Cable for submarine robot

I'm building a submarine robot that has to go in non-salty water( a lake) and I will control it with a cable. I'd like it to go at least 100 meters deep. The cable will have 7 wires, 2 for the power (24vDC and ground), 3 wires for the serial comunication between the arduino ouside the water that prints the commands and the arduino in the robot that reads them (pin 1 and 0 + ground), and 2 wires for the usb comunication beetween an HD web cam and a Pc outside the water.

Serial comunication cables can reach 50 meters and to reach more than a hundred you need some ICs like a couple of max483. The real problem is with the web cam signal, I need to see what's happening in real time and to see it on a screen. Usb cable can't reach more than 5 meters... What happens If the cable is more than that? Is there any solution?

What if I convert the signal from the web cam from usb to serial, send it on the cable as a serial signal an then convert it back to usb, so that a computer can connect to it?

Sorry for the grammar.

Have you considered ethernet instead? An onboard router would allow a much faster connection for the cameras. 100 meters is about the limit of a normal ethernet cable connection.

Have you considered converting the communication to ethernet? There you could use off the shelf solutions like switched hubs or repeaters which can deal with error correction and resending. You might also check out fiber optic transmissions, though I suspect you find more off the shelf solutions if you convert it to tcp/ip packets rather than plain signal wires.

But how do I go from web cam to ethernet? I found this on amazon http://www.amazon.com/SANOXY-over-Extension-Cable-Adapter/dp/B003BDMK3S/ref=sr_1_1?s=electronics&ie=UTF8&qid=1344427592&sr=1-1&keywords=ethernet+webcam, can I use someting like that? What if I use a 300 ft ( nearly 100 meters) CAT 5 cable instead of only 150 ft?

Maybe you should use an IP camera that has a CAT5 cable connection. Do a Google search for "ethernet camera". That route is a bit more expensive tho. Here is a start:
http://www.vivotek.com/

I don't think you will get a usb cable to go 100 meters with a usb webcam (like Logitech webcams).

giacomomarelli:
But how do I go from web cam to ethernet? I found this on amazon http://www.amazon.com/SANOXY-over-Extension-Cable-Adapter/dp/B003BDMK3S/ref=sr_1_1?s=electronics&ie=UTF8&qid=1344427592&sr=1-1&keywords=ethernet+webcam, can I use someting like that? What if I use a 300 ft ( nearly 100 meters) CAT 5 cable instead of only 150 ft?

It might work, but it might not. I suspect such devices need the cable to themselves, so you would need to run 2 cables, one for the web cam, and one for the arduino.

I would go for a web cam that knows ethernet and use that, rather than trying to convert USB to ethernet.

What ethernet/tcpip adds is putting everything into a packet that is check-summed. If the packet is malformed, the sender has to resend the packet. If you are doing straight wires, you have to essentially recreate this checking and resending, or possibly have some communication glitches.

hi,
a bloke at work had a similar problem. he used usb web cams for a security system. not underwater, but still had the problem of usb <5m. he got some cheep generic eBay USB to Ethernet converters. they worked a treat. but then you would have the problem of having more wires. they cant be run through a switch.
it has to be cam --- usb-eth --------cable------eth-usb ---- computer.
you would have to work out if any of the wires are not being used in the ethrnet cable to pipe you serial down.

otherwise, the suggestion of a Ethernet camera would work, though they are more expensive and heavier.

How about a lansheild for the arduino and ethernet camera(s)? plug it all into a simple switch and then you can send what you like up one ethernet cable.

Serial comunication cables can reach 50 meters and to reach more than a hundred you need some ICs like a couple of max483. The real problem is with the web cam signal, I need to see what's happening in real time and to see it on a screen. Usb cable can't reach more than 5 meters... What happens If the cable is more than that? Is there any solution?

Use RS422 instead of RS232. Something like the MAX485 or MAX491 chip depending on if you need half/full duplex comms. For full duplex though you will need 5 wires instead of 3.

otherwise, the suggestion of a Ethernet camera would work, though they are more expensive and heavier.

Heavy is good for a submersible. Less ballast required to submerge it. And considering the pressure at 300 feet (just short of 150 psi), the cost should be more to build the submersible hull with a non-leaking viewport and connectors. Just a thought...

SurferTim:
considering the pressure at 300 feet (just short of 150 psi), the cost should be more to build the submersible hull with a non-leaking viewport and connectors. Just a thought...

true...
not on topic of cable, but out of interest, have you already got that part sorted giacomomarelli? can you post a pic, it would be cool to see.

Thanks for the answers, I think I will try the usb to ethernet converter and buy two ethernet cables on ebay (100 meters long each). One for the usb and one for power and serial.
If it works I'll tell you,but I think it won't be before september-october.

