Abstract:
The disclosure features irrigation systems that include a base unit featuring a retractable fluid conduit, and a mobile unit coupled to the fluid conduit and including: a main body featuring an internal fluid channel having an opening; a plurality of wheel supports rotatably coupled to the main body, where the internal fluid channel extends through the wheel supports to a first plurality of apertures; two or more wheels coupled to the plurality of wheel supports; and a second plurality of apertures extending from the internal fluid channel through a wall of the main body, where during operation of the irrigation system, water enters the internal fluid channel through the opening and is dispensed from the first and second pluralities of apertures.

Description:
TECHNICAL FIELD 
       [0001]    This disclosure relates to systems for delivery of water and chemical substances to a variety of landscapes. 
       BACKGROUND 
       [0002]    Conventional in-ground irrigation systems consist of a network of pipes, sprinkler heads, valves, and other fittings to deliver water to gardens and other landscapes. The pattern in which water is delivered is pre-determined by the layout of such systems; because they are installed below grade they are not generally not re-configurable without a significant expenditure of time and money. 
         [0003]    Water delivery in conventional irrigation systems typically occurs through one or more sprinkler heads positioned close to grade level. To deliver water to a wide area, streams of water project upward and outward from the sprinkler heads. In some cases, supply water is provided at sufficient pressure so that no additional pressurization of the stream is needed to achieve a desired coverage of the landscape. In other cases, the supply water is pressurized further before delivery through the sprinkler heads to ensure adequate coverage of the landscape. 
       SUMMARY 
       [0004]    This disclosure features systems and methods for irrigating a wide variety of landscapes. The systems are self-propelled and require no external power source to operate. Further, the systems deliver water in a downward-directed spray, which irrigates landscapes in a more efficient manner than conventional sprinkler-based systems. As a result, irrigation times are reduced and the amount of water used is significantly reduced. 
         [0005]    The systems and methods disclosed herein are configurable so that a wide variety of landscapes can be irrigated. In particular, water delivery patterns can be selected as desired simply be re-routing a hose or other guide member. As a result, the systems disclosed herein can be adapted for irrigation of a wide variety of landscapes, including lawns, gardens, commercial production fields, greenhouses, and more generally, tracts of land of varying shapes and sizes. 
         [0006]    In general, in a first aspect, the disclosure features irrigation systems that include a base unit featuring a retractable fluid conduit, and a mobile unit coupled to the fluid conduit and including: a main body featuring an internal fluid channel having an opening; a plurality of wheel supports rotatably coupled to the main body, where the internal fluid channel extends through the wheel supports to a first plurality of apertures; two or more wheels coupled to the plurality of wheel supports; and a second plurality of apertures extending from the internal fluid channel through a wall of the main body, where during operation of the irrigation system, water enters the internal fluid channel through the opening and is dispensed from the first and second pluralities of apertures. 
         [0007]    Embodiments of the systems can include any one or more of the following features. 
         [0008]    The systems can include an impeller coupled to each one of the two or more wheels through a subset of the plurality of wheel supports, where during operation of the irrigation system, the water propels the mobile unit by applying a force to each impeller. The mobile unit can include a guide channel, and during operation of the irrigation system, the mobile unit can follow a guide member positioned in the guide channel. 
         [0009]    The second plurality of apertures can be positioned so that during operation of the irrigation system, water is dispersed in a downward direction onto a landscape surface from the second plurality of apertures. The retractable fluid conduit can include a flexible tube. 
         [0010]    The base unit can include a retracting mechanism for storing the fluid conduit in retracted form. The retracting mechanism can include a rotating shaft around which the fluid conduit is wound. The base unit can include a member with an internal fluid channel, and the retracting mechanism can be detachably coupled to the member. The internal fluid channel in the base unit can extend from the member through the retracting mechanism and into the fluid conduit. 
         [0011]    The systems can include a pressure regulator configured to control a pressure of the water. The systems can include a fluid reservoir connected to the internal fluid channel of the base unit, where during operation of the irrigation system, the water can flow through the fluid reservoir before entering the internal fluid channel of the base unit. 
         [0012]    The guide channel can be formed by two guide wheels spaced apart from one another. The guide member can include a hose. The guide member can include one or more guide wires. 
         [0013]    Embodiments of the systems can also include any of the other features disclosed herein, in any combination, as appropriate. 
