. As shown in  FIG. 4A , the first mounting position may be using the flange portion  48  and/or lever arm  38   c . As shown in  FIG. 6 , the second mounting position may be using the mounting bracket  116 . In the horizontal direction, tolerances are built into the frame  26   a  that may have adjustability in the distance between the two pivot arms (cross beam  32   a - b  of the frame  26   a ). 
     With reference to exploded perspective views of  FIGS. 7A and 7B , a rigid joint  46  is shown being connected between the first intra-table drive shaft  42   a  and the first output  68   b  of the second gearbox  30   b . However, persons skilled in the art would appreciate this this rigid joint is applicable to connections between respective intra-table drive shafts and gearboxes. The first intra-table drive shaft  42   a  at first end is rotatably connected to the input  66   a  of gearbox shaft  64   a  of the first gearbox  30   a , and at the second end is rotatably connected to input  66   b  of the gearbox shaft  64   b  of the second gearbox  30   b.    
     The spacer  100  includes a first through hole  102  to accommodate a fastener  104 , such a bolt, therethrough and a second through hole  106  for the cutout portion  69  of the first output  68   b  to extend therethrough. The first intra-table drive shaft  42   a  is shown as being hollow and including first and second through holes  108   a - b  extending adjacent to the terminal end  110 . The first output  68   b  includes an elongate slot  112  on the smaller shaft that allows for axial displacement (for assembly tolerances and thermal displacements). Once the fastener  104  extends through the second through hole  108   b  of the first intra-table drive shaft  42   a , through the hole  102  of the spacer  100 , the elongate slot  112  of the second gearbox  30   b , and the second through hole  108   b  of the first intra-table drive shaft  42   a , the fastener  104  may be secured with a nut  114 . A portion of the second gearbox  30   b  may be supported by a mounting bracket  116   b  coupled to the second mounting post  22   a  using a connecting structure, such as a fastener  118 , for example a nut and bolt. The elongate slot  112  on the gearbox shaft  64   b  allows for axial displacement (for assembly tolerances and thermal displacements) as shown by arrow  120 . 
     As previously described, a bracket  93  may also be included as part of the rigid joint  46 . The bracket  93  has a first end  95   a  and a second end  95   b  disposed opposite the first end  95   a , where the second end  95   b  includes first and second through holes  103   a - b . The fastener  104  may extend through the first through hole  103   a  of the second end  95   b  of the bracket  93 , the first through hole  108   a  of the first intra-table drive shaft  42   a , the first through hole  102  of the spacer  100 , the elongate slot  112  of the gearbox shaft  64   b  of the second gearbox  30   b , the second through hole  108   b  of the first intra-table drive shaft  42   a , and through the second through hole  103   b  of the second end  95   b  of the reversible bracket  93 . The fastener  104  may be secured with a nut  114 . The bracket may be secured on a side using a fastener  101 , such as a nut and bolt. 
     In  FIG. 8 , two universal joints  44  are shown, each using an alternative bracket  93   a  including a single fastener  101 . The first universal joint  44  couples the first inter-table drive shaft  16   a  to the input of the third gearbox  30   c  and includes a bracket  93   a , that functions in a similar manner to bracket  93  described above. The second universal joint  44  couples the first output  68   c  to the second inter-table drive shaft  42   b  and includes a bracket  93   a.    
     Now with reference to  FIG. 9 , which shows a flexible shaft  122  in accordance with another exemplary embodiment, which may be used instead of, the universal joint  44 , and the rigid joint  46 . While the flexible shaft is shown in place of the first inter-table drive shaft  16   a , persons skilled in the art would appreciate this this flexible shaft  122  may be used instead of the intra-table drive shaft  42   a - d  and/or the inter-table drive shaft  16   a - c . For example, a square 0.75 inch tubular flexible shaft having a wall thickness of 0.06 inches and a length of 9 feet will deflect less than 6 degrees with minimal inducement of bending stresses, while carrying a torque capable of driving more than 20 gearboxes, such as gearboxes  30   a - d.    
