ROV Roundup

I sort of abruptly stopped blogging about my homebuilt ROV project quite a while ago. Contrary to the impression that this most probably gave, I actually did come fairly close to finishing the project. At the same time, I would hesitate to call it a success.

I had started to develop quite sophisticated plans for my first ROV, the Mercury, to the point that I bought an Arduino to begin experimenting and learning with in the hopes of using it onboard the ROV (technically, I bought an "Eleven", an Australian Arduino clone). However, not too long after I ended up getting an offer of a postdoctoral position at the University of California, Berkeley, for after I finished my PhD. I didn't want to have to lug a half-built ROV to the other side of the world, finish building it there and then lug it back, so I decided to make Mercury as simple as possible and finish it up ASAP so I could leave it behind in Australia and possibly start a new and more advanced ROV in the US.

The result is that before I left I got Mercury working with no onboard computer of any kind, just five relays for turning bilge pumps, a camera and lights on and off, although I never actually got around to putting on lights. I tested it out in my bathtub (no lighting required!) and on the basis of that decided not to bother getting the lights finished and trying it out in "real water".

Probably the most important thing to note was that it was slow. I used 450 gph bilge pumps for the Mercury, 4 of them. These are at the lower end of the pump rate spectrum, but for that reason they're also the cheapest. I never laboured under the illusion that Mercury would be fast, but I also never imagined it would be as painfully slow as it was. If I were to start the project again, I would either cough up for bigger pumps and/or convert the pumps to propellors and/or take much greater pains to keep overall mass down. I did weigh the entire thing with a digital luggage scale before I packed it away and left, but I forgot to update the Mercury webpage and now I really don't remember.

The other great disappointment was the camera. I bought a very cheap car reversing camera on eBay, and thought it would be ideal. It was small, designed to run off 12V DC, to work in low light and also to be relatively resistant against moisture, which could be handy in the event of a slow leak on the ROV. It turned out to work pretty poorly. For one thing, it featured infra-red LEDs which turn on automatically in low light, and these produced terrible glare on the acrylic viewport I placed infront of it, severely reducing visibility. I had actually read about this happening online, but obviously forgot to test for it. If I were to use one of these cameras again, I would either disconnect the IR LEDs or cover them up with several layers of heavy tape or something. The other big problem was interference when I powered up the pumps. The picture got extremely fuzzy whenever even one of the pumps was on. I actually did think to test for this before enclosing the camera in its housing, and it didn't seem to cause a problem at all. However, once in the water it was definitely an issue. I don't really know why it changed: possibly the different permittivity of water compared to air, or maybe metal from the plumbing around the bath deforming electromagnetic fields. It's possible the issue wouldn't have been so bad in open water. However, even if the IR glare and motor distortion hadn't been a problem, I feel like the picture quality from the reversing camera, combined with the probable low levels of light, would still have been disappointing. A better camera definitely would have been a worth while investment. It seems that ROV building is not a hobby that rewards frugality!

I don't suspect I'll actually get any ROV work done during my time in the US. I live in a small apartment now, without a shed to work in, so it's not especially practical. I have, however, started working on some Arduino projects, which are a bit more forgiving in terms of required workspace and tools, which I'll blog about soon enough. I might give building a better ROV a go once I'm back in Australia.