Hybrid firing of effects and pyro

[bigclive]

I'd consider the idea of DMX plus dead man handle control, since it would fulfil the safety aspect if someone close to the firing area had the control over the actual effect enabling and the DMX then became just an accurate timing position in that enabled time.

 

I've not explored the LeMaitre system, but the use of a safety channel held at full plus a multiple sample of the control channel does cover most possibilities of corrupted data, since if the channels were adjacent then the garbled data would not meet the safety channel requirements, and slight glitching on a single channel would probably not meet the three subsequent identical levels requirement.

 

It does seem to be based on the usual failure modes of DMX.

[timsabre]

You'd need to program the LeMaitre system fairly carefully if running on the same DMX console as the rest of the lighting - you'd need to make sure the safety channel was HTP on the console, not LTP, or the console could easily park it at full. And you'd want to make sure that the safety channel was on a different playback/cue to the firing channel and was absolutely not included in any other cue, so that you couldn't fire it by pushing a single fader up.

 

They may have covered the DMX failure modes but there are plenty of opportunities for operator error...

[GR1]

I agree with Brian. Get rid of the unwilling crew.

[Cicero]

I'm an engineer at LeMaitre, and I agree using DMX for firing anything dangerous always needs to be analysed and operated by a professional user, who understands and manages the risks involved.

 

As we all know DMX is error prone, has no error detection and is only one-way communication after all. Unfortunately DMX is used by several companies for similar effects, and the market demands its use. We try to make things as safe as we can by having a separate safety channel, delayed arm timer, and DMX filter (which requires 5 absolutely identical values) before firing - which does add a delay of course. I agree it would be better and safer to have the safety channel at a non full value, say anywhere between 50-99%, which we are doing on any new designs going forward.

 

We suggest operating the flame machines in their own DMX universe, and always to have a manned power cable E-STOP when operating.

 

I'm open to other suggestions you may have for future safety measures we could implement, we take the safety aspect of our products very seriously.

[MusicalMuseum]

I'm open to other suggestions you may have for future safety measures we could implement, we take the safety aspect of our products very seriously.

 

Why not use a multi-channel code - e.g. 4 channels, 0-255 (so up to 12 digits) which effectively acts a PIN code - held for several seconds - as an "enable"? Highly unlikely to be replicated by random DMX frames; though of course it increases the channel count of the fixture.

 

 

Highly Unlikely /= Impossible

 

S.

[timsabre]

I'm an engineer at LeMaitre, and I agree using DMX for firing anything dangerous always needs to be analysed and operated by a professional user, who understands and manages the risks involved.

As we all know DMX is error prone, has no error detection and is only one-way communication after all. Unfortunately DMX is used by several companies for similar effects, and the market demands its use. We try to make things as safe as we can by having a separate safety channel, delayed arm timer, and DMX filter (which requires 5 absolutely identical values) before firing - which does add a delay of course. I agree it would be better and safer to have the safety channel at a non full value, say anywhere between 50-99%, which we are doing on any new designs going forward.

We suggest operating the flame machines in their own DMX universe, and always to have a manned power cable E-STOP when operating.

I'm open to other suggestions you may have for future safety measures we could implement, we take the safety aspect of our products very seriously.

 

Thanks for coming back on this, I would have expected the safety channel have a narrower active band say DMX 192-208 or something, then you definitely couldn't hit it accidentally. Also that the safety would timeout if activated and not fired within 30sec or something. Then you would have to run a deliberately timed sequence to get it to fire. I'd be worried about the safety channel accidentally being left active on the console by being included in another cue state or something.

[Cicero]

Why not use a multi-channel code - e.g. 4 channels, 0-255 (so up to 12 digits) which effectively acts a PIN code - held for several seconds - as an "enable"? Highly unlikely to be replicated by random DMX frames; though of course it increases the channel count of the fixture.

 

 

Highly Unlikely /= Impossible

 

S.

