Hi all, sorry I haven’t replied on here, I’ve been a bit busy!

 Tom and Tom – thanks for the info – useful stuff!

 John – I don’t know if you found what you need, but you could have a look at waterproof enclosures for cameras…. they are usually clear, are sealed for relatively high pressures and are fairly cheap.

Mike, thanks for the suggestion. I have considered working for an ROV company. I don’t know what formal experience BAe would want (although maybe I have what they need!) I’ll have a look on their site.

I’ve bought a cheap brushless motor and ESC from my local model shop, not really to use on the ROV, more to test that I can control it from a computer interface board etc. I’ve come accross a problem I wasn’t expecting – the ESC is rather too smart. Its designed to work with a variety of Lithium and Nicad type batteries, but it detects battery voltage and current and refuses to start up unless the power meets its requirements.

 Obviously a useful safety feature on a model plane (which is what its designed for) since you don’t really want to take off and if your battery isn’t charged, but annoying when you are trying to test out control systems!

I’m in the position of not knowing if my PWM control board will be able to generate the right signals for an ESC to use, since I can’t supply the right power. I very nearly bought an industrial transformer, but I’m loathe to spend the money on that if there is someting more fundamental wrong with my design.

I imagine I’m going to have splash for a lipo battery (or see if an old laptop battery will work?) in order to test things out first. Its frustrating because I feel the power issue is the last bit of  "research" I need to do before I can order up a load of bits and actually start the fabrication.

The more I look at the components I have, the more tempted I am to actually build my own ESC… and then I wonder whether it wouldn’t be easier to buy a coil winder and build my own motors as well! It all seems to be getting more complicated than I hoped!

Anyway needless to say I’m writing it all up, and I’ll put it on a website at some point. 

Thanks again for the help, and if anyone has a suggestion for powering a small ESC and motor on the workbench on a tight budget, I’d love to hear it!

 Or, if anyone has built their own brushless ESC, or knows where I can get plans, maybe you could give me a few pointers?

 Ken

Andrew – brushless really are the best things for this project. Theres several reasons:

* Brushless motors are much easier to "marinise" – the simplest way is just to coat the windings and the magnets with two-part paint, or embed them in a block of resin, and run open to the seawater (which provides good cooling as well). Brushed motors have brushes which you need to protect from seawater. (Bearings are a different issue, but can be run wet for at least a little while before dieing!)

* Brushless motors are much easier to pressure proof – because there aren’t brushes to protect, theres no need to expensive and failure-prone shaft seals etc. Pressure is a real killer, and very hard to keep out – better to just let it in.

* Most subtly, but possibly most importantly, brushless motors are "clean" – they don’t produce electrical noise like brushed motors do. This is important when the ROV will have onboard computers and delicate sensors (fluxgate compass, accellerometer, sonar, possibily magnetometers). 

Performance and efficiency aren’t very important – I have unlimited power (down a tether) and weight and size are of marginal importance (its going to be a big beast, probably at least 20kgs).

I may end up making my own motor and controller combo, its something I’m researching at the moment. This would allow me to make something much higher voltage (useful when trying to send power down 300m+ of cable). It would also allow me to build something slower revving.. I’m lazy enough to want to avoid this though!

Tom – Goal is to produce an ROV with similar capabilities in terms of depth and sensor platform to a SeaEye Falcon (http://www.seaeye.com/falcon.html) but with more on-board intelligence – I would like to be able to use my ROV to experiment with programming for Autonomous Underwater Vehicles (even though mine will be tethered). Simple tasks like station keeping, navigating to waypoints and performing grid searches would be a first step. 

Reasons for building the ROV… well, its mainly for my own interest, and to learn more about ROVs. I’m a sailor and a diver, and I have a background in robotics and control systems, so it seems to fit in nicely.

Some people have asked if I could commercialise it… the answer is, I don’t know. Certainly theres a market out there if they can be made cheaply enough – the SeaEye falcon is one of the cheapest ROVs, and a basic one starts at around £70k – I’m hoping to build mine for around 1% of that cost!

What did you mean about the analogue thing? Not sure what you are refering to!

Good bit of detective work to find the website BTW – and I realise I haven’t actually stated my goals in any of the articles, so I’ll have to correct that I suppose!

I’m still struggling with the whole controller/motor issue, although due to "real life" I’ve been doing other stuff and haven’t dedicated much time to it.

 Ken