Browsing by Author "Meyer, Jacques"
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- ItemTrajectory optimization inspired pneumatic locomotion on compliant terrains(Stellenbosch : Stellenbosch University, 2022-04) Meyer, Jacques; Fisher, Callen; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.ENGLISH ABSTRACT: In order to achieve true autonomy, robots have to be able to handle complex and rough terrain generally found outside of the lab. Legged robotics has become the focal point in recent years, aided by the developments in trajectory optimization methods. However, a major problem in legged robotics is dealing with hybrid contacts with different terrain types. The difference in dynamics due to the interaction between the foot and the ground makes it increasingly difficult to design controllers that successfully execute on multiple surfaces. This work investigates trajectory optimization methods for a pneumatically actuated mono-pod on rigid and compliant terrain. Trajectory optimization was utilized to obtain trajectories for acceleration, steady-state and deceleration hopping on compliant terrain, as well as rigid terrain surfaces. For the compliant terrain trajectories a novel method was developed to model the specific characteristics of the compliant terrain. Trajectories were generated using this method for two different compliant terrain types, namely: rough gravel and fine gravel. To mimic the pneumatic actuation in the trajectory optimization problem, a simplified mathematical model was developed to accommodate the bang-bang force of the pneumatic actuator. This model used complementarity constraints and node bucketing techniques to mimic the behaviour of a real pneumatic actuator with damping and delay. Once these methods and models were implemented, trajectories were executed, in open-loop, on a fixed body robotic platform that was designed and built for this thesis. The executions were compared to the trajectory results. The rigid terrain trajectories were executed successfully on a hard surface, but failed on gravel surfaces. The compliant terrain trajectories executed successfully on gravel surfaces, indicating that the method developed to model compliant terrain is a more accurate representation of the gravel surfaces compared to the rigid terrain trajectories. After these results showed that the methods used to describe the compliant terrain proved to be accurate, a free body mono-pod robot and support rig was designed and built. The support rig limited the movement of the mono-pod to the sagittal plane to mimic the limitations of the trajectory optimization model. Acceleration, steady-state and deceleration trajectories were generated for the free body mono-pod on compliant terrain surfaces and a rigid terrain surface. From these trajectories a controller was designed with the main sources of feedback being the height of the robot and the angle of the free moving body of the robot. The free body mono-pod robot used the controller to execute hopping from rest back to rest with three steady-state hops in between. For each terrain type the controller was adjusted based on the generated trajectories. The results show successful execution of the trajectories on all terrain types using the controller. Lastly multi-surface hopping was executed on the mono-pod robot platform. The controller was adjusted to hop from a hard surface to a compliant surface and executed these trajectories successfully.