Analysis and optimization for a hexapod walking robot for planetary missions

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(1) UNIVERSIDAD POLITÉCNICA DE MADRID ESCUELA TÉCNICA SUPERIOR DE INGENIEROS INDUSTRIALES. Tesis Doctoral “ANALYSIS AND OPTIMIZATION FOR A HEXAPOD WALKING ROBOT FOR PLANETARY MISSIONS ” . Autor:. Josefina Torres Redondo. Tutores:. Dr. Gregorio Romero Rey Dr. Javier Gomez-Elvira Rodriguez. Noviembre 2015 .

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(5) . Agradecimientos Quisiera empezar dando las gracias a mi tutor Gregorio Romero Rey por su apoyo y paciencia a lo largo de todos estos años y a todo el departamento. También mi recuerdo para Carlos Vera Álvarez que me hizo prometer que terminaría la tesis antes de que tuviera un niño y espero cumplirlo a un mes de dar a luz.. También quiero mostrar mi agradecimiento al departamento de Instrumentación del Centro de Astrobiología. En especial a Sara Navarro, José Antonio Rodríguez Manfredi y Javier Gómez-Elvira por su ayuda, tiempo y dedicación.. A mis padres por toda su ayuda y a Joaquín, esta tesis no hubiera posible sin ellos. No me olvido tampoco de Juan Manuel y sus tardes de correcciones.. . . .

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(7) . Abstract The autonomous machines technology has undergone a major research and development during the last decades. In many activities and environments, robots can perform operations that are tought, dangerous or simply imposible to humans. Planetary exploration is a good example of such environment where robots are needed to perform the tasks required by the scientits. Recent Mars exploration based on autonomous vehicles has shown us the capacity of the new technologies. From the invention of the wheel, which is rightly regarded as the greatest invention in the history of human transportation, nearly all-planetary vehicles are based in wheeled locomotion, but new missions demand new types of machines due to the complex tasks needed to be performed. It will be proposed in this thesis a new design of a legged robot or walking machine, which may offer clear advantages in tough environments. This Thesis will show that the proposed walking machine can travel, were terrain difficulties make wheeled vehicles ineffective, making it a perfect choice for planetary mission. A historical background of the main space missions, in particular those aimed at planetary exploration will be presented. From this study the disadvantages found in the existing wheel rovers will be analysed. The legged robot designed will be introduced as an alternative were wheeled rovers could be no longer the best option for planetary exploration. This thesis introduces the mechanical design of a six-leg robot capable of withstanding high forces and moments due to the walking motion. Once the mechanical design is concluded, and in order to analyse a machine of this complexity an understanding of its movement and behaviour is mandatory. This movement equation will be validated by two methods: kinematics and dynamics. .

(8) Two Matlab® codes have been developed to solve the systems of equations and validated by a third method, a finite element model, which also verifies the mechanical design. The legged robot presented has been designed for a Mars planetary exploration. The movement behaviour of the robot will be tested in a Matlab® code developed that allows to modify the trajectories, the type of terrain, number and height of obstacles. These terrains and initial requirements have not been chosen randomly, those are based on my experience as a member of the MSL NASA team, which operates an instrument on-board of the Curiosity rover in Mars. The walking robot developed and manufactured by the Center of Astrobiology (CAB) is based in the mechanical design and analysis that will be presented in this thesis.. .

(9) . Resumen La tecnología de las máquinas móviles autónomas ha sido objeto de una gran investigación y desarrollo en las últimas décadas. En muchas actividades y entornos, los robots pueden realizar operaciones que son duras, peligrosas o simplemente imposibles para los humanos. La exploración planetaria es un buen ejemplo de un entorno donde los robots son necesarios para realizar las tareas requeridas por los científicos. La reciente exploración de Marte con robots autónomos nos ha mostrado la capacidad de las nuevas tecnologías. Desde la invención de la rueda, que esta acertadamente considerado como el mayor invento en la historia del transporte humano, casi todos los vehículos para exploración planetaria han empleado las ruedas para su desplazamiento. Las nuevas misiones planetarias demandan maquinas cada vez mas complejas. En esta Tesis se propone un nuevo diseño de un robot con patas o maquina andante que ofrecerá claras ventajas en entornos extremos. Se demostrara que puede desplazarse en los terrenos donde los robots con ruedas son ineficientes, convirtiéndolo en una elección perfecta para misiones planetarias. Se presenta una reseña histórica de los principales misiones espaciales, en particular aquellos dirigidos a la exploración planetaria. A través de este estudio será posible analizar las desventajas de los robots con ruedas utilizados en misiones anteriores. El diseño propuesto de robot con patas será presentado como una alternativa para aquellas misiones donde los robots con ruedas puedan no ser la mejor opción. En esta tesis se presenta el diseño mecánico de un robot de seis patas capaz de soportar las grandes fuerzas y momentos derivadas del movimiento de avance. Una vez concluido el diseño mecánico es necesario realizar un análisis que permita entender el movimiento y comportamiento de una maquina .

