Abstract:
A sprinkler having a water-driven drive mechanism or motor for rotating a sprinkler head is disclosed where the drive mechanism converts a constant input rate into a variable rate to reduce tailing from overly-rapid rotation and to promote full develop of water stream discharge profile. The drive mechanism includes continuously engaged members including one or more planet gears each having an offset or eccentrically positioned engagement portion for driving a second gear member. As the planet gear rotates, the movement of the engagement portion has a radial component relative to the second gear, and the rotational velocity of the second gear is related to the radial position of the engagement portion.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a rotating sprinkler and, in particular, to a rotating sprinkler with a variable rate of rotation. 
       BACKGROUND OF THE INVENTION 
       [0002]    Currently, there are a number of systems known utilizing a variable rate moving sprinkler head directing one or more streams away from the sprinkler outlets or nozzles. For instance, a common type of yard sprinkler is referred to as an oscillating wave lawn sprinkler and includes a generally horizontally oriented and upwardly curved tube with a plurality of holes or nozzles along a top portion of the tube for discharging water. When the sprinkler is activated, the tube is rotated in an oscillating manner while the water is emitted in a wave-like pattern. As the tube is rotated, the emitted water streams from the nozzles moves over a pattern of ground to either side of the sprinkler. The tube element is rotated in a first direction, slows as it reaches a limit, pauses at the limit, and then is counter-rotated in a second direction opposite the first direction. In this manner, this type of sprinkler is referred to as a reversing sprinkler and, hence, a variable rate or velocity sprinkler. 
         [0003]    Such a form of intermittent sprinkler utilizes an irregularly-shaped cam member. The rotating cam member is typically heart-shaped, for instance, so as to have a rounded portion forming two lobes divided by a cleft. An engagement member of the drive mechanism rides against the rotating cam member so that a first angular velocity, generally constant, is produced when the engagement member follows the rounded portion of the heart-shaped cam member, and so that the angular velocity approaches zero when the engagement member approaches the cleft. The sprinkler reverses once it passes beyond the cleft. Accordingly, the sprinkler pauses at the same areas at the limit of the sprinkler travel, and the design suffers from over-watering of these areas without reducing the tailing effect throughout the cycle. 
         [0004]    With the above-described oscillating or reversing sprinkler, a greatest throw distance is only achieved at the limits of the movement. A greater amount of water is deposited at these limits, in part due to the fact that the sprinkler slows, stops, and reverses, therefore spending a disproportionate time watering an area reached by the greatest throw distance and the area adjacent thereto until the sprinkler reaches its normal rate of movement. 
         [0005]    A stationary sprinkler will produce the maximum emission or throw distance for a water stream emitted therefrom. That is, the throw distance is based on a number of variables, including the rate of rotation. If the sprinkler is stationary and the rate of rotation is zero, the throw distance is based on the characteristics of a flow path through the sprinkler, and water pressure, among others. Assuming all these variables are held constant, other than rate of rotation, the stationary sprinkler produces the greatest throw distance. To be more precise, the water stream develops a profile when emitted, and the distance any particular droplet of water is thrown is related to the exit velocity at the nozzle, to force from subsequent droplets following the same path, and to cohesive forces between water droplets. With a stationary sprinkler, each droplet of a water stream is being driven by each successive water droplet, and each preceding water droplet reduces the air resistance experienced by the subsequent droplet. 
         [0006]    When the sprinkler is rotating, each water droplet is emitted at a position somewhat offset from the preceding and succeeding droplets. Accordingly, a first water droplet does not receive as great a push from a subsequent water droplet, nor does it benefit from reduced air resistance. The faster the rotational velocity, the greater the offset between adjacent water droplets, the less each droplet is able to assist the throw distance of the other droplets. Accordingly, this interaction causes a “tailing” effect, and the faster the rotational velocity is, the greater the tailing effect. The result is that the water stream profile is not able to sufficiently develop for a desirable throw distance, and a tailing water stream is discharged an undesirable distance from the moving sprinkler head. 
