A gutter cleaning robot can traverse rain gutters to agitate and remove debris. The gutter cleaning robot is equipped with a debris auger at a front end that contacts and ejects the debris, and has a drive system for propelling the gutter cleaning robot along the rain gutter. The debris auger can include a spiral screw or various other forms of auger, and may be interchangeable by the user so as to enhance the effectiveness of the gutter cleaning robot in various environments or modes of operation.

BACKGROUND 
     Rain gutters are widely installed along the rooftop eaves of millions of homes and sloped-roof buildings in North America, Europe, and other parts of the world. These rain gutters serve an important role in properly channeling water runoff to appropriate destinations such as storm water mains or drainage ponds. By diverting roof runoff away from the walls of a building, rain gutters also reduce structural damage that would otherwise be caused by the flow of rainwater onto the walls. In addition to rainwater, substantial amounts of debris (such as leaves, tree branches, silt runoff from roof shingles, and the like) tend to accumulate in rain gutters over time, which can eventually constrict or prevent any rainwater from flowing properly. 
     Various tools have been described for facilitating rain gutter cleaning. For example, U.S. Pre-grant Appln. Pub. 2006/0289036 (incorporated herein by reference) relates to an elongated pole that emits compressed gas to blow leaves out of a gutter. Similarly, U.S. Pat. No. 6,471,271 (incorporated herein by reference) relates to a mechanical device, also including an elongated pole, in which a pair of tongs mounted at the end of the pole are opened and closed by pulling a rope to thrash debris out of a gutter. 
     However, the manual tools set forth in those documents can cause the user to fatigue his or her arms from holding heavy poles up as high as twenty feet overhead when attempting to remove debris from a gutter. For example, the user must raise the manual gutter cleaning tool up to the rain gutter and keep it raised for the duration of the cleaning. Furthermore, it may not be possible for the user to ascertain whether any residual matted debris remains in the gutter after attempting a removal, because the rain gutter is typically too high above the user for any visual inspection to be feasible. 
     SUMMARY 
     In view of the above, as well as other considerations, presently disclosed is a mobile robot for cleaning debris from rain gutters (herein referred to as a “gutter cleaning robot”). The gutter cleaning robot includes a debris auger at a front end of the main body of the gutter cleaning robot, and moves forward along the gutter while motivating the debris auger to clear debris from the gutter being traversed. Accordingly, rain gutters may be effectively cleaned without requiring a user to manipulate strenuous overhead equipment and minimize climbing a ladder. 
     In accordance with a first example, a gutter cleaning robot may have a drive system for propelling the gutter cleaning robot along a rain gutter, and a debris auger detachably connected to the gutter cleaning robot for agitating debris out of the rain gutter. 
     The gutter cleaning robot may also have a chassis (also referred to herein as a main body) including a robot connector for mechanically driving the debris auger, and a debris auger connector disposed on the debris auger for interfacing with the robot connector. 
     The debris auger connector may include one or more connector concavities extending into the debris auger connector, each connector concavity being aligned substantially parallel to a longitudinal axis of the debris auger connector, in which the robot connector includes one or more tines each arranged to extend into a respective connector concavity of the debris auger connector. Also, the robot connector may further include a locking collar concavity, in which the debris auger further includes a shroud disposed around the debris auger connector, the shroud provided for enveloping the robot connector when the debris auger is attached to the main body of the gutter cleaning robot, in which the shroud includes a locking protrusion extending from an inner surface of the shroud for engaging the locking collar concavity of the robot connector. 
     In the gutter cleaning robot, the debris auger connector may include a hexagonal concavity extending into the debris auger connector, the hexagonal concavity aligned substantially parallel to a longitudinal axis of the debris auger connector, in which the robot connector includes a hexagonal protrusion for extending into the hexagonal concavity of the debris auger connector. The debris auger may be interchangeable with one or more alternative debris augers; and/or may include a spiral screw for drilling into debris. The alternative debris augers may include a flail-type auger, a bristle-type auger, a flap-type auger, a twisting flap-type auger, an irregular protrusion-type auger, a revolving horizontal tines-type auger, a screw-and-flap-type auger, and/or a plow-type auger; and further, the debris auger may include a pneumatic tube for blowing air onto the debris. 
     The drive system of the gutter cleaning robot may include a caterpillar tread for contacting an interior surface of the rain gutter; and may also include a drive motor, at least two front wheels disposed on opposite lateral sides of the main body of the gutter cleaning robot for guiding the gutter cleaning robot along the rain gutter, and two rear wheels disposed on opposite lateral sides of the main body of the gutter cleaning robot and operably connected to the drive motor. 