     The flexible shaft  122  generally has a smaller cross-sectional area than the inter-table drive shaft  16   a , allowing the flexible shaft  122  to suitably flex such that misalignment corrects itself through the flexing in the flexible shaft  122 . In this embodiment, the flexible shaft  122  is still strong enough to carry the torque load, but flexible enough to accommodate misalignment by bending. The flexible shaft  122  may be rigidly connected at both ends, such that it does not include articulating parts that wear and may need lubrication, such as the parts composing universal joints  44  and other non-rigid joints  46 . 
       FIG. 9A  shows an enlarged portion of the first table  12   a  of  FIG. 9 , with the second support beam  34   b  being removed for added clarity. Inaccuracies of angular orientation of the mounting posts  20   a - d ,  22   a - d , and discrepancies in the vertical position of the mounting posts  20   a - d ,  22   a - d  for each table  12   a - b  may be dealt with by the self-aligning spherical bearings  124   a - b  at two support points of each table  12   a - b  that allow the axis a range of freedom. As shown, the first and second gearboxes  30   a - b  are rotationally supported on the input  66   a - b  side by first and second lever arms  38   a - b . Similarly, the first and second gearboxes  30   a - b  are supported on the first output  68   a - b  side by spherical bearings  124   a - b  free to rotate. As such, the first and second gearboxes  30   a - b  may be rotated on the spherical bearings  124   a - b  to obtain axial alignment for gearboxes on the same table (for example, the first and second gearboxes  30   a - b  as shown). However, these principles apply to other gearboxes (such as the first and second gearboxes  30   c - d  of the second table  12   b  and so on). The spherical bearings  124   a - b  allow the first and second gearboxes  30   a - b , for example, that are attached to the frame  26   a  to remain co-axially aligned regardless of the position of the mounting point (center of the spherical bearings  124   a - b ). This allows for a wide range of tolerances in installation where the mounting posts  20   a ,  22   a  have loose tolerances in x-y-z reference frame. 
     As such, the modular tracker system  10  may prevent induced loads on the rotating frame  26   a - b  resulting from mounting post  20   a - d ,  22   a - d  misalignment due to different elevations (D) and angles (A). In addition, the rotating structures are sufficiently small so that any thermal deformation is easily manageable, in contrast with a single long stiff torque tube. The short distance between the spherical bearings  124   a - b  and the mounting to the pivot arm reduces the bending load induced by the forces applied through the support on the bearing points. 
       FIG. 10A  shows an exemplary gearbox system  210 , which is removed from the modular tracker system  10  shown in  FIG. 2 . The description below provides additional description as to how the first and second tables  12   a - b  may be rotated synchronously. As shown, the gearbox system  210  includes four gearboxes, namely, the first, second, third and fourth gearboxes  30   a - d.    
     As shown, the first gearbox  30   a  starts with an input  66   a  that may be coupled to the single motor  14  and produces a first output  68   a  and a second output  50   a . The first output  68   a  may be connected to the first intra-table drive shaft  42   a  using a universal joint  44 , and the second output  50   a  may be operatively coupled to the frame  26   a  (not shown) to rotate the solar panels  28  of the first table  12   a . The second gearbox  30   b  includes an input  66   b  obtained from the first intra-table drive shaft  42   a  through a universal joint  44  and produces a first output  68   b  and a second output  50   b . The first output  68   b  may be connected to an inter-table drive shaft  16   a  using a universal joint  44 , and the second output  50   b  may be operatively coupled to the frame  26   a  of the first table  12   a  to rotate the solar panels  28  of the first table  12   a.    
     Similarly, the third gearbox  30   c  includes an input  66   c  that may be obtained from first inter-table drive shaft  16   a  through the universal joint  44 . The third gearbox  30   c  produces a first output  68   c  and a second output  50   c . The first output  68   c  may be connected to a second intra-table drive shaft  42   b  using a universal joint  44 , and the second output  50   c  may be coupled to the frame  26   b  of the second table  12   b  to rotate solar panels  28  of the second table  12   b . The fourth gearbox  30   d  includes an input  66   d  obtained from the second intra-table drive shaft  42   b  through a universal joint  44  and may produce a first output  68   d  and a second output  50   d . The first output  68   d  may be connected to a second inter-table drive shaft  16   b  using a universal joint  44 , and the second output  50   d  may be coupled to the frame  26   b  of the second table  12   b  to rotate the solar panels  28  of the second table  12   b.    