(10) de esta complejidad. Las ecuaciones de movimiento del robot serán validadas por dos métodos: cinemático y dinámico. Dos códigos Matlab® han sido desarrollados para resolver dichos sistemas de ecuaciones y han sido verificados por un tercer método, un modelo de elementos finitos, que también verifica el diseño mecánico. El robot con patas presentado, ha sido diseñado para la exploración planetaria en Marte. El comportamiento del robot durante sus desplazamientos será probado mediante un código de Matlab®, desarrollado para esta tesis, que permite modificar las trayectorias, el tipo de terreno, y el número y altura de los obstáculos. Estos terrenos y requisitos iniciales no han sido elegidos de forma aleatoria, si no que están basados en mi experiencia como miembro del equipo de MSL-NASA que opera un instrumento a bordo del rover Curiosity en Marte. El robot con patas desarrollado y fabricado por el Centro de Astrobiología (INTA-CSIC), esta basado en el diseño mecánico y análisis presentados en esta tesis.. . . .

(11) . Index 1. INTRODUCTION .............................................................................................................................. 1 2. OBJECTIVES ...................................................................................................................................... 5 3. MARS LANDERS AND WHEELED ROVERS .......................................................................... 7 3.1. Mars landers: Viking ............................................................................................................. 7 3.2. Mars landers: Pathfinder .................................................................................................... 8 3.3. Mars landers: Mars Polar Lander (MPL) ..................................................................... 9 3.4. Mars landers: Beagle 2 ..................................................................................................... 10 3.5. Mars landers: Mars Exploration Rovers Spirit and Oportunity ...................... 11 3.6. Mars landers: NetLander ................................................................................................. 13 3.7. Mars landers: Phoenix lander ........................................................................................ 13 3.8. Mars landers: MSL rover mission (Curiosity) ........................................................ 14 3.9. Future missions for Mars exploration ....................................................................... 15 3.9.1. ExoMars (Exobiology on Mars) .......................................................................... 15 3.9.2. InSight ............................................................................................................................ 15 3.9.3. Mars 2020 .................................................................................................................... 16 3.10. Historical background of exploring robots ........................................................... 16 4. STATE OF THE ART OF WALKING MACHINES ............................................................... 21 4.1. Walking machines .............................................................................................................. 22 4.1.1. Walking robots classified by their number of legs. .................................... 23 4.1.2. Moving table ................................................................................................................. 28 4.1.3. Biomimetic robots ..................................................................................................... 31 5. ACTUATORS COMMONLY USED IN ROBOTICS .............................................................. 37 5.1. Synchronous ......................................................................................................................... 37 5.2. Brushless DC Servo ............................................................................................................ 37 5.3. Stepper .................................................................................................................................... 38 5.4. Brushed DC Servo ............................................................................................................... 39 5.5. Asynchronous ....................................................................................................................... 40 5.6. AC Servo Motors .................................................................................................................. 40 5.7. Pneumatic .............................................................................................................................. 40 5.8. Hydraulic ................................................................................................................................ 40 6. A WALKING MACHINE FOR MARS ....................................................................................... 43 6.1. Design requirements ......................................................................................................... 45 6.2. Mars Terrain limitations for a Wheeled Rover ...................................................... 45 6.3. Mars Constraints for Designing a Better Moving Robot .................................... 50 7. WALKING MACHINE DESIGN CRITERIA ........................................................................... 55 7.1. Moving Table Design ......................................................................................................... 55 7.2. Six legged robot design .................................................................................................... 56 7.2.1. Gait selection for the hexapod .............................................................................. 57 7.2.2. Sizing of the legs ......................................................................................................... 61 7.2.3. Actuators for our walking machine .................................................................... 66 8. HEXAPOD DESIGN ....................................................................................................................... 73 8.1. Walking Robot Mechanical Design .............................................................................. 74 .

(12) 8.1.1. Main body Structure ................................................................................................. 74 8.1.2. Leg Structure ................................................................................................................ 76 8.2. Leg Design and Configuration ....................................................................................... 80 9. SIMULATION OF A WALKING ROBOT ................................................................................ 81 9.1. Introduction to simulation .............................................................................................. 81 9.2. Ground Reactions of the Walking Robot ................................................................... 84 9.3. Leg force analysis by Kinematics ................................................................................. 87 9.3.1. Section1 Results .......................................................................................................... 94 9.3.2. Section 2 Results ......................................................................................................... 97 9.3.3. Section 3 Results ......................................................................................................... 99 9.4. Leg Analysis by Nastran® ............................................................................................. 100 9.5. Leg force analysis by Dynamics .................................................................................. 104 9.5.1. Mathematical Modelling of One leg .................................................................. 105 9.5.2. Results by Dynamic Analysis ............................................................................... 111 9.6. Steps Followed for the leg design .............................................................................. 118 10. CURIOSITY TRAJECTORY AND DALILY OPERATION ON MARS ........................ 119 10.1. Curiosity Wheel Capability ........................................................................................ 119 10.2. Eyes and other senses .................................................................................................. 121 10.3. Where to go ...................................................................................................................... 123 10.4. Communications and Autonomous Navigation ................................................ 126 10.4.1. Mars-‐ Earth Communications .......................................................................... 126 10.4.2. Mars Rovers Autonomous Navigation .......................................................... 127 11. TRAYECTORY PLANNING OF A HEXAPOD ROBOT .................................................. 131 11.1. Movement in flat terrain ............................................................................................. 131 11.1.1. Flat terrain mesh creation ................................................................................. 131 11.1.2. Movement of the robot in flat terrain ........................................................... 135 11.2. Change of direction in Flat Terrain ........................................................................ 143 11.3. Movement in irregular terrain ................................................................................ 149 11.3.1. Irregular terrain mesh creation ...................................................................... 149 11.3.2. Movement of robot in irregular terrain ....................................................... 151 11.4. Change of Direction in irregular terrain. ............................................................. 163 11.5. Obstacle avoidance in trajectories .......................................................................... 169 11.5.1. Obstacle mesh creation ....................................................................................... 170 11.5.2. Trajectory around the obstacle ....................................................................... 170 11.5.3. Trajectory over an obstacle .............................................................................. 172 12. FUTURE MARS ROVERS ....................................................................................................... 177 12.1. Hybrid Robots .................................................................................................................. 177 12.2. Helicopters ........................................................................................................................ 181 13. CONCLUSIONS .......................................................................................................................... 183 14. FUTURE WORK ........................................................................................................................ 187 15. REFERENCES ............................................................................................................................ 189 16. PUBLICATIONS ........................................................................................................................ 193 ANNEX 1 ................................................................................................................................................. 195 . . . .

