Abstract:
A method is disclosed for a robotic vehicle to climb a step. The robotic vehicle uses tracked flippers to engage the top of the step and drives with additional tracks other than the tracked flippers. The robotic vehicle also shifts and tilts a payload in order to move the CG of the payload ahead of the vehicle chassis and past the edge of the step.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This U.S. patent application is a continuation of U.S. application Ser. No. 11/762,315, filed Jun. 13, 2007 now U.S. Pat. No. 7,891,446 which claims priority to a U.S. provisional patent application 60/828,606 filed on Oct. 6, 2006, the entire contents of which are hereby incorporated by reference. 
    
    
     STATEMENT AS TO FEDERALLY SPONSORED RESEARCH 
     This invention was in part with Government support under contract N41756-06-C-5512 awarded by the Technical Support Working Group of the Department of Defense. The Government may have certain rights in the invention. 
    
    
     TECHNICAL FIELD 
     This disclosure relates to robotic vehicles. 
     BACKGROUND 
     A new generation of robotic systems and tools is required to meet the increasing terrorist threat in the US and abroad. The lack of adaptability and limited capability of existing remote controlled systems available to Hazardous/First Response/Explosive Ordnance Disposal (EOD) teams has frustrated many teams worldwide. The unique and often dangerous tasks associated with the first responder mission require personnel to make quick decisions and often adapt their tools in the field to combat a variety of threats. The tools must be readily available, robust, and yet still provide surgical precision when required. 
     SUMMARY 
     According to one aspect of the disclosure, a robotic vehicle includes a chassis having front and rear ends and supported on right and left driven tracks, each track trained about a corresponding front wheel rotatable about a front wheel axis. Right and left elongated flippers are disposed on corresponding sides of the chassis and operable to pivot about the front wheel axis of the chassis, each flipper having a driven track about its perimeter. A linkage connects a payload deck assembly, configured to support a functional, securely mounted and integrated payload (in some cases, modular payloads, unconnected payloads and/or functional payload), to the chassis. The linkage has a first end rotatably connected to the chassis at a first pivot, and a second end rotatably connected to the deck at a second pivot. Both of the first and second pivots include independently controllable pivot drivers operable to rotatably position their corresponding pivots to control both fore-aft position (as well as vertical position, the pivots being interconnected by a linkage that makes a swept motion) and pitch orientation of the payload deck assembly with respect to the chassis. In one example, the first pivot is rotatable through an angle of at least 180 degrees. The first pivot is not necessarily limited by a range of motion of the pivot, but rather by those positions in which the linkage, deck assembly, or payload interfere with part of the robot such as the chassis or with the ground—which may depend on the character of the ground and pose of the robot. Accordingly, in another implementation, the sweep of the linkage is limited by the chassis of the robot, which is configured as small tube element connecting chassis arms. The deck assembly and linkage may sweep between the chassis arms and between the flippers in either direction, and may sweep past a horizontal line defined by one chassis track wheel and bogey, in either direction fore or aft of the pivot. In another implementation, the sweep is limited to 74 degrees to improve stability and shock resistance on open ground. In each case, the payload deck assembly, with or without payload(s), may be tilted to move the center of gravity of the robot further in a desired direction. The linkage may comprise two parallel links spaced apart laterally. 
     The independently controllable pivot drivers provide both fore-aft position (and a wide sweep range) and pitch orientation of the payload deck assembly with respect to the chassis to selectively displace a center of gravity of the payload deck assembly both forward and rearward of a center of gravity of the chassis. This provides enhanced mobility to negotiate obstacles. Hereinafter, center of gravity or center of mass may be abbreviated “CG.” 
     Rotation of the linkage about its first and second pivots enables selective positioning of a center of gravity or center of mass of the payload deck assembly both fore and aft the front wheel axis as well as both fore and aft of a center of gravity of the chassis. In one implementation, the first pivot of the linkage is located above and forward of the front wheel axis and swings the linkage for displacing the center of gravity of the payload deck assembly to a desired location. Furthermore, when the first end of the linkage is rotatably connected near the front of the chassis, the payload deck assembly is displaceable to an aftmost position in which the payload deck assembly is located within a footprint of the chassis. 
