Galloping, bounding and wheeled-leg modes of locomotion on underactuated quadrupedal robots.

摘要

This thesis presents advances in the state-of-the-art in legged locomotion through the development of bounding and galloping gaits as well as new modes of hybrid wheeled-leg modes of locomotion. Two four-legged running robots, Scout II and PAW, are examined, the latter of which is distinguished by actuated wheels at the ends of its legs.Second, through hip actuation, passive leg compliance and controlled wheel action it is possible to make the same vehicle run using a dynamically stable legged gait called the bound. Experimental evidence of this is presented and compared to similar experiments on the same robot with mechanically blocked wheels, a 3D simulation of the same, as well as bounding on a completely different quadrupedal robot, Scout II. While a casual observer finds no difference in blocked-wheel and active wheel control modes, detailed examination of the gaits reveals lower speeds and efficiency as well as decreased repeatability when the wheels are actively controlled.A new method of forward speed control is presented for the bounding gait using liftoff, as opposed to touchdown, leg angles. The liftoff angle method of speed control is shown to be particularly suited to fine-tuning of certain gait performance indices.Third, the underactuated bounding gait is extended to demonstrate, for the first time, that robotic galloping is possible and that it can be achieved in two underactuated quad-rupedal robots and with varying levels of decoupled control. In the Scout II robot the front leg pair and rear leg pairs function independently while in the PAW robot galloping is achieved with no controlled coupling between any of the four legs. The rotary gallop gait demonstrated by both robots is characterized by a significant yaw component and is compared to another bound-derived turning gait which uses liftoff angles to produce yaw. In particular, the correspondence of lead leg to yaw direction in both cases is found to match results from biology. In contrast, while it is thought that animals pivot about their lead leg to turn, the rotary gallop demonstrated by these robots shows that yaw occurs primarily in the leg behind the lead leg.First, hybrid modes of locomotion are demonstrated which use legs to dynamically reposition wheels at specific locations with respect to the body. These modes improve the stability and tire-wear of turning and braking manoeuvres and allow pitch-controlled slope ascent and descent in a wheeled-leg vehicle such as the PAW robot.