(13) . Figures Figure 1. Mechanical horse: L.A Rigg REF. 1 ............................................................................... 3 Figure 2. Bechtostsheim Patent ........................................................................................................ 3 Figure 3. Replica of a Viking Lander. REF. 3 ................................................................................ 8 Figure 4 Pathfinder. REF. 5 ................................................................................................................. 9 Figure 5 Mars Polar Lander. REF. 6 .............................................................................................. 10 Figure 6 Mars Lander: BEAGLE 2. REF. 7 .................................................................................. 11 Figure 7 Spirit Rover. REF. 8 ........................................................................................................... 12 Figure 8 Net lander prototype. REF. 11 ...................................................................................... 13 Figure 9 Curiosity MSL mission. REF. 12 ................................................................................... 14 Figure 10 Ambulatory Robotics Laboratory. REF. 15 .......................................................... 23 Figure 11 MIT biped. REF. 16 ......................................................................................................... 24 Figure 12 ASIMO. REF. 17 ................................................................................................................ 25 Figure 13 MAX ....................................................................................................................................... 26 Figure 14 Katharina ............................................................................................................................ 26 Figure 15 Lauron .................................................................................................................................. 26 Figure 16 Polypop ............................................................................................................................... 28 Figure 17 SILO 04 ............................................................................................................................... 28 Figure 18 Scout I ................................................................................................................................. 28 Figure 19. Fred II. REF. 31 ................................................................................................................ 29 Figure 20.Walking beam . REF. 32 ................................................................................................ 29 Figure 21. Zimmer. REF. 33 ............................................................................................................. 29 Figure 22. Daedulus. ........................................................................................................................... 30 Figure 23 Rhex ...................................................................................................................................... 32 Figure 24 Lobster ................................................................................................................................. 32 Figure 25 Boadicea .............................................................................................................................. 33 Figure 26 Robot II ................................................................................................................................ 34 Figure 27 Microrobot .......................................................................................................................... 35 Figure 28 Ioan ........................................................................................................................................ 35 Figure 29 Stepper motor .................................................................................................................. 39 Figure 30 Abrupt Mars terrain. REF. 50 ..................................................................................... 46 Figure 31 Mars. MSL rover auto picture .Courtesy NASA. REF. 50 ................................. 46 Figure 32 Test bed in JPL of MSL rover trying to go over a rock. REF. 50 ................... 47 Figure 33 Mount Sharp. Mars. REF. 50 ....................................................................................... 48 Figure 34 Impact crater near equator of scientific interest. REF. 50 ............................ 48 Figure 35 Areas of possible scientific interest. REF. 50 ...................................................... 49 Figure 36 Selection of landing sites. REF. 50 ........................................................................... 49 Figure 37 Moving Table .................................................................................................................... 55 Figure 38 Obstacle 0.25x0.25x0.25m. ......................................................................................... 62 Figure 39 Gait Hexapod Sequence ................................................................................................ 62 Figure 40 0.3 m of depth ................................................................................................................. 63 Figure 41 10º Slope ........................................................................................................................... 64 Figure 42 Hexapod Configuration with Pneumatic Actuators, Festo ....................... 67 Figure 43 Dc Actuator. REF. 45 .................................................................................................... 68 Figure 44 Different configurations for linear actuators. ................................................... 68 .