     In one example, the payload deck assembly includes connection points for both a functional payload power link and a functional payload communication link, which may comprise an Ethernet link. In one implementation, the functional payload communication link is a packet switched network connectable to a distribution switch or router. 
     The payload deck assembly includes an electronics bin (also “CG tub”) which holds most of the electronics of the robot (as well as the upper motor(s) for tilting the paylaod deck assembly, but excepting motor control and drivers for the drive motors, which is housed in the chassis), and supports a dockable battery unit slid into the bottom of the electronics bin as well as a accepting a modular payload deck, which defines threaded holes to accept functional payloads and includes multiple functional payload connection pads positioned to accommodate selective connection of multiple functional payload units to the payload deck. Each connection pad includes connection points for both functional payload power and functional payload communication (as well as sufficient hard points nearby for such payloads to be secured to the deck with sufficient fasteners to reliably secure the mass of the payload through tilting operations of the deck). The payload deck can accept as a payload unit a removable radio receiver unit (which can communicate with a remote controller unit) operably connected to a drive system of the chassis. A battery unit is also removable secured to the bottom of the deck, so as to place the significant weight of batteries as low as possible in the mass that is used for shifting the center of gravity of the vehicle. In one example, the payload deck constitutes between about 30 and 50 percent of a total weight of the vehicle. The payload deck may also accept an Ethernet camera as a payload unit. 
     In one implementation, the payload deck further accepts as payload units removable sensor units. The sensor may be, for example, infrared, chemical, toxic, light, noise, and weapons detection. 
     The left and right flippers comprise elongated members, wherein flipper tracks are trained about corresponding rear wheels independently rotatable about the front wheel axis. 
     The robotic vehicle can climb a step by using the independently controllable pivot drivers to control both sweep and pitch orientation of the payload deck assembly with respect to the chassis to selectively displace the center of gravity of the payload deck assembly the both forward and rearward of the center of gravity of the chassis. The robotic vehicle may initiates a step climb by pivoting the first and second flippers upward to engage the edge of the step. Different obstacles can be accommodated by different strategies that use the full range of the sweepable and tiltable CG of the entire payload deck assembly, or of the payload deck assembly when combined with a payload. An advantage of the disclosed system is that the addition of payload weight on the payload deck assembly increases the flexibility and mobility of the robot with respect to surmounting obstacles of various shapes. The robotic vehicle also positions the center of gravity of the payload deck assembly above the front end of the chassis. Next, the robotic vehicle pivots the first and second flippers downward on the edge of the step to engage the top of the step and drives forward. The robotic vehicle continues to displace the center of gravity of the payload deck assembly beyond the front of the chassis by rotating both the first and second pivots. As shown in  FIG. 14 , tilting the deck assembly further advances the center of gravity of the entire vehicle. Finally, the robotic vehicle drives forward to pull the chassis over the edge of the step. 
     In another aspect of the disclosure, a skid steered robot includes a chassis supporting a skid steered drive and a set of driven flippers, each flipper being pivotable about a first pivot axis common with a drive axis of the chassis. A linkage substantially at the leading end of the chassis is pivotable about a second pivot axis. A deck assembly is pivotable about a third pivot axis substantially at a distal end of the linkage. The deck assembly includes a power supply, a packet network connection, a modular deck support structure; and a modular deck. The modular deck includes a deck mount which fits the modular deck support structure and at least two externally available common connectors. At least one of the deck assembly or modular deck includes a power supply switching circuit that switches available power from the power supply between the at least two common connectors, and a network switch that switches packet network traffic between the at least two common connectors. 
     In another aspect of the disclosure, a skid steered robot includes a set of driven flippers, each flipper being pivotable about a first pivot axis common with a drive axis of the chassis. A deck assembly, disposed above the chassis, includes a power supply, a packet network connection, a modular deck support structure, a deck wiring harness connector including packet network cabling and power cabling, and a modular deck. The modular deck includes a deck mount which fits the modular deck support structure, at least two externally available common connectors, a power supply switching circuit that switches available power from the power supply between at least two common connectors, a network switch that switches packet network traffic between the at least two common connectors, and a deck wiring harness that connects to the deck wiring harness connector and carries power and network to and from the modular deck. 
