Abstract:
A slip-clutch assembly including a slip gear and clutch for a sprinkler motor of a sprinkler is disclosed for reducing damage to movable portions of the sprinkler is disclosed. The slip-clutch assembly allows at least a portion of a motor assembly or a sprinkler head to rotate at a rate lower than under normal operating conditions. The slip-clutch assembly includes a first component or portion with deformable portions received under normal operating conditions within recesses or cooperating structure of a second component or portion. The deformable portions are able to release or slip from the cooperating structure when the rotation of a portion of the sprinkler is impeded by a force exceeding a predetermined level. The deformable portions of the slip-clutch assembly may include deflectable arms with an engageable portion received within the cooperating structure. The engageable portion may dis-engage by camming out of the cooperating structure when the impeding force exceeds the predetermined level.

Description:
FIELD OF THE INVENTION  
       [0001]     The invention relates to a rotating sprinkler and, in particular, to a gear mechanism for rotating a portion of a sprinkler including cooperating portions that allow the mechanism to slip when rotation is resisted.  
       BACKGROUND OF THE INVENTION  
       [0002]     Currently, many types of sprinklers are known and utilized for distributing water to a desired area such as for watering plants, crops, and lawns. Some sprinklers are generally stationary and deliver water to a predetermined area dependent on the direction to which one or more outlets, such as nozzles, are pointed. Many sprinklers rely on a portion that moves relative to a stationary or fixed base portion so that the water is distributed to a particular area intermittently as water is distributed to a different area.  
         [0003]     For instance, some sprinklers rotate back and forth so, at a particular moment, a first area receives a certain amount of water while another receives less and, at a subsequent moment the first area receives less than the other area. Other sprinklers include a portion that includes one or more nozzles that rotate or sweep over a particular area so that, again, different areas receive water intermittently.  
         [0004]     One type of sprinkler is known as a motor driven sprinkler. Though there are many types of these, one example utilizes a turbine placed in the water stream. When the water stream strikes the turbine, the water forces the turbine to rotate in a predetermined direction based on vanes or vaned portions located on the turbine. The rotation of the turbine then drives a portion of the sprinkler including a nozzle in a rotary fashion. Thus, the rotation of the turbine effects the rotation of the nozzle for distributing water in a radial fashion, and portions of the surrounding area receives water for the period of time in which a spray or stream of the nozzle is directed at the surrounding area portions.  
         [0005]     Many motor driven sprinklers are pop-up sprinklers. A pop-up sprinkler is a sprinkler having a case or housing that is generally stationary relative to the ground, and a riser that is in a retracted position when the sprinkler is shut off and is extended when the sprinkler is activated by turning the water on. The riser reciprocates between the retracted and extended position within an internal cavity of the housing so that a nozzle located on the riser is free to distribute water when the riser is extended, while typically being located within the housing when the riser is retracted.  
         [0006]     In a motor driven pop-up sprinkler, the riser includes a sprinkler head portion that rotates relative to the riser when in the extended position and activated. The riser contains a motor assembly which is connected to the sprinkler head such that the sprinkler head is driven around by the motor assembly. In many cases, this motor assembly utilizes the described turbine.  
         [0007]     In use, the sprinkler head rotates upon the activation of water. Therefore, the sprinkler head rotates as the riser is extending from the housing, when the sprinkler head is extended, and as the sprinkler head is retracting as the water flow is diminishing before the water flow ceases. During this time, particulate matter may come in contact with and between the sprinkler head and the riser body. Such particulate matter may cause binding between the sprinkler head and the riser body.  
         [0008]     In addition, people often grab onto the extended and rotating sprinkler head. This may be done by a person who is trying to adjust a setting on the sprinkler head or is trying to examine the sprinkler head. At times, the sprinkler head is held by a person with negative intentions, such as a vandal.  