     It should be understood that the reference to the “input”  66   a - d  and “first output”  68   a - d  of the gearbox shaft  64   a - d  and to all other similar designations, such as: input rotatable housing  312 , second output  50   a - d , input bearing housing enclosure, and output bearing housing enclosure, are merely arbitrary conventions that have been followed in order to accurately describe the gearbox  30   a - d  and the manner of its operation. 
     With this in mind,  FIG. 10B  shows an alternative gearbox system  210   a , where each of the gearboxes  30   a - d  is rotated 180 degrees. The first and second gearboxes  30   a - b  and/or the third and fourth gearboxes  30   c - d  may operate symmetrically in that single motor  14  may be rotatably connected to either the input  66   a  of gearbox shaft  64 , as described above, or connected to the opposite first output  68   a  of gearbox shaft  64 , without in any manner altering the performance characteristics of the first gearbox  30   a  described above. Thus, when the single motor  14  may be connected to the first output  68   a  of the gearbox shaft  64 , with the second output  314  prevented from rotating, the input rotatable housing  312  may rotate, just like the second output  314  may rotate when the single motor  14  may be rotatably connected to the input  66   a  of gearbox shaft  64 . 
     As shown, the first gearbox  30   a  includes a first output  68   a  that may be coupled to the single motor  14  (not shown) and a second output  50   a . The second output  50   a  may be operatively coupled to the frame  26   a  (not shown) to rotate the solar panels  28  of the first table  12   a . The input  66   a  may be connected to the first intra-table drive shaft  42   a  using the universal joint  44 . The second gearbox  30   b  includes a first output  68   b  obtained from the first intra-table drive shaft  42   a  through a rigid joint  46  and produces a first output  68   b  and a second output  50   b . The second output  50   b  may be coupled to the frame  26   a  of the first table  12   a  to rotate the solar panels  28  of the first table  12   a . The input  66   a  may be connected to an inter-table drive shaft  16   a  using a universal joint  44 . While,  FIGS. 10A and 10B  show universal joints  44 , rigid joints  46  may alternatively be used if desirable. 
     Similarly, the third gearbox  30   c  includes a first output  68   c  obtained from first inter-table drive shaft  16   a  through the universal joint  44  and a second output  50   c . The second output  50   c  may be coupled to the frame  26   b  of the second table  12   b  to rotate solar panels  28  of the second table  12   b . The input  66   c  may be connected to a second intra-table drive shaft  42   b  using a rigid joint  46 . The fourth gearbox  30   d  includes a first output  68   d  obtained from the second intra-table drive shaft  42   b  through a rigid joint  46  and produces a first output  68   b  and a second output  50   d . The second output  50   d  is coupled to the frame  26   b  of the second table  12   b  to rotate the solar panels  28  of the second table  12   b . The input  66   d  may be connected to a second inter-table drive shaft  16   b  using a universal joint. As such, the first and second gearboxes  30   a - b  of the first table  12   a  and the third and fourth gearboxes  30   c - d  of the second table  12   b  operate symmetrically. 
     Now with reference to an alternative embodiment of the modular tracker system  10 ′ shown in  FIG. 3A , where the first table  12   a  includes a single gearbox  30   a . While the first and second tables  12   a - b  shown in the  FIG. 2  respectively include a second gearbox  30   b ,  30   d  operatively coupled to the second mounting post  22   a - b , a second gearbox  30   b ,  30   d  is not always required. Instead, as shown in  FIG. 3A , the first table  12   a  may include only a single gearbox (e.g. the first gearbox  30   a ), and the second table  12   b  may include only a single gearbox (e.g. the first gearbox  30   c ). As shown in  FIG. 3A , when the second gearbox  30   b  is not present, a spherical bearing  124   b  may be used to mount the rotating frame  26   a  (not shown) to the second mounting post  22   a - b  when the support structure includes first and second mounting posts  20   a ,  22   a . In addition, an opening through the spherical bearing  124   b  accommodates the drive shaft  42   a . Through that opening, a bearing supported shaft  126  (shown schematically without couplings in  FIG. 3A ), similar to the gearbox shaft, would be mounted to provide a torque carrying connection between intra-table drive shaft  42   a  and the inter-table drive shaft  16   a.    