         [0007]    Rotating sprinklers have been employed to make the distribution from a moving sprinkler more even. A rotating sprinkler utilizes one or more nozzles discharging water in a generally radially direction, preferably above horizontal, to throw water a distance from the sprinkler to cover an area therearound. With the above-discussed oscillating sprinkler, the water streams repeatedly discharge water to the greatest distance at the limit of the oscillation, and the area between the greatest distance is watered during the counter-rotation by the sprinkler. With a rotating sprinkler, the water stream is generally emitted a particular throw distance and would not ordinarily provide significant water to the area short of this throw distance. 
         [0008]    Various designs have been created for providing water at a varying water distances. For instance, the sprinkler may have a plurality of nozzles emitting water at various trajectories or pressures. Alternatively, the nozzle geometry may be structured to distribute water in a pattern other than a stream. 
         [0009]    Other sprinkler designs have utilized an intermittent motion to produce a varying rotational rate. A typical rotating sprinkler utilizes a drive mechanism that generally converts force from the water flow through the sprinkler into high velocity rotation in a turbine, for instance. The turbine is then mounted on an axle for driving a gear reduction mechanism for reducing the velocity into high torque. The drive mechanism then cooperates to rotate a portion of the sprinkler. 
         [0010]    An example of a rotating sprinkler having an intermittent motion is U.S. Pat. No. 5,758,827, to Van Le et al., which utilizes cooperating gears of the gear reduction mechanism with an irregular gear tooth pattern. For instance, one embodiment has a first gear with a single tooth such that the tooth engages with a second gear for a short period, and then disengages for a longer period of time. During the time the single tooth is disengaged, the second gear is generally stationary, and the water stream profile is allowed to more fully develop. The single tooth first gear then re-engages to effect a short motion of the second gear, whereupon the first gear disengages. 
         [0011]    It should be noted that such an intermittent sprinkler generally has two speeds, namely moving and stationary. That is, the sprinkler rotates at a particular speed when engaged, save for inertial effects, and then does not rotate when disengaged. In addition, there is an impulse force transmitted through the sprinkler and its mechanisms, as well as to the water flow, that causes stresses and pressure fluctuations as the turbine and gear mechanism is disengaged and re-engaged. Furthermore, the sprinkler tends to spend a period of time delivering water to a particular area, then is quickly rotated to deliver water to a subsequent area. Consequently, the sprinkler tends to localize the distribution of water in areas. This is exacerbated by the fact that such a sprinkler often waters the exact same locations on each full rotation. 
         [0012]    Accordingly, there has been a need for an improved rotating sprinkler having a varying rate or velocity that provides improved water distribution. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a perspective view of a sprinkler having a movable housing including a head portion rotated by a drive mechanism driven by water through a turbine; 
           [0014]      FIG. 2  is a cross-sectional view of the movable housing of  FIG. 1  showing the turbine and drive mechanism for rotating the head portion; 
           [0015]      FIG. 3  is a perspective view of a filter screen, a stator module, the turbine, the drive mechanism and a drive housing therearound and partially cut away, a head drive shaft, and the head portion of the sprinkler of  FIG. 1 ; 
           [0016]      FIG. 4  is an exploded view of the drive mechanism of the sprinkler of  FIG. 1 ; 
           [0017]      FIG. 5  is a cross-sectional view of the drive mechanism including carrier plates and planetary gears cooperating with the carrier plates of the sprinkler of  FIG. 1  and having a carrier plate and hub thereof removed; 
           [0018]      FIG. 6  is a side elevational view of the drive mechanism of the sprinkler of  FIG. 1 ; 
           [0019]      FIG. 7  is a perspective view of a slotted carrier plate and planetary gears of the drive mechanism of  FIG. 1 , the gears having eccentrically positioned posts for cooperating with the slots of the carrier plate; 
           [0020]      FIG. 8  is a perspective view of one of the planetary gears of  FIG. 7  including an eccentrically positioned post; 
           [0021]      FIG. 9  is a top plan view of the slotted carrier plate of  FIG. 7 ; 
           [0022]      FIG. 10  is a top plan view of the planetary gear of  FIG. 8 ; 
           [0023]      FIGS. 11   a - 11   h  is a series of top plan views showing relative positions of the slotted carrier plate and planetary gears of  FIG. 7  and a ring gear surface on the interior of drive housing; 
           [0024]      FIG. 12  is a plot of angular velocity versus time for the drive mechanism including the slotted carrier plate of the sprinkler of  FIG. 1 , and for a drive mechanism of the prior art; and 
           [0025]      FIG. 13  is a plot of angular position versus time for the drive mechanism including the slotted carrier plate of the sprinkler of  FIG. 1 , and for a drive mechanism of the prior art. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0026]    Referring initially to  FIGS. 1 ,  2 , and  4 , a representative sprinkler  10  is depicted incorporating a variable-rate speed reduction drive mechanism  16  for providing power to rotate a sprinkler head  14  around a central axis X. The drive mechanism  16  is located within a movable housing  12  that shifts from a retracted position when the water source is shut off to an extended position when the water is turned on, as illustrated in  FIG. 1 . 
