Scroller Errors - ChromaQ M2

[Neil Hampson]

I am curently having a major issue with one of my set of scrollers, (bear in mind that these are currently on hire to a friend at the other end of the country and I am trying to help remotely) Any help gratefully recieved, but as I sa I may not be able to answer questions immediatly as these units are currently in use on a show

 

The set of 4 were working on the prep, and worked in the venue for the 1st day, during the rehearsal, one of the gels jammed. the unit was removed and re-strung, and re-tensioned, this resulted in the string being torn in two as the scroller did it's calibration, the thing just didn't stop. as an 'in-field' emergency repair, I suggested trimming an inch of the offending tail and re-making the end with the metal tab.

After a few failed attempts to get the tension right, the scroller is now calibrating (i.e. runnig to the end and then back again) and returning to the 'home' position, however the 'home' position is now on the 2nd frame, not the first. the scroller responds properly to DMX other than this.

 

My first thought was that the string is too tight, however if the tension is released by the smallest increment (1/4 turn), then by the middle of the string it is so loose it runs of the spools.

 

I am not sure what else the guy has tried but I am at a bit of a loss as to probable causes.

 

The units is a ChromaQ M2 model (the 8" metal cased one) with 16 frames in the string.

 

I have asked for the following tests to be conducted at tthe earliest opportunity (which may be when the kit is returned next week)

 

1) Change the DMX address to check it's not the desk sending a random 6% or so to the unit.

 

2) Check whether the scroller responds in a linear fashion from frame 2-16 with a fader position of 0-100%, or if the first 6% of fader travel is 'dead' and the scroller responds linear from 6-100%

 

3) Swap the string with a known working unit so see if it's the scroller or the string is at fault.

 

Another question, what is the purpose of the small cotter pin on the spindle of the un-sprung, black scroll spindle, it would appear that it's this that is causing the gel to tear.

 

On a slightly related note does anyone have a template or drawing of the correct dimensions of the gel frames for this model of scroller?

 

Edit - Added the last question and the remove some of the spelling errors

[merlin24]

Here are some things to check.

 

 

 

Gel incorrectly tensioned, not enough turns on the tension. Tension by holding the black tube still and turn the Grey tube 1 1/2 - 2 turns clockwise. Gel in front as you look down on the Gel.

 

Make sure the Take Up Gel tube/spool are on the correct sides Grey Top=Right Black Top=Left, also that the Grey Top tube/spool and its centre sprung section is working and holding and not slipping. This sprung centre section is part of the Gel tensioning and if this fails it could damage the Gel.

 

Also make sure the Gel is wound so that the Gel is at the front of the scroller, if it is wound onto the tubes/spools with the Gel at the back it will cause major problems and will not work as it should. The cotter type pin is used to make the Gel run a bit better onto the tube/spool and to make the tube/spool give a tight fit on the drive shaft. If the cotter type pin is not there it will give the tube/spool a loose feel on the shaft.

 

Optical Switches (2x sensors) near the opto wheel (motor area) check they are free of dust and any other debris. This would cause the opto switches (sensors) not to sense the beginning or the end of its calibration points and would therefore continue to run at speed and tear the gel from the spool.

 

If none of these solutions are met then its more than likely one of, or both, electrical parts at fault. 1) Opto Sensors failed or failing 2) PIC chip on the main PCB.

 

 

Kind regards

Andy.

[Neil Hampson]

Here are some things to check.

 

 

Optical Switches (2x sensors) near the opto wheel (motor area) check they are free of dust and any other debris. This would cause the opto switches (sensors) not to sense the beginning or the end of its calibration points and would therefore continue to run at speed and tear the gel from the spool.

...

...2) PIC chip on the main PCB.

Andy,

 

I had not realised that there was any optical sensing on the M2's, where abouts is it and what does it actually look at, as there is no refective strip on the scroll strings themselves.

 

The biggest pain of all of this is that I can usually tension these things by feel, but how can you describe that to someone at the end of the phone. I have found that the textbook 1 1/2 turns is not always the best but usually a good starting point.

 

I realise that AC haven't made/sold these units for some time, but are there spares available?

[merlin24]

I had not realised that there was any optical sensing on the M2's, where abouts is it and what does it actually look at, as there is no refective strip on the scroll strings themselves.

 

Down by the motor you will see a small rotary fan it looks like the blades of a propellor. This passes through the optical sensors.

 

 

 

 

I realise that AC haven't made/sold these units for some time, but are there spares available?

 

Yes spares are available

[gherriott]

As the person who is on the other side of the phone dealing with these scrollers I thought I might add what I have done to try and get it to work properly. I have done all of the recommended tests by Neil, the tension is at it's optimum as far as I can see, as one 1/4 turn either way either sends the scroll off its rollers (too loose) or the scroller thinks the middle of the string is the end (too tight). I tried changing address, there is no DMX leak as this did not make a difference. I also ran it off the PSU without DMX attached and it still found its home postition to be frame 2. There is also no 'dead' section ie if move the fader up 1% and the scroll moves in relation to the fader, which tells me that the scroller 'thinks' there are only 15 frames rather than 16 due to the incorrent calibration at the start.