     While  FIGS. 10A and 10B  are described above with respect to first and second tables  12   a - b , this also applies to a continuous modular tracker system that is not broken down into discrete tables, where the gearbox system  210   c  is shown in  FIG. 10C . Like the previously disclosed embodiments shown in the Figures, the modular tracker system would include a support structure configured to be mounted in the ground, a frame supported by the support structure, a plurality of solar panels supported by the frame, first and second gearboxes  30   a - b , a single motor driving the modular tracker system, and a drive shaft  42   a  connecting the first and second gearboxes  30   a - b . The first gearbox  30   a  is supported by the support structure and defines an axis of rotation. The first gearbox  30   a  is configured to produce first and second outputs  68   a ,  50   a . The first output  68   a  has a first rotational speed and the second output  50   a  has a second rotational speed that is less than the first rotational speed. The second output  50   a  is operatively coupled to the frame. The second gearbox  30   b  is supported by the support structure and axially aligned with the first gearbox  30   a  along the axis of rotation. The second gearbox  30   b  is configured to produce first and second outputs  68   b ,  50   b . The first output  68   b  has the first rotational speed and the second output  50   b  has the second rotational speed and is operatively coupled to the frame. The drive shaft  42   a  couples the first output  68   a  of the first gearbox  30   a  with the input or output of the second gearbox  30   b , whereby the plurality of solar panels is rotated synchronously. 
     Additional gearboxes and drive shafts may be included, such as third and fourth gearboxes (which may be the first and second gearboxes  30   c - d  of the second table  12   b ) and second and third drive shafts (which are shown as the first inter-table drive shaft  16   a  and the second intra-table drive shaft  42   b  in  FIGS. 10A-B ). The third gearbox  30   c  is supported by the support structure and axially aligned with the first gearbox  30   a  along the axis of rotation (GA). The third gearbox  30   c  is configured to produce first and second outputs  68   c ,  50   c , where the first output  68   c  has the first rotational speed and the second output  68   c  has the second rotational speed that is less than the first rotational speed, and where the second output  50   c  is operatively coupled to the frame. The fourth gearbox  30   d  is supported by the support structure and is axially aligned with the third gearbox  30   c  along the axis of rotation. The fourth gearbox  30   d  is configured to produce first and second outputs  68   d ,  50   d , where the first output  68   d  has the first rotational speed and the second output  50   d  has the second rotational speed and is operatively coupled to the frame. The second drive shaft, for example the first inter-table drive shaft  16   a , connects the second and third gearboxes  30   b - 30   c . The third drive shaft, for example the second intra-table drive shaft  42   b , couples the input  66   b  of the second gearbox  30   b  with the input  66   c  of the third gearbox  30   c . The third drive shaft connects the third and fourth gearboxes  30   c - d . The third drive shaft couples the first output  68   c  of the third gearbox with the first output  68   d  of the fourth gearbox  30   d , whereby the plurality of solar panels are rotated synchronously. 
       FIG. 11  shows an exemplary modular tracker system  10   b  that includes five tables  12   a - e  coupled together in a row. Additional tables may be added, as persons skilled in the art would appreciate. As shown, the modular tracker system  10   b  includes at least first, second, third, fourth, and fifth tables  12   a - e  rotatably arranged in a row, a single motor  14  driving the tables  12   a - e , a first inter-table drive shaft  16   a  connecting the first and second tables, and a second inter-table drive shaft  16   b  connecting the second and third tables, and a third inter-table drive shaft  16   c  connecting the third and fourth tables  12   c - d , and a fourth inter-table drive shaft  16   d  connecting the fourth and fifth tables  12   d - e.    