         [0014]    In another aspect, the disclosure features irrigation systems that include a stationary base unit, a fluid conduit connected to the base unit, and a mobile unit connected to the fluid conduit and featuring two or more drive wheels connected to a fluid channel and two or more guide wheels, where during operation of the irrigation system, water supplied from the base unit enters the fluid channel of the mobile unit and propels the two or more drive wheels, and the mobile unit follows a path corresponding to a hose positioned between the two or more guide wheels. 
         [0015]    Embodiments of the system can include any one or more of the following features. 
         [0016]    The systems can include two or more impellers, where each one of the two or more impellers can be connected to a corresponding one of the two or more drive wheels, and where each of the two or more impellers can be positioned within the fluid channel. Each one of the two or more impellers can be connected to a corresponding one of the two or more drive wheels through a plurality of wheel supports, where the fluid channel extends through each of the wheel supports, and where during operation of the irrigation system, a portion of the water is dispensed from apertures located in the wheel supports. 
         [0017]    The systems can include a plurality of apertures connected to the fluid conduit, where during operation of the irrigation system, a portion of the water is dispensed from the plurality of apertures. At least some of the plurality of apertures can be positioned on an underside of the mobile unit. 
         [0018]    The base unit can include a retracting mechanism for storing the fluid conduit in retracted form, and during operation of the irrigation system, the retracting mechanism can dispense the fluid conduit as the mobile unit follows the path. 
         [0019]    Embodiments of the systems can also include any of the other features disclosed herein, in any combination, as appropriate. 
         [0020]    Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the subject matter herein, suitable methods and materials are described below. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting. 
         [0021]    The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features and advantages will be apparent from the description, drawings, and claims. 
     
    
     
       DESCRIPTION OF DRAWINGS 
         [0022]      FIG. 1  is a schematic diagram of an irrigation system. 
           [0023]      FIG. 2  is a schematic diagram of a mobile unit of an irrigation system. 
           [0024]      FIG. 3  is a schematic diagram of the mobile unit of  FIG. 2  during operation of the irrigation system. 
           [0025]      FIG. 4  is a schematic diagram showing a mobile unit of an irrigation system following a path defined by a hose. 
           [0026]      FIG. 5A  is a schematic diagram of a circular irrigation path defined by a hose. 
           [0027]      FIG. 5B  is a schematic diagram of an interleaved irrigation path defined by a hose. 
           [0028]      FIG. 6  is a cross-section diagram of a base unit of an irrigation system. 
           [0029]      FIG. 7  is a schematic diagram of a base unit that includes a fluid reservoir. 
           [0030]      FIG. 8  is a schematic diagram of a mobile unit that includes four drive wheels. 
           [0031]      FIG. 9  is a schematic diagram of an alternate guide system for the mobile unit. 
           [0032]      FIG. 10  is a schematic diagram of a mobile unit with an additional lateral arm. 
           [0033]      FIG. 11  is a schematic diagram of a mobile unit with an elevated lateral arm. 
       
    
    
       [0034]    Like reference symbols in the various drawings indicate like elements. 
       DETAILED DESCRIPTION 
       [0035]    Conventional in-ground irrigation systems, as described above, are typically installed in a fixed configuration below grade level in landscape environments. Such installations are typically costly and prone to component failure. To conduct repairs, portions of such systems are generally exposed by digging below grade, a process that is time-consuming and can also be costly. Modifications to in-ground systems can also entail significant time and expense, as they typically involve similar excavation and plumbing. Moreover, even above-ground installations involve periodic replacement of plumbing fixtures and maintenance of components, and likewise have fixed configurations relative to landscape environments. 
         [0036]    In addition, many conventional in-ground and above-ground irrigation systems deliver water to the landscape environment by spraying the water upward and outward using nozzles, sprinklers, and similar water dispersing fixtures. Much of the water sprayed in this manner is atomized and drifts away as water vapor, rather than being delivered to the landscape. This is particularly prevalent in hot and arid environments, which promote rapid evaporation of water. In such systems, therefore, significant quantities of water can be lost to the environment without being delivered to the landscape, resulting in inefficient delivery of supply water. 