 

With regards to the optical sensors...what exactly are they looking at? Because surely if it was using OPTICAL sensors there would be no need for it to rely on the tension of the string to calibrate the string size? I am a bit confused as to how it works otherwise. I am also confused as to how removing an inch off the leading gel can cause the scroller to advance one whole frame more than usual? Would it not only advance an inch more than usual?!

 

It is a very weird situation and I have used various makes of scroller recently and each comes with their own problem, but usually I can figure a way out of that problem unlike here for some reason. Any more suggestions?!

[dirkenstein]

If the internals are similar to the ChromaQ CQ1D (which they appear to be based on a diagram I scavenged off the web) - the opto sensor on these consists of two IR slotted gate sensors (not possible to tell from diagrams if they uses a photodiode or transistor) mounted next to each other and a vaned wheel which is directly attached to the motor's axle that passes between the gates of both sensors. I think the wheel has 3 vanes which pass through the sensor gates, giving you six signal transitions per motor revolution on each sensor.

By detecting which sensor sees a transition first, it appears the scroller can confirm the motor rotation direction.

 

The single motor drives both spindles by a pair of toothed belts. One belt joins the two spindles, and the other drives the leftmost spindle (viewed from the rear) from the motor take-off cog.

 

I think the scroller detects motor stall/end stop reached by absence of opto transitions. The bridge driver for the motor may of course also have a stall current detector.

 

Note that all of the above mechanism is inside the closed part of the scroller case- you can't see any of it without taking the mechanism out. The sensors do get dusty from time to time, what with the gel cooling fan. I wouldn't recommend field disassembly unless you're fairly mechanically competent- you need a slightly odd-sized set of circlip pliers to get the spindle wheels off, for instance. It's also not clear from the M2 diagram I have whether you can remove the whole mechanism from the case as a unit, as you can with the CQ1D.

 

I think these scrollers perform calibration as follows:

 

a) run all the way to one end stop(detected by motor stall).

b) set scroll length counter to 0

c) run all the way to other end stop, counting opto transitions.

d) store transition number and compare against table of 'known' scroll lengths.

(I assume the unit has a little compensation table built in for different scroll lengths fully rolled up and unrolled).

e) run the motor in reverse until the transition count is 0 or the motor stalls. If the motor stalls before 0 is reached, scream and die (blinking red light on CQ1D).

 

f) Based on known scroll lengths, divide up DMX input range into numbers of opto transitions.

 

Note that the opto sensor counts motor revolutions, not scroll revolutions or scroll movement.

Tension of the scroll, slipping drive belts (It really shouldn't happen, but one of our CQ1Ds did it until taught the error of its ways), misaligned bearings, slightly bent spindles, etc. may all make a difference. The stall detection on the CQ1D especially develops fits of unreliability when confronted with a 'sticky' scroller mechanism.

 

I think your unit calibrated itself to be using a string one gel shorter than you have.

 

It didn't just shift everything an inch because whatever the resultant number of opto transitions it counted running through the gel string was, was just small enough to fall into the '15 gel scroll' bucket rather than the '16 gel scroll' bucket. I guess it considers certain ranges of transition numbers to match each gel string length.

 

I assume there is actually some spring tension on the rollers? 1/4 turn between motor stall halfway along the gel string or so loose that the gel is unwinding from the rollers doesn't seem a lot. Unless you mean about 1/4 turn on both rollers- that might be about right.

 

I have this memory that the scroll tail dimension tolerances for ChromaQ units are really quite tight. An inch might very well throw them out of calibration.

 

Piece of 1.5" wide scrap heat shield or clear gel and HT tape is in order, methinks.

 

I'm afraid I can't seem to find the right diagrams for making up M2 gel strings.

[merlin24]

As the person who is on the other side of the phone dealing with these scrollers I thought I might add what I have done to try and get it to work properly.

 

Greg,

Can I suggest that if you are still having issues that either yourself ar probably better Neil as he seems to own them contact our technical service dept, where somebody may be able to help you directly, otherwise all I can see happening here is a lot of speculation as to what MIGHT be wrong and not what actually is wrong. The number you need is 01494 838396. Ask to speak to Graham, mention you have been talking to me on here about the M2 and he will know what you are talking about.

 

Kind Regards

Andy

[Neil Hampson]

Gents, Thanks for the advice so far. It would seem that that there is really little that can be done in the field (or church hall, I don't know which is worse)

 

As Greg is currently happy to run the set of scrolls as is, losing the O/W on one unit I am not going to risk losing the whole thing. When the scrollers come back, I will open the back and give the internals a bit of a hoover out and check for any big build up of dust around the motor drives etc. I will also measure the suspect gel string against the cutting guide that I have now obtained (Thanks Glyn) I know that one of these scrollers has ripped the string a few times, so there may be 3 or 4 inches chopped off over the last few years, looking at the above it ties in with the replies above.

 

If problems persist I will contact the AC tech support when Ican actually have the things in front of me. definatly a number to keep in the back of the diary...