         [0027]    The movable housing  12  is telescopically received within a generally fixed housing  20 , and a spring (not shown) is provided for biasing the movable housing  12  downward to the retracted position in the housing  20 . When the supply is activated, water flows into the fixed housing  20  from a source pipe  24  connected to the fixed housing  20 , such as by a threaded connection (not shown). The force of the water overcomes the bias of the spring to telescopically extend the movable housing  12  from the fixed housing  20 . As it flows through the sprinkler  10 , the water drives a turbine  30  in a rotary fashion, as will be described in greater detail below. 
         [0028]    The turbine  30  is secured to a turbine shaft  32  at a lower end such that the turbine  30  and the turbine shaft  32  rotate together. The turbine shaft  32  extends through and is connected to the drive mechanism  16 . In this manner, the turbine shaft  32  communicates the rotational power generated by the water-driven turbine  30  to the drive mechanism  16 . The drive mechanism  16  converts the high-velocity and low-torque rotation of the turbine shaft  32  and the turbine  30  into a velocity appropriate for rotating the sprinkler head  14  relative to both the movable and fixed housings  12 ,  20 . During operation, the sprinkler head  14  rotates as water is emitted from a nozzle  36  in a generally radial direction. 
         [0029]    With reference to  FIGS. 2 and 3 , the sprinkler  10  may include a number of components beneficial to its operation and described in commonly assigned U.S. Pat. No. 6,732,950 B2, to Ingham, Jr. et al., which is incorporated by reference in its entirety herein. As water enters the movable housing  12 , particulate matter is removed from the water stream by a filter unit  40  secured in a lower end of the movable housing  12 . The water then flows upwardly and into contact with a trip plate  42  and a bypass valve  44 . 
         [0030]    The trip plate  42  cooperates with the turbine  30  to provide rotational power to the sprinkler head  14 . The turbine  30  includes generally vertical vanes  52  radially oriented around a ring  54  connected to a hub  55  by spokes  57 . Facing the vanes  52  is a plurality of trip plate openings  56  having angled deflectors  58  positioned adjacent thereto. The trip plate deflectors  58  include at least one directed to rotate the turbine  30  in one direction and at least another directed to rotate the turbine  30  in the other direction. A reverse mechanism  90 , as described further below, shifts the trip plate  56  between the two different water providing directions to change the direction of rotation of the sprinkler head  14 . 
         [0031]    Water flows upwardly from the filter  40 , into the trip plate  42 , and through the openings  56 . The water forms jet streams through the openings  56 , and the deflectors  58  direct the water at an angle upwardly against the vanes  52 , thereby imparting a portion of the kinetic energy of the water to the turbine  30 . This energy rotationally drives the turbine  30  at a velocity of approximately 1000-2000 revolutions per minute. In the event the pressure from the water flow below the trip plate is above a predetermined level, the bypass valve  44  opens to permit a portion of the water to flow around the trip plate  42  without striking the vanes  52 . Instead, the water through the bypass valve  44  flows around the turbine  30  and outside of the vanes  52 . 