     Each of the tables  12   a - e  respectively includes a first mounting post  20   a - e  and a second mounting post  22   a - e  configured to be mounted in the ground, a frame  26   a - e  supported by the first and second mounting posts,  20   a - e ,  22   a - e , intra-table drive shafts  42   a - e , and gearboxes  30   a - j  defining an axis of rotation. As shown, the frames  26   a - e  respectively include cross beams  32   a - j  and support beams  34   a - j . Each gearbox  30   a - j  may be configured to produce first and second outputs, where the first output has a first rotational speed and the second output has a second rotational speed that is less than the first rotational speed, and where the second output may be operatively coupled to the frame  26   a - e . The modular tracker system  10  also includes first, second, third, fourth and fifth intra-table drive shafts  42   a - e . The first intra-table drive shaft  42   a  connects the first and second gearboxes  30   a - b  of the first table  12   a  to the frame  26   a.    
     The modular tracker system  10 ,  10   a ,  10   b  provides many benefits, such as: (1) load distribution, (2) improved gear ratios, (3) simple assembly and installation, (4) improved alignment/tracking, (5) reduced sensitivity to thermal issues, and (6) reduced sensitivity to frequency issues. Each of these associated benefits is discussed below. 
     In terms of load distribution, the modular tracker system  10  allows for the torque loads and the bending loads sustained by different members, so that the structure may be optimized for both without inefficiencies. The high reduction ratio of the gearboxes result in a low torque load on the drive shafts, and allows a long row of tables  12   a - e  to be driven by a single motor  14 . The decoupling of torsional loads handled by the gearboxes  30   a - d , from the bending loads handled by the frame  26   a - e  allows for a higher efficiency of material used to meet the structural requirements. Decomposing a long row of photovoltaic modules into modular tables circumvents concerns with thermal displacements and low resonant frequencies. In addition, the modular tracker system  10  being broken down into tables  12   a - e  may better prevent inadequacies resulting from ground undulations, thermal displacements, and low resonant frequencies that torque tube designs do not adequately address. The torque loads developed by tables  12   a - e , being relatively small in comparison to the modular tracker system  10 , are small enough that the rotating frames of the modular tracker system  10  may be driven by bending load requirements, and optimized in terms of material usage. 
     According to an exemplary embodiment describing five tables  12   a - e , driving the rotation of the tables  12   a - e  with a high gear ratio, typically over 1:300, using inter-table drive shafts  16   a - e  and intra-table drive shafts  42   a - d  allows solar panels  28  to suitably track the sun. The modular tracker system  10  allows for a very low torque requirement on the drive shafts, and a conversely very low sensitivity of the tables to torsional defection of the drive shaft. The modular tracker system  10  allows for much longer rows of tables driven by a single motor  14 , reducing the motor  14  and microcontroller cost burden on each table  12   a - e  and resulting in a lower overall cost. 
     The modular tracker system  10  table based configuration is very simple and easy to assemble, since the gearbox may integrate bearings that support the table on the axis of rotation, and the complete structure may be reduced to few components, such as the support structure, gearboxes, frame. One additional advantage of breaking up the installation into small tables is that assembly is simpler and does not require expensive machinery to use and operate to lift components. Instead, given the modular design, components are easily picked up manually by one or two installers. This reduces the number of people and equipment required for installation and simplifies logistics. This design also reduces the number of fasteners, which consequently reduces the labor required for assembly. 
     In terms of tracking alignment, with a gear ratio of 1:361, a row of 20 tables may be aligned within one degree, while single stiff torque tube solar trackers have difficulty keeping the total twist under 6 degrees (e.g. has an angle of twist of less than 6 degrees), even under moderate wind conditions. With such high gear ratio, the torque requirement on the intra-table drive shafts and the inter-table drive shafts is very low compared to the conventional torque tube designs, resulting in a very small twist over the length of the row, even at the limit torque capacity. While the shaft under load may twist over the length of multiple tables, the twist reflected on the tables is further reduced by the gear ratio resulting in a much stiffer row with little discrepancy of tilt between tables. 
