Our Tensegrity-Inspired Compliant Three degree-of-freedom (DOF) robotic joint adds omnidirectional compliance to robotic limbs while reducing sprung mass through base mounted actuation. This enables a robotic limb which is safer to operate alongside humans and fragile equipment while still capable of generating quick movements and large forces if required. Unlike many other soft robotic systems which leverage continuously soft materials, our joint is simpler to model with low order dynamic systems and has a host of embedded sensing which provide ample information of its position and velocity. We first discuss geometry selection and optimization to maximize the theoretical configuration space of the joint. We then show several of our mechatronic design solutions, which are easily generalized to a multitude of cable-driven mechanisms, and demonstrate the performance of these mechanisms within the context of our hardware prototype. We then present results on the controllable stiffness of our physical prototype. Finally, we demonstrate the strength of our prototype which is capable of lifting a 7 kg mass at a distance of 0.95 meters from the joint.

This paper proposes a novel steerable locomotion controller for six-strut tensegrity robots. Tensegrity robots are lightweight and have many promising features such as robustness, shape-shifting capabilities, and deployability, making them good candidates for exploration and scouting of remote areas. Despite these advantages, tensegrity robots are challenging to control due to their large number of degrees of freedom, nonlinear dynamics, and intrinsic compliance. Recently, many step-wise motion controllers have been employed to simplify the locomotion problem, thanks to the discrete nature of the tensegrity structure. In this paper we present a novel locomotion controller which will steer the direction of motion of a six-strut tensegrity robot when used in conjunction with any preexisting step-wise controller. We validated our controller on the SUPERball v2 robot, showing straight and curved trajectories, and an example of navigation around obstacles. Our method is computationally inexpensive, only requires knowledge about the current base triangle (e.g, via accelerometer data), and can be generalized to any six-strut tensegrity robot which can perform step-wise locomotion.

In this paper, we present the system design and initial testing of SUPERball v2, a completely re-designed 2-meter spherical six-bar tensegrity robot designed to survive high-speed landings as well as locomote to desired locations. SUPERball v2 was designed to enable a host of new actuation and experimentation. The prototype features a fully actuated six-bar design (24 actuators), compliant nylon cables (up to 15% stretch), torque-control enabled motors, and a robust mechanical structure capable of surviving impact velocities upwards of 8 m/s.

Tensegrity robots are a class of compliant robots that have many desirable traits when designing mass efficient systems that must interact with uncertain environments. Various promising control approaches have been proposed for tensegrity systems in simulation. Unfortunately, state estimation methods for tensegrity robots have not yet been thoroughly studied. In this paper, we present the design and evaluation of a state estimator for tensegrity robots. This state estimator will enable existing and future control algorithms to transfer from simulation to hardware. Our approach is based on the unscented Kalman filter (UKF) and combines inertial measurements, ultra wideband time-of-flight ranging measurements, and actuator state information. We evaluate the effectiveness of our method on the SUPERball, a tensegrity based planetary exploration robotic prototype. In particular, we conduct tests for evaluating both the robot's success in estimating global position in relation to fixed ranging base stations during rolling maneuvers as well as local behavior due to small-amplitude deformations induced by cable actuation.

Duct exploration and maintenance is a task well suited for small agile robots, which must be capable of navigating complex and irregular systems of ducts. Previously, we presented a tensegrity robot, DuCTT (Duct Climbing Tetrahedral Tensegrity), which demonstrated the plausibility of such a robot for duct exploration but was never able to successfully demonstrate climbing. Here we present DuCTTv2, redesigned from the ground up to address issues with actuator power, cable routing, compliance and synchronized control present in our first prototype. These improvements allow the prototype to be the first tensegrity robot to demonstrate duct climbing, and does so with an average climb speed of 1.4 cm/s. We also demonstrate initial tests of the prototypes ability to bend and translate its two segments relative to one another, which will allow it to navigate T-junctions and sharp corners commonly found in duct systems. Testing of the prototype is conducted to demonstrate the new faster and more robust control of motion, and analysis of dynamic simulations is presented.

Ball-balancing robots (BBRs) are endowed with rich dynamics. When properly designed and stabilized via feedback to eliminate jitter, and intuitively coordinated with a well-designed smartphone interface, BBRs exhibit a uniquely fluid and organic motion. Unlike mobile inverted pendulums (MIPs, akin to unmanned Segways), BBRs stabilize both fore/aft and left/right motions with feedback, and bank when turning. Previous research on BBRs focused on vehicles from 50cm to 2m in height; the present work is the first to build significantly smaller BBRs, with heights under 25cm. We consider the unique issues arising when miniaturizing a BBR to such a scale, which are characterized by faster time scales and reduced weight (and, thus, reduced normal force and stiction between the omniwheels and the ball). Two key patent-pending aspects of our design are (a) moving the omniwheels to contact the ball down to around 20 to 30 deg N latitude, which increases the normal force between the omniwheels and the ball, and (b) orienting the omniwheels into mutually-orthogonal planes, which improves efficiency. Design iterations were facilitated by rapid prototyping and leveraged low-cost manufacturing principles and inexpensive components. Classical successive loop closure control strategies are implemented, which prove to be remarkably effective when the BBR isn't spinning quickly, and thus the left/right and fore/aft stabilization problems decompose into two decoupled MIP problems.

A robot with the ability to traverse complex duct systems requires a large range of controllable motions as well as the ability to grip the duct walls in vertical shafts. We present a tensegrity robot with two linked tetrahedral frames, each containing a linear actuator, connected by a system of eight actuated cables. The robot climbs by alternately wedging each tetrahedron within the duct and moving one tetrahedron relative to the other. We first introduce our physical prototype, called DuCTT (Duct Climbing Tetrahedral Tensegrity). We next discuss the inverse kinematic control strategy used to actuate the robot and analyze the controller's capabilities within a physics simulation. Finally, we discuss the hardware prototype and compare its performance with simulation.