TinyVBS: Design and Implementation of a Palm-Sized Pneumatic Variable Buoyancy System for 100-Meter-Depth Operation in Compact Marine Robot

This paper presents the TinyVBS, a compact pneumatic variable buoyancy system designed for underwater robots operating at depths of up to 100 meters. The palm-sized device, weighing less than 500 grams, features a structurally simplified architecture, facilitating low-cost fabrication and effective compensation for depth-dependent elastic bladder deformation under hydrostatic pressure. By exploiting the inherent connection between bladder expansion volume and wall stress, the device obviates the need for flow or volumetric sensors. A novel pressure-adaptive control strategy dynamically modifies the behavior of the pneumatic components across variable environmental pressures. Laboratory hydrostatic environmental emulations exhibited steady closed-loop performance throughout five consecutive buoyancy adjustment cycles, achieving a total vertical movement of 700 m with a depth resolution of 0.5 m. Sea trials confirmed operational robustness to a maximum depth of 112 m, preserving functionality despite environmental disturbances including currents and thermal gradients. This advancement enables economical miniaturization of buoyancy control systems for coastal robotic applications with strict size and weight constraints.