         [0032]    The bypass valve assembly  44  includes a bypass valve opening  50  defined by a bypass valve seat plate  51  and a spring  48  for biasing a valve plunger  46  toward the bypass valve opening  50 . When the pressure differential between above and below the bypass valve opening  50  is sufficient to overcome the bias of the spring  48 , the valve plunger  46  shifts away from the bypass valve opening  50  to permit water to pass through the bypass valve opening  50  and around the trip plate  42  and the turbine  30 . 
         [0033]    As noted above, the turbine  30  receives energy from the water flow for driving the drive mechanism  16 . The hub  55  of the turbine  30  is generally secured to the turbine shaft  32  at a lower segment  66  such that the turbine  30  and turbine shaft  32  rotate together. A second segment  68  of the turbine shaft  32  is engaged with the drive mechanism  16  to communicate the rotational energy of the turbine shaft  32  and the turbine  30  to the drive mechanism  16 . 
         [0034]    Once it has flowed beyond the turbine  30 , the water continues upwardly through the movable housing  12 , around the drive mechanism  16 , and into the sprinkler head  14  for emission therefrom. As can be seen, the drive mechanism  16  is axially aligned with the turbine  30 , as well as the movable housing  12  in general. The drive mechanism  16  includes a generally cylindrical drive housing  70 . It is preferred that a small amount of water be permitted to enter the drive housing  70  for lubricating the drive mechanism  16 . It also is preferred that the water entering the drive housing  70  be filtered to prevent small debris from entering the drive housing  70  and damaging the drive mechanism  16 . The filtering can be accomplished by using small holes through the drive housing wall to allow water to enter the drive housing. 
         [0035]    Other than the small amount flowing into the drive housing  16 , the water flows from the turbine  30 , around a lower side  72  and circumferential side  74  of the drive housing  70 , and through a cavity  76  formed between the drive housing  70  and an interior surface  78  of the movable housing  12 . The water then flows around a top side  80  of the drive housing  70 , and upwardly through a flow passage  82  communicating with a lower chamber  84  of the sprinkler head  14 . The water delivered into the lower chamber  84  is subsequently emitted from the sprinkler head  14 , by way of the nozzle  36 . 
         [0036]    As noted, the sprinkler head  14  rotates relative to the movable and fixed housings  12 ,  20  to deliver water in a radial manner therefrom. In the depicted form of the sprinkler  10 , the sprinkler head  14  includes a reverse mechanism  90 . Towards this end, the sprinkler head  14  includes an upper chamber  92  in which the reverse mechanism  90  is located. The reverse mechanism  90  is connected to the lower trip plate  42  through an elongated trip shaft  41 . The shaft  41  rotates the trip plate  42  to change the deflectors to provide a different flow direction at the turbine  30  to change the direction of one sprinkler head  14 . The sprinkler head  14  includes a housing  100  having an upper cylindrical body portion  102  and a lower cylindrical skirt portion  104 . The upper portion  102  has a bottom annular edge  106  facing an upper annular edge  108  formed on the movable housing  12 . A seal member  110 , such as an O-ring, is positioned between the body bottom edge  106  and the movable housing upper edge  108  to minimize passage of foreign matter into the sprinkler  10 . Leakage is restricted by a seal  112 , such as an O-ring or a T-ring, positioned between a bottom annular edge  114  of the skirt portion  104  and an inner surface  116  formed on an annular ledge  118  of the movable housing  12 , as can be seen in  FIG. 2 . 
         [0037]    The rotation of the sprinkler head  14  is driven by the variable-rate speed reducing drive mechanism  16 . With reference to  FIG. 4 , the turbine shaft  32  is aligned with the central axis X, and the axle second segment  68  engages a main drive gear  120  and is fixedly mounted thereto such that the turbine shaft  32  and the main drive gear  120  rotate together around the axis X. The drive gear  120  includes external gear teeth  122  for communicating with a series of gear modules  130 . As explained in more detail below, each gear module  140 ,  160 ,  170 ,  180 , and  190  of the series of modules  130  includes at least one and preferably three identical planet gears cooperating via an axle with a carrier plate which rotates around the axis X. The planet gears are arranged equidistant from each other about the axis X. 
