Fibre optic tether

[rossrov]

Hi MNDeepROV. The price of the locally-sold gear is not really surprising when one considers the "security" label and that the end-users are typically bigger companies or government institutions. Prices in Australia would likely be significantly greater.
The Asian company I mentioned earlier showed many options with their converters. Maybe the only way to get a result is to have to have Queenie talking with someone like them, as long as she (or he?) can get the right specs across. Repeatability, as in spare or extra units, is a concern for me when sourcing specialised gear this way.

Have you considered a single video channel in the tether but using something like this http://www.ebay.com/itm/4-CH-Channel-CC ... 3a965f41a6 in the ROV? Quality would be down, but you could switch to back to one camera for best resolution. Could solve the housing size issue.

[hobbydude]

I thought about fibre as it is the link of choice for commercial ROV's and give 10km range easily.
My understanding is you need a pair if you want duplex comms and most reasonable priced media convertors use duplex. You can run two way comms on one fibre through a circulator however these are not cheap.
Single mode is basically long range gear, across ocean floors to join countrys for example.
Multimode (eom3) is limited to about 15k. A reasonably priced copper to fibre media convertor will give 7km at up to 1gb. The distance rating is reffered to 1310 for 7km if you are talking to suppliers. There are some less expensive options ($150) that are 100mb.
Issue with fibre is its great for light weight distance however does not carry voltage so you either run big batteries on board to be able to take advantage of range or need additional link which is not practical for the distance capability of fibre.
Most media converters are PoE A/C but there are some 5v powered ones which would suit ROV application better.

Termination type is a preference more than anything. Most media converters use ST or SC. SC is a square connector and always plastic so probably a better option for water based use.

So basically if you are running a self powered unit and can run everything over copper and want long distance then fibre could be the go.

[MNDeepROV]

Thanks for the info hobbydude.

Ross, I've been on hiatus a bit and thought I responded to you, but see that I didn't. I saw you link to the video converter you posted. Not a bad option really, at the cost of resolution/size I'm sure. Thanks for sharing. I've actually got it in my mind to try IP cameras, if I end up using more than two cameras. I'm going to start with an ethernet cable so I'll have the extra four wires to use, outside of the four for comms, and will just need to put a hub network hub in. Still doing research on how far the signal can go without degradation. I've seen some literature about a 300' limit. That's my target depth, but my tether is designed to be 500'. Maybe I'll have to make some mods to that.

I've been busy with my business so haven't had time to even get my hull finalized. Back to the shop! Hopefully some time over the holidays will allow for that.

[rossrov]

Hi guys. I'm still a fair way off actually doing anything fibre-optic. Basically doing a new ROV from scratch, bar the ESC and battery housing, which is still my old 90mm downpipe job. Looking forward to getting it all wired up, then use the old cat5 cable with waterproofed end to get new software going on bench and a short water test. Probably be doing EoP before fibre though. Too many big steps at present. New thrusters, new Arduino etc...
Personally I do not know what length of "regular" cat5 cable with Ethernet will work underwater, assuming no leaks. I suspect though that will fall well short of length in air.

[Jaman42]

And you have to know something else. If you want to use reel for tether you will need a "fiber optic rotary joint". One is 3000$(!)

Old quote but I am also planning on using a fiber optic tether and also came to the issues with the prices of the rotary joints, however I have a solution that I am gonna go with. I am going to use ethernet over fibre optics media converters so I will simply place the topside converter inside the spool and build/buy a rotary joint for the ethernet cables and perhaps power supply if I don't use a built in.

Another issue however is the connection to the pressure housing, any affordable connectors out there?

[rovdude]

BIG UPDATE:
Got my 1000 feet of Single Mode 9/125 HERE

It is tremendously light, I am truly amazed.

Now to the connectors, I am using LC connectors that will be placed on using the stripping, epoxy, and polishing method.

I am piecing together my own custom toolkit, because those kits that they sell you on are ridiculously expensive. You only need a stripper, a scoring knife, a polishing puck, the two types of polishing paper, and epoxy. I will post where I am getting all of those if anyone wants to know.

The transceivers I initially posted I am still going with, although which exact model I have not chosen. Honestly, most of them are the same with different company names/speeds (really though, how fast do you need?). They can reach 10Km, but I'm starting modest.

Ross mentioned that they are capacitively coupled with AC, which I found odd. On more research, I found that is common for ethernet, it's actually a standard now. The transceivers only need ground, positive voltage, and the RX/TX lines and their inverses (standard in ethernet).

I am using the Aruidno ethernet board to send sensor data/ receive commands from up top AND sending camera feed from a RPi camera through ethernet, using an ethernet switch. The switch will then be connected to the transceiver.

For waterproofing, I just googled waterproof fiber optic connectors, and there are TONS of connectors to put on the side of the ROV, and keep the water out. These look really good.

[fryslan76]

I am looking forward to more posts about your progress, this is high on my wish list for a second ROV.

[rossrov]

Good work rovdude! I was sure one would not need an expensive termination kit, just the critical tools and good technique.

[hobbydude]

Great to see you having a go Rov dude.
What type of connector do you think you will go with?
Be careful with the SM output of media converter. Laser not visible and some are strong enough to damage pupil.

[rovdude]

What type of connector do you think you will go with?
Be careful with the SM output of media converter. Laser not visible and some are strong enough to damage pupil.

I'm using LC connectors. Really had no reason for it except it seems to be the newest standard, and there seems to be more available for LC. LC is also a smaller form factor, but honestly that didn't matter since all the common ones are small anyway.

And I'm actually not using a media converter, I'm using a transceiver. After checking with the Fiber Optics Association http://www.thefoa.org/ (They have SO MUCH information online) , the only difference between the two is a media converter has external power from an AC wall outlet. Many transceivers do use Small Form-Factor Pluggable (SFP) interfaces, which are cards that you then plug into a media converter. See any problems with that? Luckily I found this, which breaks out the contacts on the card to pins for only $1.80. I also decided on using this transceiver.

Thanks for the safety tip, honestly wouldn't have though about that!

For tools:

SCORER
POLISHING PUCK
POLISHING PAPER
STRIPPER
EPOXY
MICROSCOPE

Now the microscope is not inherently necessary, but if something does not work I thought it would be extremely helpful at locating (or eliminating) where the problem is. There are a lot of things that can go wrong