     The gutter cleaning robot may also be usable with a remote control for operating the gutter cleaning robot via a wireless signal transmitted to the gutter cleaning robot. 
     The gutter cleaning robot may include a light emitting diode on the remote control that blinks when the remote control transmits a signal; and/or another emitting diode on the gutter cleaning robot that blinks when the gutter cleaning robot receives a signal. The gutter cleaning robot may also have a detachable handle or a tote loop disposed on the main body of the gutter cleaning robot for hanging onto a positioning hook that can hoist the gutter cleaning robot into the rain gutter; and/or an ammeter for monitoring an auger current supplied to the debris auger motor, and a controller for receiving input from the ammeter and controlling the drive motor and the debris auger motor, in which the controller can modulate the drive motor when the auger current exceeds a threshold value. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a perspective view of a house having a rain gutter and drainpipe. 
         FIG. 1B  is a detail view of a corner of the rain gutter shown in  FIG. 1A . 
         FIG. 1C  is an oblique partial cutaway view of a rain gutter having four kinds of gutter hanging braces. 
         FIG. 1D  is a partial cutaway view of a gutter cleaning robot traversing a rain gutter, in which the height of the gutter cleaning robot affords clearance to pass underneath a gutter hanging brace. 
         FIG. 2  is a partial cutaway view of a gutter cleaning robot. 
         FIGS. 3A and 3B  are front and rear aspect views, respectively, of the gutter cleaning robot shown in  FIG. 2 . 
         FIG. 4  is a schematic view of a gutter cleaning robot having caterpillar treads and a removable handle. 
         FIG. 5  is an exploded view of a gutter cleaning robot having a flattened profile, showing the placement of batteries and drive components within the chassis. 
         FIG. 6  is a diagram of a gutter cleaning robot operated by a wireless remote control. 
         FIGS. 7A and 7B  are isometric views of a debris auger  350  having flails. 
         FIGS. 8A and 8B  are isometric views of a debris auger  350  having bristles. 
         FIGS. 9A and 9B  are isometric views of a debris auger  350  having longitudinal flaps. 
         FIGS. 10A and 10B  are isometric views of a debris auger  350  having oblique flaps. 
         FIGS. 11A and 11B  are isometric views of a debris auger  350  having a screw. 
         FIGS. 12A and 12B  are isometric views of a concave debris auger  350  having rigid protrusions. 
         FIGS. 13A and 13B  are isometric views of a debris auger  350  having rigid protrusions. 
         FIGS. 14A and 14B  are isometric views of a debris auger  350  having flaps connected to a screw; 
         FIG. 14C  is an oblique view of a debris auger  350  having flaps and a bristle, which is rotatable to eject debris; 
         FIG. 14D  is an oblique view of a robot  10  traversing a gutter  51  using the auger  350  of  FIG. 14C ; 
         FIG. 15  is a front aspect view of a debris auger connector. 
         FIG. 16  is a perspective view of a debris auger  350  and a robot connector. 
         FIG. 17  is a perspective view of a debris auger  350  having flails and a debris auger connector. 
         FIG. 18  is a perspective view of a debris auger  350  having longitudinal flaps and a debris auger connector. 
         FIG. 19  is a partial cutaway view of an alternative debris auger connector having a locking shroud with a locking protrusion. 
         FIG. 20  is a partial cutaway profile view of a pneumatic debris auger  350 . 
         FIG. 21  is a photograph illustrating a variety of alternative debris augers. 
         FIG. 22  is a photograph illustrating debris being ejected from a gutter by a gutter cleaning robot. 
         FIG. 23  is a partially transparent perspective view of a gutter cleaning robot having obliquely aligned rear drive wheels and a suspension. 
         FIG. 24  is an oblique perspective view of a gutter cleaning robot having a removable handle. 
         FIG. 25  is a partial cutaway view of a gutter cleaning robot having a debris auger disposed on two longitudinal ends thereof. 
         FIGS. 26A and 26B  are isometric views of a plow-type debris auger. 
         FIG. 27  is a front aspect view of a debris auger connector having a hexagonal concavity. 
         FIG. 28  is a perspective view of a debris auger connector having a hexagonal concavity and a robot connector having a hexagonal protrusion. 
         FIG. 29  is a flowchart illustrating a method for controlling the drive motor and debris auger. 
         FIGS. 30A through 30D  are schematic diagrams illustrating possible alignments of battery cells in a gutter cleaning robot chassis. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1A  shows a house  40  having a roof  45  supported by walls  43 . The roof  45  is sloped and includes tar shingles, cedar shakes, or another roof-building material. A rain gutter  51  is disposed along the eaves of the roof  45 . Also, a drain spout  52  drains water from the gutter  51  via a hole in the bottom of the gutter  51 . As rain or other water falls on the roof  45 , the rainwater slides down to the eaves where it collects in the gutter  51  and flows down through the drain spout  52 . 
     Another example of a roof having a rain gutter is shown in  FIG. 1B , in which the rain gutter  51  includes a corner  53  where two straight sections are joined. Debris  91  also collects in the gutter  51 , and includes material such as silt, leaves, branches, and other detritus. 