         [0037]    The systems and methods disclosed herein are relatively simple in construction. Compared to many conventional systems, they have fewer components, and are therefore less costly and time-consuming to maintain. Moreover, the systems are re-configurable to allow for a wide range of patterns of water delivery to a landscape. Water is delivered in an efficient manner by directing the water downwards toward the landscape rather than upward and outward, and the direction of water delivery can be controlled in a simple manner to accurately deliver water where it is needed, and to avoid delivering (e.g., wasting) water where it is not needed. 
         [0038]      FIG. 1  shows a schematic diagram of an irrigation system  100 . Irrigation system  100  includes a base unit  110  and a mobile unit  160 . Base unit  110  includes a support structure featuring an upper member  112  and a lower member  114  connected to the upper member. Lower member  114  is mounted on a support platform  126 . Upper member  112  includes a rotating shaft  120  that is connected to, and rotates freely within, arms  113   a  and  113   b  of upper member  112 . Two conduit retainers  116  and  118  are connected to rotating shaft  120 , and rotate when the shaft is rotated. A handle  128  (e.g., implemented as a hand crank) is connected to rotating shaft  120  on the opposite side of arm  113   b  from conduit retainer  118 , and also rotates when shaft  120  is rotated. 
         [0039]    Upper member  112  also includes a connector  124  configured to releasably connect to a fluid conduit such as a hose  125  (e.g., a common half-inch diameter garden hose). An internal fluid channel  130 , indicated by dashed lines in  FIG. 1 , extends from connector  124  through the upper portion of member  112 , through each of arms  113   a  and  113   b , and into rotating spindle  120 . Fluid channel  130  is also connected to connector  132 . A fluid conduit  122  (e.g., a length of tubing) is connected to connector  132 . As a result, a continuous fluid channel is established between connector  124  and connector  132 , so that a fluid (e.g., water) that enters base unit  110  through connector  124  (e.g., water delivered to base unit  110  from hose  125 ) exits base unit  110  through connector  132  and enters fluid conduit  122 . As shown in  FIG. 1 , fluid conduit  122  is connected to mobile unit  160 . 
         [0040]    Mobile unit  160  includes a main body  162 . A plurality of wheel supports  176  and  178  are connected to, and rotate freely about, main body  162 . A wheel  168  is connected to wheel supports  176  and rotates relative to main body  162  when wheel supports  176  rotate relative to main body  162 . Similarly, a wheel  170  is connected to wheel supports  178  and rotates relative to main body  162  when wheel supports  178  rotate relative to main body  162 . An axle  173  is connected to a shaft  175  that extends through main body  162 . Axle  173  rotates freely about shaft  175  so that axle  173  can rotate through an angle of 360° relative to main body  162 . Wheels  172  and  174  are connected to, and rotate freely about, axis  173 . 
         [0041]    As shown in  FIG. 1 , fluid conduit  122  is connected to an aperture  182  formed in main body  162 . Aperture  182  is connected to an internal fluid channel  180  that extends through main body  162 . In particular, fluid channel  180  extends through neck  162   a  and through arms  162   b  and  162   c  of main body  162 . Within neck  162   a , fluid channel  180  is connected to one or more apertures that extend through main body  162  (the apertures are not shown in  FIG. 1 , but will be discussed in greater detail later). 
         [0042]    Fluid channel  180  extends through arm  162   b  and into each of wheel supports  176 , terminating at apertures  184  formed in wheel supports  176 . Similarly, fluid channel  180  extends through arm  162   c  and into each of wheel supports  178 , terminating at apertures  186  formed in wheel supports  178 . Apertures  184  and  186  are open to the environment surrounding mobile unit  160 . 
         [0043]    During operation, supply water enters aperture  24  of base unit  110 . For example, hose  125  can be connected to aperture  124 , and supply water can be delivered to aperture  124  through hose  125 . Typically, supply water is delivered from a common faucet connected to a municipal water supply system. The supply water generally has a static pressure of between about 20 pounds per square inch (PSI) and about 75 PSI. The pressure of the supply water can be adjusted, as needed, by directing the supply water to flow through a pressure regulating device (e.g., a pump to increase the pressure, or a pressure reducer to decrease the pressure) before the supply water enters aperture  124 . 
         [0044]    After entering base unit  110  through aperture  124 , the supply water flows through fluid channel  130  in the upper portion of upper member  112 , and through the portions of fluid channel  130  that extend through arms  113   a  and  113   b  of upper member  112 . The supply water then flows through shaft  120  and exits base unit  110  through connector  132 , entering fluid conduit  122 . 
