We report on the model-based development of leaping behavior in a RHex-style hexapod robot. A three-legged model is proposed to analyze the dynamic behavior of leaping, and this serves as a guide for implementing the behavior on the empirical robot. The model has a rigid body and three massless and compliant legs, which have rolling contact with the ground for better modeling the leg behavior of the empirical robot. By investigating the model's behavior, a two-step leaping maneuver is developed. The first step is utilized for adjusting the body pitch, synchronizing the phases of all six legs, and speeding up the body's forward velocity. This provides adequate initial conditions for the second step leaping, which creates a long-distance flight and adequate landing for follow-up running. In addition, we also report on the strategy of stride length regulation. With implementation of the range sensor, the robot can regulate its stride in order to reach a specific and desired position for leaping. The gait transition and initiation of leaping is fully autonomous. The behavioral development is implemented in the RHex-style robot and is evaluated experimentally.

We report on development of dynamic running behavior on the RHex-style hexapod robot. By using the Rolling SLIP (R-SLIP) model as the “template” of the robot, together with the investigation of the stability properties of the R-SLIP model, the robot implemented with the selected trajectory based on the R-SLIP motion can immediately excite its dynamic running behavior (i.e., composed of stance and flight phases) without necessity of extra tuning or optimization effort. In addition, a feedback control strategy is proposed to regulate the robot's motion when the robot's operating region is not located at the stable area of the R-SLIP model (i.e., no stable fixed point). The controller includes three portions: a body velocity estimator, a database containing a wide range of pre-computed R-SLIP trajectories, and a control law which regulates the robot motion to the desired R-SLIP profile. The proposed methodology of robot trajectory generation and strategy of running regulation are experimentally evaluated.

The algorithm of trajectory planning and four leg coordination for quasi-static stair climbing in a quadruped robot is reported. The development is based on the geometrical interactions between the robot legs and the stair, starting from single-leg analysis, followed by two-leg collaboration, and then four-leg coordination. A brief study on stability of the robot is included. In addition, the first-step and last-step algorithm which deals with the transient between the flat ground and the stair is reported as well. Finally, simulation and experimental validation are performed to evaluate the performance of the algorithm.

This video submission presents the experimental validation and testing of a leg-wheel hybrid mobile robot Quattroped. By combining the smooth and efficient motion of wheels on the flat ground with the great mobility of legs on rough terrains, the design of the robot aims for agile and versatile yet efficient locomotion in both natural and artificial environments. Compared to most hybrid platforms, which have separate mechanisms of wheels and legs, this robot is implemented with a transformation mechanism that directly changes the morphology of wheels (i.e., a full circle) into half-circle legs, each with 2 active degrees-of-freedom (i.e., combining two half circles as a leg ). The experimental testing includes flat terrain driving and turning in the wheeled mode, leg-wheel mode switching, and step crossing, bar crossing, natural rough terrain walking, and stair climbing in the legged mode.

Inspired by the observation that the cockroach changes the tripod gait to other gait to cross the step, we report on the design of the step crossing gait in a RHex-style hexapod robot which enables the robot to cross the step with height more than twice of the leg length. Similar to the cockroach's motion, the gait is composed by two stages: rearing stage to lift the front side of the body, and lifting stage to maneuver the center of mass of the body to pass the edge of the step. The inclinometer is utilized to detect the height of the step during crossing, so the robot can automatically adjust the gait to cross the steps with different heights. The performance of the algorithm is experimentally evaluated.