       FIG. 22  illustrates a gutter cleaning robot  10  traversing the gutter  51 . As the gutter cleaning robot  10  moves forward through the gutter  51 , the gutter cleaning robot  10  ejects debris  91  out from the gutter  51 . 
     In accordance with a first embodiment,  FIG. 2  shows a gutter cleaning robot  10  for traversing the gutter  51  and clearing debris  91 . The gutter cleaning robot  10  includes a main body  101  onto which rear drive wheels  175  are disposed, as well as two front wheels  176 . A drive motor  170 , such as a DC brushed or brushless motor with encoders, provides motivating force to rotate the rear wheels  175 , which may preferably be aligned in an oblique orientation so as to contact the interior side walls of the gutter  51  rather than only the bottom interior surface thereof. The power output of the drive motor  170  may be transmitted directly to the treads  179  or wheels  175 ; or, alternatively, a reducing mechanical transmission may be interposed between the drive motor  170  and the treads  179  or wheels  175 . The gutter cleaning robot  10  also includes a detachable debris auger  350  for agitating or moving the debris  91 . 
     The debris auger  350  is connected to a debris auger motor  160  within the main body  101  via a debris auger shaft  163 . The drive motor  170  and debris auger motor  160  are preferably controlled by an electronic controller having a memory store for storing computer instructions for controlling the drive motor  170  and/or the auger motor  160 . In a preferred embodiment, a microcontroller serves as the electronic controller; or, in a possible alternative embodiment, the microcontroller may be a microprocessor. As a further alternative, the electronic controller may include a PLA or FPGA device. 
     The gutter shown in  FIG. 1C  illustrates four common kinds of rain gutter hanging arrangements in which straps or braces are used. The inside hanger method employs straps  1101  spanning the width of the rain gutter  51 , in which screws or nails go through the strap from inside the gutter into a fascia board at the edge of the roof. The outside hanger method uses outside hangers  1102 A,  1102 B mounted to the fascia board behind the rain gutter  51 , and the rain gutter  51  is disposed on the outside hangers  1102 A,  1102 B. In the strap hanger method, straps  1103  are nailed under shingles into the roof sheathing. The spike and ferrule method uses spikes  1104  driven through the rain gutter  51  into the fascia board, in which ferrules are used to maintain the appropriate width of the gutter trough and to prevent the spikes  1104  from pulling against or distorting the rain gutter  51 . 
     In each of the above-noted gutter hanging arrangements, a strap or spike crosses the trough of the gutter transversely, and presents a possible obstacle to any gutter cleaning robot  10  moving along the through of the rain gutter  51 . Accordingly, in a preferred embodiment, the gutter cleaning robot  10  has an overall height profile that is low enough to afford sufficient clearance between the topmost part of the gutter cleaning robot  10  and the straps or spikes that cross over the trough of the rain gutter  51 . 
     As illustrated in  FIG. 1D , for example, a gutter cleaning robot  10  includes a detachable handle  180  and caterpillar treads  179  that are disposed so as to permit the gutter cleaning robot  10  to pass underneath spikes  1104  that support the rain gutter  51 . Another example of a gutter cleaning robot  10  including a detachable handle  180  is illustrated in  FIG. 24 . The detachable handle  180  facilitates handling and transportation of the gutter cleaning robot  10  by a user, and may be removed when the gutter cleaning robot  10  is operated in a rain gutter  51  having low overhead clearance. The detachable handle  180  may be fastened to the chassis  101  using a latch, wingnuts, magnets, velcro, or any other fastening arrangement suitable to permit attachment and removal of the detachable handle  180  to the gutter cleaning robot  10 . 
     Many rain gutters  51  have either a round trough bottom or a substantially flat trough bottom. Rain gutters for residential housing typically have a width of between four to six inches, with the typical k-style gutter being five inches wide and the typical half-round gutter being six inches wide; thus, typical widths for rain gutters  51  may range between three to seven inches. The depth of many installed rain gutters  51  is approximately 75% the width of the rain gutter, and rain gutter depths typically range between about 60% to 90% of the width of the rain gutter. drain spouts commonly installed to rain gutters typically have 2×3″, 3×4″ or 4×5″ rectangular cross-sections, and the rain gutters generally have rectangular holes of similar shape where they interface with the drain spouts. 
     The gutter cleaning robot  10  preferably has a width and caterpillar tread arrangement (or wheel, or other drive system) suitable to traverse rectangular hole of at least about three inches by four inches. The gutter cleaning robot  10  may alternatively have a width and drive system placement suitable to traverse holes having a width in the range of about two to five inches, and/or a length in the range of about two to six inches. 
