Fibre optic tether

Control Boards, Controllers, Tethers, Ect.
Post Reply
kenl
Posts: 153
Joined: Oct 19th, 2013, 8:50 am
Location: South Western Australia

Fibre optic tether

Post by kenl »

So I'm still on the hunt for a tether, no reply to my emails to cable manufacturers.

On here and elsewhere there is talk of Fibre optics, so I've had a hunt around and found THIS converter. It looks like it will do the job of video and Rs422 all on one strand of fibre?

Then the choices of actual fibre seem endless, some thing like THIS however looks to be OK.

Getting through the rear bulkhead on ROV could pose a challenge, I'm looking for connectors now.

It says in the spec that the cable has a 5.5mm diameter and weighs 25Kg/Km that would mean it would diplace 7500 ml or say 7.5kg so it's far from neutrally bouyant but better than anything else I've been able to find.

Does anyone have any experience with Fibre optics than can show me the pitfalls or suggest a better way.
User avatar
Oldsirhippy
Posts: 86
Joined: Oct 1st, 2013, 7:18 am

Re: Fibre optic tether

Post by Oldsirhippy »

How far does the cable need to carry the signals you require? Do you need a fibre optic cable for other reasons than distance?

RS422 goes to 1000m and RS485 1200m at about 100kbps, do you need more than this distance/speed?

Also - a video balun should easily match those distances.

A fibre optic cable, as you said, is heavy and requires special transmit/receive units which are likely to be expensive. A Cat5 cable is cheap, readily available and not as heavy as the fibre optic cable.

Fibre optic cable may not be as mechanically flexible as a cat5 cable, the cables are armoured to stop them bending too much. Fibres are glass and will break if bent too much.
User avatar
ROVER3D
Posts: 128
Joined: Nov 9th, 2012, 7:45 pm
Location: Wuppertal, Germany

Re: Fibre optic tether

Post by ROVER3D »

I dont think so.

Iam using fiber optic tether-system with 2 videochannels and one data. So there are many aspects... like the weight!
For me using normal "network"fiber optic you have to be (a little) carefully with your thether but you also didnt have the problems with buoyancy. The Fiber is very light. So else keep in mind you have to pay copper per meters... and over 300m you will be cheaper with fiber optics!

But this takes money.. the converters (land and rov) will be about 700$. But if your goal is deeper than 100m this is a really good investment!

@kenl
I havent seen this converter before but looks like my ones (only with one videochannel). I would use this one if i havent anyone...
Last edited by ROVER3D on Jan 14th, 2014, 5:38 pm, edited 1 time in total.
rossrov
Posts: 383
Joined: Feb 28th, 2013, 5:01 pm
Location: Australia

Re: Fibre optic tether

Post by rossrov »

Those converters look like the ideal solution to the tether issue. I was not aware media converters were available to do video and data into the one bi-directional fibre, at least not at that price and that compact. Good find. Personally I have been investigating the Ethernet/fibre approach which needs a PC at the surface and ethernet camera below but uses commonly available converters.

The cable page you linked to refers to Plastic Optical Fibre (POF). This has much less distance capability that glass. The converter specs say they will do single- or multi-mode fibres. I have never done any fibre optic stuff before but am looking at single-mode as a starting point. Just looks more suitable physically. http://www.fiberstore.com/simplex-9-125 ... pgodAU4AGw

There is a lot of info on the 'net regarding termination

Yes, the mechanical connections at each and will require a bit of thought. Well-designed strain relief important
kenl
Posts: 153
Joined: Oct 19th, 2013, 8:50 am
Location: South Western Australia

Re: Fibre optic tether

Post by kenl »

Thanks guys, I think I'll order a pair of those converters and see how they go.

That cable looks even better Ross, at that price it would be worth having a spare tether, 2.8mm diam and 6Kg/Km is near enough to neutral as well.

The spec says 100n temporary strain, I wonder what the actual breaking strain of the cable whole assembly would be? Just from a recovering a dead or stuck ROV point of view, I imagine the glass fibre would break long before the strength member, hence the thought of having a spare.