Not a bad idea really, definitely something we may explore. Thanks

 

Thanks for coming back on this, I would have expected the safety channel have a narrower active band say DMX 192-208 or something, then you definitely couldn't hit it accidentally. Also that the safety would timeout if activated and not fired within 30sec or something. Then you would have to run a deliberately timed sequence to get it to fire. I'd be worried about the safety channel accidentally being left active on the console by being included in another cue state or something.

Yeah, for sure. Its common to have a smaller band of 60-80%, it should be small enough to be intentional, but needs to be large enough to hit easily with a slider. I could imagine many operators having issues with a deliberate timeout though, especially if they're doing manual firing instead of a timed preprogrammed sequence.

[cedd]

I'm open to other suggestions you may have for future safety measures we could implement, we take the safety aspect of our products very seriously.

Having read a few things about safety channels on here (has to be at 100% before the control channel will fire) I wondered if the concept could be improved. It doesn't mitigate against somebody doing a rig check or doing a "1-512 @ 100%". What I'd wondered was if this safety channel could only arm the device if it was taken to 100% before the control channel - maybe by a second or so. If they both came up together then it wouldn't work. And that it had a time window before it deactivated again (maybe with a counter that reset every time a pyro was fired, so you could do multiple fires without having to be watching the clock, but if you forgot to pull the safety channel down at the end then after maybe 30 seconds it'd deactivate anyway and need pulling down and back up again to work.

Not wanting to enter the argument on if it should be done or not, just an observation of how it could be done better.

 

 

[Brian]

The Galaxis G-Flame uses two DMX channels, a flame channel and a safety channel.

 

The safety channel is only active in the 60%-80% range and will only be recognised if the flame channel is below 6% when it is activated.

 

The flame channel is only active if it is at least 90%. To re-trigger it must drop below 6% before returning to the +90% value for the second firing.

[Shez]

Its common to have a smaller band of 60-80%, it should be small enough to be intentional, but needs to be large enough to hit easily with a slider.

Are you anticipating that a significant proportion of users will be using manual desks for control? You could perhaps draw comparisons with the control channel in a moving head fixture - there are often many different functions, including the lamp off, which can only be activated by a very narrow range of DMX values. In the case of lamp off, it's very deliberately narrow to avoid accidental operation, much as we're discussing here. I'd suggest you could use a much narrower range than 20% - no even remotely competent desk will struggle to hit an exact value on cue.

[Brian]

Are you anticipating that a significant proportion of users will be using manual desks for control?

 

For flames, the answer is almost certainly 'yes', the vast majority will be manually controlled.

[DrV]

As others have suggested, I think a safety channel should use an explicit non-zero and non-full value. The waveform of a zero and a 255 is too easily replicated by a fault. Adding a sequential element, as in the case of the G-flame mentioned above, then create a belt and braces interlock. The danger I see is that the more complicated the firing sequence becomes the more tempting it is to store the whole sequence under a single button or fader or stored cue which then makes it easier to initiate it inadvertently.

[empyfree]

Thought, would it be a good move for manufacturers to put the control/safety channel onto a completely separate DMX input? That way you could choose (depending on your risk assessment) to link the two inputs and control from a single desk, or to have a secondary desk (perhaps near the stage, with a better line of site to the pyro) which would be in charge of the safety function leaving fine tuning of a fire command from the first desk.

 

Edit. I’m aware others have mentioned having redundant/secondary controls, but unless manufacturers come up with a sensible way of implementing something it will always get worked around.

[Brian]

...a secondary desk (perhaps near the stage, with a better line of site to the pyro) which would be in charge of the safety function...

 

No need for another DMX line, the G-Flames already have an input for a dead-mans handle. Not sure about the Le Maitre units.

[empyfree]

...a secondary desk (perhaps near the stage, with a better line of site to the pyro) which would be in charge of the safety function...

 

No need for another DMX line, the G-Flames already have an input for a dead-mans handle. Not sure about the Le Maitre units.

 

How many units can you link / control from one “dead mans handle”? I can see that working well for a single unit, or a couple maybe, but it could end up like a bell ringing exercise trying to keep a dozen or more held in at the right time!