     In another aspect of the disclosure, a modular deck for a robotic vehicle includes a base configured to be secured to the vehicle, wherein the base receives both a power link and a communication link from the robotic vehicle. A platform configured to support a removable functional payload is secured to the base and has at least one connection point for both a functional payload power link and a functional payload communication link. The connection point is linked to both the base power link and the base communication link. 
     The details of one or more implementations of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view of a robotic vehicle. 
         FIG. 2  is an exploded view of the robotic vehicle. 
         FIG. 3  is a front view of the robotic vehicle. 
         FIG. 4  is a back view of the robotic vehicle. 
         FIG. 5  is a top view of the robotic vehicle. 
         FIG. 6  is a bottom view of the robotic vehicle. 
         FIG. 7  is an exploded perspective view of the robotic vehicle. 
         FIG. 8  is a side view of the robotic vehicle. 
         FIG. 9  is an side view of the robotic vehicle. 
         FIG. 10  is a perspective view of a payload deck for a robotic vehicle. 
         FIG. 11  is a perspective view of a payload deck for a robotic vehicle. 
         FIG. 12  is a perspective view of a payload deck for a robotic vehicle. 
         FIG. 13  is a perspective view of the robotic vehicle with a manipulator arm. 
         FIGS. 14-17  are side views of a robotic vehicle climbing. 
         FIGS. 18-21  are side views of a robotic vehicle climbing. 
         FIG. 22  is a side view of a robotic vehicle climbing stairs. 
         FIG. 23  is a front view of a robotic vehicle traversing an incline. 
         FIG. 24  is a perspective view of a robotic vehicle in a neutral posture. 
         FIG. 25  is a perspective view of a robotic vehicle in a standing posture. 
         FIG. 26  is a perspective view of a robotic vehicle in a kneeling posture. 
         FIG. 27  is a perspective view of a robotic vehicle in a kneeling posture. 
         FIG. 28  is a side view of a robotic vehicle. 
     
    
    
     Like reference symbols in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , a robotic vehicle  10 , in one implementation, is a remotely operated vehicle that enables the performance of manpower intensive or high-risk functions (i.e., explosive ordnance disposal; urban intelligence, surveillance, and reconnaissance (ISR) missions; minefield and obstacle reduction; chemical/toxic industrial chemicals (TIC)/toxic industrial materials (TIM); etc.) without exposing operators directly to a hazard. These functions often require the robotic vehicle  10  to drive quickly out to a location, perform a task, and either return quickly or tow something back. The robotic vehicle  10  is operable from a stationary position, on the move, and in various environments and conditions. 
     Referring to  FIGS. 1-6 , a robotic vehicle  10  includes a chassis  20  that is supported on right and left drive track assemblies,  30  and  40  respectively, having driven tracks,  34  and  44  respectively. Each driven track  34 ,  44 , is trained about a corresponding front wheel,  32  and  42  respectively, which rotates about front wheel axis  15 . Right and left flippers  50  and  60  are disposed on corresponding sides of the chassis  20  and are operable to pivot about the front wheel axis  15  of the chassis  20 . Each flipper  50 ,  60  has a driven track,  54  and  64  respectively, about its perimeter that is trained about a corresponding rear wheel,  52  and  62  respectively, which rotates about the front wheel axis  15 . 
     Referring to  FIG. 7 , in one implementation, the robotic vehicle  10  includes right and left motor drivers,  36  and  46 , driving corresponding drive tracks,  34  and  44 , and flipper tracks,  54  and  64 , which are supported between their front and rear ends by bogie wheels  28 . A flipper actuator module  55  is supported by the chassis  20  and is operable to rotate the flippers,  50  and  60 . In one example, the flippers  50 ,  60  are actuated in unison. In other examples, the flippers  50 ,  60  are actuated independently by right and left flipper actuators  55 . 
