SPPIRO: a Soft, Power-autonomous, Proprioceptive In-pipe Robot for adaptive inspection in complex pipeline environments

Abstract Subterranean and industrial pipelines are critical infrastructure for transporting water, oil, and gas, yet their internal complexity—featuring varying diameters, sharp turns, and multi-directional junctions—poses significant challenges for conventional inspection robots. We present SPPIRO, a fully untethered soft robot designed for adaptive pipeline inspection in such environments. SPPIRO integrates compact, custom-designed PCBs for onboard power, sensing, and control, enabling fully untethered operation. Its anchoring modules use motor-driven six-bar linkages with 3D-printed, honeycomb-inspired soft wheels, allowing adaptation to pipeline diameters ranging from 140 mm to 200 mm. The propulsion module consists of three self-sensing pneumatic Kresling origami actuators arranged at 120◦, providing omnidirectional steering and real-time body shape estimation. Using a Piecewise Constant Curvature (PCC) model, SPPIRO reconstructs both its own configuration and the surrounding pipe geometry during motion. Liquid-metal-based capacitive sensors embedded in the feet enable contact-aware anchoring, even in opaque pipelines. Experiments demonstrate SPPIRO’s ability to traverse vertical and horizontal segments, 90-degree turns, and T-junctions, achieving speeds up to 7.86 mm/s—outperforming prior untethered soft in-pipe robots. These results position SPPIRO as a promising platform for autonomous, geometry-aware pipeline inspection.