120m underwater DMX

[mutley]

Does it have to lie on the bottom of the lake? As a SCUBA diver, I can tell you that in just 10m of water, the pressure is double what it is at the surface, therefore increasing the likelihood of water penetration. Deeper water is always colder too, so the cable will be more susceptible to damage.

 

Could you not use the swimming pool lane-dividing idea of putting floats on the cable to keep it at the water surface?

 

As an approved cable for DMX, I'd use 'Outdoor Cat5', attached to floats.

 

Floats could be anything really: empty drinks bottles, swimming arm bands (high-vis, and simple to fit)...

 

I wouldn't try to use multiple cores for the same 'wires' though, as this can cause problems. If you want some redundancy, just make it into two separate lines, a primary, and a back-up.

[bruce]

For a short term installation, standard cat5 should be just fine. If it were going to be underwater for months I might worry about water penetration, but not for less than a day.

 

"outdoor" cat5 will make little difference - the only significant difference is that the outer PVC jacket is more UV-resistant than the standard stuff.

 

You may have to weight the cable down.

 

I'd suspect that the "swimming pool lane" idea might actually put more physical stress on the cable. It'd need a floating "catenary rope", if you know what I mean!

 

How is power getting to the pontoon?

[DonkiDonki]

As Bruce hinted at, getting power to the pontoon will likely be an interesting job.

 

Personally I think this is a situation ideally suited to a wireless DMX solution. You should have a near-perfect line of site from transmitter to reciever, hence little or no interference. Any half-decent wireless DMX system should cope with that without issues.

[bruce]

The reason I mentioned power is that, if it's a cabled solution, then it will face the same challenges. There may also be options for using a ethernet-over-power combined with DMX-over-ethernet. If it's a gennie, then we don't have that option.

 

I have no experience of wireless DMX devices, but I do know that you can get strange effects with other wireless data services over water if there are regular waves/ripples

[TomLyall]

If you did want the cable floating then maybe using flexi-conduit / hose to float the cable in would be less stressful for it than individual floats. (This isn't my way of volunteering to feed 120m of cable into a hose...)

 

would probably be worth adding a buffer at the start and a merge at the other to give a fair bit of redundancy.

 

Surely that would mean that if one line started acting a bit funny (as opposed to going completely open-circuit), then any jitters/errors/whatever you want to call it would get carried through to the rig? I'd agree that some sort of redundancy is in order, but there should really be a way of removing a faulty line completely, if required.

 

I guess this would depend on the merge used. You could always pull the line at the transmit end, though that would take some trial and error, which probably isn't best. I assume there'll not be someone on the barge during the show?

 

Now starts speculation that should probably be affirmed / shot down by someone more suited to answering this...

 

I'd assume that the most probable failure mode in this case is likely to be open / short circuit, given the lack electrical noise at the bottom of a lake. You've also only got 2 nodes with a single connection between them, so no odd wiriing (tees, loops, etc) to cause corrupt signals.

[scjb]

Hire a Firelite?

[Jivemaster]

Hire a firelight with the full personality set for my old NJD scanners? I Realise what you are thinking but it's not! That bit is covered with some twin flex that I can get in 250m reels!

[scjb]

Sorry, couldn't resist! Sounds like an interesting project anyway, have fun.

[Keeper of the Keys]

The reason I mentioned power is that, if it's a cabled solution, then it will face the same challenges. There may also be options for using a ethernet-over-power combined with DMX-over-ethernet. If it's a gennie, then we don't have that option.

 

I have no experience of wireless DMX devices, but I do know that you can get strange effects with other wireless data services over water if there are regular waves/ripples

Ethernet only allows for cable length of up to 100m longer length leads to wonky unpredictable networks, so the OP's 120m is just over the edge.

 

Though if there is power at the other end (which surely there is) you could use glass-fiber as the Ethernet-carrier which then allows distances of up to at least 2km and use ArtNet or some other DMX over Ethernet protocol.

But glass-fiber solutions are at least as expensive or more expensive then good wireless DMX gear.

 

Another solution that might be perfect for you if your running power cables from the shore is Avolites mDMX which allows the transport of 4 DMX universes down mains cables for up to 250m.