         [0009]     In the event the sprinkler head is held stationary or bound so that it is prevented from rotating, damage can occur to the sprinkler head. The components utilized between the motor and the sprinkler head operate in a wet environment, and using steel, for example, is often not beneficial to the life of the sprinkler head. On the other hand, the plastic or polymer components often used are typically not strong enough to halt the rotation of the motor assembly, such as the turbine in the water stream. The force of the water is great enough that the turbine continues to spin, and the internal components between the turbine and the sprinkler head can strip each other.  
         [0010]     Accordingly, there has been a need for an improved motor assembly for preventing damage to a sprinkler head when rotation is impeded. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  is a side elevational cross-sectional view of a pop-up sprinkler with a rotating sprinkler head including a motor assembly including a slip gear in accordance with an aspect of the present invention;  
         [0012]      FIG. 2  is a perspective view of the pop-up sprinkler with a riser and sprinkler head in an extended position for distributing water therefrom;  
         [0013]      FIG. 3  is a perspective view of a motor assembly for rotating the sprinkler head relative to the riser showing a turbine, a motor housing, and a direction assembly;  
         [0014]      FIG. 4  is a perspective view of the turbine and the motor housing showing an opening for cooperating with the direction assembly;  
         [0015]      FIG. 5  is a side elevational view of the turbine and the direction assembly and a gear assembly of the motor assembly;  
         [0016]      FIG. 6  is a perspective view of the gear assembly and the turbine;  
         [0017]      FIG. 7  is a perspective view of a slip-clutch assembly of the gear assembly showing a ratchet gear extending through and received in a sleeve gear;  
         [0018]      FIG. 8  is a perspective view of the ratchet gear showing a plurality of ratchet legs extending about a periphery of a lower portion of the ratchet gear;  
         [0019]      FIG. 9  is a bottom plan view of the ratchet gear;  
         [0020]      FIG. 10  is a side elevational view of the ratchet gear;  
         [0021]      FIG. 11  is a perspective view of the sleeve gear showing an opening through which the ratchet gear is received;  
         [0022]      FIG. 12  is a bottom plan view of the sleeve gear showing ratchet teeth for cooperating with the ratchet legs of the ratchet gear;  
         [0023]      FIG. 13  is a bottom plan view of the ratchet legs of the ratchet gear cooperating with the ratchet teeth of the sleeve gear, and showing radial arms on the ratchet gear cooperating with an annular stepped collar on the sleeve gear for maintaining the ratchet gear and sleeve gear in a coaxial relationship;  
         [0024]      FIG. 14  is a cross-sectional view of the slip-clutch assembly showing the radial arms positioned against the stepped collar and showing a snap-fit connection between the ratchet gear and sleeve gear;  
         [0025]      FIG. 15  is a perspective view of the bottom of the direction assembly showing a drive gear received within the opening of the motor housing of  FIG. 4 ;  
         [0026]      FIG. 16  is a cross-sectional view of an alternative embodiment slip-clutch assembly being formed on the drive gear;  
         [0027]      FIG. 17  is a perspective view of the drive gear;  
         [0028]      FIG. 18  is a fragmentary cross-sectional view of the drive gear showing a slip gear positioned within a clutch gear;  
         [0029]      FIG. 19  is a perspective view of the slip gear showing slip fingers and a central opening for non-rotationally receiving an axle;  
         [0030]      FIG. 20  is a side elevational view of the slip gear; and  
         [0031]      FIG. 21  is a perspective view of the clutch gear showing structure for cooperating with the slip fingers of the slip gear. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0032]     Referring initially to  FIGS. 1 and 2 , a pop-up sprinkler  10  is depicted having a housing  12 , a riser  14 , a rotating sprinkler head  16 , and a motor assembly  18 . As will be discussed herein, the motor assembly  18  includes a turbine  70  located in the water flow stream. During use, the turbine  70  rotates at a rate in the order of 1890 revolutions per minute (RPMs), while the sprinkler head  16  preferably rotates approximately 1 revolution per minute.  
