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LAN_403

radiotech

Fri Jan 20 2012, 09:13PM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546

If transformers were used, they could operate at 800 Hz, which would reduce the
weight and make them more foolproof at the ROV end. Perhaps the robotics and
lighting details will be revealed. Higher frequency than that will be too lossy due to
skin effect.

I wonder what conductors were used in the STS-75 tether?

0joze0

Sat Jan 21 2012, 10:29AM

Registered Member #4346 Joined: Tue Jan 17 2012, 10:16AM
Location: Slovenia
Posts: 9

At ROV, the buoyancy is achieved with buoyancy foam, and the size of foam is calculated that the ROV is slightly pozitive buoyanced.
If ROV has a big weight there must be large buoyancy foam which makes rov less maneuverable.
I didn calculated yet, what would be battery set up weight to achieve my power demands for 6 hours to operate continiously and what type of battery should use. Now I have LiFePo4.

Sulaiman

Sat Jan 21 2012, 11:28AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141

Is it possible for you to use co-axial cable such as RG8, RG213, RG214 etc?
One co-ax cable could carry ac/dc power at up to 2.5 kVac/3.5kVdc
with about 5 Ohms dc resistance loop for 300m
AND you can use it as a co-ax data/video cable with a little filtering/coupling.
The inner solid dielectric provides crushing strength and excellent insulation even if the outer jacket water seal is compromised.

P.S. An email (@corporation/institution NOT @hotmail etc.) to companies such a Belden with a brief project description may prove useful, advice/samples etc.

Steve Conner

Sat Jan 21 2012, 11:40AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Are you sure?! The last time I used some RG213, the centre conductor was copper-plated steel and the resistance was terrible.

MOTs would be a natural choice if it weren't for the high magnetising current, which wastes voltage drop in the cable. Maybe you could use a couple of MO caps at the receiving end to "PFC" it. But they also tend to overheat without fan cooling, even at idle.

I'm puzzled by Grenadier's buoyancy control system. In order to compress air, you have to add more air to it. But the total amount of air on board a submarine can't increase. Full size submarines use air from the onboard supply to displace water from ballast tanks.

I remember one research submarine built along the lines of a hot-air balloon, the "balloon" being a big bag full of gasoline, which is less dense than water, and almost incompressible.

Sulaiman

Sat Jan 21 2012, 11:52AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141

RG213 is about 6 Ohm/km inner and 4.5 Ohm/km outer

= 10.5 Ohm km = 3.15 Ohm loop resistance for 300m
.... did you get yours from eBay?

P.S. just went to my shed to check,
I have RG213/U and it's 7-strand solid copper inner
maybe it's the /U at the end?

I like the microvave oven transformer option,
if the shunts are knocked out and the operating voltage reduced
(I don't know how far, 20% maybe)
I'd expect the magnetizing current/saturation losses should be low/ok.

Steve Conner

Sat Jan 21 2012, 12:43PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Hmm. I think I got confused with RG-174, the really thin stuff.

Edit: I like the idea of using it as the data connection. Wi-fi would probably work even with RG213. It has terrible loss at 2.4GHz, but I bet it's still better than a free space path between antennas. Some unmodified Wi-fi dongles could be coupled to the cable through small HV capacitors.

Sulaiman

Sat Jan 21 2012, 01:40PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141

Or good old 802.3 ethernet 10/100 Mbps?
300m should be no problem though I think 75 Ohm cable would be 'ideal'

Steve Conner

Sat Jan 21 2012, 02:38PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

No reason not to use 75 ohm cable, then. Power over Ethernet 4hv style! :)

The biggest problem would be finding Ethernet hardware that still supports coax. I don't know if 100Mbit coax transceivers were ever made. You can't use the common Cat5 type, because they're full duplex, one twisted pair for each direction.

Also Ethernet is that much closer to baseband than wi-fi, so possibly harder to separate the data from the high voltage crud.

radiotech

Sat Jan 21 2012, 06:07PM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546

For such a project it would be nice to your budget. Not in money, but as percentage
distribution, for hull, motors, controls, lights, manipulators, and power system.

What is the total weight?

Erlend^SE

Sun Jan 22 2012, 12:56AM

Registered Member #1565 Joined: Wed Jun 25 2008, 09:08PM
Location: Norway
Posts: 159

As for Ethernet, can't it be used over twin-wire coax? and would that allow some usefull voltage to shielding?

I recall that ethernet transformers are specified for 2 or 4 KV(don't recall) cable side to circuit side. You would need a DC path that doesn't involve the transformer windings.

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