Fault-Tolerant, Rigidity-Preserving Control of Inflatable Truss Robots

Isoperimetric robotic trusses can adapt to different tasks and environments because they have a high strength-to-weight ratio, can change their own shape dramatically, and can be reconfigured into a variety of different shapes. However, motor failures in operational environments can severely limit operational capabilities if not properly addressed. This paper presents a fault-tolerant control framework for an inflatable robotic truss that maintains functionality despite motor failures, shown through three key contributions. First, we extend the kinematic optimization to handle arbitrary combinations of motor failures by imposing equality constraints to ensure failed actuators are not used. Second, we introduce discrete-time control barrier function (DTCBF) constraints that mathematically guarantee structural rigidity while maximizing workspace utilization, a critical requirement for reliable operation of truss robots under discrete-time control. Third, we implement closed-loop position control using onboard encoder feedback and a forward kinematics-based state estimator, improving positional accuracy in the presence of disturbances. We validate our approach through simulation and hardware experiments on a 2D isoperimetric truss testbed. For a 2D configuration with 6 actuators, we demonstrate >69% workspace preservation under single-motor failures and a >25% improvement in tracking accuracy with closed-loop control. These results establish a foundation for more robust and resilient isoperimetric truss robots operating under degraded actuation.

Modular Isoperimetric Soft Robotic Truss for Lunar Applications

We introduce a large-scale robotic system designed as a lightweight, modular, and reconfigurable structure for lunar applications. The system consists of truss-like robotic triangles formed by continuous inflated fabric tubes routed through two robotic roller units and a connecting unit. A newly developed spherical joint enables up to three triangles to connect at a vertex, allowing construction of truss assemblies beyond a single octahedron. When deflated, the triangles compact to approximately the volume of the roller units, achieving a stowed-to-deployed volume ratio of 1:18.3. Upon inflation, the roller units pinch the tubes, locally reducing bending stiffness to form effective joints. Electric motors then translate the roller units along the tube, shifting the pinch point by lengthening one edge while shortening another at the same rate, thereby preserving a constant perimeter (isoperimetric). This shape-changing process requires no additional compressed air, enabling untethered operation after initial inflation. We demonstrate the system as a 12-degree-of-freedom solar array capable of tilting up to 60 degrees and sweeping 360 degrees, and as a 14-degree-of-freedom locomotion device using a step-and-slide gait. This modular, shape-adaptive system addresses key challenges for sustainable lunar operations and future space missions.

Triangle-Decomposable Graphs for Isoperimetric Robots

Isoperimetric robots are large scale, untethered inflatable robots that can undergo large shape changes, but have only been demonstrated in one 3D shape -- an octahedron. These robots consist of independent triangles that can change shape while maintaining their perimeter by moving the relative position of their joints. We introduce an optimization routine that determines if an arbitrary graph can be partitioned into unique triangles, and thus be constructed as an isoperimetric robotic system. We enumerate all minimally rigid graphs that can be constructed with unique triangles up to 9 nodes (7 triangles), and characterize the workspace of one node of each these robots. We also present a method for constructing larger graphs that can be partitioned by assembling subgraphs that are already partitioned into triangles. This enables a wide variety of isoperimetric robot configurations.