(14) Figure 45 SKF CARR 22 Actuator. REF. 46 ............................................................................... 69 Figure 46 Actuator CARR 22x200x1 Drawing. REF. 46 ....................................................... 70 Figure 47 Box dimension of the Design. .................................................................................... 73 Figure 48 Main body structure ...................................................................................................... 74 Figure 49 Main body aluminium panel assembly .................................................................. 75 Figure 50 Main body structure ...................................................................................................... 75 Figure 51 Leg structure ..................................................................................................................... 76 Figure 52 Detail of the bottom section 3 attachment. .......................................................... 77 Figure 53 Detail of the section 3 motor attachment. ............................................................ 78 Figure 54 Detail of the section 3 top attachment ................................................................... 78 Figure 55 Detail of the section 1 top attachment ................................................................... 79 Figure 56 Detail of the section 1 to actuator 2 attachment. .............................................. 79 Figure 57 Attachment and function of the actuators ......................................................... 80 Figure 58 Ground Reactions ......................................................................................................... 85 Figure 59 First section analysis ..................................................................................................... 87 Figure 60 Second section analysis ................................................................................................ 89 Figure 61 Third section analysis ................................................................................................... 91 Figure 62 Reduction to known cases .......................................................................................... 92 Figure 63 Section 1 Forces Results .............................................................................................. 95 Figure 64 Section 1 Ground Reactions ....................................................................................... 95 Figure 65 Section 2 Forces Results .............................................................................................. 97 Figure 66 Section 3 Bearing Reactions ..................................................................................... 100 Figure 67 Robot Finite Element Model. .................................................................................... 101 Figure 68 Robot Bar and MPC elements. ................................................................................. 102 Figure 69 FEM material data. ....................................................................................................... 102 Figure 70 Finite Element Validation .......................................................................................... 103 Figure 71 Composition of the prototype design. ................................................................. 104 Figure 72 Movement of three actuators per leg. .................................................................. 105 Figure 73 Moving elements of the hexapod leg. ................................................................... 106 Figure 74 Movement due to mass and gravity ................................................................... 112 Figure 75 Movement due to 50N load in F1. ....................................................................... 113 Figure 76 Real movement of the instrument box .............................................................. 114 Figure 77 Movement due to 50N load in F1 for six legs. .............................................. 115 Figure 78 Maximum movement of the legs ............................................................................ 116 Figure 79 X6 distance of Leg6 vs. Reaction ....................................................................... 116 Figure 80 Comparison of Reaction Results ......................................................................... 117 Figure 81 Curiosity Rover. REF. 47 ......................................................................................... 120 Figure 82 Curiosity Reading the Rover's Tracks. REF. 48 ................................................... 121 Figure 83 Curiosity landing site. REF. 49 .................................................................................. 122 Figure 84 Mount Sharp. REF. 49 ................................................................................................... 122 Figure 85"Point Lake". REF. 49 .................................................................................................... 123 Figure 86 RSVP interface. REF. 50 .............................................................................................. 124 Figure 87 Mars yard. REF. 50 ........................................................................................................ 124 Figure 88 RSVP Tool Close up. REF. 51 .................................................................................... 125 Figure 89 Spirit, Opportunity and Curiosity communications system. ...................... 127 Figure 90 3-‐D Terrain maps generated by the rover software. REF. 52 .................... 130 Figure 91 Flat terrain creation in matlab ®with simplified robot geometry. ......... 132 Figure 92 Angle position per leg. ................................................................................................ 134 Figure 93 Movement in flat terrain ............................................................................................ 135 .

(15) Figure 94 Flat terrain: robot standing in all its legs .......................................................... 136 Figure 95 Step 1. Robot standing in three legs ................................................................. 137 Figure 96 Moving leg 1, 2, and 3 gamma angles for forward motion .................... 138 Figure 97 Step 1. Max gamma displacement of the legs ............................................. 138 Figure 98 Step 1. Six legs in the floor .................................................................................... 139 Figure 99 Step 2. Three legs in the air .................................................................................. 140 Figure 100 Step 2. Six legs in the floor, final configuration. ....................................... 140 Figure 101 Kinematic Forces and reactions from point A to B of leg 2. ............... 141 Figure 102 Change from 6 leg configuration to 3 leg. .................................................... 142 Figure 103 Movement of actuators. ......................................................................................... 143 Figure 104 Six Legs in the ground Configuration. ........................................................... 144 Figure 105 Turning Sequence, three legs lift. .................................................................... 144 Figure 106 Turning Sequence, 20º gamma rotation. ..................................................... 145 Figure 107 Turning Sequence, resulting motion. ............................................................. 146 Figure 108 Forces and Reactions on leg 1 before and after the turn. ................... 147 Figure 109 Forces and Reactions on leg 2 before and after the turn. ................... 148 Figure 110 Forces and Reactions on leg 3 before and after the turn. ................... 148 Figure 111 Robot in random generated mesh. .................................................................. 150 Figure 112 Robot in its six legs to start the walking cadence ........................................ 151 Figure 113 Leg adaptation to the surface generated by the code ........................... 152 Figure 114 Leg 1, Forces and reaction irregular terrain ............................................... 153 Figure 115 Leg 2, Forces and reaction irregular terrain ............................................... 154 Figure 116 Leg 3, Forces and reaction irregular terrain ............................................... 155 Figure 117 Leg 4, Forces and reaction irregular terrain ............................................... 156 Figure 118 Leg 5, Forces and reaction irregular terrain ............................................... 157 Figure 119 Leg 6, Forces and reaction irregular terrain. .............................................. 158 Figure 120 Robot trajectory on irregular terrain. ............................................................... 159 Figure 121 Leg1. Forces and reactions for the complete trajectory. ...................... 160 Figure 122 Leg2. Forces and reactions for the complete trajectory. ...................... 161 Figure 123 Leg3. Forces and reactions for the complete trajectory. ...................... 162 Figure 124 0.2 m mesh generation. ........................................................................................ 163 Figure 125 Forces and Reactions on leg 2 before turning. ......................................... 164 Figure 126 Turning Sequence in irregular terrain. ........................................................... 165 Figure 127 Turning Sequence in irregular terrain. Three legs in the ground. ... 166 Figure 128 Turning Sequence in irregular terrain. Six legs on the ground. ........ 166 Figure 129 Turning Sequence in irregular terrain. Robot Top view. ...................... 167 Figure 130 Forces and Reactions on leg 2 after turning. ............................................. 168 Figure 131 Obstacle Mesh ........................................................................................................... 169 Figure 132 Obstacle avoidance trajectory. .......................................................................... 171 Figure 133 Robot trajectory over an obstacle .................................................................... 172 Figure 134 Robot over obstacle. ............................................................................................... 173 Figure 135 Leg 1. Forces and reactions during the planned trajectory ................ 174 Figure 136 Trajectory over a 0.25 m obstacle ................................................................... 175 Figure 137 Leg1 trajectory over a 0.25 m obstacle ......................................................... 175 Figure 138 Mission Terraforming. REF. 53 .............................................................................. 178 Figure 139 Athelete with lunar modules. REF. 54 ............................................................ 178 Figure 140 Athelete second generation. REF. 54 ............................................................. 179 Figure 141 Athelete over obstacle. REF. 55 ............................................................................ 181 Figure 142 Mars Helicopter. REF. 56 ......................................................................................... 181 .