     Many installed rain gutters  51  can support up to about 50 pounds per lineal foot. Accordingly, the gutter cleaning robot  10  preferably has a weight sufficiently low so as to be supported by the weight load capacity of common rain gutters, taking into account the weight of a typical load of debris  91 . 
       FIG. 3A  shows a rear aspect view of the gutter cleaning robot  10 . In this example, the debris auger  350  has flaps, the end portions of which extend beyond the outer perimeter of the main body  101  and are thus visible. Also,  FIG. 3B  shows a front aspect view of the gutter cleaning robot  10 . Because the gutter cleaning robot  10  may be required to traverse both flat-bottom rain gutters and round-bottom rain gutters, in a preferred embodiment the gutter cleaning robot  10  has a longitudinal cross-section having a substantially rounded bottom and a substantially flattened top, as illustrated in  FIG. 5  or  FIG. 23  (as non-limiting examples), in order to facilitate movement along either round-bottom or flat-bottom rain gutters while affording sufficient overhead clearance to permit the gutter cleaning robot  10  to pass underneath obstacles such as support braces. Alternatively, the gutter cleaning robot  10  may have other types of longitudinal cross-section outline such as a cylinder, rectangle, or other polygonal shape. 
       FIG. 4  illustrates an embodiment of a gutter cleaning robot  10  having caterpillar treads  179  as a traction drive and a removable handle  180  disposed on top of the chassis  101  of the gutter cleaning robot  51 . In addition, batteries  177  are disposed within the chassis  101 . The batteries  177  may include a single rechargeable cell, or include one or more commercially available cells, such as “D”-size alkaline cells, NiCd cells, nickel metal hydride cells, lithium cells, or any other kind of battery suitable for providing sufficient current and power the drive system  170  and auger  350  of the gutter cleaning robot  10 . 
     In a preferred embodiment, the treads  179  or wheels  175  are disposed toward the edges of the gutter cleaning robot  10  so that they are separated horizontally by a distance of at least about 2 inches. Because drain spouts  52  often have a width in the range of about two to six inches, the wheels  175  or treads  179  are preferably disposed apart by a distance sufficient to enable the gutter cleaning robot  10  to straddle a hole while moving forward through a rain gutter  51 . As an example, the horizontal distance between the wheels  175  or treads  179  may be chosen from a range extending from substantially two inches to substantially six inches. 
     The wheels  175  or treads  179  may be spring mounted to the chassis  101  of the gutter cleaning robot  10 , to increase the traction pressure applied by the wheels  175  or treads against the side walls of the rain gutter  51 . This increased traction pressure minimizes torsion caused by the action of the auger  350 , and/or may further ensure that the gutter cleaning robot  10  remains within the rain gutter  51  during operation, such as when the gutter cleaning robot  10  is performing an escape behavior in response to becoming stuck. 
     In  FIG. 5 , a preferred embodiment is illustrated in which the gutter cleaning robot  10  includes caterpillar treads  179 , and has a top chassis section  101 B and a bottom chassis section  101 A that house the drive system  170 , batteries  177  and the auger motor  160 . The batteries  177  are disposed substantially laterally in an in-line arrangement, so as to minimize the necessary height of the chassis sections  101 A,  101 B. The top and bottom chassis sections  101 A,  101 B are contoured so as to closely conform to the shape of the components housed therewithin, providing a compact, substantially flat profile of the assembled gutter cleaning robot  10 . Accordingly, the height of the gutter cleaning robot  10  may be minimized, and overhead clearance optimized. 
     A typical clearance between the bottom-most point of a common rain gutter  51  and a fastening strap is 2.75 inches. Preferably, the gutter cleaning robot  10  has a maximum height and diameter of about 2.5 inches; or, alternatively, the gutter cleaning robot  10  may have a height and/or diameter up to substantially 2.75 inches, or to another distance representing the clearance from a rain gutter bottom to a fastening strap or brace. 
     A typical “D” size battery has a diameter of approximately 1.3465 inches. Thus where “D” size batteries are used, the gutter cleaning robot  10  preferably has a diameter equal to or slightly larger than the diameter of a standard D cell battery. For example, the gutter cleaning robot  10  may have a height of at least 1.4 inches. Alternatively, the gutter cleaning robot  10  may have a height and/or diameter within the range of between about 1.4 inches to about 2.5 inches; or a height and/or diameter of at least 1.4 inches, inter alia. 
     In one example, as shown in  FIG. 4 , a gutter cleaning robot  10  has a chassis 2.5 inches in diameter, and uses “D” size batteries  177  disposed within the chassis  101 . Because the “D” size batteries  177  have a width of 1.3465 inches, no more than two “D” size batteries can be placed on top of the other, or else they will not fit within the chassis  101 . Several example battery arrangements are illustrated in  FIGS. 30A through 30D :  FIG. 30A  shows four batteries  177  arranged one battery high in a square pattern;  FIG. 30B  shows four batteries arranged squarely two batteries high, with two sets of two batteries next to each other and stacked on top of one another;  FIG. 30C  shows three batteries, in which first and second batteries are arranged horizontally aligned, one atop the other, and the third battery is disposed perpendicular to the other two batteries; and  FIG. 30D  shows three batteries arranged in a triangular pattern such that a first battery is disposed on top of second and third batteries placed side by side, all in horizontal alignment. In embodiments in which other types of batteries are used, the gutter cleaning robot  10  may have a height or diameter equal to or greater than at least the exterior diameter of that type of battery, for example. 
