Cable for submarine robot

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.

For the communication they use a Ethernet to Single Twisted Pair Adapter.

I have my arduino ethernet shield connected to my router using cat3 four conductor telephone wire in a 10BaseT setup. I suggest you start by making test housings of your ROV and lowering them to the max depth you intend to encounter. Probably a good learning experience.

100m is a long way down. It is going to be very dark, you are going to need power for lights. As was mentioned cable weight and management will be a problem. The pressure at 100m will 10 atmospheres above the surface pressure. Are you going to pressurise the interior of the ROV or are you hoping to keep a watertight seal against 10 atmospheres? How will you connect the cable to the ROV preventing water entering either the ROV or the cable sheaths?

You should try to experiment in a swimming pool first. In the first 10m of your dive the pressure will double halving the volume of any compressible spaces.

If you get a length of CAT-5 cable seal the ends and chuck it in a bath/pool is there enough air between the conductors and the sheath to make it buoyant? Or could you put neutrally buoyant floats every few meters on the cable to reduce the weight problem. You will still suffer inertial problems and be susceptible to water currents though.

Hi.
i have just started a similar project. Since posting last night, I did a bit more research and found a sight where a guy has built an ROV and has plans for another using ethernet cable (cat5) Check out "Building BOB" and thier project "Building Bart". Also check out Roborealm. Software to receive video and control an arduino or other serial interface.
My plan is to use 100m of cat5 and run the ROV at about 30m. the weight of the cable shouldn't be a problem as when it is in water in will "weigh" a lot less. I think a bouy on the surface with the cable feeding through it and running directly down to the ROV will be the way to go. then a few fishing net bouys to float the rest of the cable. I saw a picture of a winding drum for the cable that had a shaft coming out the center with 5 or 6 copper disks that had the wires from the pc stretched over the copper disks so you could wind the cable with out twisting one end. Ill see if I can find a pic. Found it. Attached below. also check out "homebuiltrovs"
Good luck.

slipringreel16.jpg

I was curious about the weight, and 500' (152m) of bulk cat5e/6 cable weighs about 14-16 pounds (6.3-7.5kg), including the box and spool it comes in. Fiber of course weighs a lot less, but you do have to factor in the weight of digital to fiber conversion.

In physics, buoyancy (play /?b??.?nsi/) is an upward force exerted by a liquid, gas or other fluid, that opposes the weight of an immersed object. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus a column of fluid, or an object submerged in the fluid, experiences greater pressure at the bottom of the column than at the top. This difference in pressure results in a net force that tends to accelerate an object upwards.

eg. 7mm dia cable x 100m is pi x 3.5 squared which is about 3.8 kg
So the cable would "weigh" 3.8 kg less in water.

could be wrong.
Also a little negitive weight in the cable help to keep the rov down...
There is a drag issue though, having to tow 100m of cable. Especially if there is any current...

radman:
100m is a long way down. It is going to be very dark, you are going to need power for lights. As was mentioned cable weight and management will be a problem. The pressure at 100m will 10 atmospheres above the surface pressure. Are you going to pressurise the interior of the ROV or are you hoping to keep a watertight seal against 10 atmospheres? How will you connect the cable to the ROV preventing water entering either the ROV or the cable sheaths?

You should try to experiment in a swimming pool first. In the first 10m of your dive the pressure will double halving the volume of any compressible spaces.

Very good idea about starting at shallower depths.

However, just because giacomomerilli wants a 100 m cable doesn't mean that is the sub's intended maximum depth. 100 m just means that the farthest potential straight-line distance between the sub and it's top-side controller in any direction (Max. Depth^2 + Max. Range^2 = Cable Length^2), not just straight down. For example, 100 m of cable would allow a range of a little less than 99.5 m at a 10 m depth.

Far-seeker, sorry I did assume he wanted to go deep. If he stays shallow but at the end of the tether then the weight of the cable becomes as issue as the ROV will have to pull the cable.
I think the cable will describe one half of a catenary as in the cables of a suspension bridge?