         [0045]    The supply water propagates through fluid conduit  122  and enters main body  162  of mobile unit  160  through aperture  182 . Once inside main body  162 , the supply water flows through fluid channel  180  and into neck  162   a  of main body  162 . The supply water exits main body  162  through the one more apertures that are connected to fluid channel  180  in neck  162   a  (not shown in  FIG. 1 ). 
         [0046]    A portion of the supply water also flows through fluid channel  180  and into arms  162   b  and  162   c  of main body  162 . The supply water continues to flow through fluid channel  180  within wheel supports  176 , and exits the wheel supports through apertures  184 . In addition, the supply water flows through fluid channel  180  within wheel supports  178 , and exits the wheel supports through apertures  186 . 
         [0047]      FIG. 2  is a schematic side view of mobile unit  160 . In  FIG. 2 , apertures  188  are shown on the underside of neck  162   a  of main body  162 . As discussed above, apertures  188  are in fluid communication with fluid conduit  180  so that water and/or other fluids that flow through conduit  180  can exit main body  162  through apertures  188  on the underside of neck  162   a . Also shown in FIG. are apertures  186  positioned at the ends of wheel supports  178 , which are also in fluid communication with conduit  180 . When water and/or other fluids flow through conduit  180 , the water and/or other fluids can exit wheel supports  178  through apertures  186 . 
         [0048]    Referring again to  FIG. 1 , during operation of system  100 , supply water flows from base unit  110  to mobile unit  160 . As the pressurized supply water flows through fluid channel  180  in main body  162 , the water passes through impellers  181  in arms  162   b  and  162   c  of main body  162 . Impellers  181  are configured so that when the pressurized water contacts the impellers, the impellers rotate wheel supports  176  and  178  in a single direction with respect to arms  162   b  and  162   c . In particular, when pressurized water flows through impellers  181  on the way to apertures  184  and  186 , impellers  181  rotate wheel supports  176  and  178  in a forward direction. Wheels  168  and  170 , which are connected to wheel supports  176  and  178 , respectively, also rotate in a forward direction. As a result, the entire mobile unit  160  moves in a forward direction, i.e., in the direction of arrow  102  in  FIG. 1 . 
         [0049]    As the pressurized supply water flows through fluid channel  180 , the water exits main body  162  through the various apertures discussed above.  FIG. 3  shows a schematic side view of mobile unit  160  during operation. As is evident in  FIG. 3 , supply water exits main body  162  through apertures  188  formed in neck  162   a , in a plurality of streams  192 . Streams  192  are directed downwards toward the surface (e.g., the landscape grade) on which wheels  168 ,  170 ,  172 , and  174  rest. 
         [0050]    Supply water also exits main body  162  through apertures  184  and  186  in wheel supports  176  and  178 , respectively, in a plurality of streams  190 . As shown in  FIG. 3 , streams  190  are directed approximately orthogonal to the ground-contacting surfaces of wheels  168  and  170 . Because wheels  168  and  170  are in continuous rotation as mobile unit  160  moves forward, much of the water in streams  190  flows approximately in a direction toward the surface (e.g., the landscape grade) on which wheels  168 ,  170 ,  172 , and  174  rest. 
         [0051]    As discussed previously, directing the flow of streams  190  and  192  toward the landscape that is being watered, rather than dispersing the water upward into the air as in many conventional irrigation systems, provides a number of important advantages. First, water can be applied to the landscape in more targeted fashion, ensuring that water is delivered to only those portions of the landscape for which irrigation is desired. Because water is not dispersed in a wide-area, indiscriminate spraying pattern, highly controlled irrigation can be achieved. 
         [0052]    Second, because water is applied in controlled fashion, a significant amount of water is saved relative to many conventional irrigation systems. Accordingly, a smaller volume of water can be used to irrigate landscapes than when using conventional systems. Water savings arise from the targeted delivery of water to only those portions of the landscape where irrigation is desired; water is not wasted by applying it to portions of the landscape where no irrigation is intended. Further, in hot, arid climates, water savings arise because significantly smaller quantities of water are dispersed upward into the air, relative to conventional systems. Dispersal of water into the air in hot, arid environments can lead to a significant fraction of the dispersed water evaporating before it effectively irrigates the landscape. System  100  avoids much of this evaporation by delivering water in a downward direction, directly onto the portions of the landscape for which irrigation is desired. 