[smalljoshua]

The proposed use of Cat5 cable isn't to carry DMX over Ethernet though. It is as a DMX cable. I would use as many different ways of transporting the DMX as possible.

 

mDMX and Wireless DMX if you can find units to hire.

 

Can you perhaps send a Cat5 Line tied to the Mains cable and also one totally separately.

 

Josh

[obsoperator]

Please, wireless DMX is not some newfangled idea with no record, West End shows, or lab testing! Have look at this,

City Theatrical SHoW DMX

or call their Surrey office, or one of their 8 U.K. dealers!

 

You don't need to rediscover the transatlantic cable-laying technology of the previous century. Use another wireless DMX company if you like, but don't waste time underwater!

 

(posted by a satisfied U.S. customer, not an employee)

[indyld]

You don't need to rediscover the transatlantic cable-laying technology of the previous century. Use another wireless DMX company if you like, but don't waste time underwater!

 

I totally agree, having watched this thread seem to find any solution but the right one - Wireless DMX. As for the "fact" that Cable is always going to be more reliable than wireless - how's that, then? Cables get damaged, shorted, driven over, Sticklebacks might brush past them quickly underwater.....

 

On one outdoor Orbit gig last summer, I spent the whole weekend using the ZeroWire Wireless system (which seems to work pretty well, Zero88) from Tower to Stage with no problems. On the PMs instruction, we had laid a backup 100 DMX cable which he insisted would be used for the headliner act. This struck me as odd - you either trust the control system or your don't. Anyway...

 

When it came to the turnaround into the headliner, out comes the Wireless, in goes the cable. Well, a quick test produced whacky LED effects, random head waggles and all other nasties associated with bad DMX. So the Wireless made a swift comeback.

 

Whether some punter had stuck a shooting stick through it or a rabid mole had bitten into it, it just goes to show that cables can be damaged . Even mulitple cables don't give you complete security. On another gig last year I had a 5 wire FOH loom which had at least one cable fault on every single DMX line. Probably due the the long term mechanical damage that an outdoor FOH run is likely to be subjected to over a few seasons.

 

Why so much suspicion of Wireless DMX? 10 years ago I was working with old school LD's who had such a suspicion of a single DMX cable that they would insist on running masssive analogue looms to the dimmers.

[Jivemaster]

In 2008 I worked on a show with radio mic, wireless controlled stage/arena pyro and big firework shells. The radio mic was obviously wireless and tested before rigging, the wireless pyro was a well regarded pro setup tested before in the workshop. The fireworks were fired by cable from using pyromate P45 and five slats/rails and lots of cable.

 

On site the radio mic had a range of 3 metres rather than the usual 100+ and the pyro controller couldn't talk to the pyros. So the MD had to make the welcome speech from the desk rather than the podium and the pyros failed to fire, and the pyros should have been cues 1 & 2 on the firework timng so the handover was lost. The fireworks fired perfectly!

 

Both wireless systems returned to full range off the show site without alteration. So IMO thre was a site specific problem with wireless propagation, either wideband interference or multipath reflection issues possible. If anyone is a world class radio propagation expert I would like to discuss this by PM.

 

On that occasion some running between sites (100m or so) started the firework show so we got away with the ending so it looked OK. ON the show I'm planning there will be no-one on the pontoon to do manual firing or drive the beams from the scanners..

 

No I'm not firing the fireworks from DMX.

 

My desk has four buffered outputs So four lengths of cat5 should drive 1/4 of the show each and not lose all of it til four cables get soaked or severed.

[bruce]

Ethernet only allows for cable length of up to 100m longer length leads to wonky unpredictable networks, so the OP's 120m is just over the edge.

[pedant]Actually, that's completely wrong. The Ethernet protocol contains no such distance limits.[/pedant]

There is a limit of 100m on a single ethernet-over-CAT5 link, but nowhere has that been suggested.

[Keeper of the Keys]

Ethernet only allows for cable length of up to 100m longer length leads to wonky unpredictable networks, so the OP's 120m is just over the edge.

[pedant]Actually, that's completely wrong. The Ethernet protocol contains no such distance limits.[/pedant]

There is a limit of 100m on a single ethernet-over-CAT5 link, but nowhere has that been suggested.

 

I must have misunderstood your post, sorry...