I can't believe I've been sitting on this post for over a year.

During senior year of college (2014) I was head of electrical engineering for the marine technology club and designed the control system for our ROV, Draugr. I ended up receiving credit for it as an independent study course and later wrote a paper which won a prize in the IEEE student paper contest.

The goal of the competition that year was to investigate a mockup shipwreck on the floor of a 17' pool. The club partnered with the Society for Mechanical Engineers to build the frame on the mechanical engineering department's waterjet table provided they could have use of the ROV for their own manufacturing design competition.

The body of the ROV was constructed from three flat HDPE sheets connected by brackets. Buoyancy was provided by a large PVC tube at the top of the ROV which also served to strengthen the frame and keep the center of buoyancy high above the center of mass. Under the deck was a metal plate with regularly spaced holes for mounting equipment and ballast trim weights.

Propulsion was provided by six bilge pump motors with attached propellers and shrouds. Instead of the previous year's incredibly massive metal drybox we decided to use an off the shelf plastic otterbox to house the electronics. Holes were drilled into the side and the seacon waterproof electrical fittings from the previous year's ROV were installed.

The overall footprint of the ROV fit within a rectangular box with rounded edges approximately the size of a all-in-one office printer which could easily be lifted by a single person leaning over the edge of a swimming pool, dock or boat.

The design of the electrical system diverged wildly from previous years. We opted for a two board design: one small carrier for a 48-12V DC-DC step-down converter and another large board holding the control system, power regulation, communications and motor drivers. The tether was a two cable system: one carried 48V power and the other was an extended length (something like 50') USB cable. This allowed both control signals and video to be carried by the same cable. In order to actually make the 50' run the USB cable required a mid-length repeater that was housed in-line within waterproof plastic potting (we double potted it ourselves just to be sure).

The whole super-long USB tether idea came about due to an image processing mission objective given by MATE as part of that year's challenge. Traditionally most ROVs in our class used analog cameras connected to a monitor at the surface. We had to make panoramic images of objects on the pool's floor and waterproof webcams were far cheaper than building a control console with an analog image capture card in it. At first we considered placing an embedded computer like a RasPi or beaglebone onboard the ROV and talking to it over ethernet but in the end we went with this USB-supertether concept for some reason that I can't really remember now.

Anyway, the motherboard had a built-in USB hub (more about that later) that had an internal connection to an atmega microcontroller. The computer at the surface on the other end of the tether would see a USB-serial device and could command the motors to spin, sensors to take measurements, actuators to move, etc. The hub also had breakouts for other USB devices onboard the ROV, namely webcams. We weren't even limited to one webcam, in fact I went a bit overboard and attached two waterproof webcams about 2.5" apart and fed them into a pair of stereo vision goggles I build out of a cellphone, cardboard and a couple fresnel lenses. (This was pre-google cardboard so we couldn't just order one.)

VR undersea adventures! Unfortunately it was a gimmick and we didn't have time to make the camera mounts steady (they were made of velcro for easy changes) or the stereo goggles reliable enough to use off the test bench. You can see the how ridiculously adorable the ROV looked with the dual mounted cameras though.

The surface control console we ended up settling with was a laptop running an application one of our team members wrote that showed the webcam steam onscreen with the ability to save image snapshots. It also took commands from an xbox controller and passed them on to the microcontroller to run the motors. It ended up being simple and intuitive enough that we allowed random people to use it in one of the school's fountains.

In the end we didn't qualify for the national competition due to an electrical failure. After several hours of successful testing at the regional MATE competition we attempted to preform our qualification trial. While transferring the ROV to the qualification pool we forgot the battery supply at our table. Instead of walking across the room to retrieve them another nearby team (not naming any names) offered us their batteries for the qualification test. Long story short, we plugged them in and they killed the ROV. We were unable to restart it despite subsequent attempts using our own batteries.

During post-mortem testing that evening at metrix we realized that our batteries had internal current limiters that would only allow them to provide a few amps max. The batteries we borrowed had no such limitation. Upon powerup the inrush current was considerable and the powerful batteries were all too happy to provide enough current to burn out a trace on one of our PCBs. Here's where the failure gets a bit complicated.

Due to a design oversight on my part the specific package of the USB hub IC required for the motherboard was out of stock. As an alternative we purchased a small USB hub which required modification (USB connectors were too large to be passed directly through the waterproof cable penetrators and had to be cut). Space was so limited within the drybox that we couldn't simply reattach the ends of the USB cables and plug them into the hub, instead we had to wire them directly into the electronics with terminal blocks.

We desoldered the USB hub's ports and created a simple PCB on copper-clad board that converted them to terminal blocks to which we attached the stripped USB cables. It was on this board that one of the overly-thin traces burned out, cutting off power to the in-line repeater on the tether cable.

The failure could have been avoided numerous ways: the onboard hub could have been constructed with the proper IC package, the trace on the impromptu PCB could have been thicker, the drybox could have been large enough for real USB connections, we could have walked across the room to retrieve our own batteries, we could have had a replacement electronics package in the event of failure or the design architecture of the ROV could have eliminated the USB system altogether.

After greenwiring over the failed PCB trace the ROV was once again functional and went on to be tested in operational conditions at a local lake. A senior from the mechanical engineering department constructed a stabilization system enclosed within a waterproof tube which we mounted to the metal plate on the ROV's underside. The tube contained a leadscrew which drove a weight fore and aft, adjusting the trim of the ROV. It was controlled automatically by an accelerometer and had manual override signals to allow us to angle the ROV as we liked.

Currently the ROV is in storage at WWU and will probably be reusued for parts during the next MATE competition. I have to say, despite the team never making it to nationals I think we have more fun building creative new ROVs than we would making incremental improvements year after year to the same frame like most teams do.

I'm sure one of my classmates has the videos and photos from the lake test and trim system, if I can get ahold of them I'll make an update.

You can see the firmware and pcb design files at the git repo.