Exciting development!

[Bob Abell 2Participant @bobabell2]

Dermis……Can you get me a 100m roll of the RS wire…….Probably need a spare anyway

 

Thanks a lot

 

If it`s a problem, it doesn`t matter

 

UB74

[Bob Abell 2Participant @bobabell2]

Ashley

 

This is the specially constructed Galvanometer instrument that will be fitted to both ends of the cable, supplied by the TV people

 

Mark…….Do you think the cable can withstands the amps?

Got a bad feeling about this now!

 

Fingers crossed….Again!

 

Bob

[ashley needhamParticipant @ashleyneedham69188]

without knowing the spec of this detector i should think its a bit difficult.. the lamp may be the killer??? perhaps and LED in its place might be better but without knowing ..

do the telly bods have an idea of its current requirements.. have they built one yet?

 

An alternative to not knowing would be to have a sensitive detector at either end using low currents across the cable, and this in turn operates the galvanometer !! it need not be seen, and would be better suited to the very small cable you are laying, and lets face it, you are a bit limited in the size of cable you will be able to lay,,unless the lay was shorter and so a larger cable could be used.

 

Then perhaps we are theorising too much and what is needed is the cable tested first

 

Ash

[DermisParticipant @dermis]

Guys,

 

The galvanometer measures the current used by the bulb. It uses a minimal amount of power, just milliamps.

 

The supply is 12volts. The max current for the wire is 1amp. Therefore. P=IV

 

12V x 1A = 12watts.

 

So, thats the maximum size bulb you can use. 10 watt bulbs are commonplace.

[Mark Beard 1Participant @markbeard1]

Bob, that’s a good scheme, providing two different visual indications and an identical setup each end.

 

Since the galvanometer is connected in series across the bulb, it measures the voltage rather than the current. Still, a reasonably sensitive galvanometer will take a negligible current, so the main factor remains the current drawn by the bulb.

 

A 10W 12V bulb is similar to a car side-light, it will be visible for many hundreds of yards. Perhaps it would be overkill? The bulb I’m sending Bob is 1.2W (0.1 Amps) and is perfectly visible at a sensible close range.

 

By the way, the 1 Amp limit is my personal estimate for wire of this sort, and may be a little conservative. Neither the Maplin nor RS version have a specified current limit as these cables are usually used for audio signals not power. Still, I’m sure it will be quite suitable for the job.

 

Just let the Beeb techies know that we recommend a 1 Amp current limit and I’m sure they’ll be able to keep to that for the kit used for filming.

[Bob Abell 2Participant @bobabell2]

Thank you Mark

 

I`ve got the TV people involved now

 

Just tried a Maplins buzzer on 12v down the wire and all is well

 

Bob

[DermisParticipant @dermis]

Guys,

 

From the schematic, the galvanometer is wired in parallel with the bulb and does indeed measure voltage.

 

 

 

Edited By Dermis on 03/06/2011 13:55:43

[Bob Abell 2Participant @bobabell2]

Thank you, Dermis

I think you may have spotted an error in the proposed plan and also a good idea for reducing the wire loading tt!

I shall have a look at the master plan again, to see iif both circuits are the same

Well done, Steve

UB74

[Mark Beard 1Participant @markbeard1]

So long as there is a hand-over protocol, so only one side transmits at a time, having both sides identical will be fine. But You are right Dermis, if they clash there will be smoke! I guess in the olden days battery impedance limited the s/c current. And, if my calcs are correct, the transatlantic cable would have had an impedance of around 5000 ohms. So not that much of a problem back then. Bob, just keep your TV boys in line and all will be well

[DermisParticipant @dermis]

Having thought about the circuit, it is possible to have it identical at both ends. The paddle switch must be a momentary switch, defaulting to centre “off” position. Moving the switch from side to side would cause the galvanometer needle to swing accordingly and the bulbs light up. I guess the protocol for preventing a short circuit, is “don’t use the switch if the light is on and the needle swinging!!”

[Mark Beard 1Participant @markbeard1]

I think that’s the idea, like a 2-way morse key.

[DermisParticipant @dermis]

Exactly! It was a telegraph cable, after all. =]

 

Now, about them flags…

 

From the pictures I’ve seen of GE in cable laying mode, she is flying:

The union jack, the stars and stripes, the red ensign and the flag of the Trans Atlantic cable company, which is a red diagonal cross on white background. The company initials T,A,C,and C, one in each white quadrant.

[Bob Abell 2Participant @bobabell2]

The wire has finally arrived….

 

Note the random manner in which it is wound. The wire will be wound onto the correct drum in a similar manner and see how it performs.

 

Need to make an anti over run device now

 

We`re getting there, boys!

 

Bob

[Bob Abell 2Participant @bobabell2]

We rewound the 100m onto the storage drum in less than 10 minutes……So that`s not a problem if we need to rewind at the pond

 

This what 100 m look like on the storage drum….plenty of room, so neat rewinding is not necessary.

 

We could go up in wire size if it`s necessary

 

The storage drum in position. The wire ran OK through the system and out over the stern. Pulling the wire, simulating cable laying, the drum sides touched the hatch side, and the wire stopped unwinding and buried itself into the main coil!