Ordinary Cat5 cable is probably bouyant on the surface but it will lose bouancy at depth as it gets compressed. Sounds a bit complicated to work out. He could just swim/dive with a spring balance attached to some cable to find out the forces involved.

I took a look at homebuiltrovs it is great to see video from working ROVs. It would have been good to see video of the ROVs operating. Note the target depth for some designs was 3m.

I just want the cable as long as possible, and I think 100 meters is plenty. That doesn't mean I want to go at 100 meters deep. I'm going to use it (after all the tests) in a lake and it means that 100 meters is the distance between the pc and the robot. I still don't know what the maximum depth will be.

I'm not working on it at the moment, I'll post more info as soon as I get back to work.

Thanks for all the advices and help!!!

I'm going to use one of these, it can reach 60-70 meters using an ethernet cable, max speed 12mbs -usb1.1. Already test it, and it works. You can find better ones that reach 100 meters but they are pricy. 60 meters is fine to start with.
Connection will be: pc----->usb ethernet converter----->60-70meters of cat5 cable----->ethernet to usb converter----->usb hub----->hd webcam(port1). / arduino mega(port2)

Does anybody knows if A 12mbs usb connection supports an HD 720p webcam??
The problem is that the computer will comunicate with the arduino, using serial comunication, on the same cable of the webcam. I'm not shore that 12mbs is enough for both. Any body knows how many mbs takes an hd webcam? Otherwise I can always use a normal webcam.

This is a drawing of the electronic connections inside th rov + some photos of the electronics box already finished.





The electronic box works at 12 Vdc. It contains:
Arduino mega
Relays for outside Leds
Relays for internal strip Leds (just for fun)
Relays for 2 motors direction (fw-left/bw-left+ fw-right/bw-right)
Tip31c transistors for motors speed
5v voltage regulator (for steppers)
Plus 2 smal pc fans for cooling the transistors and the volt reg

Motors:

We've bought 2 RE-540/1 dc motor (MFACOMODRILLS.COM) and propellers (different sizes to test, from 35mm to 50mm).
These will move the Rov underwater. One on the left and one on the right side, so you can go forward, backward, and 360 degres turning by giving opposite directions.
Behind the motors there are rudders (controlled by stepper motors) for going up and down.

The dc motor will stay in the water, because normal brush motor(and some brushless) can go undervater with no problem. The trick is to spray it with products like CRC Marine 6-66 or WD40.
Tests seem to confirm. I've only tried with unsalted water.

Does anybody knows if A 12mbs usb connection supports an HD 720p webcam??

I'm sure that USB 1.1 is to slow for HD webcam and feeding 2 of them + Arduino control would surly be to much. Could you use an Ethernet shield and a 4 port Ethernet switch to plug I/P webcams and Arduino into? You would then get faster data transfer and could maybe use power over Ethernet to drive the ROV but have on-board backup battery.

Ip cameras cost a lot. Probably it is better to have a normal web cam for driving and in the fututre we'll buy something for recording in hq. Like go pro cameras.

giacomomarelli:
Ip cameras cost a lot. Probably it is better to have a normal web cam for driving and in the fututre we'll buy something for recording in hq. Like go pro cameras.

While it's always nice to have a clear picture for navigation, standard quaility web cam is probably sufficient. Although you'd have to create your own water-proof housing here's an example of HD camera with a built-in microSD card drive and designed to be easy to interface with microcontrollers or other control circuitry. Something like this would at least allow you to record in HD for later access, even if a live HD feed is impractical right now.

I bought a logitech c170, non hd. It works without problems with the cable we have.
I can send serial to arduino mega while The webcam is working.

I think the topic is resolved.

If you like you can follow the project on twitter (https://twitter.com/dip_ROV). I'm sorry it is written in italian.

Thanks to everyone!