There are several possible approaches to build your ROV. The mechanical design at openrov.com/page/openrov-2-0 is quite elegant and available for purchase as a complete kit or as component parts. At openrov.com/page/open-rov-designs-1, there is a simpler yet similar design. At www.instructables.com/id/Underwater-ROV/, there is another design that is very different from the first. All of these designs could certainly use the BeagleBone Black as the embedded controller.

My physical design is based more on the latter design, using mostly plastic PVC piping as shown in the following image:

This hardware design was done using standard PVC for the main chamber and the two chambers that hold the ballast. The main chamber is 12 inches long and 6 inches in diameter. The two smaller chambers are made from two PVC pipes that are 20 inches long and 2 inches in diameter. These small chambers are capped at both ends and hold the weight required to make your ROV neutrally...