         [0033]     Where the rotation of the sprinkler head  16  is impeded by, for instance, a person holding the sprinkler head  16  stationary when the sprinkler  10  is activated, some portion of the motor assembly  18  must account for this stress. As the power delivered by the water stream on the turbine  70  is often too great for the turbine  70  to be stopped, the stress may be borne by components deforming, gears of the motor assembly  18  shearing teeth, or gears fixedly attached to axles slipping around the axles.  
         [0034]     To provide a non-destructive, high-life cycle mechanism for responding to impedance of the rotation of the sprinkler head  16 , the motor assembly  18  is provided with a slip-clutch assembly, as will be described below. In simple terms, the slip-clutch assembly replaces one of the components of the motor assembly with a pair of components which, when a threshold level of stress is experienced, slip relative to each other until the stress is relieved. Once the impedance ceases, the pair of components re-engage, and the sprinkler  10  continues to operate normally.  
         [0035]     The housing  12  has a lower end  22  with an inlet  24  that is threaded to connect to a pipe (not shown) for delivering water to the sprinkler  10  from a water source (not shown). The sprinkler  10  may be one of a number of sprinklers  10  connected to an irrigation network for distributing water over a particular area and including controls for activating and shutting off the water supply.  
         [0036]     In use, the sprinkler  10  is generally embedded into ground or soil for distributing water to an area surrounding the sprinkler  10 , and an upper end  26  of the housing  12  is generally at ground or grade level. The sprinkler  10  has a retracted position, shown in  FIG. 1 , and an extended position represented in  FIG. 2 . When the water is shut off, the riser  14  and the sprinkler head  16  are in the retracted position and generally located within the housing  12  so that a top surface  28  of the sprinkler head  16  is generally just above the ground level.  
         [0037]     The housing  12  is generally cylindrical and defines a cavity  40  therein, and the riser  14  has a generally cylindrical outer surface  42 . The riser  14  has a lower end  44  with an annular shoulder  46  extending thereabout. In a preferred embodiment, the shoulder  46  includes notches (not shown) for receiving ribs (not shown) located on an inner surface  48  of the housing  12 . The notches cooperate with the ribs so that the riser  14  shifts generally linearly within the housing  12  between the retracted and extended positions.  
         [0038]     The sprinkler  10  includes a bias member in the form of a coil spring  60  having an top coil  62  that contacts an inner shoulder  52  of the housing  12 , as can be seen in  FIG. 1 . The spring  60  further includes a bottom coil  64  that contacts the riser ratchet shoulder  46 . When the water is shut off, the spring  60  biases the riser  14  and sprinkler head  16  towards the retracted position.  
         [0039]     Activation of the water into the housing  12  causes the riser  14  to extend from the housing  12 . The extended riser  14  allows the sprinkler head  16  and a nozzle  20  located thereon to be exposed, and water is directed in the direction of the nozzle  20 . The upward shifting of the riser  14  in response to water pressure compresses the spring  60  between the riser shoulder  46  and the housing inner shoulder  52 . When the water is shut off, the spring  60  directs the riser  14  to return to its original, retracted position.  
         [0040]     During activation with the riser  14  extended, water flows through the riser  14  and causes the sprinkler head  16  to rotate. Broadly stated, the water flowing through the riser  14  drives the motor assembly  18  to rotate the sprinkler head  16 . Specifically, the water strikes a turbine  70  located in a water passage  72  and connected to an axle  74 . The turbine  70  rapidly rotates, such as in the order of 1890 RPMs. The axle  74  is connected to a first of a series of reduction gears of a gear assembly  80  of the motor assembly  18 . The gear assembly  80  reduces the rotation so that the sprinkler head  16  rotates at approximately 1 RPM. This conversion or reduction results in a great deal of torque for driving the sprinkler head  16 .  
