Design and Modeling of a Mobile Robot

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1 Design and Modeling of a Mobile Robot with an Optimal Obstacle-Climbing Mode The pen WHEEL Project Jean-Christophe FAUROUX Morgann FORLOROU Belhassen Chedli BOUZGARROU Frédéric CHAPELLE 1/33 LaMI / TIMS / IFMA / UBP,, Véhicules en Milieux Naturels

2 Summary 2. Existing mobile robots 3. Design workspace for mobile robots with climbing capacities 4. Structural design 5. Designing a climbing sequence 6. Conclusions and future work 2/33

3 Introduction Terrestrial vehicles Wheeled vehicles prevail (energetic efficiency?) Blocked on slope discontinuities of the ground Legs / Tracks regain interest for climbing Interface with the ground Crawler + multiples contacts, can cross obstacles and rough terrain - require high energy, moderate speed, complex control Leg + can cross obstacles and go fast on rough terrain - contact discontinuity, energy cost, stability control Wheel + fast on smooth surface, energy efficient - cannot climb obstacles or run on rough terrain Track + permanent stability, high traction - high friction energy loss, particularly during steering Mechanical architecture 3/33 No locomotion mode is perfect Improved wheeled architectures should be developed Engines distributed on the wheels Innovative architectures already exist (e.g. for spatial robots)

4 Existing mobile robots Robots with articulated frame Robots with axles and several modes of locomotion RobuROC 6 Micro5 Lama Nomad 4/33 Hilos Robots with legs and several modes of locomotion Azimut laborius/ Workpartner / Hybtor

5 Existing mobile robots Robots with minimally actuated frame Crab Shrimp Robots with rocker-bogie and stability improvement SRR2 5/33 Rocky 7 Robots with tracks Helios et Genryu

6 Design process of a climbing robot Purpose of the work Designing innovative robots with advanced wheeled mobility A general platform of wheeled vehicles : the Open WHEEL project Quasi-static climbing of obstacles Minimal number of actuators Proposed strategy 6/33 1. Design workspace definition Which type / architecture of mechanism? 2. Structural synthesis Which mechanism? Mobility analysis 3. Dimensional synthesis Which optimal dimensions? (not covered in this work)

7 Proposed design workspace Open WHEEL Open -> Open architecture for advanced mechanical concepts WHEEL -> Keeping the good efficiency of the wheel A generic framework for building a family of wheeled robots with canonical components and axle-based architecture Wireless connection A3 Rear CAN Bus W 32 S 32 Control S 31 Wheel W31 A2 I2 S 21 W21 7/33 Swing arm Double wishbone Innovative suspension W12 Camera S22 S 12 A1 Control Suspension mechanism Saw W22 Control I1 S 11 W11 nt Fro Z X Y Inter-axle mechanism Ia Serial Parallel Innovative mechanism mechanism mechanism

8 Structural design Key ideas Idea1 : a chair with 3 feet is always stable Idea2 : 4 wheels are good Exploring wheel Tricycle : dynamic stability problems Side-car : directional problems Conclusion 8/33 Design a robot with 3+1 wheels Dynamic stability on 4 wheels at high speed Always stable on 3 wheels when climbing Permanent static stability via adjustment of the centre of mass One 'exploring' wheel goes on top of the obstacle Support triangle V v N o

9 Structural design Mobility analysis The exploring wheel W11 should have an ascending movement in the plane Π 11 X translation for bringing the wheel towards the obstacle Z translation for lifting the wheel over the obstacle Y translation allowed during lifting but the track width of the vehicle should not change after landing Exploring wheel W22 Z Y 9/33 W12 S22 S12 A2 Re I1 ar S21 X A1 W11 S11 W21 Possible climbing trajectories

Example: Open WHEEL i3r Naming convention Naming the Inter-Axle Mechanisms Naming the Suspension Mechanisms Ex : irrr or i3r Ex : srpr Concepts of Open WHEEL i3r 10/33 Only one central R actuator

10 Example: Open WHEEL i3r Naming convention Naming the Inter-Axle Mechanisms Naming the Suspension Mechanisms Ex : irrr or i3r Ex : srpr Concepts of Open WHEEL i3r 10/33 Only one central R actuator allows to lift the four wheels according to mass repartition [IROS 2006] Capable to climb step obstacles via a specific climbing process All the work is on the inter-axle mechanism. No suspension. ar Re W21 W22 t n Fro W11 W12