     Referring to  FIG. 8 , a linkage  70  connects the payload deck assembly  80  to the chassis  20 . The linkage  70  has a first end  70 A rotatably connected to the chassis  20  at a first pivot  71 , and a second end  70 B rotatably connected to the payload deck  80  at a second pivot  73 . Both of the first and second pivots,  71  and  73  respectively, include respective independently controllable pivot drivers,  72  and  74 , operable to rotatably position their corresponding pivots to control both fore-aft position and pitch orientation of the payload deck assembly  80  with respect to the chassis  20 . As shown in  FIGS. 1-2 , the linkage  70  may comprise two parallel links spaced apart laterally. 
     Referring to  FIG. 9 , the first end  70 A of the linkage  70  is rotatably connected near the front of the chassis  20  such that the payload deck assembly  80  is displaceable to an aftmost position in which the payload deck assembly  80  is located within a footprint of the chassis  20 . Furthermore, as shown in  FIGS. 1-2 , the first pivot  71  of the linkage  70  is located above and forward of the front wheel axis  15 . The first pivot  71  is rotatable through an angle of at least 180 degrees (optionally, 74 degrees), in one example. Rotation of the linkage  70  about its first and second pivots,  71  and  73  respectively, enables selective positioning of center of gravity  410  of payload deck assembly  80  both fore and aft front wheel axis  15  as well as both fore and aft a center of gravity  400  of the chassis  20 . In another example, the independently controllable pivot drivers  72 ,  74  provide both fore-aft position (as part of sweep) and pitch orientation of the payload deck assembly  80  with respect to the chassis  20  to selectively displace the center of gravity  410  of the payload deck assembly  80  both forward and rearward of the center of gravity  400  of the chassis  20 , displacing a center of gravity  450  of the entire robot  10 . 
     The robotic vehicle  10  is electrically powered (e.g. a bank of nine standard military BB- 2590  replaceable and rechargeable lithium-ion batteries). Referring to  FIGS. 2-3 , the payload deck assembly  80 , specifically the electronics tub  90 , accommodates a slidable, removable battery unit  92 . Skid pad  94 , as shown in  FIG. 6 , may be secured to the bottom of the battery unit  92  to protect the battery  92  and aid manageability. The payload deck assembly  80  may carry an additional battery supply on one of the selectable connection pads  810 , increasing the available power capacity (e.g. an additional bank of nine batteries may be carried on payload deck). 
     Referring again to  FIGS. 2-6 , a payload deck assembly  80 , including an electronics bin  90  and payload deck  806  (D 1 , D 2 , D 3  in other drawings herein), is configured to support a removable functional payload  500 .  FIGS. 3-4  illustrate the robotic vehicle  10  with the payload deck assembly  80  including front and rear functional payload power connectors,  200  and  210 , and a user interface panel  220 .  FIG. 2  illustrates one example where the payload deck assembly  80  includes front and rear sensor pods,  240  and  250  respectively. In some implementations, the sensor pods  240 ,  250  provide infrared, chemical, toxic, light, noise, and weapons detection, as well as other types of sensors and detection systems. A primary driving sensor may be housed in a separate audio/camera sensor module mounted to the payload deck assembly  80  that contains at least one visible spectrum camera. Audio detection and generation is realized using an audio/camera sensor module mounted to the payload deck assembly  80 , in one example. 
     In some implementations, robotic vehicle  10  tows a trailer connected to rear payload connector  290 , as shown in  FIG. 5 . Exemplary payloads for the trailer include a small generator, which significantly extends both range and mission duration of robotic vehicle, field equipment, and additional functional payload units  500  attachable to the payload deck assembly  80 . 
