DMX should not be used for pyro/laser

[Brian]

Considering that the chance of a DMX fault resulting in the 'safety channel' being between 40 and 60% AND the actual 'fire' channel being up are less likely than a glitch on a single channel...

And the great thing is, you can actually work out what this 'chance' is.

[bigclive]

There have been DMX controlled pyro interfaces that used fairly complex sequences to ensure a low risk of false triggering. I'd say that's acceptable in a low risk environment with actors not directly standing over live devices before their cue. However, garbled DMX can send a lot of random "codes" in a very short time.

 

That said, there are lots of professional pyro firing systems with complex communications protocls that still manage to fire stuff inadvertently with or without human intervention. Again, ANY crashed system can send a lot of random data out in a very short time.

 

Perhaps on the receiving end it's useful to detect when a string of false firing sequences have occurred and go into a failsafe mode.

 

I've still got my adorable Chinese DMX flame thrower.... Totally non secured firing by virtue of it's generic smoke-machine DMX card.

[scjb]

In all seriousness Clive, what are your experiences with high-end kit firing uncommanded? I have only ever seen fail-to-fire through dodgy comms.

 

EDIT: Sounds too defensive, really isn't! Genuine question.

[vinntec]

And don't forget the biggest variables of all - actors who have stood in a precise position performance after performance can suddenly turn up where you least expect them or a stagehand might suddenly find an opportune moment to get under the set to make repairs... So if there is the slightest chance of anyone wandering into the range of a pyro, then there has to be someone with a clear view who is solely charged with operating the device or operating a "permission to fire" switch if timing is critical. I think this is common sense as it is better to ruin an effect than potentially ruin someone's life.

 

I speak not as someone who is an expert at pyro operation but one who has set a lion's [actor] tail on fire when he got too close to a DMX smoke machine! He walked around the backstage area for some time before the panicking DSM worked out where the burning smell was coming from (bit like an old candid camera sketch). Just an illustration that you have to expect the unexpected - tails [or gowns] that hang down where you didn't expect or people that wander into the firing line.

[bigclive]

In all seriousness Clive, what are your experiences with high-end kit firing uncommanded? I have only ever seen fail-to-fire through dodgy comms.

 

EDIT: Sounds too defensive, really isn't! Genuine question.

 

I've only ever experienced non-firing. And when you read about the control systems where major stuff went wrong there's always that nagging suspicion that operator error was involved.

 

However, it's always wise to plan for the unexpected, since it only takes one incident to cause all manner of complications on an ongoing basis.

 

I like to leave pyro to the pyro guys and only get involved when they experience technical issues with the equipment. That way I don't lose sleep when stuff happens. (Which it does.)

[norty303]

Although I don't like it, DMX control for lasers is fine, because you do not use DMX as the safety device.

So in the example of the micro YAG earlier, throwing the beam around via a DMX control board is fine, providing the operator/installer has taken care of the issues of beams in the crowd/hazardous areas.

Most people use physical beam blocks for this, such as masking apertures with BlackTak. You could change the geometry of the pattern too with DMX, but this is one area where full ILDA software control is far superior to DMX, and the provision for zoning (for the aesthetics) along with masking (for the safety)

 

The problem is that most 'operators' (using the term loosely) consider their job/responsibility starts and ends with applying power and running some patterns, and the manufacturers are not yet good at advising what their additional responsibilities may be (depending on geographical location).

 

If someone is doing their job right, there shouldn't be the possibility for an 'accident' because its all appropriately covered, but generally not through DMX.

[ImagineerTom]

The problem with DMX control is not so much the safety of the control protocal (because there's plenty of ways of adding additional security to make it as safe as any other system) but rather because DMX doesn't provide the fault reporting/checking proprietary systems have and also because at the bottom end of the market it will mean an increase in the number of "one man bands" who provide lighting, sound, lasers and pyro's all operated by one person using a laptop and the cheapest cables / software / units available for £50 a night. The proprietary control systems for powerful lasers (to a lesser extent) and pyro's / Fire effects acts as a very good barrier to entry for the under-resourced and unskilled, as well as ensuring that when you do use the equipment you're physically forced to employ more people and put more thought in to your useage precisely because it cannot all be blindly automated and left to run itself.