For effective operation in challenging outdoor environments, mobile unmanned robots face stiff and competing demands including payload capacity, driving speed, range, as well as the ability to traverse rough terrain. To address these issues we introduce the hybrid wheel-leg quadrupedal robot WaLTER. WaLTER utilizes a unique combination of continuously rotating distal leg joints, actuated wheels, and a roll body DOF to efficiently drive on flat ground and effectively tumble over stairs and difficult, broken terrain. We developed an intuitive teleoperation scheme and employed deep reinforcement learning as proof of concept control techniques for the novel morphology. To test its capabilities, we constructed a multi-body simulation in MuJoCo and a 2.1 kg physical prototype for experimentation on traversability and energy economy. Our testing demonstrated the ability to traverse rougher terrain relative to larger-wheeled counterparts and reliable stair-climbing while maintaining a 4 km range on a 24.4 Wh battery (COT: 1.21).

This paper investigates the robustness of underconstrained cable-driven robots to external disturbance wrenches (force/moment combinations). Two cases are considered: impulsive disturbance wrenches and static (constant) disturbance wrenches. In the analysis of these cases a mapping to an intermediate space is introduced, which allows a restatement of Gauss' principle of least constraint in a simpler form. Two measures are developed: the impulsive disturbance robustness measure and the static disturbance robustness measure. It is then shown that these two measures can be expressed as a single disturbance robustness measure, R. This single measure enables underconstrained cable robots to be designed for maximum robustness to both impulsive and static disturbances

This paper presents a method for analytically generating the boundaries of the wrench-feasible workspace (WFW) for cable robots. This method uses the available net wrench set, which is the set of all wrenches that a cable robot can apply to its surroundings without violating tension limits in the cables. The geometric properties of this set permit calculation of the boundaries of the WFW for planar, spatial, and point-mass cable robots. Complete analytical expressions for the WFW boundaries are detailed for a planar cable robot and a spatial point-mass cable robot. The analytically determined boundaries are verified by comparison with numerical results. Based on this, several workspace properties are shown for point-mass cable robots. Finally, it is shown how this workspace-generation approach can be used to analytically formulate other workspaces

This paper introduces a slope-based measure of the stability of a pose of an underconstrained cable robot. In order to define this measure, the set of twists that the end-effector can instantaneously undergo is found. The measure is then derived using an energy-based approach to generalize the definition of slope for mixed-dimensional twists. In order to more easily understand and calculate the measure an intermediate space is introduced. An example is worked out for a sample manipulator and the stability measure is used to define a measure of overall manipulator stability.

This paper introduces the available net wrench set, which is the set of all wrenches that a cable robot can apply to its surroundings without violating tension limits in the cables. This set is used as a framework for understanding and computing wrench-feasibility of a pose of the robot, allowing wrench-feasibility to be tested in the task space. The geometric properties of the available net wrench set are then exploited to permit simple geometric calculation of the boundaries of the wrench-feasible workspace. This workspace generation is extended to two other workspaces as well. Other design tools, including payload specification and failure analysis, are also presented.

The paper presents the spherical joint mechanism, a new mechanism for implementing multiple collocated spherical joints. The mechanism is designed to be strong, rigid, easy to build and have a large range of motion. Two different design concepts are presented and compared to other implementations of spherical joints previously proposed. Finally, implementation issues and potential applications of the spherical joint mechanism are discussed.

This paper examines the kinematic design of digital clay, a new type of computer interface that creates 3-D shapes that a user can interact with. After enumerating the design specifications for the digital clay, a new set of kinematic architectures is introduced: the formable crust architectures. These formable crust mechanisms can form shapes in much the same way a piece of fabric would and have tremendous potential for shape generation. Two measures, the surface freedom measure and the freedom from ground measure, are introduced to aid in evaluating potential designs. Finally, the various architectures are evaluated and compared.

The NSF Digital Clay project is focused on the design, prototyping, integration, and validation of a computer-controlled physical device capable of taking any of a wide range of possible shapes in response to changes in a digital 3D model or to changes in the pressure exercised upon it by human hands. Although it clearly is a natural and unavoidable evolution of 3D graphical user interfaces, its unprecedented capabilities constitute a major leap in technologies and paradigms for 3D display, for 3D input, and for collaborative 3D design. In this paper, we provide an overview of the Digital Clay project and discuss the challenges, design choices, and initial solutions for a new finger sculpting interface designed for the Digital Clay and prototyped using conventional 3D I/O hardware.