The latest edition of this control system and all circuits can be found here: ROV Control Sketches – Fourth Edition
The electronic circuit for the ROV is relatively simple because most of it is concerned with connecting fairly sophisticated equipment such as the speed controllers to the various pins on the Arduino. The only circuits of substance are those associated with monitoring the battery voltage and controlling the light array.
At this stage the board for the circuits is just cobbled together on veroboard. Once the circuit design as settled a proper circuit board will be developed.
The diagram presented above is able to be downloaded from here in vectorgraphic formats such as DWG, DXF, and TurboCAD formats. The circuit diagram is also available as a pdf here - ROV_Circuit_Diagram.pdf.
More detail of the Video system can be found here