         [0038]    The first gear module  140  includes three identical planet gears  142  cooperating via an axle  143  with a carrier plate  150 . The axle  143  secures the planet gear  142  to the carrier plate and permits rotation of the planet gear  142  relative to the carrier plate  150 . More specifically, the drive gear  120  is received between and in geared relationship with the planet gears  142  of the first gear module  140 . The planet gears  142  are further in geared relationship with an internal splined or gear-toothed surface  144  of the drive housing  70 , such that the drive housing  70  forms a ring gear. As the drive gear  120  rotates, its teeth  122  cooperate with the planet gears  142 , thereby driving the planet gears  142  around the drive housing inner surface  144 . The first carrier plate  150  rotates at a rate equal to the rate at which the planet gears  142  travel around the inner ring gear surface  144  and around the X axis. 
         [0039]    The drive gear  120  has fewer teeth  122  than are located on each of the generally identical planet gears  142 . Accordingly, a single rotation of the drive gear  120  effects less than a full rotation of each planet gear  142 , resulting in a gear reduction. A further gear reduction is provided between the planet gears  142  and the ring gear surface  144 . The ring gear surface  144  has many more teeth than each of the planet gears  142  such that a single rotation of the planet gear  142  around its axle  143  effects less than a full rotation around the ring gear surface  144 . Therefore, multiple rotations of the planet gear  142  are required to complete a rotation around the inner surface  144 . Accordingly, the relative gearing between the planet gear  142  and the ring gear surface  144  effect a further gear reduction. 
         [0040]    The first carrier plate  150  transmits the reduced speed rotation to a top drive gear  154  fixedly secured to, and preferably integral with, the plate portion  150 . The top drive gear  154  is axially aligned along the central longitudinal axis X so that its rotation is coaxial with the carrier plate  150  and with the turbine shaft  32 . 
         [0041]    As mentioned above, the drive mechanism  16  includes a series of gear modules  130 , including modules  140 ,  160 ,  170 ,  180  and  190 , generally providing a similar gear reduction. The top drive gear  154  of the first gear module  140  is generally identical in size and teeth to the main drive gear  120 , discussed above. As such, the top drive gear  154  cooperates with a second gear module  160  generally identical to the first gear module  140  and having planet gears  162  rotating around axles  164  secured to a carrier plate  166  having a top drive gear  168  rotating co-axially with the turbine shaft  32 . 
         [0042]    The top drive gear  168  of the second carrier plate  166  then cooperates with planet gears  172  attached to a third carrier plate  174  of a third gear module  170 . The third carrier plate  174  rotates a top drive gear  178 , which cooperates, in turn, with planet gears  182  of a fourth gear module  180 . The planet gears  182  of the fourth gear module  180  are attached to a fourth carrier plate  184  having a top drive gear  188 . The drive gear  188  cooperates with planet gears  192  of a fifth gear module  190  having a fifth carrier plate  198  with an output hub  221  mounted thereon. 
         [0043]    The planet gears  142 ,  162 ,  172 ,  182 , and  192  of each gear module  140 ,  160 ,  170 ,  180 ,  190  further cooperate with the ring gear surface  144 . As each gear module  140 ,  160 ,  170 ,  180 , and  190  provides the described gear reduction, the input speed from the turbine shaft  32  is reduced, for example, from the above-mentioned 1000-2000 revolutions per minute to an output speed at the output hub  220  of approximately ⅓ of a revolution per minute. It should be noted that the gear reduction, and speed reduction, is dependent on the teeth and size of the gears, and may easily be selectively provided as desired. 
         [0044]    As stated, the drive mechanism  16  provides a variable rate of rotation, the rotation being communicated via the output hub  220 . More specifically, one of the gear modules in the module series  130  provides a variable rate of rotation. In the preferred embodiment, the carrier plates  150 ,  166 , and  184  for the first, second, and fourth gear modules  140 ,  160 ,  180 , respectively, are generally identical, as are their respective top drive gears  154 ,  168 ,  188 , while the fifth gear module  190  includes the output hub  220 . In addition, the planet gears  142 ,  162 ,  182 , and  192  for the first, second, fourth and fifth gear modules  140 ,  160 ,  180 ,  190  are generally identical. 
