Is this cable suitable for???

RonHebbard

Well-Known Member
Premium Member
Joined
Jun 12, 2004
Location
Waterdown, ON, CA
Hello; Rather than swerving and veering the thread discussing DMX cables, I've elected to begin a new thread.
@JD I was going to aim this in your direction but I'll throw it out to anyone; play along at home or pile on.
Basically the thrust of my post is you can try any cable(s) you want for any applications within the following guidelines:
- Nobody gets hurt.
- Nobody gets electrocuted.
- Insulation ratings exceed the voltages you're conducting.
- Current ratings are heeded.
- You're not creating a trip hazard.
(Don't use this appliance in bathtub while bathing. [ Oops! Sorry!!] Basically Cover Your Butt, and mine too.)

To veer off and site a few practical examples:
In the mid 1990's, the theatre I was working for ANNOYED me, I gave notice, and found myself working in a scenery and automation shop. I'm not a carpenter, never played one on TV. The shop was completing their first set using three AC servo motors for a production in Toronto. At the time, all the other 'Big Boy' automation shops, read three out of three in NYC building for Broadway, were still using DC servos.

One of our shop's two owners chose to take a SERIOUS shot at building and supplying AC servo automation systems. Several manufacturers were manufacturing AC servo drives for industrial / precision / assembly line applications but no one was developing systems and software with theatre in mind.

I'll wrap up this chapter of my novel and then get to the point of my post.
- A handful of employees made the magic happen.
- The main mover and shaker behind the automation department is now the owner / operator of his own automation company with 37 full time employees, a proven track record, and many projects world wide.
- The gentleman who wrote and finessed all of the software that spoke in 'theatre speak' moved on to Disney, began in California, spent several years in Paris, followed by Japan and hasn't looked back.
- The third gentleman owns and operates his own IA scenery shop and is another happy camper.

Returning to my original topic.

When the shop built their first set with three AC servo drives, they went with Emerson Electric, three of their 4120's and three of their matching drive electronics.
So far, so good.
They purchased all of their required cables from their Emerson dealer.
Emerson (being used to assembly line applications where their drive controllers were immediately adjacent to their drives close along side precision machining and automotive assembly lines) offered a selection of pre-manufactured, fully connectorized, cables in lengths of ( Don't hold me to the exact lengths, this is all from memory: 5', 10', 15', 20' and maybe even 25' [ They could easily have been cut in Metric lengths ])
In the several pounds of documentation accompanying each and every Emerson drive, several pages stressed the use of only factory manufactured and terminated cables with CAUTIONS to contact their factory if / when contemplating applications which may require longer cables.
Emerson laughed loud and long when our shop's owner called regarding 75' cables.

Cutting closer to the chase: We shipped 24 Emerson AC servo drives to Frankfurt, Germany with the Who's musical "Tommy". We'd surveyed the theatre and ended up with six cables in the neighborhood of 35', several 50' and 75' cables and at least two at 150'.
Of course, we also included spare cables of each length.

In addition to supplying 3 phase motive power and control data to each of the drive electronics, each motor drive requires 3 additional cables between each dedicated drive and its motor.
I'll quickly gloss over the requirements of these latter three cables:

- The cable powering the actual motor has to contain 4 conductors, three to power the motor and one to ground its frame. Additionally this cable has to have an overall shield, normally grounded at only one end to minimize ground loops. In this case, the shield is NOT to keep interference out but to keep drives from annoying everything and everybody else: Computer users, cell phones, wireless mics, wireless coms, guitar pickups, the world at large DOES NOT want to be pestered by spurious emissions from the motor drives.
Shielded 4 conductor 12 gauge is difficult to source. Shielded four conductor 10 and 8 gauge is normally a special order from your friendliest custom cable shop.

- Cable connecting each motor's resolver to its control electronics is typically 22 gauge shielded and, pardon me, I can't remember the exact quantity of pairs but my memory's remembering DB15 connectors. Shielding of the cable and the shells of the DB's was IMPORTANT, in this case to keep EVIL interference OUT.

- The third cable could be little better than 'wet string' as it carries only low voltage DC for three mechanical limit switches; Absolute fail safe over travel limits in both directions plus one hard limit, anywhere in between, for initial calibration of the drive and whatever it's controlling; typically a horizontal or vertical winch or possibly a wildly gyrating, pyro-spewing, pinball machine which blows its cool with precise repeatability which the actor portraying Tommy learns and anticipates to the nth degree like any good dancer learns choreography.

