Real AUVs (autonomous underwater vehicles) separate two control mechanisms that ground robots don't need. Ballast tanks pump seawater in or out of the hull, changing the vehicle's mass without changing its volume — so its average density rises above or falls below that of seawater. A denser vehicle sinks, a less-dense one floats, and at exactly seawater's density it hovers at any depth for free: this is neutral buoyancy, the same principle submarines use, and it costs no thruster energy at all.
Thruster vectoring handles everything ballast can't: horizontal motion and rotation. Four angled thrusters (T1–T4) combine their individual thrust to produce forward/back (surge), side-to-side (sway) and turning (yaw) — push all four forward for surge, spin the port and starboard pairs opposite ways for yaw, without any rudder. Two vertical thrusters (T5–T6) provide fine depth trim.
- Ballast fill — above 50% the tanks are net-flooded (denser than water, sinks); below 50% they're net-purged (less dense, rises); at 50% the vehicle is neutrally buoyant and holds depth.
- Directional buttons — fire the specific thruster combination a real AUV uses for that motion; the six bars on the left show each thruster's live output.
- Together, six independently controllable axes (surge, sway, heave, roll, pitch, yaw) are what "6-DOF underwater control" means. This 2D port shows the top-down view (surge/sway/yaw) and a depth-profile view (ballast/heave) side by side — toggle between them on small screens.