         [0045]    The third gear module  170  has modified planet gears  172  and a modified carrier plate  174  to provide the desired intermittent or variable rotation watering capability. More specifically, the third gear module  170  receives a generally constant input rate of rotation and produces a variable rate of rotation as an output. As best illustrated in  FIG. 7 , the third carrier plate  174  defines at least one and preferably three radially extending slots  200 . The third set of planet gears  172  are sized and geared generally identically to the other planet gears  142 ,  162 ,  182 , and  192 . However, the planet gears  172  are provided with a fixed post  176 , thereby omitting axles  143 ,  164 ,  183 ,  193  utilized with the other planet gears  142 ,  162 ,  182 , and  192 . The post  176  is eccentrically positioned relative to the axis Y on a top surface  202  of each of the planet gears  172  and is aligned parallel to the central axis Y of rotation of each of the planet gears  172 . Each planet gear  172  cooperates with the top drive gear  168  of the second gear module  160  and with the inner ring surface  144 , as described above. 
         [0046]    The eccentric posts  176  of the planet gears  172  drive the carrier plate  174  with a varying rate of rotation. Each post  176  is received in a respective plate slot  200  and is generally free to move therealong. In comparison, the axle  143  for the planet gears  132  of the module  130 , around which each planet gear  132  rotates, is centrally positioned on the axis of rotation of the planet gear  132 . Accordingly, the axle  143  remains at a constant distance from the ring gear surface  144 . As the planet gear  132  rotates, the axle  143  follows a generally constant circular path within the ring gear surface  144 . This path is generally a constant distance from the axis X to the position of the axle  143  on the carrier plate  134 . The planet gear  132  rotates around the axle  143  at a generally constant velocity, the axle  143  itself will follow its path with a generally constant velocity. The carrier plate  134  rotates based on being directed around by the axles  143  secured thereto, thus being a constant rate of rotation for the planet gears  132 . This is the same for each of the modules  140 ,  160 ,  180 , and  190 , but not for the modified module  170 . 
         [0047]    The slotted carrier plate  174  takes its variable rate of rotation from the rate of angular change in position for the posts  176 . As noted, the fixed axles  143 ,  164 ,  183 , and  193  have a fixed position relative to their respective carrier plate  150 ,  166 ,  184 ,  198 , and along the center of rotation of their respective planet gears  142 ,  162 ,  182 , and  192 , so that their axles  143 ,  164 ,  183 , and  193  follow a circular path with a generally constant distance from the axis X. In contrast, the posts  176  are not fixed relative to the slotted carrier plate  174 , instead being permitted to move along the slots  200 , and do not follow a circular path. In addition, the rate of rotation for the slotted carrier plate  174  is related to not only the gear ratio between the ring gear  144  and the planet gear  172 , but is also related to the position of the post  176  in the slot relative to the axis X. 
         [0048]    With reference to  FIGS. 11-13 , the post  176  moves towards and away from the axis X to drive the carrier plate  174  with a rotation equal to the change in radial angular position (angular velocity) relative to the axis X traveled by the post  176 . As the planet gear  172  has a constant rotational rate, the post  176  has a constant rate of change of angular position (angular velocity) about its axis Y. When the post  176  is positioned midway along the slot  200 , the translation of the post  176  is generally in the radial direction relative to the axis X such that the angular change relative thereto is relatively constant. However, as the post  176  approaches the central axis X, translation achieved by post  176  effects a greater angular change relative to the axis X such that the carrier plate  174  is accelerated. Conversely, as the post  176  moves away from a position close to the central axis X, the carrier plate is decelerated. Furthermore, the carrier plate  174  continues to decelerate as the post  176  approaches a position close to the ring gear surface  144 . Once the post  176  has begun to return towards the central axis X along the slot  200 , the carrier plate  174  is once again accelerated. 
         [0049]    In  FIGS. 12 and 13 , the post  176  being positioned at its minimal radial distance from the axis X is represented by Σ, and the post  176  being positioned at its maximum radial distance is represented by Φ. 