To gr0p3r & surferTim: I haven't got any pictures yet, I'm running the project with four friends of mine and one of them is sorting out the mecanical point of view. The structure will be a steel tube (170 mm diam, 480 mm long), motor and propeller at the back and web cam at the front. No static immersion, only dynamic through propeller job. Another friend an I are doing the electronic part.
It will go in lake Como (italy).

To Riva: how do I chose to use a RS422? When I connect two arduino with pin 1, pin0 and ground is it using RS232? I'm not really practical of these things..

Thank you!

how do I chose to use a RS422? When I connect two arduino with pin 1, pin0 and ground is it using RS232? I'm not really practical of these things..

You will need an external chip like the MAX485 or MAX491 Mixed-signal and digital signal processing ICs | Analog Devices to do RS422. Connect to a couple of pins on the UNO and use software serial or on the Mega use one of the other serial ports. It may even work using TX/RX pins on UNO but I have not tried this (Only used RS422 on PIC chip)

I'd put a small ethernet hub or router in the sub and connect the IP cam and arduino with ethernet shield to it.

giacomomarelli:
If it works I'll tell you,but I think it won't be before september-october.

A few things - cable related-wise:

  1. Have you thought about how heavy 100 meters of cable will be - will your ROV have enough power to overcome the mass to move it?
  2. Can you provide enough power down such a cable (taking into account resistance losses, etc) to move the entire mass of cable and ROV?
  3. What about your cable management system? How are you going to pay out and pull back in that amount of cable (and keep it organized and untangled)?
  4. Is the cable jacket certified to withstand the water pressure at that depth? What will you do to keep water out?
  5. Most ethernet cable is made with solid-core wires - these don't stand up to repeated flexing. Multi-stranded wire ethernet cable does exist - but it ain't cheap. The problem is, you want something even more flexible than that ($$$$); such specialist cable does exist, but it makes the stranded stuff look inexpensive.

As far as keeping water out of the ROV itself:

I would look into using BLDC motors and an on-board battery pack; run the motors in the water - spray them with silicone lube before immersion, and do a complete tear-down and cleaning after the run. The battery pack should be sized to allow the ROV to move the mass of the tether/cable. Add floats to the tether to make it more bouyant; I can't tell you how to manage 100 meters of tether/cable, though. Some kind of winch and spool with slip-ring connections would be needed, most likely. On the interior of the ROV, you'll want to displace the air with oil (mineral oil would work well - it's non-conductive, so you can immerse your electronics in it, and it won't spoil).

That's about the limit of my knowledge of these things; most homebrew ROVs don't even get close to 100 meters in depth...

I forgot to mention there was a kickstarter project for an open source underwater ROV recently. You might check them out to see what the competition is doing, and possibly get some ideas. So far, while they also plan to do 100' depth, they've only tested it to 20'. http://www.kickstarter.com/projects/openrov/openrov-the-open-source-underwater-robot?ref=card.

An option might be to keep all power on board and use a wireless router on the rov and a laptop on the surface with a wireless adapter. To connect the two use very thin coax/shielded type wire as a long antenna wire between the two.

I just saw the video of the OpenROV that MichaelMeissner linked (thank you!), it's a very interesting project. They obviously use battery to supply power to the ROV, I think I'll be better using rechargeable batteries too. Just need to be shure they supply enough current for the motor I'm using and all the other electronics.
For the communication they use a Ethernet to Single Twisted Pair Adapter. Wouldn't that be better? It looks more simple.
I connect the Arduino and the web cam to a router and the go trough the single twisted pair adapter.

To cr0sh: Thanks for the advices. We already went trough those problems and we still need to choose the motor for the Rov. (We where thinking to get this: http://it.rs-online.com/web/p/motori-cc/2483671/, it has 3500rpm max without load, 10Ncm torque. It can't go faster than 3000rpm because of the oil-seil we have.)
An ethernet cable isn't actually the best thing for a ROV, but if I use the adapter I'd just have 2 wires...

giacomomarelli:
I just saw the video of the OpenROV that MichaelMeissner linked (thank you!), it's a very interesting project. They obviously use battery to supply power to the ROV, I think I'll be better using rechargeable batteries too. Just need to be shure they supply enough current for the motor I'm using and all the other electronics.

Having on-board power is a good idea, IMHO. It would allow the sub to react to a lose of communication (i.e. if the cable was damaged or snapped), like trying to resurface by emptying ballast tanks or turning on flashing emergency lights and emmiting a low frequency sound that could be tracked with a hydrophone. Then you'd have a greater chance to get your sub back if something went wrong.