     The wheel  175  or tread  179  assembly may include a mechanical switch to determine whether the gutter cleaning robot  10  has fallen out of the rain gutter  51 , or whether one of the wheels  175  is stuck in a hole. The switch is activated by a decrease in spring tension between the wheels  175  or treads  179  and the walls of the rain gutter  51 . When the spring's tension is low enough to activate the mechanical switch, the gutter cleaning robot may alert the user and promptly cease powering the drive motor  170  and auger motor  160 . This switch's state is preferably reset each time the gutter cleaning robot  10  is powered up, and may be ignored until after initialization. Furthermore, the switch is preferably only active when the gutter cleaning robot  10  is powered on; also, in at least one embodiment, a dip switch can be included on the gutter cleaning robot  10  to cause the gutter cleaning robot  10  to either monitor or ignore the switch. 
     The gutter cleaning robot  10  may be directed using a remote control  6 , as shown in  FIG. 6 . The remote control  6  includes a joystick and/or buttons for entering commands to be sent to the gutter cleaning robot  10  (such as, for example, start/stop commands). The remote control  6  may transmit user-entered commands to the gutter cleaning robot  10  via radio frequency communication, which the gutter cleaning robot  10  receives via antennae  116 . The remote control  6  and the gutter cleaning robot  10  may each include a respective light emitting diode (LED) or other visual or audible indicator, such as a light bulb or buzzer, for indicating when the remote control  6  is transmitting and/or when the gutter cleaning robot  10  is receiving a signal from the remote control  6 . For example, when the remote control  6  is transmitting a signal, the LED on the remote control may blink; and/or when the gutter cleaning robot  10  receives a signal from the remote control  6 , the LED on the gutter cleaning robot  10  may blink. 
       FIGS. 7A through 14B  illustrate isometric views of various augers that may be interchangeably attached to the gutter cleaning robot  10 . These debris augers may be replaced with another debris auger  350  when appropriate; for example, when matted debris is clogging a gutter, the user may affix a screw-type debris auger  350  to the gutter cleaning robot  10  for effectively penetrating the matted debris. Later, if the user desires not to drop debris  91  onto a walkway below the gutter  51  but instead to move the debris  91  to another portion of the gutter  51 , the user can detach the screw-type debris auger  350  and then affix a plow-type debris auger  350  that can push the debris  91  rather than move it out of the gutter  51 . 
     The auger  350  preferably has a diameter at least equal to the diameter of the chassis  101  of the gutter cleaning robot  10 , as measured tip-to-tip. In one embodiment, the auger  350  has a diameter no greater than substantially 3 inches. Alternatively, the diameter of the auger  350  may be within the range of between about 2.5 inches to about 3.5 inches. The auger  350  preferably operates at a speed in the range of between about 1000 RPM (rotations per minute) to about 1500 RPM. The auger  350  may be made of a substantially flexible material, such as a polymer or plastic, that can deform when it comes into contact with rigid objects. Because the diameter of the auger  350  may exceed the clearance between the gutter's floor and a support strap or brace, the auger  350  may come into contact with straps or braces as the gutter cleaning robot  350  travels under the straps or braces. In order to ensure mobility, the auger  350  is preferably made of a material that deforms when it comes into contact with the type of strap or brace used to support the rain gutter  51 . 
     In  FIGS. 7A and 7B , a flail-type debris auger  350  includes several flexible protruding flails. When the flail-type debris auger  350  is rotated under the power of the debris auger motor  160 , the flails contact debris  91  and fling the debris  91  out of the gutter  51 . 
       FIGS. 8A and 8B  illustrate a brush-type debris auger  350  having several rows of bristles affixed to a central wire, similar to a pipe cleaner. The bristles rotate, thereby agitating debris  91  and moving it out of the gutter  51 . 
       FIGS. 9A and 9B  illustrate a flap-type debris auger  350  including flexible flaps centrally connected to a spool. The flaps may include a rubber or elastomeric material that adheres to debris  91 , to effectively grab the debris  91  and facilitate removal of the debris  91  from the gutter  51 . 
     A twisting flap-type debris auger  350  is shown in  FIGS. 10A and 10B . The twisting flap-type debris auger  350  may be similar to the flap-type debris auger  350  shown in  FIGS. 9A and 9B , differing in that the flaps are connected along a twisting path to the central spool rather than in a straight (parallel to the longitudinal axis) arrangement. 