         [0041]     The sprinkler head  16  has a central axle  86  around which it rotates relative to the riser  14 . The central axle  86  is generally cylindrical and communicates with the riser water passage  72  to receive water therethrough. The water is then delivered to the nozzle  20  for emission from the sprinkler head  16 . As can be seen in  FIG. 3 , the central axle  86  is received in a port  87  in a direction assembly  94  of the motor assembly  18 .  
         [0042]     The sprinkler head  16  includes gearing  17  for engaging the motor assembly  18 , as will be discussed below. In this manner, the motor assembly  18  converts the energy and force of the water striking the turbine  70  into rotational force and torque for rotating the sprinkler head  16 .  
         [0043]     Referring now to FIGS.  3  to  6 , the motor assembly  18  of the sprinkler head  16  is depicted. The motor assembly  18  includes the turbine  70 , a motor housing  90 , the reduction gear assembly  80  located within the motor housing  90 , and a direction assembly  94 . The turbine  70  is connected to a lower portion  76  of the axle  74  such that the turbine  70  and axle  74  rotate together. An upper portion  78  of the axle  74  includes a pinion gear  79  that also rotates with the turbine  70  and axle  74 .  
         [0044]     The gear assembly  80  utilizes a plurality of paired gears  100  to communicate the rotation of the turbine  70  to the direction assembly  94 . Each paired gear  100  has a larger lower portion  102  and an smaller upper portion  104  that rotate together freely around an axle  106 . Both portions  102  and  104  of each paired gear  100  include gear teeth  105 . However, the lower portion  102  has significantly more teeth  105  than the upper portion  104 . Each paired gear  100  is mated and cooperates with another paired gear  100  so that the smaller upper portion  104  of a paired gear  100  cooperates with the larger lower portion  102  of a subsequent paired gear  100 . In this manner, a single rotation of a larger lower portion  102  is effected by a plurality of rotations of a smaller upper portion  104 .  
         [0045]     The pinion gear  79  mates with a first paired gear  100   a  of the gear assembly  80 . The pinion gear  79  is relatively small in comparison to the larger lower portion  102   a  of the first paired gear  100   a  and, accordingly, a plurality of rotations of the turbine  70  and pinion gear  79  is required to rotate the first paired gear  100   a  a single revolution. In this manner, the high revolutions per minute of the turbine  70 , noted above, are reduced with a consequent increase in torque.  
         [0046]     The gear assembly  80 , as depicted, includes four paired gears  100   a ,  100   b ,  100   c , and  100   d . The paired gear  100   d  cooperates with a direction assembly pinion gear  110 , as can be seen in  FIG. 5 , to transmit the drive from the turbine  70  to the direction assembly  94 .  
         [0047]     The direction assembly pinion gear  110  is non-rotationally secured to an axle  112  at an axle lower portion  114 . An upper portion  117  of the axle  116  includes a distribution gear  118 . The pinion gear  110  is received within an opening  120  in the motor housing  90  (see  FIG. 4 ) so that teeth  105  on the pinion gear  110  are mated with teeth  105  on the upper portion  104   d  of the fourth paired gear  100   d . Thus, the power of the turbine  70  is transmitted through to the direction assembly  94 .  
         [0048]     The direction assembly  94  includes a rotation sub-assembly  122 . The rotation sub-assembly  122  cooperates with the gearing  17  located on a portion of the sprinkler head  16  (see  FIG. 1 ) so that the rotation sub-assembly  122  directly effects rotation of the sprinkler head  16 . The rotation sub-assembly  122  includes the distribution gear  118  which communicates with two drive gears  124  via intermediate gears  126 . Rotation of the distribution gear  118  causes the other gears  124 ,  126  to rotate around axles  128 . However, each gear  118 ,  124 ,  126  rotates in a direction counter to any gear with which it is mated. In the present embodiment, two intermediate gears  126  are communicate between the distribution gear  118  and a first drive gear  124   a , while one intermediate gear  126  communicates between the distribution gear  118  and a second drive gear  124   b . Accordingly, rotation in a particular direction by the distribution gear  118  causes the drive gears  124  to rotate in opposite directions.  
