The two most common modes of locomotion used by humans are legged mode and wheeled mode, the former an inherent gift while the latter being an ingenious invention on their part. While both have their advantages, they may fall short in some aspects for instance, legs may fail in terms of high speeds and wheels might prove not so handy in the more demanding and uneven terrains Thus, a leg-wheel hybrid platform promises to ensure both high speeds and good stability on a variety of terrains 

JAISWAL, GAURAV KUMAR

UPADHYAY, HARSHAL

English

Interscience Research Network

International Journal of Instrumentation Control and Automation Volume 1 Issue 4 Article 9 January 2012 MECHANICAL DESIGN OF A LEGGED-WHEEL HYBRID QUADRUPED ROBOT FOR MULTI-TERRAIN NAVIGATION HARSHAL UPADHYAY School Of Mechanical & Building Sciences, VIT University, Vellore, India, harshal91upadhyay@gmail.com GAURAV KUMAR JAISWAL School Of Mechanical & Building Sciences, VIT University, Vellore, India, grvkjaiswal@gmail.com Follow this and additional works at: https://www.interscience.in/ijica  Part of the Aerospace Engineering Commons, and the Mechanical Engineering Commons Recommended Citation UPADHYAY, HARSHAL and JAISWAL, GAURAV KUMAR (2012) "MECHANICAL DESIGN OF A LEGGED-WHEEL HYBRID QUADRUPED ROBOT FOR MULTI-TERRAIN NAVIGATION," International Journal of Instrumentation Control and Automation: Vol. 1 : Iss. 4 , Article 9. DOI: 10.47893/IJICA.2012.1048 Available at: https://www.interscience.in/ijica/vol1/iss4/9 This Article is brought to you for free and open access by the Interscience Journals at Interscience Research Network. It has been accepted for inclusion in International Journal of Instrumentation Control and Automation by an authorized editor of Interscience Research Network. For more information, please contact sritampatnaik@gmail.com. Mechanical Design Of A Legged-Wheel Hybrid Quadruped Robot For Multi-Terrain Navigation   MECHANICAL DESIGN OF A LEGGED-WHEEL HYBRID QUADRUPED ROBOT FOR MULTI-TERRAIN NAVIGATION  HARSHAL UPADHYAY1 & GAURAV KUMAR JAISWAL2  1,2School Of Mechanical & Building Sciences, VIT University, Vellore, India Email:harshal91upadhyay@gmail.com, grvkjaiswal@gmail.com   Abstract : The two most common modes of locomotion used by humans are legged mode and wheeled mode, the former an inherent gift while the latter being an ingenious invention on their part. While both have  their advantages, they may fall short in some aspects for instance, legs may fail in terms of high speeds and wheels might prove not so handy in the more  demanding and uneven terrains  Thus, a leg-wheel hybrid platform promises to ensure both high speeds and good stability on a variety of terrains .    1.  INTRODUCTION    Based on the combination of the two modes(legged and wheeled) of operation many robots have been built in order to optimise the performance in terms of speeds and  stability. One of  such examples is  Stair-climbing robot Zero Carrier [1] with eight legs having four active and four passive legs designed to provide mobility on plain surfaces. Similarly [2] “Wheeleg” employs 2 3-DOF front legs which are pneumatically actuated along with 2 independent rear wheels  and Chariot III [8] has two big wheels and four 3-DOF legs for similar functioning.  Quadruped design is also a very popular choice for the design of such robots because of the stability it provides to the robot given its inherent    symmetry. Robot PAW [5] has four active wheels installed on the ends of its legs of the original quadruped Scott II and so do  the robots Walk’n Roll [6] and Hylos [7]  (with  active 2-DOF suspension mechanisms). Also  there are robots built with transition mechanism between wheeled and legged mode to facilitate the aforementioned optimization.  For example, Roller Walker [8] with a passive wheel on the foot of the 3 (DOF) legs and Bipedal walker WS-2 with wheel driving mode when the wheeled foot module W-16 is mounted [9]. There are many more such examples using different techniques in making such robots.  For example, Octal Wheel [10], which  has a special wheel-arm mechanism comprising of  an arm with two wheels on each side,  and hence  is capable of climbing over  obstacles  such as stairs. Whegs driven by four 3-spoke wheels without”rims”  can easily move over flat and rough terrains both.  After  going  through   and  analysing  the existing types of such robots, we have tied to come up with a quadruped  design (for the stability on uneven terrains)      for the robot with inbuilt transition mechanism between wheeled and legged modes of locomotion (for higher speeds).    2.  DESIGN CONCEPT       The basic design is based on a quadruped geometry. The reason behind selecting a quadruped  design is its  ability to remain stable in different conditions. The design proposed in this paper consists of various components. There are 4 legs provided in the design each symmetrically placed. Each individual leg    further has  2 links which are connected via rotary joints. Joint 1 provides 1DOF (vertical motion) for  the links to adjust according to the terrain. Joint 2 connects the leg to the centre disc and enables motion in horizontal direction. The bottom portion of the legged configuration is provided with a wheel transition mechanism, which will be required for the wheeled mode locomotion. There is also a provision for a vertical axis rotary joint  (joint 3) which provides directional change to the motion of wheels.  