(16) Figure 143 CAB-‐INTA Hexapod Robot. ..................................................................................... 186 . .

(17) . Tables Table 1 Exploring Robots ................................................................................................................ 19 Table 2 Advantages of legged Vs wheeled robots. REF. 44 ............................................... 53 Table 3 Initial estimations due to the design requirements .................................................... 65 Table 4 Types of actuators selected. .............................................................................................. 66 Table 5 CARR 22x200x1 Dimensions. REF. 46 ....................................................................... 71 Table 6 SKF CAR 22 Technical data. REF. 46 .......................................................................... 71 Table 7 Verification of equations ............................................................................................... 111 Table 8 Forces and Reactions in flat terrain ....................................................................... 134 Table 9 Forces and reactions with three and six legs ................................................... 142 Table 10 Leg 1, Relevant forces and reactions. .................................................................... 153 Table 11 Leg 2, Relevant forces and reactions. .................................................................... 154 Table 12 Leg 3, Relevant forces and reactions. .................................................................... 155 Table 13 Leg 4, Relevant forces and reactions. .................................................................... 156 Table 14 Leg 5, Relevant forces and reactions. .................................................................... 157 Table 15 Leg 6, Relevant forces and reactions. .................................................................... 158 . . .

(18) Equations Equation 1 ............................................................................................................................................... 58 Equation 2 ............................................................................................................................................... 58 Equation 3 ............................................................................................................................................... 60 Equation 4 ............................................................................................................................................... 60 Equation 5 ............................................................................................................................................... 86 Equation 6 ............................................................................................................................................... 88 Equation 7 ............................................................................................................................................... 90 Equation 8 ............................................................................................................................................... 92 Equation 9 ............................................................................................................................................... 92 Equation 10 ............................................................................................................................................ 93 Equation 11 ............................................................................................................................................ 93 Equation 12 ............................................................................................................................................ 93 Equation 13 ............................................................................................................................................ 93 Equation 14 ............................................................................................................................................ 93 Equation 15 ............................................................................................................................................ 93 Equation 16 ............................................................................................................................................ 93 Equation 17 ............................................................................................................................................ 93 Equation 18 ............................................................................................................................................ 93 Equation 19 ............................................................................................................................................ 93 Equation 20 ............................................................................................................................................ 94 Equation 21 ............................................................................................................................................ 94 Equation 22 .......................................................................................................................................... 107 Equation 23 .......................................................................................................................................... 107 Equation 24 .......................................................................................................................................... 107 Equation 25 .......................................................................................................................................... 107 Equation 26 .......................................................................................................................................... 107 Equation 27 .......................................................................................................................................... 107 Equation 28 .......................................................................................................................................... 107 Equation 29 .......................................................................................................................................... 108 Equation 30 .......................................................................................................................................... 108 Equation 31 .......................................................................................................................................... 108 Equation 32 .......................................................................................................................................... 108 Equation 33 .......................................................................................................................................... 108 Equation 34 .......................................................................................................................................... 108 Equation 35 .......................................................................................................................................... 109 Equation 36 .......................................................................................................................................... 109 Equation 37 .......................................................................................................................................... 109 Equation 38 .......................................................................................................................................... 109 Equation 39 .......................................................................................................................................... 109 Equation 40 .......................................................................................................................................... 109 Equation 41 .......................................................................................................................................... 110 Equation 42 .......................................................................................................................................... 110 . .

(19) . Acronyms AC: Alternating Current. CAB: Centro de Astrobiologia. CSIC : Centro Superior de Invesitgaciones Cientificas. CW: Clockwise. DC: Direct Current. DOF: Degree of Freedom. EMI: Electromagnetic Interference. ESA : European Space Agency. ESS: Environmental Sensors Suite INTA : Instituto Nacional de Tecnica Aeroespacial. JPL : Jet Propulsion Laboratory. LIDAR: Light Detection and Ranging. MEMS: Microelectromechanical Systems. MER: Mars Exploration Rover. MPL: Mars Polar Lander. MSL: Mars Science Laboratory. NASA: National Aeronautics and Space Administration. PBL: Planetary Boundary Layer RPM: Revolutions per minute. RSVP: Rover Sequencing and Visualization Program. RTG: Radioisotope Thermal Generator. UHF: Ultra High Frequency. USSR: Union of Soviet Socialist Republics. USA: United States of America UV: Ultra Violet. . . .

