Keep Rollin' - Whole-Body Motion Control and Planning for Wheeled Quadrupedal Robots

We show dynamic locomotion strategies for wheeled quadrupedal robots, which combine the advantages of both walking and driving. The developed optimization framework tightly integrates the additional degrees of freedom introduced by the wheels. Our approach relies on a zero-moment point based motion optimization which continuously updates reference trajectories. The reference motions are tracked by a hierarchical whole-body controller which computes optimal generalized accelerations and contact forces by solving a sequence of prioritized tasks including the nonholonomic rolling constraints. Our approach has been tested on ANYmal, a quadrupedal robot that is fully torque-controlled including the non-steerable wheels attached to its legs. We conducted experiments on flat and inclined terrains as well as over steps, whereby we show that integrating the wheels into the motion control and planning framework results in intuitive motion trajectories, which enable more robust and dynamic locomotion compared to other wheeled-legged robots. Moreover, with a speed of 4 m/s and a reduction of the cost of transport by 83 % we prove the superiority of wheeled-legged robots compared to their legged counterparts.Comment: IEEE Robotics and Automation Letter

Suspension effect in tip-over stability and steerability of robots moving on terrain discontinuities

[ES] En este artículo se estudia el efecto que produce el sistema de suspensión sobre la estabilidad al vuelco y la capacidad de direccionamiento en un robot móvil Skid Steer, cuando este se enfrenta a distintas discontinuidades del terreno: descenso (frontal y lateral) y ascenso sobre escalones, además del desplazamiento sobre zanjas. Específicamente, se estudió el instante cuando se generan cargas de impacto producto del movimiento del robot sobre la irregularidad del terreno. En cada caso se hizo un análisis correlacional del efecto sobre la estabilidad al vuelco y el direccionamiento (cuantificadas con métricas fundamentadas en las fuerzas de reacción de las ruedas con el suelo), al variar cuatro parámetros que definen el sistema de suspensión: constante de rigidez en los resortes, constante de amortiguamiento en los amortiguadores y las constantes de rigidez y amortiguamiento en las ruedas. Por último se estimó para cada caso, qué magnitudes deberían adquirir estos parámetros para garantizar una mejor estabilidad y direccionamiento del robot.[EN] This article studies the effect produced by the suspension system in tip-over stability and steerability of a Skid Steer mobile robot, when it faces different terrain discontinuities: descent (front and side) and ascent on steps, plus displacement over ditches. Specifically, the moment was studied when impact loads producted by the robot's movement on the irregularity of the terrain are generated. In each case, a correlational analysis was made about the effect in tip-over stability and steerability (quantified with metrics based on the reaction forces of the wheels with the ground), by varying four parameters that define the suspension system: stiffness constant in the springs, damping constant in the dampers and the stiffness and damping constants in the wheels. Finally, it was estimated for each case, what magnitudes these parameters should acquire to ensure better stability and steerability of robot.Este trabajo ha sido realizado parcialmente gracias al apoyo del Decanato de Investigación de la Universidad Nacional Experimental del Táchira bajo los proyectos 01-025-2016 y 01-008-2018.García, JM.; Valero, A.; Bohórquez, A. (2020). Efecto de la suspensión en la estabilidad al vuelco y direccionamiento de robots moviéndose sobre discontinuidades de terreno. Revista Iberoamericana de Automática e Informática industrial. 17(2):202-214. https://doi.org/10.4995/riai.2020.12308OJS202214172Abo-Shanab, R., & Sepehri, N., 2005. Tip-over stability of manipulator-like mobile hydraulic machines. Journal of Dynamic Systems, Measurement and Control , 127 (2), 295-301. https://doi.org/10.1115/1.1898239Bluethmann, B., Herrera, E., Hulse, A., Figuered, J., Junkin, L., Markee, M., y otros., 2010. An active suspension system for lunar crew mobility. 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Revista iberoamericana de automática e informática , 10 (2), 121-132. https://doi.org/10.1016/j.riai.2013.03.002Kang, S., Lee, W., Kim, M., & Shin, K., 2005. Robhaz-rescue: Rough-terrain negotiable teleoperated mobile robot for rescue mission. IEEE International Workshop on Safety, Security and Rescue Robotics, (págs. 105-110). Kobe.Lei, X., Zhang, G., Li, S., Qian, H., & Xu, Y., 2017. Dual-spring AGV shock absorption system design: Dynamic analysis and simulations. IEEE International Conference on Robotics and Biomimetics (ROBIO), (págs. 1-7). Macau. https://doi.org/10.1109/ROBIO.2017.8324559Li, B., Ma, S., Liu, J., Wang, M., Liu, T., & Wang, Y., 2009. Amoeba-I: a shape-shifting modular robot for urban search and rescue. Advanced Robotics , 23 (9), 1057-1083. https://doi.org/10.1163/156855309X452485Liu, Y., Meng, X., & Zhang, M., 2008. Research on mobile manipulator tip-over stability and compensation. 8th WSEAS International Conference on Robotics, control and Manufacturing Technology, (págs. 114-120). Hangzhou.Luo, Z., Shang, J., Wei, G., & Ren, L., 2018. Module-based structure design of wheeled mobile robot. Mechanical Sciences , 9 (1), 103-121. https://doi.org/10.5194/ms-9-103-2018Mihon, L., & Lontiș, N., 2019. Modeling and analysis of a vehicle suspension. En N. Burnete, & B. Varga (Ed.), Proceedings of the 4th International Congress of Automotive and Transport Engineering (AMMA 2018), (págs. 113-121). https://doi.org/10.1007/978-3-319-94409-8_14Moosavian, A., Alipour, K., & Bahramzadeh, Y., 2007. Dynamics modeling and tip-over stability of suspended wheeled mobile robots with multiple arms. IEEE/RSJ International Conference on Intelligent Robots and Systems, (págs. 1210-1215). San Diego. https://doi.org/10.1109/IROS.2007.4398999Reid, W., Pérez-Grau, F., Göktogan, A., & Sukkarieh, S., 2016. 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Design and development of a low-cost hybrid wheeled-leg for an agricultural robot : a thesis presented in partial fulfilment of the requirements for the degree of Master of Engineering in Mechatronics at Massey University, Manawatū Campus, Palmerson North, New Zealand