         [0049]     The direction assembly  94  includes a lever  130  that is moved between two positions so as to adjust the position of the rotation sub-assembly  122  relative to the sprinkler head  16 . In a first position, the first drive gear  124   a  is mated with the sprinkler head gearing  17  to effect rotation of the sprinkler head  16  in a first direction and the second drive gear  124   b  is disengaged from the sprinkler head gearing  17 . In the second position, the first drive gear  124   a  is disengaged from the sprinkler head gearing  17  and the second drive gear  124   b  is engaged so that the sprinkler head  16  is rotated in a second, opposite direction.  
         [0050]     As discussed above, the revolutions per minute of the turbine  70  are in the order of 1890 RPMs, and the sprinkler head  16  rotates at approximately 1 RPM. To respond to rotational impedance of the sprinkler head  16 , the motor assembly  18  is provide with a slip-clutch assembly including a two or more components which are able to slip when a threshold level of stress is experienced and re-engage once the impedance is removed.  
         [0051]     The slip-clutch assembly may be incorporated into any of the gears of the motor assembly  18 . However, the further down-line from the turbine  70  the slip-clutch assembly is located, the greater its efficacy. For instance, if the slip-clutch assembly were incorporated into pinion  79  connected to the turbine  70 , a single revolution prevented by a stationary sprinkler head  16  would require the pinion  79  to slip enough times to provide for approximately 1890 revolutions of the turbine  70 . In contrast, if the slip-clutch assembly were incorporated at a subsequent gear in the motor assembly  18 , the slips required for a missed rotation of the sprinkler head  16  would be reduced by the amount that the rotations had been reduced by the motor assembly rotation reduction.  
         [0052]     In the preferred embodiment, the fourth paired gear  100   d  is provided as a slip-clutch assembly  150 , as depicted in  FIGS. 5-14  with particular emphasis on  FIGS. 7-14 . The slip-clutch  150  includes a sleeve gear  154  and a ratchet gear  152  received by the sleeve gear  154 . The sleeve gear  154  includes recesses or troughs  178  that, ratchet-like, cooperate with arms  192  of the ratchet gear  152  to permit uni-directional movement between the sleeve gear  154  and the ratchet gear  152 . As will be discussed in greater detail below, the arms  192  are able to deflect inward to cam in and out of the troughs  178 .  
         [0053]     The sleeve gear  154  includes a generally annular ring  160  and an annular top plate portion  162 . An external surface  163  of the ring  160  includes gear teeth  105  corresponding to the gear teeth of lower portion  102  of a paired gear  100 . The plate portion  162  includes a central opening  164  that is circular and has a center co-axial with the sleeve gear  154 . Within the ring  160  is a cavity  166 , and the ratchet gear  152  is received within the cavity  166  and through the opening  164 , as will be discussed below.  
         [0054]     An internal surface  168  of the ring  160  is stepped to form an upper portion  170  and a lower portion  172 . The upper portion  170  has inwardly extending ridges or ratchet teeth  174  formed within the ring  160  evenly spaced around and theron. The ratchet teeth  174  define peaks  176  and troughs  178  for receiving portions of the ratchet gear  152 , as will be discussed. The lower portion  172  is relatively smooth and has a diameter equal to that of the troughs  178  of the upper portion  170 . Accordingly, a radially extending shoulder  179  is formed between the upper and lower portions  170 ,  172 .  
         [0055]     The ratchet gear  152  includes a central portion  180  that is generally cylindrical. The central portion  180  has an upper portion  182  including teeth  105  corresponding to gear teeth of the upper portion  104  of a paired gear  100 .  