     In terms of thermal expansion, the modular tracker system  10  absorbs the changes in geometry at the table level rather than at the row level as is the case with a stiff long torque tube. The magnitude of thermal displacements is small such that, even under wide daily temperature changes, the bearings are negligibly displaced. For instance, with a daily thermal variation of 50° C., the maximum displacement induced at each bearing location is less than 0.±030 inches. Furthermore, the compliance in the connections between tables  12   a - d  insulates consecutive tables from additive thermal displacements. 
     In terms of frequency response, the modular tables have high natural frequencies, well above the problematic range of frequencies stimulated by wind gust effects. Any dynamic effect on a table is not transferred to the drive shaft in a way that may systematically affect the whole row, so natural frequencies are high, and amplitudes are small, resulting in a more robust design compared to conventional torque tubes. 
     An exemplary gearbox  310  for use with the modular tracker system  10 ,  10   a ,  10   b  is shown in  FIG. 12A-13B . The gearbox  310  includes an input rotatable housing  312  and a second output  314  (e.g. a second output). The input rotatable housing  312  has a cylindrical sidewall  316  having a closed end  318  and an open end  320  opposite from the closed end  318 . The second output  314  has a cylindrical sidewall  324  having a closed end  326  and an open end  328  opposite from the closed end  326 , with the open end  320  of the cylindrical sidewall  316  adjacent to the open end  328  of the cylindrical sidewall  324  forming a gear housing enclosure  330  having a cylindrical shape. The input rotatable housing  312  also has a cylindrical opening  334  within the closed end  318  of the cylindrical sidewall  316  of the input rotatable housing  312 , and the second output  314  also has a cylindrical opening  336  within the closed end  326  of the cylindrical sidewall  324  of the second output  314 , which is opposite from the cylindrical opening  334 . The open end  320  of the cylindrical sidewall  316  of input rotatable housing  312  may be concentrically disposed within the open end  328  of the cylindrical sidewall  324  of the second output  314 , such that the cylindrical sidewall  324  partially overlaps the cylindrical sidewall  316 , thereby creating partially overlapping cylindrical sidewalls. An O-ring  332  may be concentrically positioned between the partially overlapping cylindrical sidewalls and disposed within a concentric groove  332   a  in an outside perimeter of the cylindrical sidewall  316 . The O-ring  332  may create a rotatable seal between the cylindrical sidewall  316  of input rotatable housing  312  and the cylindrical sidewall  324  second output  314 . 
     The gearbox  310  also includes an input bearing housing enclosure  338  and an output bearing housing enclosure  342 , with the input and output bearing housing enclosures,  338  and  342 , integral with the gear housing enclosure  330 . The input bearing housing enclosure  338  has a cylindrical shape with an open end  338   a  and an opposite open end  338   b , with open end  338   a  concentrically integral with the cylindrical opening  334  of the input rotatable housing  312 . A rotatable securing ring  340  is disposed within the open end  338   b  of the input bearing housing enclosure  338 , with the rotatable securing ring  340  having an integral securing ring extension  344  that is not disposed within the open end of  338 B of the input bearing housing enclosure  338 . Preferably, an O-ring  340   a  may be positioned around the rotatable securing ring  340  and disposed within a concentric groove  340   b  around an outside perimeter of the rotatable securing ring  340 . An elongate securing pin  344   a  may be inserted within a radial bore opening  344   b  that extends through the integral securing ring extension  344 . Similarly, the output bearing housing enclosure  342  has a cylindrical shape with an open end  342   a  and an opposite open end  342   b , with open end  342   a  concentrically integral with the cylindrical opening  336  of the second output  314 . A rotatable securing ring  346  is disposed within the open end  342   b  of the output bearing housing enclosure  342 , with the rotatable securing ring  346  having an integral securing ring extension  348  that is not disposed within the open end of  342   b  of output bearing housing enclosure  342 . An O-ring  346   a  may be positioned around the rotatable securing ring  346  and disposed within a concentric groove  346   b  around an outside perimeter of the rotatable securing ring  346 . An elongate securing pin  348   a  may be inserted within a radial bore opening  348   b  that extends through the integral securing ring extension  348 . As will be described in greater detail below, the gearbox  310  also includes a gearbox shaft  350  that may be secured within the gearbox  310  by utilizing the integral securing ring extensions,  344 ,  348 , and corresponding elongate securing pins  344   a  and  348   a.    
