In January 2016 I participated in an Underwater Conservation Photography course at MIT. As part of this class, in teams we were to build and modify underwater drones that we would then use on week-long underwater conservation photography trip in Belize. Specifically, we started with the OpenROV 2.8 kit, a low-cost, open source underwater robot for exploration and education. The kit included all parts and instructions in order to make a functioning underwater robot complete with three thrusters (two in the back for maneuvering side-to-side and one at the top for moving up and down), an HD webcam on a tilt servo, four LEDs, a 100 m long tether, and an area to carry a payload. The entire ROV was controlled using an Arduino MEGA through a web browser interface.
After the entire ROV was assembled, our team decided that adding an additional Inertial Measurement Unit (IMU) to our ROV would allow us to have better control over the ROV when it was very far away and hard to see underwater. Additionally, we added on two external lights to enable us to be able to use our ROV at night as the four LEDs were not sufficient for nighttime navigation.
Another modification that our team decided to make for the ROV was a WiFi enabled tether management system. This would allow us to our computer wirelessly to the tether on the underwater ROV in order to control it. We felt this would be really beneficial in enabling us to control the underwater ROV from a safe distance away. I took the lead on this modification and used acrylic to create the frame for the tether wheel, a slip ring to ensure electrical contact between the tether as it is wound up, an adjustable camera tripod to allow for easy mounting of the reel, a nano-sized router to relay the signal of the tether wirelessly to a computer, and USB power bank to power the entire system. Some of the documents I built upon for this modification can be found here and here.