Camera details and some suggestions of Tethers


#1

Is anyone an expert on making a tethered camera that is USB at a 300 foot length?

Basically, how do you adequately boost the signal? 1/3 Sony CCD

Also: if you need a Zero-buoyancy tether - basically a weightless tether - let me know - I use several sources. I also have "self-healing" and just about anything you could think of - Need 20 ton capacity?

David


#2

USB can't get there. The protocol has a maximum round-trip time which limits you to about 75 feet. Try using a phone-drone to convert to something else.


#3

You could always use a standard ccd and at the computer use a video-usb adapter. I have an old Dazzle that works good, otherwise dealextreme has many options, I'm not sure how good they are. Of course that's an additional cable, but a 300' usb cable won't work with most USB devices.


#4

This is what I would do. I have one I bought on amazon for like 8 bucks that works great. The USB spec is 16 feet. You can get around this with USB baluns, but they don't have enough bandwidth for video, nor do they seem to work. Alternatively, they make "active" baluns that do true conversions, but for the price, it'd make more sense to do it with a usb conversion at the computer end. I've used muxlab video baluns over cat5 cable with great success.


#5

depending on space avalableyou could use a USB ethernet converter and then convertitback at the other end


#6

David,

It is possible to extend USB a little bit, but if you can get into Ethernet format, that is much better. You can use a data over powerline system as shown here <http://openrov.com/forum/topics/twowire-tether> (it may be possible to also use a lower voltage with this system for safety) or you can even get these nifty do-dads which allow you to talk 10BaseT over a single twisted pair.

Anyway, I'm interested in talking tether with you- we've been using 28awg stranded twisted pair for tether because it is cheap, easy to mend, agile, and negligibly massive. I'd be interested in exploring other options although what we have seems to work pretty well. What's your philosophy on tether?? Also, we've been able to keep OpenROV under 20 tons so far, but it's good to know we can find that resource if needed! lol


#7

The video feed directly from a Sony camera can go up to 1000ft before requiring additional boost
We use Security cameras 3 wires out power, ground and video out with oboard power by 8 AA batteries. The complete camera system is the size of a very small flashlight which we have used in the past as a housing. With on board power we only have two small wires coming out ground and video
Using a common ground to the surface in the teher, video is only a one wire connection in our tether per camera. Sony security cameras can be found for about $20 and up depending if you want night vision etc…last year I bought 10 Sony night vision security cameras at Fry’s for $20 each being discontinued.


#8

how about ip based :), it is more known...


#9

David,

I'm definitely interested in sources you may have for tethers! Can you post them to this thread?

-Ben


#10

Actually, we're having some trouble finding the right one and we'd love input. The one we used was from a hardware surplus store here in Silicon Vally, so that might not be very repeatable. One option is to take apart a 300' Ethernet cable (preferably with stranded wires rather then solid) and extract the four twisted pairs from each. I'll keep you posted as I learn more!


Eric


#11

My company occasionally orders custom cable. If we can figure out what we want in a tether, we may be able to order enough of it to get a reasonable price - minimum quantities are usually 1000 feet or less, so all we need is a couple willing to commit. I'll ask around tomorrow.

-Ben


#12

Companies who advertise that they make ROV tethers:

  • South Bay Cable Corporation
  • Cortland Company

Our cable is substantially simpler than what these guys advertise, so I didn't request a quote from them on this first pass - these seem like the guys that would charge a premium.

Other custom cable manufacturers:

  • Calmont Wire and Cable*
  • New England Wire Technologies*
  • Cooner Wire*

* = I have requested a quote (see below)

Note: there are dozens, if not hundreds, of companies in the US that can do this sort of work. I list these few as my company has dealt with them before.

-------------------------------------------

Here's the details of my quote request. I punted on some of the values - I figure that once we have a ballpark price, we can decide if more features are necessary and have a more detailed discussion of the specs.

  • Two conductors (~28 Ga, UTP)
  • waterproof, abrasion resistant sheath material
  • neutral buoyancy in water (weighs ~1 gram per cm^3)**
  • OD should be as small as reasonably possible - on the order of 0.060" (we're flexible on this number)
  • Should be strong enough to support 40 - 50 lbs (40 is acceptable, 50 is better.)