         [0053]    As discussed above, when pressurized supply water flows through fluid channel  180 , the water drives impellers  181 , which in turn cause wheel supports  176  and  178 , and wheels  168  and  170  attached thereto, respectively, to rotate in a forward direction, causing mobile unit  160  to move forward. The pattern traveled by mobile unit  160  over the landscape surface is entirely configurable, and can be modified simply and easily prior to, or during, movement of mobile unit  160 . In particular, the entire pattern of travel of mobile unit  160  can be controlled using a common garden hose. 
         [0054]      FIG. 4  is a schematic diagram showing base unit  110  and mobile unit  160  positioned on a landscape surface to irrigate the surface. As shown in  FIG. 4 , a hose  194  connects base unit  110  to a water source  196  (e.g., a faucet). Hose  194  is positioned on the landscape surface such that it defines the path that mobile unit  160  follows as it moves forward. In particular, wheels  172  and  174  of mobile unit  160  are positioned on either side of hose  194 . As mobile unit  160  moves forward, hose  194  acts as a guide or track for wheels  172  and  174 , remain on either side of the hose. Because wheels  172  and  174  rotate freely on axle  173  relative to main body  162 , the wheels follow the contours of hose  194 , which allows mobile unit  160  to follow a wide variety of linear and nonlinear paths defined by hose  194 . As an example, in  FIG. 4 , hose  194  defines a serpentine path, which is followed by mobile unit  160  as it moves forward in the directions indicated by arrows  198 . 
         [0055]    The total distance traveled by mobile unit  160  is controlled by the length of fluid conduit  122 . Prior to irrigating a landscape, most of the length of fluid conduit  122  is wound around rotating shaft  120 . As mobile unit  160  travels in the directions indicated by arrows  198 , the mobile unit applies a force to fluid conduit  122 , which in turn causes shaft  120  to rotate, releasing additional lengths of fluid conduit  122  while base unit  110  remains stationary. In this manner, the length of unwound fluid conduit  122  extending between base unit  110  and mobile unit  160  increases as the mobile unit follows the path defined by hose  194 . 
         [0056]    Mobile unit  160  continues to follow the path defined by hose  194  until fluid conduit  122  is fully unwound from shaft  120 , at which point further forward motion of mobile unit  160  is prevented by fluid conduit  122 . Accordingly, the total path length traveled by mobile unit  160  (i.e., the length of the irrigation path) can be regulated by controlling the length of fluid conduit  122 . Typically, fluid conduit  122  has a length of approximately 10 feet or more (e.g., 15 feet or more, 25 feet or more, 50 feet or more, 75 feet or more, 100 feet or more, 200 feet or more, 300 feet or more, 500 feet or more, 1000 feet or more). 
         [0057]    After mobile unit  160  has completed its path and/or fluid conduit  122  is fully extended, mobile unit  160  can be returned to base unit  110  by retracting fluid conduit  122 . Retraction of fluid conduit  122  can occur with supply water continuing to be delivered to base unit  110 . Alternatively, retraction of fluid conduit  122  can be performed after first halting the delivery of supply water to base unit  110  (e.g., by closing a valve in faucet  196 ). To retract fluid conduit  122 , shaft  120  can be rotated in a direction opposite to its direction of rotation during forward motion of mobile unit  160 . As discussed previously, handle  128  (shown in  FIG. 1 ) is connected to shaft  120 , and the shaft can be rotated in the opposite direction by turning handle  128 . 
         [0058]    When shaft  120  is rotated to retract fluid conduit  122 , the fluid conduit is once again rolled onto shaft  120 . Conduit retainers  116  and  118  ensure that fluid conduit  122  is rolled onto, and contained within, the central portion of shaft  120 , so that the shaft&#39;s rotational motion is not impeded by fluid conduit  122 . 
         [0059]    A significant advantage of system  100  relative to in-ground irrigation systems is that system  100  typically includes many fewer components that are prone to failure and replacement. For example, components such as plumbing fittings (e.g., sprinklers, joints) can fail after repeated use and may need to be replaced. In-ground irrigation systems typically include many such components, and replacement entails uncovering the failed components by excavating below grade. In contrast, system  100  includes comparatively few such components, and thus, requires significantly less maintenance. Moreover, should a component of system  100  fail, the component can be replaced easily without excavation or troubleshooting to locate failed components that are hidden from view. 
