Scalable mechanical design for quadruped robots

Abstract

Nowadays, the vital role of robots in human life is not only undeniable, but it is also essential. Quadruped robots, in particular, which mimic four-legged animals, have been significantly crucial in emergency and critical situations. In this thesis, we deeply focused on different mechanical parameters affecting the design of quadruped robots while considering the dimensional scaling of both robot parts and trajectory length and height, thereby potentially leading us to achieve a scalable control architecture for Quadruped Robots (QRs). The scalability of QRs can significantly enhance their capabilities. If a QR can adjust its size, it can quickly conceal itself under debris to observe enemy operations or navigate through narrow pathways under earthquake rubble. Achieving this ability necessitates a scalable mechanical design, which in turn requires a scalable control architecture. Such an architecture relies heavily on mechanical parameters. To realize this scalable control architecture, it is imperative to meticulously monitor the behavior of these parameters and establish relationships among them. In this thesis, we conducted simulations involving a standard commercial quadruped robot, Unitree A1, walking on a flat surface at a constant speed across five distinct scenarios. Given that contemporary quadruped robots typically feature four motors in the hips and four in the elbows, our simulation followed this configuration, employing a total of eight motors. We just focused on walking forward direction. So lateral movements and turning and other disturbance rejection capabilities are ignored. There are four different sizes of the robot, each expanding the robot size by 30%. In the first scenario, we define the length and height of the trajectory as 120 mm and 27 mm, respectively to observe the effect of scaling. In the second scenario, we increased the length of the trajectory from 120 mm to 165 mm to observe the effect of length increase in trajectory. Then in the third scenario, we defined the length of the trajectory as 165 mm while increasing the height of the trajectory from 27 mm to 40 mm to observe the effect of the step height increase. The fourth scenario maintains the same trajectory length and height as the second scenario, and robot scaling remains consistent except for the Torso to observe the effect of Torso. The Torso retains the dimensions of the Torso of the fourth robot in scenario two (the longest). The linear velocity in all scenarios is 250 mm/s and the robots walk on a flat terrain. Due to the unavailability of precise dimension drawings of the Unitree A1 robot, we endeavored to design its various components in CATIA software, approximating existing robot dimensions. Subsequently, the parts were assembled using SolidWorks software. Leveraging the motion analysis tool within SolidWorks, our thesis aims to generate diverse outcomes, including motor torque, power consumption of the motors, reaction forces, motor angular displacements, linear velocity of the robots, and the mechanical cost of transport (MCOT). By comparing these outcomes, our goal is to establish logical relationships among the mechanical parameters of a standard commercial quadruped robot. The findings of this study hold implications for various actuation design architectures, such as Quasi Direct Drive (QQDs) and series elastic robots. They provide valuable insights that can inform the development and optimization of such architectures while scaling. In conclusion, to the best of our knowledge, there have been no studies examining changes in the mechanical principles of quadruped robots during scaling. Quadruped robots are highly effective in specialized tasks, especially in disaster scenarios like earthquakes, where their mobility outperforms fixed robots. However, altering the dimensions of these robots significantly affects their mechanical and control requirements. This study examined key mechanical parameters, including hip and calf torque, power consumption, reaction forces, and mechanical cost of transport across five different scaling scenarios using simulations with a Unitree A1 quadruped robot. The simulations revealed that while the behavioral patterns of the robots remained consistent, the mechanical demands increased with the elongation of the torso, arms, and legs. Significant changes in angular velocity and displacement of limbs were observed, correlating with motor performance. Successful scaling depends on the motors' ability to handle maximum torque and power consumption requirements while maintaining necessary angular velocity. The study found a consistent mechanical cost of transport (MCOT) across scenarios, with a decrease as trajectory length and height increased, highlighting the importance of minor mechanical variations on energy efficiency. These results provide valuable insights for designing various actuator architectures, not limited to a single actuator type, thereby enhancing their applicability. The research identifies a clear pattern of torques, power consumptions, and reaction forces as the robots scale in size. Future research aims to use this data to develop a scalable control architecture, integrating machine learning. Our research elucidates the behavior of these mechanical parameters during scaling, thereby offering a novel perspective on scalable control architecture in quadruped robots. On the other hand, in scenario five, only the Torso is scaled while the arms and legs retain the dimensions of robot three in scenario two.