         [0056]     The central portion  180  further has an intermediate portion  184  that includes a protruding circumferential rib  186  located a short distance below the geared upper portion  182 . To assemble the slip-clutch assembly  150 , the upper portion  182  is inserted into the opening  164  of the sleeve gear  150 . The intermediate portion  184  is sized so as to closely match the diameter of the opening  164  while permitting rotation relative thereto. The protruding rib  186  is larger than the size of the intermediate portion  184 , and consequently requires being forced through the opening  164  to secure the ratchet gear  152  with the sleeve gear  154 .  
         [0057]     The ratchet gear central portion  180  also has a lower portion  190  which is located in the cavity  166  of the sleeve gear  150 . The lower portion  190  includes a series of arms  192  extending outward from the central portion  180  for cooperating with the ratchet teeth  174  of the sleeve gear  152 . During normal operation, the arms  192  are engaged with the ratchet teeth  174  of the sleeve gear  152 . When stress on the slip-clutch assembly  150  reaches a predetermined threshold in a particular direction due to impedance of the rotation of the sprinkler head  16 , the arms  192  deflect inward so that they slip over the sleeve gear ratchet teeth  174 , thus preventing damage to the sprinkler motor assembly  18 .  
         [0058]     Each arm  192  has a number of portions. The arm  192  includes a branch portion  194  extending in a radial direction from a base  196  at the central portion  180 , a leg portion  200  extending circumferentially from the branch portion  194 , and a foot portion  202  extending co-linearly from the branch portion  194  and radially from the central portion  180 . Each branch  194  is generally secured and, preferably, formed integral with the central portion  180 .  
         [0059]     In the event the arm  192  is deflected inward, it is preferred that the leg portion  200  principally deform. In this manner, the circumferentially extending leg  200  need only deform a small amount to disengage from the ratchet teeth  174 . More specifically, each leg  200  has a toe  210  having a first surface  212  generally formed in plane that is skewed outward from the leg  200 . With reference to  FIG. 13 , when the ratchet gear  152  is rotated relative to the sleeve gear  154  in the direction of arrow R, the first surface  212  cams over the ratchet teeth  174  as the leg  200  deflects inward. The toe  210  furthermore has a second surface  214  set at approximately 90° inward from the first surface  212 . In this manner, if the ratchet gear  152  were to attempt to rotate counter to the direction of arrow R, the leg  200  would not deflect as easily as the forces are generally resolved as a compression force on the leg  200 . However, this counter-rotation would be in the direction that the turbine  70  is rotating due to the force of the water and, hence, would not likely be met with significant resistance. In other words, the arrow R represents the direction of rotation of the ratchet gear  152  rotates relative to the sleeve gear  154  when slipping, and the counter direction is the drive direction. To promote the deformation due to deflection occurring principally in the leg  200 , a central portion  200   a  is thinner than the rest of the leg  200  and thinner than the branch portion  194 .  
         [0060]     When stressed and torqued, gears will tend to deflect away from each other. This results in improper mating, higher stress, and oftentimes damage. Accordingly, it is desired to provide the ratchet gear  152  and sleeve gear  154  with cooperating structure to prevent the gears  152 ,  154  from tilting with respect to each other. Towards this end, the arm  192  is provided with the foot  202 , as noted above. The foot  202  extends beyond the ratchet teeth  174  and to the lower portion  172  of the internal surface  168  of the sleeve gear ring  160 . The foot  202  has a top surface  216  that abuts and slides against the shoulder  179  formed between the upper and lower portions  170 ,  172  of the ring internal surface  168 , and has an end surface  218  that is slightly arcuate for abutting and sliding against the internal surface lower portion  170 .  
         [0061]     In this manner, the ratchet gear  152  and sleeve  154  are reinforced against any force between tending to cause a relative tilt therebetween. The combination of the radially extending branch  194  and foot  202  act as a spoke between the central portion  180  and the ring  160 . In addition, the surface  216  and shoulder  179  cooperate so that any tilting would require the arms  192  to deflect downward.  