         [0060]    As discussed above, the irrigation path followed by mobile unit  160  is easily configurable and re-configurable, so that water can be applied to a landscape in a wide variety of patterns.  FIG. 4  shows mobile unit  160  following a serpentine pattern defined by hose  194 . More generally, however, hose  194  can be positioned to define any desired pattern.  FIGS. 5A and 5B  show examples of alternate irrigation patterns that can be used, simply by re-positioning hose  194 . In  FIG. 5A , hose  194  is connected to faucet  196  and is positioned to define a circular irrigation pattern for mobile unit  160 . In  FIG. 5B , hose  194  is positioned to define an interleaved irrigation pattern for mobile unit  160 . The interleaved pattern can be advantageous because the end of the irrigation path is near its beginning (e.g., near the location where mobile unit  160  begins). Accordingly, retrieval of mobile unit  160  after the irrigation path has been traversed is particularly straightforward, as it involves relatively minor displacement of mobile unit  160 . 
         [0061]    Returning to  FIG. 1 , upper member  112  and lower member  114  of base unit  110  can be formed from a variety of materials. In some embodiments, for example members  112  and  114  can be formed from pipe, such as polyvinyl chloride (PVC) pipe. Shaft  120 , conduit retainers  116  and  118 , and handle  128  can be formed from a variety of materials, including various metals and/or various plastic materials. As an example, these components can be formed from PVC pipe. 
         [0062]    Support platform  126  is typically formed from one or more materials that are relatively rigid to support the other components of base unit  110 . For example, support platform  126  can be formed from wood, from various plastic materials, and/or from various engineered materials such as fiberboard, pressboard, and various laminate materials. In general, the material(s) used for support platform  126  are relatively water resistant, so they do not degrade when exposed to water during irrigation, and relatively heavy to provide stability for base unit  110  (e.g., so that mobile unit  160  does not drag base unit  110  when it moves forward). In some embodiments, support platform  126  can include a plurality of anchors  197  (shown in  FIG. 1 ) that can be inserted below grade (e.g., by hammering or pressing the anchors into the ground) to further prevent movement of base unit  110  when mobile unit  160  moves forward. 
         [0063]    To further prevent motion of base unit  110 , in some embodiments, lower member  114  can be filled with a heavy material. A variety of common materials can be used for this purpose, including sand, stone dust, and crushed aggregate material. 
         [0064]    Fluid conduit  122  is typically formed from a lightweight, flexible tubing material. Examples of materials that can be used to form fluid conduit  122  include latex, silicone, polyethylenes, polyvinyls, polypropylenes, polyurethanes, nylons, and polycarbonates. By selecting a material that is lightweight and flexible, mobile unit  160  is capable of pulling fluid conduit  122  behind it as it moves forward. In contrast, heavier tubing materials such as garden hoses are more difficult for mobile unit  160  to pull, and supply water at higher pressure may be needed to drive the mobile unit&#39;s wheels. 
         [0065]    The main body  162  of mobile unit  160  can be formed from a variety of lightweight materials. Plastic materials such as PVC pipe are particularly well suited for main body  162 . Wheel supports  176  and  178  can be formed from a variety of plastic materials such as PVC, polyethylene, and polypropylene. Wheel supports  176  and  178  can be also be formed from metal materials such as aluminum, brass, and bronze. In some embodiments, rotating sprinkler heads can be used to form wheel supports  176  and  178 . 
         [0066]    Axle  173  and shaft  175  can generally be formed from various plastic and/or metal materials, including any of the plastic and metal materials disclosed above. Similarly, wheels  168 ,  170 ,  172 , and  174  can be formed from any of the plastic and/or metal materials disclosed above. In particular, relatively lightweight materials are typically chosen for wheels  168 ,  170 ,  172 , and  174  to ensure that the wheels do not contribute substantial weight to mobile unit  160 . In this manner, only relatively modest supply water pressure is required to drive mobile unit  160  in the forward direction. 
