Buoyancy Compensation for Underwater Robots (2D)

An underwater ROV or AUV that must hold a steady depth to inspect a structure or take a sample is fighting a genuinely unstable system: rising water pressure compresses any gas-filled volume in its housing, which reduces buoyancy exactly as depth increases, which pushes it deeper still. This 2D side-view companion to the site's 3D underwater-robot buoyancy model drops two identical robots at the same target depth — one with a fixed, uncontrolled buoyant volume, one with an active ballast pump that senses depth error and corrects it — so the runaway and the correction can be watched side by side, both in the water column and on the depth-vs-time trace.