     The payload deck assembly  80  accepts the mounting of one or more functional payload modules  500  that may include robotic arms, chemical, biological and radiation detectors, and a sample container. The robotic vehicle  10  automatically detects the presence and type of an installed functional payload  500  upon start-up. Referring to  FIG. 5 , the payload deck  806  defines threaded holes  808  to accept a functional payload  500 .  FIG. 5  also illustrates one or more functional payload connection pads  810  positioned on the payload deck assembly  80  to accommodate selective connection of multiple functional payload units  500 . Each functional payload connection pad  810  delivers power, ground and communications to a functional payload unit  500 . For example, robotic vehicle  10  may provide up to 300 W (threshold), 500 W (goal) of power to a payload  500  at 42V, up to 18 A. The communication link may include Ethernet link communications. In one example, payload deck assembly  80  constitutes between about 30 and 70 percent of the vehicle&#39;s total weight. The payload deck assembly  80  further includes a removable controller unit  350  operably connected to a drive system (e.g. the motor drivers  36 ,  46 ) of the chassis  20 . The robotic vehicle  10  communicates with an operator control unit (OCU) through optional communication functional payload module(s)  500 . The robotic vehicle  10  is capable of accepting and communicating with a radio functional payload module  500 . 
     Referring to  FIGS. 10-12 , modular decks D 1 , D 2 , D 3  are removable payload decks  806  modularly secured to the electronics bin  90  to form the payload deck assembly  80 . The modular decks D 1 , D 2 , D 3  maintain connectivity to functional payloads  500  located on the decks D 1 , D 2 , D 3  while allowing interchangeability with a payload deck assembly base. The modular decks D 1 , D 2 , D 3  receive power and communication from a deck connector  802  attached by a wiring harness  804 .  FIG. 10  depicts a development deck D 1  including sparsely spaced connector pads  806 .  FIG. 11  depicts a mule deck D 2  including netting for carrying loads and at least one connector pad.  FIG. 12  depicts a manipulator deck D 3  including an integral bracing for a large manipulator arm. The integral bracing  810  housing at least one connector pad. The connectors pads  810  available on the decks D 1 , D 2 , D 3  each carry 42V, up to 18 A power; ground; and Ethernet, for example. FET switches connected to each connector pad  810  are overload protected and are controlled by a digital signal processor (DSP) on the deck to distribute power. The DSP is controlled via a controller area network (CAN) bus, a known industrial and automotive control bus. 
       FIG. 13  illustrates a robotic arm module  600  as a functional payload  500  attached to the payload deck assembly  80 . The robotic arm module  600  provides full hemispherical reach (or more, limited only by interference; or less, limited by other needs of the robot  10 ) around the robotic vehicle  10 . The robotic arm module  600  provides lifting capacity and an additional means for shifting the robotic vehicle&#39;s center of gravity  450  forward, e.g. when ascending steep inclines, and rearward, e.g. for additional traction. 
     The robotic vehicle  10  may sense elements of balance through the linkage  70  (e.g., via motor load(s), strain gauges, and piezoelectric sensors), allowing an operator or autonomous dynamic balancing routines to control the center of gravity  410  of the payload deck assembly  80  and the center of gravity  430  of the linkage  70  for enhanced mobility, such as to avoid tip over while traversing difficult terrain. 
       FIGS. 14-17  illustrate the robotic vehicle  10  climbing a step by using the independently controllable pivot drivers  72  and  74  to control both fore-aft position and pitch orientation of the payload deck assembly  80  with respect to the chassis  20  to selectively displace the center of gravity  410  of the payload deck assembly  80  both forward and rearward of the center of gravity  400  of the chassis  20 . Referring to  FIG. 14 , in step  51 , the robotic vehicle  10  initiates step climbing by pivoting the first and second flippers  50  and  60 , respectively, upward to engage the edge  902  of the step  900 . The robotic vehicle  10  also positions the center of gravity  410  of the payload deck assembly  80  above the front end of chassis  20 . Next, as shown in  FIGS. 15-16 , in steps S 2  and S 3 , the robotic vehicle  10  pivots the first and second flippers  50  and  60  downward on the edge  902  of the step  900  to engage the top  904  of the step and drives forward. In  FIG. 15 , illustrating step S 2 , the payload deck assembly  80  is further tilted to advance the center of gravity  450  of the robot  10  (permitting higher obstacles to be climbed). In step S 3 , the robotic vehicle  10  continues to displace the center of gravity  410  of the payload deck assembly  80  beyond the front of the chassis  20 , as shown in  FIG. 16 , by rotating both the first and second pivots,  71  and  73  respectively. Finally, in step S 4 , as shown in  FIG. 17 , the robotic vehicle  10  drives forward to pull the chassis  20  over the edge  902  of the step  900 .  FIGS. 18-21  illustrates the robotic vehicle  10  initiating and completing steps S 1 -S 4  for obstacle climbing with a functional payload  500  secured to the payload deck assembly  80 . 