         [0067]    As discussed above, the length of the irrigation path traveled by mobile unit  160  is controlled by the length of fluid conduit  122 . Accordingly, in some embodiments, shaft  120  is de-mountable from upper member  112  to allow for spools with different lengths of fluid conduit  122  to be quickly and interchangeably inserted into base unit  110 .  FIG. 6  shows a schematic cross-sectional diagram of base unit  110 . In  FIG. 6 , shaft  120  releasably engages with locking members  202 , which hold shaft  120  in position within upper member  112 . To remove shaft  120 , the shaft is disengaged from locking members  202 , and the entire shaft, conduit retainers  116  and  118 , and fluid conduit  122  wound around shaft  120 , are removed from upper member  112 . Another shaft  120 , e.g., with a different length of fluid conduit  122  wound around the shaft, can then be inserted into locking members  202 . As such, the length of the path traveled by mobile unit  160  during irrigation can be quickly and easily adjusted. Locking members  202  can use a variety of different mechanisms to engage shaft  120 , including multi-armed or -fingered jaws, deformable apertures, pin-type fasteners such as screws or threaded rods, and magnet-based mounts. 
         [0068]    In  FIG. 1 , handle  128  is connected to shaft  120  and used to retract fluid conduit  122  by rotating shaft  120 . More generally, a variety of different mechanisms can be used to retract fluid conduit  122 . In some embodiments, for example, shaft  120  can be connected to a motorized winch. When mobile unit  160  can reached the end of the irrigation path (e.g., when fluid conduit  122  has been fully unwound from shaft  120 ), the motorized winch can be activated and can retract conduit  122  by rotating shaft  120 . The winch can be activated by a human operator, for example. Alternatively, system  100  can include a sensor that determines when fluid conduit  122  is fully unwound (e.g., by detecting the absence of rotational motion by shaft  120 ), and activates the motorized winch automatically. 
         [0069]    In some embodiments, base unit  110  can include a fluid reservoir that allows other substances to be dispersed by mobile unit  160 , in addition to supply water.  FIG. 7  shows a schematic diagram of an embodiment of base unit  110  that includes a reservoir  208 . Reservoir  208  is connected to upper member  112  by a fluid conduit  204 , and is connected to a water source by fluid conduit  206  (e.g., a common garden hose). Reservoir  208  includes an aperture  210  through which compounds in liquid or solid form can be added to the reservoir. 
         [0070]    During operation, supply water provided by fluid conduit  206  enters reservoir  208  and mixes with the substances therein. The mixed solution then enters upper member  112  of base unit  110  through fluid conduit  204 , and is eventually dispersed onto the landscape through mobile unit  160 . A variety of different substances can be added to reservoir  208  for dispersal onto the landscape. These can include, for example, fertilizers, weed killers, vegetation killers, and various other chemical and/or biological substances. 
         [0071]    The speed at which mobile unit  160  moves forward depends on the pressure of the water supplied to the mobile unit through fluid conduit  122 . In some embodiments, system  100  includes an optional pressure regulator for controlling the pressure of the water entering mobile unit  160  to adjust the speed of mobile unit  160 . Referring again to  FIG. 1 , a pressure regulator  155  is positioned in-line along fluid conduit  122  between base unit  110  and mobile unit  160 . Pressure regulator  155  can adjustably decrease the water pressure in conduit  122  to reduce the speed of mobile unit  160 , or increase the water pressure in conduit  122  to increase the speed of mobile unit  160 . Although positioned along fluid conduit  122  in  FIG. 1 , pressure regulator  122  can also be located in different positions within system  100 . In some embodiments, for example, pressure regular  155  is positioned between hose  125  and aperture  124  to regulate the pressure of supply water before the water enters upper member  112  of base unit  110 . 
         [0072]    Although mobile unit  160  has two larger wheels  168  and  170 , and two smaller wheels  172  and  174 , in  FIG. 1 , more generally, mobile unit  160  can include different wheel configurations for enhanced stability, particularly when traveling over rougher landscapes.  FIG. 8  is a schematic diagram showing an embodiment of mobile unit  160  that includes four large wheels  168   a ,  168   b ,  170   a , and  170   b . The large wheels are connected to main body  162  through wheel supports  176   a ,  176   b ,  178   a , and  178   b , respectively. Water that enters main body  162  through aperture  182  flows through each of wheel supports  176   a ,  176   b ,  178   a , and  178   b  through a common interior fluid channel that extends through neck  162   a  and arms  162   b ,  162   c ,  162   d , and  162   e  of main body  162 , and into wheel supports  176   a ,  176   b ,  178   a , and  178   b , in a manner analogous to fluid channel  180  in  FIG. 1 . During operation, water emerges from mobile unit  160  through apertures at the ends of each of wheel supports  176   a ,  176   b ,  178   a , and  178   b , and through apertures  188  formed in neck  162   a , as described previously. 