         [0062]     As noted, it is preferred that the slip-clutch assembly  150  be provided as the fourth paired gear  100   d . However, it should be noted that the greatest reduction ratio is experienced at the direction assembly pinion gear  110 . Accordingly, the sprinkler  10  may alternatively be provided a slip-clutch assembly  250  as the direction assembly pinion gear  110 .  
         [0063]     Referring now to  FIGS. 15-21 , the slip-clutch assembly  250  is shown in the direction assembly  94 . The slip-clutch assembly  250  includes a drive gear  252  and a slip gear  254 , which is non-rotationally secured to the axle  112 . More specifically, the slip gear  254  is provided with a hub  260  having a hub opening  262  (see  FIG. 19 ) that is non-circular for receiving a portion of the axle  112  similarly configured. In this manner, rotation of the slip gear  254  necessitates rotation of the axle  112 . As can best be seen in  FIGS. 19 and 20 , the slip gear  254  also includes a top plate portion  264  extending radially from a top portion  265  of the hub  260 .  
         [0064]     The drive gear  252  includes an external surface  270  including gear teeth  105 , as described above for the direction assembly pinion gear  110 . The drive gear  252  is similar to the sleeve gear  154  in that it has an annular ring  272  including the external geared surface  270  and a bottom plate  274  including an annular central opening  276  co-axial with the drive gear  252  itself. The ring  272  and bottom plate  274  define a cavity  278  into which the slip gear  254  is received, and the axle  112  is received in the opening  276  and a clip  280  is secured around a lower portion  282  of the axle  112  for retaining the drive gear  252  thereon. In addition, the opening  276  has an inner surface  284  that acts as a bushing against the axle  112 , and the bushing  284  combines with the clip  280  to retard relative tilting between the drive gear  252  and the axle  112 .  
         [0065]     The slip gear  254  and drive gear  252  are provided with cooperating structure that allows the slip gear  254  to slip relative to the drive gear  252  when stress due to an impedance of the sprinkler head  16  rotation is exceeded. Specifically, a number of fingers  266  depend downward from the top plate  264  and are received by structure  290  located within the cavity  278  of the drive gear  252 . The structure  290  is generally a series of circumferential walls sections  292  located at a shoulder  293  formed between the ring  272  and the bottom plate  274  of the drive gear  252 . However, each wall section  292  is separated from an adjacent wall section  292  by a short gap  294  into which the slip gear fingers  266  are received.  
         [0066]     Each finger  266  is provided with side surfaces  298  that are set at an angle inward from the outer circumference of the slip gear top plate  264 . It is preferable that the angle be between 15° and 90°. The fingers  266  mate with the wall sections  292  in the gaps  294  therebetween, and these side surfaces  298  mate with similarly configured side surfaces  300  formed on the wall sections  292 .  
         [0067]     Under normal conditions, rotation of the drive gear  252  is transmitted to the slip gear  254  by driving the wall section side surfaces  300  against the finger side surfaces  298 . When stress exceeds a predetermined level, the angled surfaces  298 ,  300  cam against each other, thereby forcing the fingers  266  to deflect inward. In this manner, the slip gear  254  and drive gear  252  are able to slip and relative to each other. When the stress is relieved, the fingers  266  return to a position located in the gaps  294  between the wall sections  292  to re-engage the slip and drive gears  254 ,  252 .  
         [0068]     It should be noted that the slip-clutch assembly may allow the turbine  70  and other components of the motor assembly  18  to rotate independently of the sprinkler head  16 , which includes allowing the rates of rotation under normal conditions to be varied due to the impedance. This is particularly true considering that the slip-clutch assemblies disclosed herein utilize either friction or interference for transmitting power therethrough. Because the components of the slip-clutch assemblies remain generally in contact, this friction or interference is not completely removed. In this manner, the slip-clutch assembly re-engages very soon, if not immediately, after the impedance falls below the predetermined threshold level.  
         [0069]     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 systems and techniques that fall within the spirit and scope of the invention as set forth in the appended claims.