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Moving Head Positioning Problem


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I've noticed a problem with one of our Robe moving heads which is beginning to get a little irritating. One head in particular seems to progressively drift off from it's predefined position.


To clarify:

-At the beginning of a show, the head will move to the correct position.

-The next time it is told to move to that position, it will be out by say a small number of degrees.

-Then the next time a couple of degrees more

...and so on.


The heads are regularly opened up and cleaned out with a compressor etc, but I do know that they are in need of lubrication.


So my questions are:


-What lubrication do you recommend for the units?

-Could the lack of lubrication be responsible for the progressive loss of position? If not, what could be cause of the fault?


Thanks in Advance.


Edit: The fault occurs using two completely seperate controllers, so I'm fairly convinced the head is at fault.

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Cleaning them is only a minor step in the world of maintenance.


Is it only one attribute (read: does it get tilt correct, but pan is off, or are both wrong)?


It could be many things; the first ideas that pop into my head are: bad stepper motor, loose belt, wrong belt, bad encoder, DMX card is dying...


Others will be here soon to hone and add.



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I've had similar problems with VL's.


I don't know specifics of Robe parts but most are all the same. Check belt and all related components, especially drive cog mounting to motor spindle.


If you have more than one unit and it is possible, try swapping encoder sensor and see if problem migrates.

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We had a positional problem with our Mac250's, which I solved by turning off the feedback. Not sure if your lights have feedback controls on them, but I'd check the settings (I wonder if they have have been off).


You say the unit is out by a few degrees each time you ask it to move. Is it always, say, a few degrees under? over? or does it mix it up (sometimes over, sometimes under)?

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Best thing to do, which will eliminate a lot of things is boot the head up and try to physically pull the pan/tilt. If there is slop ie little resistance and the head freely moves a small amount before the encoder picks up whats going on then you most likely have a belt tension problem. The encoders are usually bolted straight to the motors, so slop in the belt would not usually be picked up, although if the motor is bad then the fixture will try and correct the problem and will eventually achieve it as it doesn't sound like its gone completely, hence I would discount the motor being the issue for the time being.


If the encoder is missing steps for whatever reason then your fixture will think that the head hasn't made it to it's destination and will add a few steps until it does. If this is the case then the fixture should offer up resistance when pulled. The encoder is only missing a couple of steps so should start trying to counteract your pulling straight away.


What fixture is it, and does it have two pan/tilt motors?

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Rob's advice is good, also the Pan encoder may need cleaning as they can get chock full of muck (or the sensor dry jointed). If the belt is stretched then you can only adjust it so far before teeth begin to jump simply by the head moving...the teeth go out of pitch with the drive spines and like jumping though the belt may be tight.
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