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Automated Fixtures I-cue w/ Tremor

Discussion in 'Lighting and Electrics' started by Charc, Jun 17, 2008.

  1. Charc

    Charc Well-Known Member

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    Saw a show tonight at a regional theater which had a moving mirror for specials. I couldn't help but notice the darn spot shaking all night. I was wondering what the likely cause of this was.

    My first thought was HVAC, will an I-Cue near a vent shake? If so, this could be interesting for LDs to note. Is it possible this was a data issue with a sorta slight flicker in the DMX value?

    Just curious...
     
  2. sound_nerd

    sound_nerd Active Member

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    How much of a shake? Data issues with I-Cues I've seen get very small and sparratic shakes. Nothing that's very repetative or solid. A vent is possible, never seen it happen though, the stepper motors should be enough to prevent most of that sort of thing from happening.
    I'm thinking data issue, as I've seen the same sort of p/t problems with full out "intelligent" fixtures (techno's, MAC's, etc..) that are suffering bad data. Most recently with me was a bad output on an optosplitter giving a few MAC 250's in the chain the p/t shakes and the shutter shakes.
     
  3. JD

    JD Well-Known Member

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    Intel's use stepper motors, each is fed by two phase sources, one, a constant, and the second, a variable. Depending on which leads and lags, the motor steps one way or the other. I have ran in a situation or two where the "constant" pulse generator is messed up. The result is a bit of epilepsy, for lack of a better description. Could be what you saw.
     
  4. Charc

    Charc Well-Known Member

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    The shake was minimal, on the edge of not being perceptible, but for the lighting folks, I think they'd all pick up on it. It was a constant shake, so thinking about HVAC, unless the air was coming out all night, that wouldn't really account for it. So it could have been data or motors? Interesting.
     
  5. midgetgreen11

    midgetgreen11 Active Member

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    Here's what I have to say: The HVAC vents in our auditorium, are directly behind the FOW catwalk; like while you're focusing you can feel cold air blowing at you.

    And, isn't I-Cue an internet program teachers use for entering grades?
     
  6. soundman

    soundman Well-Known Member

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    The summer stock theatre I worked at in the past had 4 I-cues and they all had a bit of a shake to them. Not very noticeable with a cut of frost in them but one of them had to be sharp and that was a bit more noticeable. We tried swapping everything and nothing would fix the problem. We took everything down and put a light in the booth with the mirror and swapped every possible cable with no success. In the end it wasn't that big of a deal for the LD.
     
  7. Charc

    Charc Well-Known Member

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    Yea this unit was a little sharp for my taste, but it was a two day thing, by an LD who just did it as a favor, I suspect.
     
  8. elite1trek

    elite1trek Active Member

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    I really don't know much about this, so correct me if I'm wrong, but this sounds like a problem with the transmission of the dmx data. The controller in the fixture might be getting bad data, and the shake is how it responds to it.

    But I state again that I dont know much about this.
     
  9. porkchop

    porkchop Well-Known Member

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    Ok I have a few ideas that haven't been mentioned yet.

    1: No terminator at the end of the chain.
    I'd call that my most likely suspect. The old techno's I used hated life without their terminator and shook in what sounds like a similar manor.

    2: Long run of crappy DMX cable.
    DMX is digital signal and therefore really shouldn't be bothered by noise (if someone wants to argue I'll post a link to a very thorough article on why this is true), but in an extreme case (long run, crappy cable, atmosphere with lots of noise causing things) you might have situations that there is data that gets messed up, though I would guess that this would be a quick jolt and a restore almost immediately every once and a while, not shaking. Personally I'd guess a bad splitter before this scenario but that's already been mentioned.

    Personally I don't buy it being HVAC unless it was only one I-cue that was doing it (thought process being HVAC directly on that unit could move it). If more than one had a shake but all the fixed lighting stayed put then I really don't think that the I-cue on the end of the fixture would cause it to start to shake while other fixtures stay put. If you have movement across all of the I-cues then it's hard to believe the airflow is direct and therefore it should effect the other fixtures too.
     
    Last edited: Jun 18, 2008
  10. Charc

    Charc Well-Known Member

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    Only one intelligent anything, the solitary I-cue, so I suspect the data run was pretty short. I also suspect they didn't use a terminator, which is a good call.
     

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