Preliminary Evaluation on the Operational Use of Magnetic Connections in the Deployment of a Rapid-Deployment Amphibious Robotic Chassis

Project CIPACTLI (Compact Integrated Polymer Amphibian for Coastal and Littoral Investigation) evaluated whether rare-earth neodymium (N52) magnetic couplings provided an operational advantage over flexible magnetic tape in a rapid-deployment, cannon-launched amphibious robotic chassis intended for search-and-rescue (SAR) and environmental-monitoring use. Two prototype iterations were tested across a towed transit-rate proxy for movement performance, static structural loading, and ballistic-launch survivability. The first prototype was a tensegrity-inspired, segmented soft robot with inflatable buoyancy modules joined by magnetic couplings; a 23 factorial design varied core tendon material (nylon vs. steel), substrate (land vs. water), and magnet type (flexible tape vs. N52 neodymium). Tendon material was the dominant driver of transit rate (partial η2 = 0.637, p < 0.001); magnet type showed no significant main effect (p = 0.507). Because the per-cell sample size (n = 3) yielded low statistical power (~0.15), the null result was additionally evaluated with a two one-sided-tests equivalence procedure at a pre-specified margin of ±0.20 m/s (≈18% of the grand mean); the reconstructed 90% confidence interval for the magnet-type difference (−0.067 to +0.152 m/s) fell entirely inside this margin, supporting statistical equivalence at that margin, though a narrower margin could not be resolved with the present sample. Both magnet types achieved 3/3 survival under ballistic launch. The second prototype eliminated magnetic couplings and inflatable bladders in favor of a monolithic PLA body with integrated buoyancy; this design change (which altered four construction variables simultaneously and therefore cannot isolate any single feature’s contribution) was associated with a 6.96-fold increase in quasi-static compressive load capacity (p = 0.001), equivalent ballistic survivability, and a 24.9% reduction in towed aquatic transit rate. Tethered-deployment trials (n = 6 per condition) showed no observed tether-related failures. Within this bounded operational envelope—one magnet geometry and grade, one mounting scheme, one energy level, ambient chlorinated fresh water, and room temperature—rare-earth N52 magnets conferred no measurable transit rate or survivability advantage over flexible magnetic tape. Corrosion in saline water, thermal cycling, and long-duration exposure, which govern neodymium performance in actual maritime service, were not evaluated and are identified as priority future work before any broader material-substitution recommendation is warranted.