Each leg is connected to a basal disc which acts as its  connector to the entire body of the robot. The bottom portion of the base disc consists of the four legs and the upper portion consists of the arm base plates and the robotic arms. The connecting rod, on  which the arm base plate lies, can vary the height according to the requirements.  The arms attached on to the upper base plate are provided 2 DOFs .  For example, one  of the arms can  to be used for drilling purposes and the other for the picking and placing of the  sample.  The application of the arms  can be varied using different gripper mechanisms.    International Journal of Instrumentation, Control and Automation (IJICA) ISSN: 2231-1890, Volume-1, Issue-4261Mechanical Design Of A Legged-Wheel Hybrid Quadruped Robot For Multi-Terrain Navigation     (a)                     3.     STABILITY CONDITIONS IN     DIFFERENT TERRAINS:    The stability of any rover is dependent on the design criteria of the robot. The quadruped design is such that all the 4 legs tend to be symmetrically placed in almost all the types of terrains.  Fig.2.(a) shows the position of the quadruped as on a stable or flat terrain. At this position the centre of mass of the structure is located at almost the geometric centre of the body, thus making it the most stable position. The exact positions of the  centre of mass obtained from the  DS Solidworks  software are also shown along with the figure.         Fig. 2(b) shows the position of the robot on and uneven terrain . It can be seen that the position of centre of ass is slightly off set but this eccentricity does  not affect the  overall  stability of the robot. The normal reaction in the two right most legs causes a moment about the centre but the normal  forces  from  the symmetrically opposite forces are capable of balancing such moments.  Fig .2. (c) shows the vertical height adjustment. During this  motion, again,  the centre of mass moves  only in Z direction, thus preventing any sideways sways.     Fig .2.  Stability conditions (a) Stable terrain (b) Uneven rough terrain (c) Vertical height adjustment.  International Journal of Instrumentation, Control and Automation (IJICA) ISSN: 2231-1890, Volume-1, Issue-4262Mechanical Design Of A Legged-Wheel Hybrid Quadruped Robot For Multi-Terrain Navigation    4.  MOTION STUDY:      This quadruped robot has four limbs which move in a predefined sequence in order for the whole robot to move ahead. In addition to the legs the robot also has got the wheel transition which  can help in wheeled motion too. The configuration used is as shown in the adjoining figure and the numbering is as mentioned.  The motion can be done in 2 ways:  1.  Wheeled motion.   2.  Legged motion.     WHEELED MOTION:    During the wheeled motion, the transition mechanism proposed later in this paper, lowers the wheels and enables the wheeled  mode. When operating in this mode,  the robot makes an adjustment in the level of the legs. The adjustment tries to bring the axis of  the horizontal link of leg, in parallel with the ground. After this adjustments each of the wheels in the 4 legs align themselves in the  same direction. The rotary joint attached just above the wheel enables this directional change. The figure below shows  the directional alignment and the adjustment of the horizontal link.  Fig.3.a Wheeled mode.  Fig.3.b Wheel alignment. Legged motion:  Motion  ,as proposed, can be divided into six steps as shown in the following diagram. The sequence used in the locomotion is 1-2-3-4, as  shown in figure 4.a.  Further motion of each leg can be subdivided into two steps: each of the steps occurs simultaneously. One being horizontal motion and the other being vertical lift of the limb. In the step 1 limb 1 moves while the other 3 are resting. In the step 2, while the first is in air, the limb 2 starts moving while the other two are still at rest. By the step 3, first and second have reached their positions and by this time, limb 3 starts to move whereas fourth is still resting. As we can see by this time the body is progressively moving forward with the help of the motion of the limbs. In the step  4 we can see the third limb is  undergoing the vertical lift while the fourth limb starts moving. Step 5 sees the start of motion of the fourth limb, the other 3 having reached their position. Finally in the sixth step, the robot  has  completed its desired motion with all the limbs at their new positions. The figure below shows these steps in the direction of motion as shown. The starting line, intermediate line and the finishing line have been tentatively shown as well.    International Journal of Instrumentation, Control and Automation (IJICA) ISSN: 2231-1890, Volume-1, Issue-4263Mechanical Design Of A Legged-Wheel Hybrid Quadruped Robot For Multi-Terrain Navigation    Fig 4.b: the figure shows movement of the robot within the given starting and finishing lines.  5.  