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(21) INTRODUCTION. 1. INTRODUCTION The etymology of robot word comes after the Czech writer Kerel Capek and means work or hard work. This meaning fits well with the idea that robots helps men in hard and repetitive works, mainly in every day tasks from which many of us would like to be freed. Robots development have created a new multidisciplinary branch of technology known as robotics (after Isaac Asimov, fiction-science writer) A robot may be defined as a self-controlled device consisting of electronic, electrical and mechanical units. More generally, it is a machine that functions in place of a living agent. Robots are especially desirable for certain work functions because, unlike humans, they never get tired; they can endure physical conditions that are uncomfortable or even dangerous, and they can operate in airless conditions. Robots are especially valuable to Space exploration. Not only can they travel to environments too hostile or too distant for human explorers, but they can also enhance the work schedule of a manned space mission. Space Robotics may be classified as Orbital Robotics (Manipulation, operations and satellite servicing) and Planetary Rovers, like for Mars and lunar exploration with mobile robots on its surfaces. The Soviet Lunokhod 1 lunar rover can be called the first mobile robot to explore an extra-terrestrial body. In 1970 it rolled out onto the Moon's surface from the Luna 17 spacecraft and was remotely controlled by Soviet scientists. One of its autonomous functions was the ability to sense when it was going to tip over and automatically stop and wait for signal from Earth to help it proceed. New future missions including robotic exploration will be performed on the Moon and Mars. In the last decades, outstanding developments have been achieved in Space technology providing the capability of sending robots to outer Space or landing on others Solar System bodies. The dream of stepping into the outer reaches of the Earth's atmosphere was driven by the fiction of Jules Verne and H. G. Wells; rocket technology was . 1 .

(22) ANALYSIS AND OPTIMIZATION FOR A HEXAPOD WALKING ROBOT FOR PLANETARY MISSIONS. developed to try to realize this vision. The German V2 was the first rocket to travel into space, overcoming the problems of thrust and material failure. During the final days of World War II both the Americans and Soviets, evolving to the technology that we know today, obtained this technology. The desire of mankind to improve and learn has made space exploration a reality, were we want to know the origin, evolution and future of our planet Earth by investigating near planets of the Solar System, whose evolution could tell us were our planet could evolve to. From the first successful orbital launch of the soviet unmanned Sputnik1 (satellite1) mission on October 4, 1957, and later the successful mission of taking people to the moon and returning them safely back to Earth in 1969, has opened a door for engineering; designing vehicles that can be sent today autonomously and later on work together with the astronauts. From the invention of the wheel, which is rightly regarded as the greatest invention in the history of human transportation, at the present time, nearly allterrestrial vehicles are based in wheeled locomotion. Wheels are so entrenched in our culture that it is difficult to think in other locomotion schemes. However, in the past and without the technology that we have today, inventors attempted to design walking machines. In 1893 L.A Rigg obtained a patent for the design of a mechanical horse. However, there is no evidence to prove that he actually built this machine.. 2 . .

(23) INTRODUCTION. Figure 1. Mechanical horse: L.A Rigg REF. 1 . More examples show the interest of designing walking machines. In 1913 Bechtostsheim obtained a patent for the design of a four-legged machine as shown below in Figure 2. Figure 2. Bechtostsheim Patent . In the mid 1950´s a number of research groups started to study and develop walking machines. The reason for such slow progress mainly arises from the . 3 .

(24) ANALYSIS AND OPTIMIZATION FOR A HEXAPOD WALKING ROBOT FOR PLANETARY MISSIONS. complexity of leg coordination control. Until the 1980´s sufficiently compact and powerful computers to perform the necessary calculations were not available due to size and cost. However with the research efforts in robotics and microcomputers major improvements have and will be made. In a book by Bekker REF. 2 explained the superior mobility of legged locomotion exhibited by animals in comparison to wheeled vehicles, that is, a wheel sinks into soft soil and produces a depression, legs create discrete footprints in which any back slip pushes up soil behind the foot which increases traction. Irregular terrain favours legged locomotion and at least five potential advantages can be found in rough terrains REF. 13. 1. Higher speed 2. Better fuel economy 3. Greater mobility 4. Better isolation from terrain irregularities 5. Less environmental damage A walking machine, which can travel were terrain difficulties make wheeled vehicles ineffective, makes it a perfect choice for planetary exploration. Walking legged robots can be classified by their number of legs, usually ranging from eight to one. There is also a different two other concepts of walking robots called moving tables and biomimetic robots. . 4 . .

(25) OBJECTIVES. 2. OBJECTIVES This thesis introduces the mechanical design, analysis and simulation of a hexapod-legged robot for planetary missions, it will introduce the design and analysis of a legged robot in Mars like environment analysing and comparing with the state of the art and past missions. The walking robot developed and manufactured by the Center of Astrobiology (CAB) is based in the mechanical design and analysis that will be presented in this thesis. Legged machines can be effectively used for exploration of abrupt and harsh terrains. A walking robot seems like the best option for this kind of terrain and can be the future of autonomous robots for planetary explorations as they can be more versatile. Some of the advantages are:. •. They do not need a continuous terrain;. •. Less problems with sliding;. •. Greater capacity to overcome obstacles;. •. They produce less harm to the environment that the scientist wants to explore;. From the mechanical design point of view they present a design challenge, also there is a high complexity that has to be taken into account in the static and dynamic analysis problem. But they can represent an alternative to the existing planetary-wheeled rover designs, which have drawbacks that these legged robots could solve; this will also be deeply analysed in this thesis. The following objectives will be addressed in this thesis;. •. Introduction to space exploration history.. •. State of the art in walking robots and machines. . 5 .