We think, smoothing the sides and waxing may solve the problem.

Another Bell end is required above the motor and an over run device is definitely required. Perhaps a roller each side of the drum will do the trick?

 

All this means, we won`t be sailing tomorrow

 

Bob

[Mark Beard 1Participant @markbeard1]

So perhaps you could get 300m on that drum! Maybe some of my calculations do work after all!

 

Since you don’t need that much, perhaps you could afford to shorten the drum slightly. I think rollers or jockey wheels either side would be a great idea for keeping the drum central and stopping it fouling on the hatch sides.

 

Not sure that the drum rubbing against the hatch coaming would cause the wire to become buried in the coil, (I take it you mean it was wound into the coil of wire on the drum). I do have concerns that rewinding in a haphazard manner rather than layers could cause precisely this issue. I wonder if the unwinding stoppage could actually have been caused by the wire being buried during winding.

 

I’ll have a think about auto-layering solutions…

[Bob Abell 2Participant @bobabell2]

Hello Mark

 

I was about to congratulate on your wire capacity calculation….Well done!

 

We wound the wire in a sloppy manner to simulate a pond rewind, so the core of wire was probably soft, hence the digging in. Thicker wire would be an advantage, but we`ll carry on with the present wire for the time being.

 

I can easily reduce the width of the drum and fit brass leaf springs or rollers, to press on the drum sides, which would also act as an anti overrun device

 

Making a bell end to keep the wire clear of the motor at the moment.

 

Have you sent the bulb yet?

 

Bob

[Bob Abell 2Participant @bobabell2]

Just for the record, for those who may be slightly interested…….. when the drum edge touches the hatch, it`s not just a rubbing action….it`s a wedging action because the flange is out of true and creates a braking effect

 

We wondered why it locked up so strongly!

 

Shoddy workmanship chaps!…….Drum needs stripping down……Ugh!

 

No problem…….Using the lathe to rewind the shop drum!…….Great fun!

 

Bob

 

Edited By Bob Abell on 04/06/2011 21:06:20

[Bob Abell 2Participant @bobabell2]

Latest state of play…

The drum is 12mm narrower now and is contained by two side guides around the axle area

Had to drill the holes with a gimlet……..It worked quite nicely

Managed to find a longer length of plastic tube for quick cable feed through the system. The Bell end has a good range of adjustment

The drum was stripped down, shortened and trued up

 

The next and final job is the drum over run thingy……..Hopefully

 

Can`t imagine what would have happened, if we had filmed at the end of May as originally planned?………….. It has taken two months work up to now!

Feeling more confident now

 

Bob

[DuckyParticipant @ducky]

Thats looking the business now Bob, will run truer now won’t it!

That longer plastic tube and ajustabell bell end will be easier to manage on the day won’t it.

 

[Bob Abell 2Participant @bobabell2]

Mark

 

What would be the next size up of Co-ax cable please?

 

The TV chappie thinks 1 amp may be ok, but is asking the question

 

Bob

[Bob Abell 2Participant @bobabell2]

Congrats to Dermis and Mark for spotting the deliberate error!

 

There is a risk of a short circuit and the TV expert is considering a circuit modification.

As the paddle boxes are not made yet, there`s no real problem

 

Also 1 amp wire will be OK

 

Bob

[Mark Beard 1Participant @markbeard1]

A solution as simple as a fuse will do the trick!

[ashley needhamParticipant @ashleyneedham69188]

Bob, you have the wire, stick a battery across it and a meter the other end and see whats watt… try a very small bulb and go from there !!

 

PS will the drum be “on view” on deck and so need to be “victorianised”??

 

Ash

[DermisParticipant @dermis]

A bit of research reveals…

Initially messages were sent by an operator sending Morse code, a series of dots and dashes. The reception was very bad on the 1858 cable, and it took 2 minutes to transmit just one character (a single letter or a single number), which translates to about 0.1 words per minute. This is despite the use of a highly sensitive mirror galvanometer, a new invention of the time.
The first message on the 1858 cable took over 17 hours to transmit.
For the first few messages, 600 volts was applied at the sending end, but the speed (two minutes per letter) was very slow, and the sending-end battery was boosted to 2,000 volts in an effort to increase the working speed. The speed was increased, but the higher voltage overstressed the cable insulation, it began failing in a few hours and went competely dead on September 3, 1858. It was to be six years before telegraph messages were again sent across the Atlantic.

 

I wouldn’t fancy a short circuit at 2000 volts!

 

Might be a clue here “sending-end battery”…if you’re not sending, then disconnect the battery!

 

Best regards.

[DermisParticipant @dermis]

Following on from this…

 

The original mirror gavanometer, detected tiny fluctuations in current. A coil and magnet arrangement, rotated a mirror which was illuminated with a lamp. As the mirror moved, a beam of light was projected onto a screen.

 

I don’t think it is neccesary to swap the polarity of the supply with the 3 position switch arrangement, just a single on/off switch to achieve Morse code. No more short circuit problem!

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