Looking for DMX controlled extender bars

[tomStrand]

Good evening gentlemen and ladies,

 

I was on a job last year that had a row of DMX controllable drop in bars. They were capable of holding VL3500s and had a movement range of about 10 meters.

 

I cant for the life of me find any information on these things. Could one of you kind people point me in the right direction?

[Ynot]

Hmmm... ™ ©

 

I must say I'd probably put these in the same 'DANGER Will Robinson' category as DMX controlled pyro.

 

Relying on DMX to control something as potentially lethal as dropping in fly-bars to me is a recipe for disaster.

Just think of the incident reports and likely court write-ups for the night where you hit '1 thru 150 @ 00' for example as a blanket command to clear the desk, only to find those VLs dropping on the heads of the back row of chorus...

 

There could very well be a rather good reason you can't find any online.

[Stuart91]

Are you absolutely certain that these were DMX controlled, and that there wasn't some other show control involved?

[ocfe]

Is this what you're thinking of:

http://prolifts.es/products/Show-lifts/

[ontoprigger]

you should not have any winches or hoists controlled by DMX as it dose not have the safety protocols required, DMX is not recognised by automation companies as a control source or input to initiate a cue, they require time code, Midi or similar.

 

if someone is making DMX controlled hoists, I don't think they will meet any of the current standards.

 

 

 

[musht]

Another issue with DMX for motion control is its one way, no way of reporting back position.

 

Some small DMX wnches around but weight limit is usually a couple of kilos for LED balls.

 

Bigger weight be someat more specialised than DMX

 

http://www.cyber-motion.com/

 

http://www.kinesys.co.uk/

[Jivemaster]

More things are controlled by DMX then the spec permits, but only because the spec was written for dimmers feeding tungsten lights. Even if there is some load bearing winch system that controls by DMX you shouldn't be planning to use it where any failure could put people or property at risk.

[tomStrand]

Thanks for your replies,

 

I'm not 100% sure that they were DMX controlled. The were run off a MA2 and the operator claimed they were.

 

I'm looking for a rigid system rather that a chain hoist. Midi or timecode would be fine too. Do you have suggestions?

[Jivemaster]

Realistically I'd want to look at specialist lifting/rigging companies, specifying what you want in terms of load and lift range and lift speed (and speed ramping). I'd not ask for a DMX solution because the standard for DMX prohibits the use of DMX for safety critical functions. You'd also have to consider getting the power and control to the lantern on the lift which may require cable winches.

 

As you came across this system on previous work have you contacts with anyone from that job? Was the show written up in any of the magazines (L&SI for example) the write up will contain useful information.

[trussmonkey]

off the top of my head you would be looking at an actuator (either electric or hydraulic) that would then be controlled by something like the Kinesys Velocity 2 drive. Kinesys kit can be linked to a DMX lighting desk.

 

These systems are not normally off the shelf products but speak to Dave Weatherhead at Kinesys and see what they recommend.

 

TM

[kitlane]

you should not have any winches or hoists controlled by DMX as it dose not have the safety protocols required, DMX is not recognised by automation companies as a control source or input to initiate a cue, they require time code, Midi or similar.

 

if someone is making DMX controlled hoists, I don't think they will meet any of the current standards.

 

 

 

 

Why is MIDI or Timecode any safer than DMX?

[alistermorton]

you should not have any winches or hoists controlled by DMX as it dose not have the safety protocols required, DMX is not recognised by automation companies as a control source or input to initiate a cue, they require time code, Midi or similar.

 

if someone is making DMX controlled hoists, I don't think they will meet any of the current standards.

 

 

 

 

Why is MIDI or Timecode any safer than DMX?

 

 

 

I wondered that, too. On the surface, I can see nothing that makes a midi message inherently safer than a DMX message.

[dbuckley]

In a safety controlled system, there is no problem using DMX, MIDI, or timecode to control what some dangerous thing does. The critical requirement is that even under failure of the data, the dangerous bits must not be able to injure people. This means either intrinsic protection or separation so that the thing / person interaction cant occur, or wrapping a safety system with human enablement control around the scary stuff, usually a dead mans handle, and if possible and/or necessary, having sensors.

 

A few eons back, I did some work on factory automation stuff, and thus had to learn a bit about safety systems in an industrial context. The PLCs and software that controls really scary industrial stuff that will whip a limb off or kill one are only a little more reliable than theatre stuff, but there is a separate safety system that keeps body parts and moving steel from interacting in a bloody way.

 

There is lots of publicly findable information on safety systems, under the now superseded standard EN 954, but EN 954 is easy to understand, and most of the world's heavy machinery is still operating under this standard. The essential thing to work out is the level of risk and how safe one needs to be, as the further these two are apart, the further up the list of categories from 1 to 4 one must build the system to. As an intro, have a read of something like Safety-Related Control System Structure Considerations.

 

Frankly, if one is building a simple deadmans with scary dangerous stuff, category 3 is where I would start, which is easily implemented with a safety PLC and safety enablement contactor(s) to the dangerous stuff.

 

Finally, one needs to consider unusual failure situations. A deadmans is a great enabler in telling the system "it is now safe to move thing X", and DMX from the console provides the positioning information, so the LX and thing move together, but if Lx op accidentally hits the DBO and DMX drops to zero in the middle of an enabled move, what happens then? If thing X can move 20m in less than a second, then by the time the deadman's has been released there could be a train wreck.

 

This isn't new knowledge; a simpler form is this is espoused in the first edition of the Show Control handbook, along with examples, but the examples use off-the-shelf PLCs and the like, rather than safety rated components with brand names like Banner and Pilz, and lack an examination of system failure conditions, and thinking about the system integrity levels required.

[ImagineerTom]

Why is MIDI or Timecode any safer than DMX?

 

Surely the bigger risk is not in the protocol itself but the way in which it is commonly used. If you have a DMX controlled "thing" then it's probably going to end up being tied to the lighting desk. I can't think of a single time I've seen a programming session underway when there hasn't been an odd extra light turn on, a move that wasn't expected or some other (relatively minor) error occurring but it doesn't actually matter because the possibility of injury or damage is so minor that no-one builds safeguards in to DMX desks or operator & programmer training to spot and actively prevent those errors occuring. As soon as you add a physical object (ie a winch/motor/automation) in to the DMX world you have to go right back to basics and ensure that every operator and programmer who touches any part of the system is working to much stricter tolerances & standards because the risk of injury or damage has increased by several orders of magnitude. You could mitigate against the risk by incorporating dozens of sensors and a PLC controller on to each automated piece, as well as putting a deadman's in to the control system but now you're in the position of having to employ a person and build a whole complicated safety control system just so that you can interface with DMX in order to save yourself from having to buy a dedicated control system and operator......

[alistermorton]

Like Kit, though, I can see nothing which inherently makes MIDI safer than DMX. If hitting dead blackout can drop the rig on your head, surely so can an all controls to 0 command over MIDI?

 

When we've used DMX to control things like pyro it's been as a synchronising signal, for example, rather than a s the only control. The responsible person still has to enable firing with the system key and the circuit selector and the dead man's handle, the DMX just gives slightly finer control over the exact firing time. Surely in that sort of system there's little to choose between DMX, MIDI or some other potentially failure prone open loop system?

 

EDIT : spilling and triping.