     A first internal gear  362   a  is disposed within the gear housing enclosure  330  and is integral with the cylindrical sidewall  316 , with the first internal gear  362   a  having a pitch diameter D 1 . A second internal gear  362   b  is similarly disposed within the gear housing enclosure  330  and is integral with the cylindrical sidewall  324 , with the second internal gear  362   b  having a pitch diameter D 2 , which may be either larger or smaller than the pitch diameter D 1  of the first internal gear  362   a . As an example, the figures illustrate that the first internal gear  362   a  has a pitch diameter that is smaller than the pitch diameter of internal gear  362   b . A first external gear ring  360   a  and a second external gear ring  360   b  are concentrically connected to form an integral differential gear ring  360  that is disposed within the gear housing enclosure  330 , with the integral differential gear ring  360  having a concentric opening  364  through the integral differential gear ring  360 . The first external gear ring  360   a  has a pitch diameter D 3  that is smaller than the pitch diameter D 1  of the first internal gear  362   a , and the second external gear ring  360   b  has a pitch diameter D 4  that is smaller than the pitch diameter D 2  of the second internal gear  362   b , with the first external gear ring  360   a  in partial engagement with the first internal gear  362   a , as shown in  FIG. 4A  and with the second external gear ring  360   b  in partial engagement with the second internal gear  362   b  as shown in  FIG. 4B . 
     The gearbox shaft  350 , having an input  350   a  and a first output  350   b , is disposed and secured within the gearbox  310 . Specifically, the gearbox shaft  350  is disposed within: the gear housing enclosure  330 ; the input bearing housing enclosure,  338 , including rotatable securing ring  340  and corresponding integral securing ring extension  344 ; and the output bearing housing enclosure  342 , including rotatable securing ring  346  and corresponding integral securing ring extension  348 . The input  350   a  of gearbox shaft  350  may extend a predetermined distance outside of the corresponding integral securing ring extensions  344 ,  348  and, thus, extend outside of the gearbox  310 . The gearbox shaft  350  may be secured within the gearbox  310  by utilizing the integral securing ring extensions  344 ,  348 , and corresponding elongate securing pins,  344   a ,  348   a . The elongate securing pins,  344   a ,  348   a , may be inserted through corresponding radial bore openings  344   b ,  348   b , within corresponding integral securing ring extensions  344 ,  348 , with the elongate securing pins  344   a ,  348   a  similarly inserted through corresponding radial bore openings  350   c ,  350   d , within the gearbox shaft  350 . 
     The drive shaft also comprises a rotor  352  that is integral with and eccentrically disposed around a center portion of the gearbox shaft  350 , with the rotor  352  also disposed within the concentric opening  364  within the integral differential gear ring  360 . The gearbox shaft  350  is supported, in part, within gearbox  310  by using several bearings. A rotor bearing  354 , preferably a ball bearing, is journaled for rotation between the rotor  352  and the integral differential gear ring  360 . A drive shaft bearing  356   a , preferably a roller bearing, is journaled for rotation between the gearbox shaft  350  and the cylindrical opening  334 , integral with input bearing enclosure  338 , of rotatable housing  312 , and another drive shaft bearing  356   b , preferably a roller bearing, is similarly journaled for rotation between the gearbox shaft  350  and cylindrical opening  336 , integral with input bearing enclosure  342 , of second output  314 , with drive shaft bearings  356   a - b , adjacent to opposite sides of the rotor  352 , respectively. An additional drive shaft bearing  358   a , such as a roller bearing, is journaled for rotation between the gearbox shaft  350  and input bearing housing enclosure  338 , and another drive shaft bearing  358   b , preferably a roller bearing, is journaled for rotation between the gearbox shaft  350  and output bearing housing enclosure  342 , with the drive shaft bearings,  358   a - b , adjacent to rotatable securing rings  340  and  346 , respectively. 