- Often a fourth cable is included, usually a twisted 18 gauge pair with overall shield. This latter cable again has its shield grounded at only one end to again minimize ground loops and contain any emissions caused by the suddenly collapsing fields of coils operating spring applied / magnetically released mechanical brakes.
( Why would you want independent mechanical brakes on your precision drives (You ask)) ???
To lock them in place in case of power failure. The drives will maintain their precise positions when commanded to BUT, if / when power fails, gravity is NOT your friend when heavy pieces flown overhead are unwinding their way down neither under control nor with any spring applied brakes.

TAGGING THIS NOVELLA BACK TO ITS PREAMBLE.
When Emerson specified their cable lengths, they were thinking in terms of controlling machines such as precision lathes where parts are being machined, REPEATABLY, to tolerances of a thousandth or less.
If / when you're positioning scenery on stage, horizontally or vertically; directors, actors, SM's, deck and fly carps, et al are pleased as punch with accuracy measured in sixteenths or eighths of an inch.

Precision accuracy and repeatability is all a question of expectations and scale.

For our drives, we purchased raw cables in 1,000' lengths, connectorized them ourselves, tested them controlling raw, unloaded, motors where there was ZERO chance of injuring anything or anybody, marked their shafts with masking tape and Sharpies, spun them up to maximum speed then commanded them to stop on a dime and noted the precise rotational position of their drive shafts. If they were repeatably accurate to within 90 degrees, NO PROBLEM. By the time they've driven gear trains, and LONG, horizontal (saggy) lengths of aircraft cable, repeatable accuracy within 90 degrees of their drive shaft amounts to close to zilch in terms of positioning six pinball machines on stage, flying in six windows, or closing a traveller; you've got the picture.

We'd connectorize both ends of thousand foot lengths and give 'er a go.
If 1,000' was a little 'ratty', we'd chop the 1,000' down to 500' and found more than ample repeatable precision for anything we were doing.
There was NEVER a hint of trouble with the 150' lengths in Germany nor were there any problems with the 200' lengths we needed when we built all of 'Tommy' a year later in 1996 for London, England's Shaftesbury Theatre I believe it was.
Bottom Line: When it comes to cable, don't be afraid to try things for yourself AS LONG AS, you're experimenting and TESTING under SAFE, and controlled conditions in your own facility with the doors closed to protect casual visitors.
REMEMBER: You read this on the internet, posted by some old retired geezer you've neither met, heard, nor seen. Use your judgement and STAY SAFE!

O.K. Whip me, beat me, make me write bad cheques. Kevlar undies in place; I'm ready.
Toodleoo!
Ron (posting from safely outside Donald's walls) Hebbard
 
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TimMc

Well-Known Member
Joined
Feb 15, 2017
Kevlar®? You need Nomex® because asbestos is so last century.

While I'm all about experimentation I'm more sanguine about someone deciding that if something works in an experimental setting that the same results will be consistently achieved in the field, in deliberate ignorance or defiance of standards and specifications.
 
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JD

Well-Known Member
Joined
Jan 1, 2005
Location
North Wales PA
Being from the 70's and 80's, most everything that is "standard practice" today, was experimentation back then!
Remember welding cable with Tweco connectors for power distribution? And that was "doing it right" back then, where it was common to see lengths of aluminum triplex held down with cinder blocks!
Slowly, we learned and adopted what are now considered Standard Practices.
 

TimMc

Well-Known Member
Joined
Feb 15, 2017
Being from the 70's and 80's, most everything that is "standard practice" today, was experimentation back then!
Remember welding cable with Tweco connectors for power distribution? And that was "doing it right" back then, where it was common to see lengths of aluminum triplex held down with cinder blocks!
Slowly, we learned and adopted what are now considered Standard Practices.
Yeah, I remember big blue sparks, loud bangs and much cursing when the Twecos fell off...

You're right that we've been learning as we go. We've been doing it for a long time, too, and the early results with electricity and lots of heat left a lot of death and property damage.

Playing with non-DMX cables for LX, by themselves doesn't present much risk but controlling a device or fixture that could present a hazard if it were to randomly operate or stop responding is a much bigger deal.

I'm all about setting up stuff and experimenting - it provides valuable opportunities to observe behavior/results in controllable (or at least consistent) environments - and can lead to better understanding of the hows and whys behind things. My abundance of caution is based on seeing too many things that didn't fail in experiment but that failed at critical times. Think of it this way: if a wire rope sling has a breaking strength of 20,000 lbs, why do we load-limit it to 10% or 20% of that, especially if we put a 20,000 lbs pull on it in the shop and it did not catastrophically fail? It's about the false sense of adequacy/security that an experiment or exercise could leave with people, and that's where my concern is.

So funky DMX hurts nothing in the shop, is potentially embarrassing at showtime, but controlling the lasers might be a different matter entirely.