         [0050]    The positions and velocity for the carrier plate  174  can be seen by comparing  FIG. 11  with  FIGS. 12 and 13 .  FIG. 11   a  shows the post  176  positioned approximately midway along the slot  200 . At this position, the angular acceleration of the post  176  is relatively constant such that its angular velocity increases somewhat linearly, represented generally by A in the plots of  FIGS. 12 and 13 . As the post  176  travels from the position of  FIG. 11   a  to a position of  FIG. 11   b,  the post  176  moves closer to the central axis X, the plate  174  rotates around the axis X faster than the planet gear  172  rotates about its center of rotation axis Y of the planet gear  172 , as the slot  200  moves closer to the center of rotation axis Y. In doing so, the post  176  moving inward increases the angular velocity of the carrier plate  174  because the angular velocity of the post  176  about the central axis X also increases, as represented by B in the plots of  FIGS. 12 and 13 . As the post  176  and the axis Y of the center of rotation of the planet gear  172  ( FIG. 11   c ) become aligned with the slot  200 , the angular velocity of the post  176  approaches its maximum, as represented by C (as well as L) in  FIGS. 12 and 13 . Further rotation of the planet gear  172  moves the slot  200  away from the center of rotation axis Y ( FIG. 11   d ), and the angular velocity decreases, as represented by D in  FIGS. 12 and 13 . The carrier plate  174  also slows with an angular deceleration equal in magnitude to the acceleration through the portion of B in  FIGS. 12 and 13 . 
         [0051]    As the post  176  moves to the position represented by  FIG. 11   e  and represented as E in  FIGS. 12 and 13 , the angular velocity of the plate  174  decreases. In positions represented by F, G, and H of  FIGS. 12 and 13  and shown in  FIGS. 11   f - 11   h,  the angular translation of the post  176  about the Y-axis effects a relatively small angular velocity for the carrier plate  174 , approaching though not entirely reaching zero, as represented by Φ in  FIGS. 12 and 13 . 
         [0052]    Accordingly, the rate of rotation of the carrier plate  174 , and its top drive gear  178 , is varied in relation to the rate of rotation of the planet gears  172 . Therefore, when the planet gears  172  receive a constant rotational velocity, the carrier plate  176  is provided with a variable rotation rate. For the drive mechanism  16 , a constant rate of rotation is provided by the main drive gear  120 , reduced by the first gear module  140 . This is communicated to the second gear module  160 , which, in turn, reduces the rate of rotation and communicates the reduced rate to the third gear module  170 . The third gear module  170  reduces the average rate of rotation, varies the rate through the slotted carrier plate  174  and the planet gears  172 , and outputs this to the top drive gear  178 , which, in turn, is transmitted to the fourth and fifth gear modules  180 ,  190  for further reduction. Ultimately, the output hub  220  communicates the reduced and variable rotation to the sprinkler head  14 . 
         [0053]    Thus, the sprinkler  10  provided with a generally constant water flow rate includes the sprinkler head  14  rotating with the variable rate. The output hub  220  communicates the varying reduced speed rotation from the drive mechanism  16  to the sprinkler head  14 . The output hub  220  includes a cylindrical shell  221  rising along the axis X from the carrier plate  198  of the fifth gear module  190 . The output hub  220  further includes a centrally formed non-circular socket  222  open upwardly so as to receive a drive shaft  224  ( FIGS. 2 and 3 ) secured to the sprinkler head  14 . The drive shaft  224  has a non-circular lower portion  226  to matingly cooperate with the socket  222  such that the drive shaft  224  rotates with the output hub  220 . 
         [0054]    The housing  70  is generally sealed from the flow of water. With reference to  FIGS. 2-4 , the top side  80  of the housing  70  includes an axially extending splined ring  230 . A cap  240  is positioned around the drive shaft  224  and has splines for mating the splines of the ring  230 . A seal may be located between the drive shaft  224  and the cap  240 , or between the drive shaft  224  and the output hub  220 . 
         [0055]    While the invention has been described with respect to specific examples, including presently preferred modes of carrying out the invention, those skilled in the art will appreciate that there are numerous variations and permutations of the above described apparatuses and methods that fall within the spirit and scope of the invention as set forth in the appended claims.