Design and control of multimodal single-legged vehicles with variable geometry reaction wheel arrays
- Author(s): Schmidt-Wetekam, Christopher
- et al.
This dissertation presents the mechanical and control design of single-legged reaction wheel stabilized robots with wheeled and monopedal locomotion capabilities. The incorporation of variable-geometry reaction wheel arrays (RWAs) increases control authority, as compared to conventional RWAs, and is facilitated by the design of spring-loaded mechanical linkages, which complement high- speed/low-torque actuation and enable the directed release of gradually-accumulated spring energy. The design of the final prototype enables roving, self-uprighting, quasi- static stair-climbing maneuvers, and conventional or end- over-end monopedal locomotion. Linear time-varying (LTV) linear quadratic regulator (LQR) control gains for the stabilization of continuous single-legged hopping maneuvers are solved for, based on the linearization of equations of motion that incorporte nonlinear dampers in order to emulate the no-slip and no-penetration conditions. These controllers are demonstrated in simulation and have been tested on the latest physical prototype. Comparison against high-speed video has revealed that significant angular estimate drift is a key limiting factor towards robust stabilization in practice. A key challenge arises from the excitation of structural modes during the touchdown portion of continuous hopping. The frequencies of these vibrations lie within the controller bandwidth, due to the limited control authority of the system, leading to instability from positive feedback. Significant over-estimation of the forward velocity has been observed to result from foot slip near takeoff. A method of estimating the instantaneous rotation center position using offset accelerometers is developed in order to detect foot slip