       FIGS. 11A and 11B  illustrate a screw-type debris auger  350 . The screw-type debris auger  350  includes a conical spiral screw, similar to a drill bit, having screwed threading for effectively penetrating matted debris  91  and motivating loosened debris material out of the gutter  51 . 
     An irregular protrusion-type debris auger  350  is shown in  FIGS. 12A and 12B , having a hemispherical portion from which irregular finger-like protrusions extend to effectively seize chunks of debris  91 . The irregular protrusion-type debris auger  350  may have a form similar to a spaghetti mixer, as a non-limiting example. 
       FIGS. 13A and 13B  illustrate a horizontal tines-type debris auger  350  that has straight tines extending forward from a circular outer track. The tines, when revolving, can agitate large masses of debris  91 . 
       FIGS. 14A and 14B  illustrate an screw-and-flaps-type debris auger  350  combining the features of the screw-type debris auger  350  with the flaps of the flap-type debris auger  350 . Accordingly, the screw-and-flaps-type debris auger  350  can both penetrate matted debris  91  and also seize granular debris  91  that may be agitated loose from the matted debris  91  during a cleaning operation of the gutter cleaning robot  10 . 
     Although the debris augers shown in  FIGS. 7A through 14B  are illustrated as non-limiting examples, the varieties and types of debris augers are not limited thereto. As further non-limiting examples,  FIG. 20  illustrates a pneumatic debris auger  350  and  FIGS. 26A and 26B  illustrate a plow-type debris auger  350 . 
     The pneumatic-type debris auger  350  shown in  FIG. 20  includes a conical portion that may include screwed threading like the screw-type debris auger  350  shown in  FIGS. 11A and 11B , for example. In addition, the pneumatic-type debris auger  350  includes a hollow central passage  333  and openings  335  through which a fluid, such as pressurized gas (which may include air, nitrogen, helium, or any other suitable gas or combination of gases) or liquid may be passed. The pressurized air preferably emerges from the openings  335  at a velocity and rate of flow sufficient to agitate the debris  91 . Accordingly, the breaking up of matted or chunky debris  91  is further enhanced by the action of the pressurized gas. Alternatively, pressurized liquid—such as water—may instead be passed through the central passage  333  and openings  335 , and likewise applied to the debris  91 . The pressurized liquid may include any suitable liquid, such as water or an aqueous cleaning solution (for example, detergents or surfactants dissolved in water); furthermore, the liquid may be heated above the ambient temperature, in order to aid in the break-up of leaf resin or tar and to promote agitation of the debris  91 , for example. 
       FIGS. 26A and 26B  illustrate a plow-type debris auger  350  having a form similar to a cow-catcher. When the plow-type debris auger  350  is affixed to the gutter cleaning robot  10 , the gutter cleaning robot  10  pushes the debris  91  forward through the gutter  51  instead of ejecting the debris  91  out of the gutter  51 . This can be useful when the user prefers to avoid debris  91  from spilling onto a clean area of ground below the gutter  51 , for example. After the debris  91  is pushed to a more appropriate section of the gutter  51 , the user can exchange the plow-type debris auger  350  with another debris auger  350  for ejecting the debris  91 . 
     Also,  FIG. 21  illustrates various additional non-limiting examples of debris augers. 
     The debris auger  350  may be non-interchangeably connected to the gutter cleaning robot  10 , by forming the debris auger  350  integrally with the gutter cleaning robot  10  or by permanently affixing the debris auger  350  to the gutter cleaning robot  10  by welding or using adhesives, for example. Preferably, however, the debris auger  350  is detachably and interchangeably connectable to the gutter cleaning robot  10 . As shown in  FIG. 15 , the debris auger  350  may include a debris auger connector  310  disposed on a gutter cleaning robot  10 —facing end of the debris auger  350 . The debris auger connector  310  includes one or more concavities, such as first, second and third concavities  321 ,  322 ,  333 , for example. 
       FIG. 16  illustrates a conical screw-with-sweeping-flaps-type debris auger  351  having a debris auger connector  310  for interfacing with a corresponding robot connector  130  disposed on the gutter cleaning robot  10  (for example, the robot connector  130  may be provided as part of, and/or at the distal end of, the debris auger shaft  163 ). The robot connector  130  includes one or more protrusions, such as first, second and third protrusions  131 ,  132 ,  133  that each extend into a respective concavity  321 ,  322  or  323  in the debris auger connector  310 . 
     When the debris auger  351  is affixed to the gutter cleaning robot  10 , the protrusions of the robot connector  130  impart rotating force against the inner surfaces of the concavities of the debris auger connector  321 , thus motivating the debris auger  361 .  FIG. 17  shows another example, in which a flail-type debris auger  352  includes a debris auger connector  310 ; and  FIG. 18  illustrates an example of a flap-type debris auger  353  having a debris auger connector  310 . 
     In accordance with another embodiment, a shroud  315  may be provided surrounding the debris auger connector  310 . As shown in  FIG. 19 , the shroud  315  may extend outward from the surface onto which the debris auger connector  310  is disposed, so as to envelope or extend over the robot connector  130  when the debris auger  350  is connected to the gutter cleaning robot  10 . 