I offered that we'd probably place orders for 2000-3000 feet at a go, and we are willing to adjust specs to control price

** I'm assuming that the tether should be neutral in fresh water - specifically, it should not sink, since there is usually lots of stuff to get tangled in at the bottom of ponds, lakes, rivers, caves, etc. This means the tether will float in saltwater, which seems fairly safe - overhead environments could result in tangles, but that's the trade off. If we decide that we are interested in a saltwater-neutral cable, the cost will probably be very similar.

.

-Ben


#13

I just got my first reply to my tether inquiries today.

First, it was an estimate, not a quote - as yet, no one has made a promise to make the cable I specified at any price.

The folks who got back to me said they had made similar cable with the following price structure:

  • Minimum order is 1000 ft,
  • 1000 feet costs $1650
  • 2500 feet costs $3000

That seems like a lot - a 100 meter tether would cost roughly as much as the rest of the ROV.

If we do the math this works out to:

  • ~$750 setup charge
  • ~$0.90 per foot

So, even if we could order enough to amortize the setup costs to nothing, it would still be a pretty expensive cable. Unless someone thinks otherwise, I'm going to tell this guy that we can't possibly afford this cable and see if he has anything off the shelf that is "close enough". I still have a couple of other feelers out - I'll post more information as I get it back.

-Ben


#14

why even use a USB camera. use an ethernet cam or an RF CAM. RF camera cables can go hundreds of feet without a repeater. Think of a security cam in an office building.


#15

Hi Mike,

If you wan't to do anything like video processing on the ROV itself (think about autonomous ROVs) USB is the easiest. Beside that, running another cable (beside the communication one) to the surface could be problematic (weight/buoyancy of the tether).


#16

USB is problematic on the ROV. IF you use a dazzle or EasyCap or similar on the topside, you'll do ok. A video balun and topside usb video input device attached to any standard RCA output camera is the easiest and likely the cheapest option.


#17

If nothing is done underwater with the camera, I would look at Coaxpress since this new standard uses a cheap analog cable for high rate data transfer, it does require specific camera on the ROV which is not expensive but it will allow high data rates with cheap standard cables, beside you can send your control channel next to the image channels

Let me know if you need any ideas/help on this direction


#18

Ben,

Thank you so much for looking into this. Even though it's been more then two months, this sort of data is really useful. Currently I'm loosing the most sleep over choosing the right tether for the ROV. The general dilemma is whether to use a thicker tether with an outer jacket that is more likely to be electrically reliable, but will be heavy and have lots of drag in the water, or to go with a much thinner, lighter single twisted pair that may get damaged, but will allow the ROV to be more agile (which is what I've been using so far).

Strangely, it's very hard to find a supplier for the low profile 28AWG stranded single twisted pair that I found at an electronics surplus store, so the first option (thicker and stronger, but less agile) is really the only one I have a clear path too. For that, I've been reviewing Beldin 1353A which runs about $120 for a 1000' roll or about $40 per 100m tether. 1353 uses 7x32 stranded copper to make two twisted pairs of 24AWG wire inside a PVC jacket. The whole wire ends up being about 3mm diameter and is very similar in feel and appearance to a mouse cable. It sinks in water and even without the PVC jacket, it's considerably stiffer then the 28awg pair I have.

Any leads you can find or advice you have would be great, and again, thanks for the help so far!

Eric


#19

Eric,

Thanks for the encouragement. I contacted a couple of places, and one did respond with a quote, but it was pretty expensive for small quantities (i.e. 1000 ft.)

Things have changed since then - you have a gangbusters kickstarter project, and lots of people who are interested, so it may be time to revisit that quote - economies of scale may be kicking in.

Let me dig it out and send you a copy. Then we should perhaps have a longer discussion about what we are willing to pay for a cable. Once I have a better idea of what you want, I can talk to the cable manufacturers again.

-Ben


#20

I think that the best way to minimize video processing and get the best picture for the fewest bits would be to choose a webcam (probably USB) that has on-board H.264 compression. Cheap hardware compression is very effective and is available in a number of webcams.

If you don't do compression, you may be forced into lower resolution, lower frame rate, or both. It would be highly desirable not to make those compromises.

BTW: I am a consultant working with real-time H.264 compression of HDTV and have been working in TV for about 40 years.