Fault with scanner

[richardc1983]

DMX controller came this morning, it works fine. have plugged it in and off I go… now discovered a fault with one of my scanners. I know it’s the scanner that’s at fault I think when it strobes or goes fast the gobo isn’t in sync with the other light (I have them on the same DMX address as prefer this way) Its ok for a few minutes when on slow but when it goes any faster the gobo wheel on one of the scanners seems to go out of line and then u end up with a different gobo half and half.

 

There are 2 scanners connected and its only the one scanners that is doing it. I have tried changing the DMX cables over so know it isnt there.

 

Its as though the gobo seems to forget where it is.

 

And the only way to get it back to how it was is to reset the scanner.

 

Any ideas how to fix?

 

Didn’t really notice this on sound to light unless it was on the fast mode scanning.

 

When you reset the lights it fixes itself for a bit.

 

They are geni mojo scan 2's

[3guk]

Probably just a knackered stepper motor, I doubt these things use any form of feedback and hence if it misses a step it is unable to correct itself, until you get a new stepper, you will just have to send a reset command each time this happens/

[greenalien]

Assuming that you've checked that the gobo wheel isn't loose on its shaft, this is not so much a fault as a feature - the stepper motor that controls the gobo position has no positional feedback - i.e. it doesn't 'know' where it is continuously. On power-up, the gobo wheel will rotate in one direction until it hits a stop or a fixed sensor. At that point, it 'knows' where it is. After that, all positional moves are relative to that fixed point; this system works OK for slow moves, but a sequence of quick moves - like using the gobo wheel as a strobe shutter - can easily make it lose track of its current position. The only solution is to reset the fixture - there may be a programmable code to do this that you can build into the desk program - just don't do it to all your lights at the same time in the middle of a show. :) If there is no general reset code, you may be able to improvise a reset by just telling the gobo wheel to go to one of its limits - DMX code 0 or 255. Another typical situation where this may occur is using sound-triggered X/Y mirror movement - after a while, the beams will no longer point where you want them to be. Although the Mojo Scan 2 isn't exactly the most expensive scan on the market, this problem occurs on virtually all similar devices, even expensive ones, although it's also one of the reasons why better quality kit has a separate strobe shutter.

[richardc1983]

The thing is though sometimes ive notices slightly on both fixtures that the gobo wheel is never fully in position u may get a very slight corner of the gobo missing although not too bothered as long as it dont do what one of the fixtures has done and I have to reset all the time it does it now.There has always been a problem since ive had the lights one has always had this problem with gobos overlapping slightly, couldn’t get anything done about it though as the company went bankrupt therefore I didn’t have to pay for them. Never this bad.I have checked the gobo and colour wheels and both of them appear to be very loose on the shaft. Although I have tried to tighten but doesn’t stop the movement. I can move it forward and backwards on the shaft, possibly this is the fault. Both wheels seem to catch each other sometimes and move loosely up and down the shaft.How can I tighten them up it doesn’t seem to go any tighter than it currently is.I need this working for tmrw and can’t afford to buy more lights at this stage.I haven’t noticed this in sound to light where it gets completely lost only when it’s been strobing and cycling through many gobos at once but it has always gone onto the full gobo despite it being the wrong one, this time it isnt even there it is just stuck.ok so the gobo wheel seems to be stuck on there fine as this fits to the shaft but the colour wheel seems to be loose on the shaft, has always been like that, can wiggle it a bit.

[KevinE]

Firstly the wheels shouldnt move at all on the shafts, normally there's one or two allen grub screws to hold them fast and sometimes a dab of studlock as well.

 

The gobos and colours shouldn't really go out of sync just because they're a cheap light! Its either a faulty drive circuit, faulty wiring to the motor (mainly affects moving heads) or, as already described, a stiff or worn stepper motor. When the magnetism weakens (due to age or overheating in the past) it loses steps when asked to run or accelerate quickly though slow scrolls are fine. If the gobo wheel is used to strobe, this is a real test of a motors integrity and it'll go out here more easily due to the fast strobing motion. In fact most modern lights have to increase the winding current during strobing, they then turn it down at standstill or dimming. (this is why some steppers make weird whistling or singing noises, its the micro altering the current in the windings by PWM).

 

The firmware in the pcb will take account of acceleration curves and pwm current control in the windings to prevent steps jumping or skipping or starting/stopping too quickly...on a good motor.

 

Swap the motor with the other one to prove the point.

 

If the colour or gobo is always missing a slight chunk out of it (ie in partial eclipse!) even straight after a reset, it's sometimes because the motor shaft needs rotating with respect to the mechanical stop on the wheel. This is because of the way feedbackless motors park during the reset, the motor has to 'stall' on the correct driving phase.

[richardc1983]

Thanks guys have tried all your points above, Had it in pieces tonight and took the drive belt off, tightened a few things up ... not too tight though. And then put it back together again! And yes it works, its prob better than before. There is a slight over lap from the next gobo but I dont think its anything to worry about.

 

Got my party tmrw night so we will see then how well ive done it.

 

Anyway thanks a lot for all your advice and tips I owe you all a beer!!!

 

Rich.