(26) ANALYSIS AND OPTIMIZATION FOR A HEXAPOD WALKING ROBOT FOR PLANETARY MISSIONS. •. Reasons for development of the proposed walking robot: Design of the hexapod, types of actuators, number of legs, etc.. •. Kinematic and Dynamic analysis of the hexapod robot: Forces and Reactions.. •. Planetary terrain trajectory selection.. •. 3D trajectory modelling of the designed hexapod robot.. •. Future robots for space exploration: A walking machine?. 6 . .

(27) MARS LANDERS AND WHEELED ROVERS. 3. MARS LANDERS AND WHEELED ROVERS Mars has always been of great interest to scientists as it could explain how Earth could be millions of years from now as it is a planet very like Earth were once could have had a similar atmosphere and most important liquid water, were life could have been formed three thousand million years ago. Since 1970 several missions have landed on Mars surface, they were formed by static and moving robots. Landers can provide atmospheric information both during their descent phase (atmospheric profiles of temperature, pressure, and wind) and once on the surface, geological, biological and atmospheric data. These records help our understanding of Mars in present day, how it has evolved and what Earth could evolve to. The data records provide useful information for the planning of future missions. These landers have been over time static or in the last decades wheeled rovers that can explore the terrain with limited mobility. Past lander missions to the planet Mars will now be described. This will provide an overview of the state of the art in planetary missions an unmanned operations, it also shows the difficulty of such missions and the years of research needed to become a success.. 3.1.. Mars landers: Viking . The two Viking Landers (VL-1 and VL-2) were the first man-made craft ever to return data successfully from the Martian surface in 1977. A photo of a Viking lander is shown in Figure 3. They were generously funded, which had several beneficial results for the mission. Firstly, their scientific instruments had been exhaustively tested and secondly, the landers were robust enough to survive for several Mars years, providing a useful long-term record of surface conditions in . 7 .

(28) ANALYSIS AND OPTIMIZATION FOR A HEXAPOD WALKING ROBOT FOR PLANETARY MISSIONS. all Martian seasons. VL-1 returned meteorological data for 3.3 Mars years, VL-2 for 1.7 Mars years (5.6 and 3.2 Earth years respectively).. Figure 3. Replica of a Viking Lander. REF. 3 . . 3.2.. Mars landers: Pathfinder . The first mission to include rovers, Mars Pathfinder, reached Mars in 1997. It consisted of a small six- wheeled rover and a base station which provided power and telecommunications. The base station also carried a suite of meteorological sensors measuring wind, temperature and pressure REF. 4. One great addition to Pathfinder’s meteorological package (compared with Viking data) was the inclusion of temperature sensors at different heights: at 0.25 m, 0.5 m, and 1.0 m above the lander base. The Soujourner was a six wheeled vehicle with 10.5kg of weight and it could move 500 m from the Lander. Its maximum velocity was 1cm per second. During its 83 days of operation in the Mars surface, the Souyourner sent to Earth 550 photographs from its cameras. and completed chemical analysis. with its x-ray spectrometer from 16 different locations. The rover dimensions were 65centimeters long, 48 width and 30 centimeters of height. Its weight on Earth was of 10,5kg while in mars due to the lower gravity, its weight was equivalent to 4kg. It has a suspension system that was capable of overcoming 13cm obstacles. 8 . .

(29) MARS LANDERS AND WHEELED ROVERS. Figure 4 Pathfinder. REF. 5 . . 3.3.. Mars landers: Mars Polar Lander (MPL) . Mars Polar Lander was a NASA-funded mission programmed to land in the South Polar Region in late 1999. Unfortunately it was lost during atmospheric entry. Its meteorology package was similar to those described above, with two novel features. Firstly, atmospheric humidity was to be measured using a customized diode laser spectrometer. Secondly, temperature and wind measurements were to be made both on a primary mast above the lander, and on a secondary mast deployed downwards from the lander body. This would have allowed more extensive determination of temperature and wind profiles. It should be noted that the primary wind sensor used on the MPL was re-used on future missions.. . 9 .

(30) ANALYSIS AND OPTIMIZATION FOR A HEXAPOD WALKING ROBOT FOR PLANETARY MISSIONS. Figure 5 Mars Polar Lander. REF. 6 . 3.4.. Mars landers: Beagle 2 . The Beagle 2 lander, an European ESA mission launched in June 2003, is a small (landed mass ~35 kg) single lander station. The main stated aim of the lander is 'to search for life, or for environments conductive to life’ [Sims et al., 1999]. The payload includes an Environmental Sensors Suite (ESS), which will measure air temperature at two heights, atmospheric pressure, wind speed and direction, salted grain momentum, UV flux (diffuse and direct at five wavelengths), the total accumulated radiation dose and investigate the nature of the oxidizing environment. Wind and temperature sensors were mounted on the end of a jointed, motorized arm, ~ 0.9 m in length, allowing them to be positioned at several locations around the lander body. Beagle2 was lost during its entry to Mars.. 10 . .