     In some implementations, the robotic vehicle  10  is configured to negotiate obstacles, curbs and steps having a height of about 0.3 m (12 inches), and across a horizontal gap of about 0.61 m (24 inches). The robotic vehicle  10  has side-to-side horizontal dimensions smaller than standard exterior doorways (e.g. 32 inches) and interior doors (e.g. 30 inches). Referring to  FIGS. 22-23 , the robotic vehicle  10  is configured as to ascend and descend a flight of stairs having up to a climb angle, β, of about 37 degrees, as well as climb and descend an inclined slope, including stopping and starting, on a hard dry surface slope angle, β, of about 50 degrees. Similarly, the robotic vehicle  10  is physically configured as described herein to climb and descend, including stopping and starting, an inclined grass covered slope having an angle, β, of about 35 degree grade. The robotic vehicle  10  is configured to laterally traverse, including stopping and starting, on a grass slope angle, φ, of about 30 degrees. Furthermore, the robotic vehicle  10  is configured to maneuver in standing water (fresh/sewage) having a depth of about 0.3 m (12 inches) and maintain a speed of about 20 kph (12 mph) on a paved surface, and about 8 kph (5 mph) through sand and mud. 
     The robotic vehicle  10  supports assisted teleoperation behavior, which prevents the operator from hitting obstacles while using on board obstacle detection/obstacle avoidance (ODOA) sensors and responsive ODOA behaviors (turn away; turn around; stop before obstacle). The robotic vehicle  10  assumes a stair climbing pose, as illustrated in  FIG. 13 , or a descending preparation pose (similar to the pose shown in  FIG. 13 , but with the flippers  50 ,  60  pointing downward) when a stair climbing or stair descending assist behavior is activated, respectively. The robotic vehicle  10  stair climbing behaviors can be configured to control (tilt) the flippers  50 ,  60  and control the position of the center of gravity shifter  70  as the robot  10  negotiates stairs. A stair climbing assist behavior keeps the robotic vehicle  10  on a straight path up stairs and, in one example, may maintain a roll angle of about zero degrees. 
     The robotic vehicle&#39;s  10  control software provides autonomous capabilities that include debris field mapping, obstacle avoidance, and GPS waypoint navigation. The robotic vehicle  10  can determine position via a global positioning system (GPS) receiver, housed in a separate sensor module  500 . 
     The robotic vehicle  10  is fully operational after exposure to a temperature range of about −40° C. to about 71° C. (−40° F. to 160° F.) in a non-operating mode and is fully operational in a temperature range of about −32° C. to about 60° C. (−26° F. to 140° F.). The robotic vehicle operates during and after exposure to relative humidity up to about 80 percent, in varied weather conditions. The robotic vehicle  10  also operates during and after exposure to blowing sand and/or rain, freezing rain/ice, and in snowfall up to about 0.1 m (4 inches) in depth. 
     Referring to  FIGS. 24-28 , the robotic vehicle  10  may exhibit a variety of postures or poses to perform tasks and negotiate obstacles. The linkage  70  together with the deck assembly  80 , chassis  20 , and flippers  50 ,  60  all move to attain a number of standing postures.  FIG. 24  depicts robotic vehicle  10  in a neutral posture.  FIG. 25  depicts the robotic vehicle  10  in one standing posture wherein the distal end of flippers  50  and  60  approaches the leading end of the chassis  20  to form an acute angle between the flippers  50  and  60  and the chassis  20 . The linkage  70  is entirely above a common axis  15  of the flippers  50  and  60  and the chassis  20 . In one example, the deck assembly  80  tilts independently with respect to the robotic vehicle  10 . The acute angle achieved between the flippers  50  and  60  and the chassis  20  varies the standing positions without changing the orientation of the deck assembly  80  with respect to the ground. In some examples, the linkage  70  is positionable at least parallel to an imaginary line between the distal and pivot ends of flippers  50  and  60 . In additional examples, the second end  70 B of the linkage  70  is positionable below an imaginary line between the distal and pivot ends of flippers  50  and  60 . In another implementation, the linkage  70  together with the deck assembly  80 , chassis  20 , and flippers  50  and  60  can move to attain a first kneeling position, as shown in  FIG. 26 , and a second kneeling position, as shown in  FIG. 27 . 