11 Structural design Mobility analysis & suspension leg synthesis (a) (b) (c) (d) Suspension design : many mechanisms allow the required frontward-upward movement Current work in progress for extensive enumeration s4r : high DOF but low stiffness srpr : needs two DOF to position the wheel center spr : only one DOF if a angle allows ascending movement srr : frontward-upward movement is obtained in the south-east part of the circular trajectory a) s4r legleg (a) s4r b) srpr legleg (b) srpr R c) spr (c) sprleg leg -90 < <0 R P R 11/33 0 < <90 P R R d) srr (d) srrleg leg R R R R

12 Structural design A common architecture : 4sRR Gofor, JPL, /33 NanoRover, JPL, 1994 ar e R OpenWheel 4sRR, 2005 W22 Z t Y W21 W12 W11 X n Fro Our goal : defining a climbing strategy

four wheels or only on three wheels The global centre of mass Gg is updated mc 4m l 4mw The

13 Designing a climbing sequence Design principles Gg = mc. Gc 4ml. Gl 4mw. Gw 13/33 Find the sequence of leg positions that allow stable climbing Vehicle can be on four wheels or only on three wheels The global centre of mass Gg is updated mc 4m l 4mw The support polygon is updated too The stability margin S is computed at every position S = min (Si ) from to i=1 i=3 or 4

Design tool : GeoGebra Algebraic & geometric tools -> 2,5D model Geometrical construction tools Computing the centers of masses Geometrical model Side view

14 Design tool : GeoGebra Algebraic & geometric tools -> 2,5D model Geometrical construction tools Computing the centers of masses Geometrical model Side view Analytical expressions Handles for interactive location adjustment A 2.5 D Model Adjustable design parameters Geometrical model Top view Construction protocol 14/33

15 A climbing sequence Structure 16 stages separated by single functional motions 6 phases from A to F Successive lifting of the four wheels 01 A B C D E 15/33 16 F

16 Stage 01 Detailed views 16/33 Side view Top view Real model A - Approach

17 Stage 02 17/33 B Wfl climbing

18 Stage 03 18/33 B Wfl climbing

19 Stage 04 19/33 B Wfl climbing

20 Stage 05 20/33 B Wfl climbing

21 Stage 06 21/33 C Wfr climbing

22 Stage 07 22/33 C Wfr climbing

23 Stage 08 23/33 C Wfr climbing

24 Stage 09 24/33 C Wfr climbing

25 Stage 10 25/33 D Wrr climbing

26 Stage 11 26/33 D Wrr climbing

27 Stage 12 27/33 D Wrr climbing

28 Stage 13 28/33 E Wrl climbing

29 Stage 14 29/33 E Wrl climbing

30 Stage 15 30/33 E Wrl climbing

31 Stage 16 31/33 F Conclusion

32 Conclusion Conclusions A general method for designing and modeling mobile robots with an optimal obstacle-climbing mode for a single step Design process in three stages: 1) Design workspace is the OpenWHEEL framework (axle-based architecture) 2) Structural synthesis showed the interest of the 4sRR kinematics for climbing 3) Dimensional synthesis (future work) 32/33 An original tool mixing algebra and geometry (Geogebra) proved its efficiency for preliminary design A 2.5D model and a reduced model were built A climbing sequence was created and demonstrated

Future work Four tracks for the future Explore all the feasible kinematics i3r 4sRR ar Re

other climbing sequences Example : After lifting Wfr, should we lift Wrr or Wrl?

simultaneously structural and kinematical parameters on the 16 stages -> Tough!

33 Future work Four tracks for the future Explore all the feasible kinematics i3r 4sRR ar Re W21 W22 n Fro W11 t W12 Re ar W22 Z t Y W21 Innovative frame W12 W11 X n Fro Explore the other climbing sequences Example : After lifting Wfr, should we lift Wrr or Wrl? Design branching 33/33 Stage 14 Optimizing the climbing sequence: optimizing simultaneously structural and kinematical parameters on the 16 stages -> Tough! Solution: Bringing Gg forward? Minimizing the number of actuators: using one actuator for two revolute joints Stage 03

Spring Locomotion Concepts. Roland Siegwart, Margarita Chli, Martin Rufli. ASL Autonomous Systems Lab. Autonomous Mobile Robots

Spring Locomotion Concepts. Roland Siegwart, Margarita Chli, Martin Rufli. ASL Autonomous Systems Lab. Autonomous Mobile Robots Spring 2016 Locomotion Concepts Locomotion Concepts 01.03.2016 1 Locomotion Concepts: Principles Found in Nature ASL Autonomous Systems Lab On ground Locomotion Concepts 01.03.2016 2 Locomotion Concepts