(31) MARS LANDERS AND WHEELED ROVERS. Figure 6 Mars Lander: BEAGLE 2. REF. 7 . 3.5.. Mars landers: Mars Exploration Rovers Spirit and Oportunity . There are two identical Mars Exploration Rovers, MER-A and MER-B. They landed in 2004. The MER Rovers have a smaller science payload than Beagle 2, but a higher data downlink rate thanks to their on-board high-gain antennae. The science payload includes spectrometers and a microscope to examine the rocks, but no dedicated meteorology package. This is presumably because the mobile rovers were not considered a good meteorology platform (unlike Pathfinder, the MER mission will not have a ‘base station’ where a static meteorological mast could be erected, because all communications and power systems are on-board the rover). The payload does include a thermal emission spectrometer (mini-TES), which will periodically be used to take spectra of the sky. Spirit and Opportunity completed their 90-day primary missions in late April 2004. A remarkable six years and five mission extensions later, the rovers continue exploring, gaining renown as one of the most remarkable Mars missions in space exploration history. Spirit has roved across nearly five miles (~8 km) of the Martian landscape, while Opportunity has traversed almost twelve miles (~19 km). From all cameras combined, the rovers have together returned more than 260,000 images, which have assisted in revealing many mysteries ranging from Mars's current climate to its deep geologic past. They have provided more evidence for long-ago Martian surface water, photographed . 11 .

(32) ANALYSIS AND OPTIMIZATION FOR A HEXAPOD WALKING ROBOT FOR PLANETARY MISSIONS. dust-devils, and helped reconstruct the impacts associated with nearby craters. Even though the Spirit rover has been unable to move since January 2010, it continues to return valuable data to this day. Opportunity continues to move far beyond its originally planned path toward new and beckoning destinations.. Figure 7 Spirit Rover. REF. 8 . The Mars Exploration Rovers consists of a box-like chassis mounted on six wheels. The chassis contains the warm electronics box (WEB). On top is the triangular rover equipment deck, on which is mounted the Pancam mast assembly, high gain, low gain, and UHF antennas, and a camera calibration target. Attached to the two forward sides of the equipment deck are solar arrays which are level with the deck and extend outward with the appearance of a pair of swept-back wings. Attached to the lower front is the instrument deployment device, a long hinged arm which protrudes in front of the rover. The wheels are attached to a rocker-bogie suspension system. Each wheel has its own motor and the two front and two rear wheels are independently steerable. The rover has a top speed of 5 cm per second, but the average speed over time on flat hard ground would be 1 cm/s or less due to the hazard avoidance protocols. The rover is designed to withstand a tilt of 45 degrees without falling over, but is programmed to avoid exceeding tilts of 30 degrees. The warm electronics box, houses the computer, batteries, and other electronic components.. 12 . .

(33) MARS LANDERS AND WHEELED ROVERS. 3.6.. Mars landers: NetLander . The proposed Mars NetLander European project consisted of four surface stations. carrying. identical. scientific. instruments. for. seismology. and. meteorology. Components of the meteorology package include: pressure sensors, temperature sensors at three different levels, and a humidity sensor that is much lower in mass than the MPL sensor REF. 9. A specific aim of the NetLander mission is network science, i.e. the analysis of measurements taken simultaneously at different locations. It has been shown that such a network of surface pressure measurement provides useful insight into global atmosphere REF. 10. NetLander mission was cancelled.. Figure 8 Net lander prototype. REF. 11 . 3.7. Mars landers: Phoenix lander NASA landed again in Mars with a lander in 2007. Called Phoenix, it landed at high latitudes (roughly 70°N) and recaptured many of the science goals addressed by Mars Polar Lander and by another cancelled lander in 2001. It includes a digging arm, which will dig a trench up to 1 m deep. Its meteorology package will include a LIDAR instrument, which will probe the Martian atmosphere up to an altitude of 20 km. The LIDAR should be able to measure PBL depth, and return information about dust devils, clouds, and fog in the lower atmosphere. The meteorology package also includes a pressure sensor and thermocouples for temperature measurement; thermocouples are included . 13 .

(34) ANALYSIS AND OPTIMIZATION FOR A HEXAPOD WALKING ROBOT FOR PLANETARY MISSIONS. at several points along the arm to allow temperature profiles to be obtained.. 3.8. Mars landers: MSL rover mission (Curiosity) In August 2012 another rover mission reach Mars, as the mission name indicates MSL (Mars Science Laboratory). The large rover in size is like a small car; it is highly equipped with geological, biological and atmospheric instruments. It provides a robot arm that can dig and recover soil samples, which can later analyse in situ. It is a mission with an expected long life of 2 years as the power source is a radioactive source. The main goal of the mission is to identify if there were ever was liquid water in the planet and how it has evolved to present day. The Center of Astrobiology and the instrumentation group which I form part of are very proud to be part of the MSL mission. My group together with different universities and Spanish companies have designed the weather station that is on board the rover, it is located in the rover mast and will be an important instrument as it will help to understand the climate change through the operation sols (mars day).. . Figure 9 Curiosity MSL mission. REF. 12 . 14 . .

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