       FIG. 28  illustrates an implementation of centers of gravity of a robotic vehicle  1000  and distances between them. The locations of the centers of gravity within the chassis  20 , deck  80 , linkage  70 , and flippers  50  and  60  and with respect to each other individually may be varied to attain a number of advantages in terms of maneuverability and the ability to perform certain tasks. 
     There are several advantages to the present “two-bar” linkage  70  (having independent, powered pivots  71 ,  73  at the deck assembly end  70 B and the chassis end  70 A of the linkage  70 ) with respect to other structures for shifting a center of gravity. 
     For example, a robot equipped with a “two-bar” linkage  70  can scale higher obstacles relative to a robot without such a linkage. In order to do so, the deck assembly  80  is tilted and/or pivoted further forward, moving the overall center of gravity  450  higher and farther forward. A robot equipped with the two-bar linkage  70  can scale higher obstacles when bearing a payload  500  on top of the deck assembly  80  than without a payload  500 . A high, heavy payload  500  can be tipped with the two-bar linkage  70  to provide a more pronounced shift of the center of gravity  450  forward than an empty deck assembly  80 . The two bar linkage  70  may raise the deck assembly  80  and an attached a sensor pod module  500  higher in a standing position, as shown in  FIG. 25 , even with a level deck, because the linkage  70  is connected at one point  73  at the top of the range and also at one point  71  at the bottom of the range. This is valuable because the linkage  70  may place a sensor such as a camera, perception sensor (e.g., laser scanner) or payload sensors  500  relatively higher. Other linkage systems may require connection at more than one point, which may limit the height and/or may also tilt the deck assembly  80  at the highest position while in the standing position. 
     A two bar linkage  70  has a theoretical pivot range, limited only by interference with other parts of the robot, of greater than 180 degrees. If positioned concentrically with the flipper-chassis joining axis  15 , the linkage rotation range could be 360 degrees. Other constraints designed herein and other advantages obtainable in other positions can change this. For example, if the first pivot  71  of the linkage  70  is positioned above and forward of the common chassis-flipper axis  15  (e.g., about 20 mm forward and about 70 mm above), it is possible to have a unitary structure for the chassis  20  (casting). 
     A straight shaft may join both flippers  50 , 60  directly, allowing the bottom pivoting actuator  72  to be placed off center with the flipper actuator  55 . Additional pivot range past 180 degrees may be obtained, as with additional standing height, by increasing the distance between the first pivot  71  and the common chassis-flipper axis  15 . 
     Other systems may have a range of considerably less than 180 degrees, for example if the parts of such systems are limited in a pivoting or movement range by interference among the system members. Still further, a two bar linkage has a longer effective forward extending range, since the linkage  70  is substantially stowable to the chassis  20 . The distance between more than one chassis connections of the other systems may shorten the effective forward extending range. As one additional advantage, a deck-side actuator  74  of the two-bar linkage  70  can be used to “nod” (auxiliary scan) a scanning (main scanning) sensor such as a 2D LADAR or LIDAR to give a 3D depth map. 
     Other robotic vehicle details and features combinable with those described herein may be found in a U.S. patent application Ser. No. 11/842,868, now U.S. Pat. 7,654,348 entitled “MANEUVERING ROBOTIC VEHICLES HAVING A POSITIONABLE SENSOR HEAD”, which claims priority to a Provisional application filed Oct. 6, 2006, entitled “MANEUVERING ROBOTIC VEHICLES” and assigned Ser. No. 60/828,611, the entire contents of which are hereby incorporated by reference. 
     A number of implementations of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, flippers of varied length and payload decks with other means of functional payload attachment, such as snap-on, clamps, and magnets. Accordingly, other implementations are within the scope of the following claims.