The following Figures are re-used with the publishers' permission: 9a, 11c, 13b, 14a, 16a, 19. These Figures are re-used with permission from IEEE: 10a ©2005 IEEE; 10b ©2008 IEEE; 11b ©2011 IEEE; 12a ©2010 IEEE; 13a ©2015 IEEE; 13c ©2010 IEEE; 14b ©2013 IEEE; 14c ©2010 IEEE; 15 & 22 ©2016 IEEE; 16b ©2017 IEEE; 18a, b &c ©2005 IEEE; 20a & b ©2011 IEEE; 21 ©2009 IEEE; 23 ©2016 IEEE. Other Figures are either in the public domain, or re-used under a Creative Commons license.Currently, New Zealand is financially dependent on its agricultural industry quite heavily. However, the agricultural sector faces several problems such as labour shortages, environmental issues and increasing costs. In other industries, robotics and automation have been used to combat these issues successfully. Yet, in agriculture, robotics and automation have only been adopted in horticulture but not in pastoral farming (dairy, sheep, and cattle). This is because the tasks and terrain in horticultural are well defined and structured, whereas, in pastoral farming, the terrain and tasks are unstructured and dynamic. The locomotion used by current horticulture robots is either not capable of operating in unstructured terrain or are inefficient. Therefore, pastoral farming will need to adopt new forms of locomotion in automation platforms. In this thesis, it is proposed that hybrid wheel-leg locomotion will enable robots to operate in unstructured and dynamic environments. With this in mind, a low-cost prototype hybrid wheeled leg has been designed and built. The leg has been designed to specifications which were developed based on the tasks that a multipurpose horticultural and pastoral farming robot is expected to do. A joint actuator is extremely influential towards the performance of any robotic leg. Due to the unstructured terrain, in which the leg will operate, it was concluded, that a mechanically compliant actuator is required. Because of the prohibitive cost of commercially available actuators, a prototype high torque, low-cost mechanically compliant actuator was designed and built to meet the specified torque requirements. This was in addition to the design and fabrication of the leg itself. Once the leg was assembled, the sensors, actuators and the motor were interfaced with ROS™ (Robot Operating System). ROS makes it easy to coherently control each leg's DOF (Degrees of Freedom) and makes it easy to combine and control multiple legs into a robot. Testing of the leg produced very encouraging results, but there were two issues with the performance of the actuator. The first issue is due to the poor implementation of the position control algorithm that came standard with the actuator motor driver. The problem can be resolved through software or the purchase of a different motor driver. The second issue is that the actuator only outputs 23 Nm of torque, but the motor used is rated at 50 Nm. This is due to the cheap drill motor used which is from an unknown brand; it is hoped that a more powerful drill motor from a well known reputable brand will be able to output its rated torque

System Design, Motion Modelling and Planning for a Recon figurable Wheeled Mobile Robot

Over the past ve decades the use of mobile robotic rovers to perform in-situ scienti c investigations on the surfaces of the Moon and Mars has been tremendously in uential in shaping our understanding of these extraterrestrial environments. As robotic missions have evolved there has been a greater desire to explore more unstructured terrain. This has exposed mobility limitations with conventional rover designs such as getting stuck in soft soil or simply not being able to access rugged terrain. Increased mobility and terrain traversability are key requirements when considering designs for next generation planetary rovers. Coupled with these requirements is the need to autonomously navigate unstructured terrain by taking full advantage of increased mobility. To address these issues, a high degree-of-freedom recon gurable platform that is capable of energy intensive legged locomotion in obstacle-rich terrain as well as wheeled locomotion in benign terrain is proposed. The complexities of the planning task that considers the high degree-of-freedom state space of this platform are considerable. A variant of asymptotically optimal sampling-based planners that exploits the presence of dominant sub-spaces within a recon gurable mobile robot's kinematic structure is proposed to increase path quality and ensure platform safety. The contributions of this thesis include: the design and implementation of a highly mobile planetary analogue rover; motion modelling of the platform to enable novel locomotion modes, along with experimental validation of each of these capabilities; the sampling-based HBFMT* planner that hierarchically considers sub-spaces to better guide search of the complete state space; and experimental validation of the planner with the physical platform that demonstrates how the planner exploits the robot's capabilities to uidly transition between various physical geometric con gurations and wheeled/legged locomotion modes