     As to each gearbox  310  out of the first pair of gearboxes  310 , the rotating gearbox shaft  350  imparts an eccentric rotation to the rotor  352  around the rotating gearbox shaft  350 , which in turn imparts an eccentric rotation to the first external gear ring  360   a  and to the second external gear ring  360   b , with the first external gear ring  360   a  eccentrically rotating in engagement with the first internal gear  362   a  and with the second external gear ring  360   b  eccentrically rotating in engagement with the second internal gear  362   b , and which in turn imparts a rotation to the second internal gear  362   b  and in turn a rotation to the second output  314  as it rotates around the rotating gearbox shaft  350 , with the rotating second output  314  having an angular velocity that is less than the angular velocity of the rotating drive shaft, with the rotating second output  314  having a torque that is greater than the torque of the rotating gearbox shaft  350 . The single motor  14  causes the gearbox shaft  350  to rotate within the gearbox  310  by rotating within the gear housing enclosure  330 , the input and output bearing housing enclosures  338 ,  342 , and corresponding integral securing ring extensions  344 ,  348 . 
     With respect to the operation of the gearbox  310 , when the single motor  14  is rotatably connected to the input  350   a  of gearbox shaft  350 , the input rotatable housing  312  must be prevented from rotating by, for example, connecting the input rotatable housing  312  to a stationary structure, thereby converting the input rotatable housing  312 , which may rotate, to an input rotatable housing  312 , which is stationary and may not rotate. In this manner, the dual function gearbox  310  may impart a rotational motion to the second output  314 . More specifically, when rotational motion is imparted by the single motor  14  to the input  350   a  of the gearbox shaft  350 , the rotating gearbox shaft  350  imparts an eccentric rotation to the rotor  352  around the rotating gearbox shaft  350 ; which in turn imparts an eccentric rotation to the first external gear ring  360   a  and to the second external gear ring  360   b , with the first external gear ring  360   a  eccentrically rotating in engagement with the first internal gear  362   a , which does not rotate since the first internal gear  362   a  is integral with the input rotatable housing  312  which is prevented from rotating, and with the second external gear ring  360   b  eccentrically rotating in engagement with the second internal gear  362   b , and which in turn imparts a rotation to the second internal gear  362   b  and in turn imparts a rotation to the integral second output  314  that rotates around the rotating gearbox shaft  350 , with the rotating second output  314  having an angular velocity that is less than the angular velocity of the rotating drive shaft, and with the rotating second output  314  having a torque that is greater than the torque of the rotating gearbox shaft  350 . 
     As previously described, a feature of the dual function gearbox  310  is that it can operate symmetrically in that motor  14  can be rotatably connected to either the input end  530   a  of the gearbox shaft  350 , as described above, or connected to the opposite first output  350   b  of gearbox shaft  550 , without in any manner altering the performance characteristics of the dual function gearbox  310  described above. Thus, when the motor  14  is connected to the first output  350   b  of the drive shaft  50 , with the second output  314  prevented from rotating, the input rotatable housing  312  can rotate, just like the second output  314  can rotate when the motor  14  is rotatably connected to the input  350   a  of gearbox shaft  350 . As a result, it should be understood that the reference to the “input”  350   a  and “first output”  350   b  of the gearbox shaft  350  and to all other similar designations, such as: input rotatable housing  312 , second output  314 , input bearing housing enclosure  338 , and output bearing housing enclosure  42 , are merely arbitrary conventions that have been followed to accurately describe the dual function gearbox  310  and the manner of its operation. 
     While the present invention has been illustrated by the description of various embodiments thereof, and while the embodiments have been described in considerable detail, it is not intended to restrict or in any way limit the scope of the appended claims to such detail. Thus, the various features discussed herein may be used alone or in any combination. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the scope of the general inventive concept.