     The shroud  315  may further include an annular locking protrusion  316  extending partially inward toward the central longitudinal axis of the shroud  315 , with the robot connector  130  correspondingly including a locking collar concavity  138  disposed therealong. When the debris auger  350  having the shroud  315  is attached to the gutter cleaning robot  10 , the annular locking protrusion  316  flexibly extends into the locking collar concavity of the robot connector  130 , thus tending to retain the debris auger  350  in connection with the gutter cleaning robot  10  until force sufficient to dislodge the annular locking protrusion  316  out of the locking collar concavity  136  is applied to separate the debris auger  350  from the gutter cleaning robot  10 . 
       FIG. 23  illustrates a suspension of the gutter cleaning robot  10 . The rear wheels  175  are obliquely angled with regard to the vertical axis, in order to wedge the rear wheels  175  against the side and/or bottom surfaces of the gutter and improve tractional contact therebetween. Also, a spring suspension may further be provided to permit the rear wheels  175  (driven by the drive motor  170 ) to remain in frictional contact with the gutter  51  even when the main body  101  is jolted during a cleaning operation. Accordingly, even when the gutter cleaning robot  10  encounters a section of gutter  51  having a hole at the bottom where the drain spout  52  connects to the gutter  51 , the gutter cleaning robot  10  can nonetheless safely traverse the hole. 
     In accordance with another embodiment, the gutter cleaning robot  10  may include a debris auger shaft  163  that extends both to the front and rear end portions of the main body  101 . Accordingly, as illustrated in  FIG. 25 , a debris auger  350  may be affixed to either end (or even both ends simultaneously) of the gutter cleaning robot  10 . Accordingly, in this embodiment, the user can detach the debris auger  350  from one end of the gutter cleaning robot  10  and attach it to the opposite end, without having to remove the gutter cleaning robot  10  from the rain gutter  51 , for example. 
     As shown in  FIG. 27 , the debris auger connector  310  may include a single concavity  324  that preferably has an outline suitable for imparting rotational force to the debris auger connector  310 . The debris auger connector  310  in the example of  FIG. 27  has a hexagonal concavity  324 .  FIG. 28  illustrates a robot connector  130  that has a single hexagonal protrusion for inserting into the hexagonal concavity  324  of the debris auger connector  310 . 
     The gutter cleaning robot  10  may operate entirely under the control of the user using a remote control  6 ; alternatively, the gutter cleaning robot  10  may operate autonomously or semi-autonomously. For example, the gutter cleaning robot  10  may include an on-board controller that executes a control routine for modulating the forward motion of the gutter cleaning robot  10  through the gutter  51 . The gutter cleaning robot  10  may include sensors and monitors, such as an ammeter for monitoring the drive current provided to the drive motor  160  and/or the debris auger  350  current provided to the debris auger motor  170 . 
       FIG. 29  illustrates a method for controlling the drive motor  160  and the debris auger motor  170  in response to a mechanical drive resistance as ascertained by an ammeter monitoring the drive current supplied to the drive motor  160 . At step  2901 , the routine ascertains the drive current from the ammeter (for example, by reading a memory-mapped register that is updated by the ammeter). If step  2902  determines that the drive current exceeds a deadlock threshold current value (which corresponds to a drive current high enough to indicate that the gutter cleaning robot  10  is futilely attempting to proceed against an obstacle that prevents any forward motion by the gutter cleaning robot  10 ), then step  2903  halts both the drive motor  160  and the debris auger motor  170  in order to prevent burnout or damage to the gutter cleaning robot  10  or debris auger  350 . 
     Otherwise, step  2904  determines whether the drive current exceeds a bogged threshold (that is, a threshold current value corresponding to a state in which the gutter cleaning robot  10  can proceed, but only slowly because of copious debris  91  in the gutter  51 , referred to as being “bogged”). If not, the routine returns to step  2901 ; otherwise, step  2905  reduces the commanded drive speed of the drive motor  160 . 
     Accordingly, the example method illustrated in  FIG. 29  monitors the drive current and appropriately responds to obstacles or resistance encountered when traversing the gutter  51 —if the gutter cleaning robot  10  is entirely prevented from moving forward, then the gutter cleaning robot  10  is halted so that the user can remedy the situation; if instead the gutter cleaning robot  10  is moving forward, albeit slowly, then the gutter cleaning robot  10  reduces the commanded velocity of traversal. 
     The gutter cleaning robot  10  may perform an escape behavior when triggered by appropriate sensor conditions. For example, the operating speed and/or direction of the drive motor  170  and/or the auger motor  160  may be repeatedly or cyclically shifted, in order to agitate or break free of an obstacle. Tables 1 illustrates various current sensor conditions and example escape behavior responses: 
     