         [0073]    Although in the preceding discussion a hose (e.g., hose  194 ) was used to define the irrigation path followed by mobile unit  160 , more generally other guiding mechanisms can be used to define the irrigation path.  FIG. 9  shows a schematic diagram of a mobile unit  160  configured for operation with an alternate guiding mechanism. In  FIG. 9 , a support member  220  and guide block  222  are attached to the main body  162  of mobile unit  160 . Guide block  222  is dimensioned to engage with guide member  224 . When mobile unit  160  is driven forward by supply water, guide block  222  and support member  220  ensure that a fixed relationship is maintained between mobile unit  160  and guide member  224 . In this manner, guide member  224  defines the irrigation path followed by mobile unit  160 . 
         [0074]    Guide member  224  can be implemented in various ways. In some embodiments, for example, guide member  224  can be implemented as a guide wire, either at grade level or elevated above the ground. The guide wire can be positioned relative to a landscape in a manner similar to hose  194  to define a desired irrigation pattern. Alternatively, in certain embodiments, guide member  224  can be implemented as a system of rails, tracks, or other similar members, to define an irrigation pathway for mobile unit  160 . Systems of guide wires can be used, for example, to define irrigation patterns for crop-bearing fields, allowing mobile unit  160  to efficiently and quickly deliver water to the plants themselves, and preventing delivery of water to portions of the field between rows of plants. 
         [0075]    As shown in  FIG. 1 , mobile unit  160  delivers water in a downward spray pattern through a series of apertures  188  on the underside of neck  162   a . In some embodiments, mobile unit  160  can include additional arms for delivering water, and in particular, for delivering water in a downward spray pattern. Moreover, by including additional arms, water can be delivered to one side or the other of mobile unit  160 .  FIG. 10  is a schematic diagram showing a portion of mobile unit  160 . In  FIG. 10 , an additional arm  162   f  extends laterally from neck  162   a  (i.e., in a direction parallel to arm  162   c  in  FIG. 1 ). Fluid conduit  180  extends into arm  162   f  and terminates in a series of apertures  226 . During operation of mobile unit  160 , water is sprayed in a downward pattern onto the landscape through apertures  226 . 
         [0076]    Arm  162   f  can be implemented in addition to, or as an alternative to, apertures  188  on the underside of neck  162   a . Thus, water delivery can occur from both neck  162   a  and arm  162   f , or from arm  162   f  alone. The configuration shown in  FIG. 10  can be particularly advantageous for delivering water to one side of mobile unit  160 , such as when watering crops or other plants arranged in rows, e.g., in a field. Although mobile unit  160  includes a single additional arm  162   f  in  FIG. 10 , more generally, mobile unit  160  can include one or more additional arms, each configured to deliver water in a downward spray pattern similar to arm  162   f  in  FIG. 10 . The additional arms can extend from either side of main body  162 , or from both sides of the main body. 
         [0077]    In some embodiments, mobile unit  160  can include elevated arms.  FIG. 11  is a schematic diagram showing a portion of a mobile unit  160  in which an additional arm  162   g  extends upward and laterally from neck  162   a . Fluid conduit  180  extends into arm  162   g  and terminates in a series of apertures  228 . During operation of mobile unit  160 , water is sprayed in a downward pattern on the landscape through apertures  228 . 
         [0078]    Elevated arms such as arm  162   g  can be implemented in addition to, or as alternatives to, lateral arms such as arm  162   f , and apertures  188  in neck  162   a . As such, water can be delivered in a downward spray from various heights above the landscape surface. As described above in connection with  FIG. 10 , elevated arms such as arm  162   g  can be positioned on one or both sides of main body  162 . 
         [0079]    Mobile units with elevated arms such as arm  162   g  can be particularly useful for irrigating crops and other plants that are relatively tall. For example, a mobile unit such as unit  160  in  FIG. 11  can be used to irrigate such plants, where other mobile units might instead collide with the plants due to their height above grade. 
       Other Embodiments 
       [0080]    A number of embodiments have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. Accordingly, other embodiments are within the scope of the following claims.