[Solved] Behaviour of dmx fog machine vs LED par

[Mibmusic]

Hi all,

This weekend we had our first band gig with QLC+ to support us with a few lights and fog. All went well except 1 thing. In the intro the fog machine went on but didn’t stop, hahaha.
Today I have gone through my show file and I think I could use some help. There must be a difference in default behaviour of the fog machine versus a LED bar/par or something. I hope this explains what I am looking for.

This first picture shows a very simple sequence. Lights go on, lights go off. This kind of sequences work with all the lights we have and no issues.

This second picture shows the second step of a sequence of our Chauvet P7 fog + LED machine. Lights + fog the first step (channel 1 to 255 but not shown) and only lights the second step. At the end of the sequence, lights go off, as expected.

So far so good but the behaviour of the sequence in picture 3 is different.The sequence just needs to activate fog for 2 seconds and then stop. So equal to the first picture I just added 1 step.

But as soon as the first step is fired the fog starts and stays on for about 8 seconds and then warms up again and goes on again. That part is the behaviour of the fog machine but why does it not stop at the end of the sequence? What is the difference between the sequences of picture 1 and 3? And why does the fog machine in picture 2 work as expected.

My questions are:

- Is QLC+ sending something to the lights at the end of sequence to make it go off? Or is the duration send via dmx? How does that work? I am trying to understand if the fog machine has a bug.
- In general, does a fog machine need to recieve a ‘stop' through a second step in the sequence? This because picture 2 works fine!
- Maybe 2 seconds is below minimum for the fog machine and does not handle the off message, if any? (trying to find that out)
- If I need to sent a ‘stop' in a second step. What length should that step have?

Sorry for asking but I would like to understand what is going on.

Gerard

[GGGss]

Gerard,

A good start to debug is actually look at the DMX monitor... What you are outputting.
Even without the fogger connected you can simulate what is going on.

if you select -during designing- something (cue, sequence ...) the output is simulated.
If you go live the behavior is a chain of events.
and yes - it needs a '0' value to stop - if your definition is correct then the fogger channel should be in LTP mode. Now you have to send a value to override previous ones. (Latest Takes Precedence)

But now I question you - why do you use 1 step sequences? That is the same as a Cue...
If you'd start with 3 cues and then put them together in one chaser you will have a lot more overview what's going on. (and a last step there might be the '0' fogger channel value = reset everything)

and to be honest - I don't understand why you include picture 1 ... has nothing to do with your Geyser - this doesn't help me debugging 8-/
be warned that in picture 2 - you set blue channels to 0 ... why? It doesn't make sense since it is never set to anything else __ in this sequence of events __

Try to structure your work a little bit more and you will debug very fast in the future.

[Mibmusic]

Hi GGGss, thank you for the quick respons.

As far as I know the DMX monitor does not show channel 1 so I never know if there is fog. All the other sequences I tested with the monitor.

Ok so if the fog of the Geyser is LTP, should that be in the documentation of the device? That would explain why fog stays on. If I sent a value to stop fog in step 2 of the sequence, what duration do you recommend? 500ms?

To answer you question. I use a Roland SPD-SX to start a show function (button on VC) via MIDI and these sequences are used in that show on a backing track. We are not done yet but it works for us.

Picture 1 shows 1 step. Lights go on and off at the end. So this is a big differ from picture 3. If the Geyser is LTP, then the LED par is not.

And the last thing. In step 2 of picture 2 blue is off indeed but I am not sure if that was a mistake. I think if I use blue in step 1 (for testing) it is still selected in step 2.

But from what I understand I need to find out if fog is LTP so it needs a second step. And I don't need a second step for HTP?

[edogawa]

Gerard, If you go to fixtures tab/channel properties dialog you'll see that the fog channel is handled as LTP.

As a general rule in lighting, everything that outputs light intensities is preferably handled as HTP - single conventional dimmers, as well as master dimmers and color channels in intelligent lights. When the HTP level information isn't sent anymore the receiving channel goes off.

Everything else usually is LTP. These are sane defaults made by QLC, in the properties dialog you can change the rule if you like, and see if that works better in your case.
When LTP information isn't sent anymore because the sequence stops, the channel stays at the last value received.

That's not a behaviour inherent to the fixture, it's logic provided by the control device, QLC in this case.

I'd simply add a step to explicitely turn fog off, and be fine.

[Mibmusic]

Lesson learned and I understand now. Thank you Edgar! I will post some video's so you can see what we've done.

Best regards,

Gerard

[Mibmusic]

Edgar,

What is the normal duration for a second step, if any? 500ms?

Best regards, Gerard

[GGGss]

1 tick - so 1ms should be enough.
To be on the sure side look at the tact frequency of your dmx interface and take that time + something small. Now you are sure the signal is transmitted.

[Mibmusic]

Thank you, that’s what I was looking for. I am sorry for asking so many questions. But you guys are great in helping me understand.