TRANSITION MECHANISM:    The transition between legged mode and wheel mode is done using a screw mechanism as shown in the figure (fig 5.a). The cylinder part just above the leg is grooved with inner threading of the same pitch and  size as given to the outer threading  on another inner cylindrical part which is fitted in turn, with two shafts(one above and one below).The upper shaft is connected to a motor whose direction of rotation decides the lift or fall of the wheel and whose rotation leads to the relative motion of the two cylinders along the threading given (up and down).This motion of inner cylinder lifts or drops the wheel attachment of the limb, connected via the bottom shaft. Further the threading helps in the locking mechanism required to hold the wheel in its desired position whether up or down (i.e. in legged or wheel mode)  as the suitable amount of force needed by the attachment to hold its position can be easily withstood by this screw mechanism ,thus making it highly efficient as well as reliable. The mechanism can be easily understood with the help of the figure 5.b. the upper shaft when attached to a motor will rotate the inner cylinder in the direction of rotation of the motor, which will ultimately move the cylinder  along the  grooves of the threading given (up or down).Along with the cylinder, will move the bottom shaft attached, fixed  to the shaft of the wheel attachment  setup,thus  moving the wheel up or down as required.    Fig 5. a) Embedded version of the screw mechanism used. b) Screw mechanism functioning.    International Journal of Instrumentation, Control and Automation (IJICA) ISSN: 2231-1890, Volume-1, Issue-4264Mechanical Design Of A Legged-Wheel Hybrid Quadruped Robot For Multi-Terrain Navigation    6. CONCLUSION AND FUTURE WORK:    We  have reported on the design of a leg-wheel hybrid platform quadruped  which includes a transformation mechanism capable of directly changing the morphology of four wheels  of the platform into 2 degree-of-freedom legs.  The locomotion behaviours of this robot can be switched between a four-wheel-drive vehicle (wheel mode) and a quadruped (leg mode). We  have also discussed the stability criteria for the quadruped robot.  We are currently in the process of mechanical stress analysis of the design. This would further require kinematic and load analysis. We further  intend to test the design and mechanisms involved on a practical basis by experimental analysis of the system. This  would further require the control system studies  and  mechatronics  involved  in working of such a design.                         7. ACKNOWLEDGMENT:    We would like to thank all the professors and colleagues who have helped us through this paper with their valuable comments and insight.     REFERENCES:     [1]  J. Yuan and S. Hirose, “Research on leg-wheel hybrid stairclimbing robot,zero carrier,” in IEEE International Conference on Robotics and Biomimetics, vol. 1, 2004, pp.  654–659.  Systems, vol. 1, 2004, pp. 2440–2445.                                    [2]  M. Lacagnina, G. Muscato, and R. Sinatra, “Kinematics,  dynamics and control of a hybrid robot wheeleg,” Robotics  and Autonomous Systems, pp. 161–180, 2003.   [3]  S. Nakajima, E. Nakano, and T. Takahashi, “Motion control  technique for practical use of a leg-wheel robot on unknown  outdoor rough,” in IEEE/RSJ International Conference on  Intelligent Robots and Systems, vol. 1, 2004, pp. 1353–1358.   [4]  F. Michaud and S. Caron, “Multi-modal locomotion robotic  platform using leg-track-wheel articulations,” Autonomous  Robots, pp. 137–156, 2005.   [5]  J. A. Smith, I. Sharf, and M. Trentini, “Bounding gait in a hybrid wheeled-leg robot,” in IEEE/RSJ International  Conference on Intelligent Robots and Systems, vol. 1, 2006,  pp. 5750–5755.  [6]  H.Adachi, N.Koyachi, T.Arai, A.Skua, and Y.Nogami, “Mechanism and control of a leg-wheel hybrid mobile robot,” in IEEE/RSJ International Conference on Intelligent  Robots and Systems, 1999, pp. 1792–1797.  [7]  C. Grand, F. Benamar, F. Plumet, and P. Bidaud, “Stability  and traction optimization of a reconfigurable wheel-legged  robot,” The International Journal of Robotics Research, pp.  1041–1058, 2004.  [8]  G. Endo and S. Hirose, “Study on roller-walker,” in IEEE  International Conference on Robotics and Automation, vol. 1,  1999, pp. 2032–237.  [9]  J. Hashimoto, T. Hosobata, Y. Sugahara, Y. Mikuriya, H. Sunazuka, M. Kawase, H. ok Lim, and A.Takanishi, “Realization by biped leg-wheeled robot of biped walking and wheel-driven locomotion,” in IEEE International Conference on Robotics and Automation, vol. 1, 2005, pp.  2970–2975.  [10]  Y. Takita, N. Shimoi, and H. Date, “Development of a wheeled mobile robot ”octal wheel”realized climbing up and  down stairs,” in IEEE/RSJ International Conference on Intelligent Robots and        International Journal of Instrumentation, Control and Automation (IJICA) ISSN: 2231-1890, Volume-1, Issue-4265

MECHANICAL DESIGN OF A LEGGED-WHEEL HYBRID QUADRUPED ROBOT FOR MULTI-TERRAIN NAVIGATION

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MECHANICAL DESIGN OF A LEGGED-WHEEL HYBRID QUADRUPED ROBOT FOR MULTI-TERRAIN NAVIGATION

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