@ Oldsirhippy, I had seen the armoured cable but was not thinking of using it, The cat5 and alarm cable I have lying around the house is about 30kg/Km, I haven't been able to find commercially available 3 twisted pair cable any lighter than that, though I'm sure it exists.
User avatar
Oldsirhippy
Posts: 86
Joined: Oct 1st, 2013, 7:18 am

Re: Fibre optic tether

Post by Oldsirhippy »

Thanks guys - I had dismissed fibre optics for my tether. You have opened the door again :-)

I had wrongly assumed :oops: that a fibre optic tether was
a) too expensive
b) too heavy, with its armoured casing
c) impractical for DIY ROVs

But sites like http://openrov.com/profile/Beau and http://en.wikipedia.org/wiki/Toslink makes me want to investigate fibre.

Drat - yet another project ... :lol:
User avatar
ROVER3D
Posts: 128
Joined: Nov 9th, 2012, 7:45 pm
Location: Wuppertal, Germany

Re: Fibre optic tether

Post by ROVER3D »

Please be aware that you're not able to "crimp" connectors to cable like coaxial or else. You will need a special and very expensive tool. So just look for network-fiberoptics ready to use (ST/ST connector). You will get it up to 100m and you can use connectors to connect more than one cable in line (i use 6x 50m so i can easy change one 50m piece)

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$(!)

So there aren't only good arguments for using fiber!

*Toslink is not useable! Search for 50/125um ST/ST Multimode
rossrov
Posts: 383
Joined: Feb 28th, 2013, 5:01 pm
Location: Australia

Re: Fibre optic tether

Post by rossrov »

Yep, another project. Difficult to go back to simple when these options offer so much and are totally do-able on a hobby budget. Adding this one to the new ROV specification along with compact thrusters, Sonar, radical hull and nav. assist. I'll never get it built going at this rate :?

ROVER3D, good to see that pre-made cables are available, and I would definitely use these if they are cheap enough, but why do you think manual termination is difficult or expensive? Also I wouldn't rule out a homebuilt optic rotary joint. Alternatively the media converter can be rotated with the spool and signals coupled through electrical rotary joint or by radio, which Ken was talking about doing in another thread. Thinking laterally, you can also wind without any sort of rotating coupling at all.

Just like our commercial ROV counterparts, industrial and research gear is often priced high because there is no lower-priced competition and customers believe that they need to pay that much for their application. Easy to spend on a big budget especially when the money is someone else's

http://www.thefoa.org/tech/ref/basic/term.html
kenl
Posts: 153
Joined: Oct 19th, 2013, 8:50 am
Location: South Western Australia

Re: Fibre optic tether

Post by kenl »

Interesting, thank you ROVER3D, I was looking a different field connectors, mostly the FC ones because that is what is on the converter. But reading some of the link posted by Ross, it looks like field connectors don't apply to singlemode, so at this point I have to say I don't know what mode I would be working in because I don't know the difference. More reading.....

@ROVER3D are the ST/ST connectors waterproof? And are they strong?
Also from my days of Hooka diving, the connectors are heavy so they need floatation to stop them get stuck on the bottom.

I will probably make my own reel and it will have wireless connection to the PS2 control and to the video, all of the topside electronics will be in the hub of the reel getting dizzy :lol:
martinw
Posts: 91
Joined: Sep 20th, 2011, 11:02 am
Location: Aberdeenshire

Re: Fibre optic tether

Post by martinw »

You can think of multimode fibers as a wider pipe and a single mode fiber as a narrower pipe (in very simple terms :))

Multimode fibers are more tolerant to misalignment through connections (more surface area on their faces), whereas singlemode fibers can transfer information faster (a bit counter intuitive) due to having less dispersion than multimode.

http://www.fiber-optics.info/articles/fiber_dispersion

The simple reason for this is the light will "bounce" (sort of) from one wall of the fiber to the next, along the fiber and with a narrower pipe all the light will bounce at similar angles (causing less dispersion), whereas in a larger pipe some of the light may bounce at very acute angles and some will bounce at very obtuse angles, varying the time the light exits the fiber at the far end and causing more dispersion (in very simple terms :))

Hope this helps.

Martin
Post Reply