       
         
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Circumstances 
                 Drive Motor Current 
                 Auger Motor Current 
                 Action/Response 
               
               
                   
               
             
             
               
                 Auger and Wheels stuck 
                 current > TH 
                 current > TH 
                 Spin both the wheels and 
               
               
                   
                   
                   
                 the auger quickly in a 
               
               
                   
                   
                   
                 direction opposite to the 
               
               
                   
                   
                   
                 direction of movement 
               
               
                 Auger is stuck 
                 current <= TH 
                 current > TH 
                 Spin the auger quickly in a 
               
               
                   
                   
                   
                 direction opposite to the 
               
               
                   
                   
                   
                 direction of movement 
               
               
                 Wheels are stuck 
                 current > TH 
                 current <= TH 
                 Spin the wheels quickly in a 
               
               
                   
                   
                   
                 direction opposite to the 
               
               
                   
                   
                   
                 direction of movement 
               
               
                   
               
             
          
         
       
     
     When the gutter cleaning robot  10  has already performed an escape behavior but the triggering sensor conditions have not been resolved after an appropriate length of time, the gutter cleaning robot  10  may then perform a panic behavior as a second level response. Table 1 illustrates example panic behaviors that may be performed in response to various conditions: 
     
       
         
               
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                   
                 Drive Motor 
                 Auger Motor 
                   
                   
               
               
                 Circumstances 
                 Current 
                 Current 
                 Previous Behaviors Used 
                 Present Action/Response 
               
               
                   
               
             
             
               
                 Auger/Wheels stuck 
                 current > TH 
                 current > TH 
                 Behavior: Spinning both the 
                 Power down the device and 
               
               
                   
                   
                   
                 wheels and the auger quickly in a 
                 alert the user. 
               
               
                   
                   
                   
                 opposite direction. 
               
               
                   
                   
                   
                 Duration: Executed six times- 
               
               
                   
                   
                   
                 three times forward and three 
               
               
                   
                   
                   
                 times backward. 
               
               
                 Auger is stuck 
                 current <= TH 
                 current > TH 
                 Behavior: Spinning the auger 
                 Spin the drive motor in an 
               
               
                   
                   
                   
                 quickly in an opposite direction. 
                 opposite direction. Then spin 
               
               
                   
                   
                   
                 Duration: Executed six times- 
                 the auger motor in 10 quick 
               
               
                   
                   
                   
                 three times forward and three 
                 bursts of forward and backward 
               
               
                   
                   
                   
                 times backward. 
                 movement. 
               
               
                 Wheels are stuck 
                 current > TH 
                 current <= TH 
                 Behavior: Spinning the wheels 
                 Power down the device and 
               
               
                   
                   
                   
                 quickly in an opposite direction. 
                 alert the user. 
               
               
                   
                   
                   
                 Duration: Executed six times- 
               
               
                   
                   
                   
                 three times forward and three 
               
               
                   
                   
                   
                 times backward.