The design for this ROV is a little unusual. Most ROVs are usually built around a minimum of three thrusters: left, right and up/down. With that setup you essentially have tank like navigation within the horizontal plane, and a third thruster to move the craft up and down in the water.

But this design only has left and right thrusters; so how is that going to work? Well the ROV consists of two major parts: the outer thruster ring which contains the domes to seal the inners from the water, and the inner robot assembly which hangs from the outer ring and allows it to pivot. The inner robot assembly will always maintain a horizontal position in the water (due to the low ballast tank and the wonders of gravity) while using a servo to pivot the outer assembly around it. This lets the thrusters pivoted up and down, allowing the ROV to change the angle of the plane it flies in, and so providing angled ascent and descent.

Is this a good idea? That's debatable, but it's been an interesting adventure in engineering to find a way to build it. More on the challenges later.