Troubleshooting/improving galvo respose

[Shasta]

Hey all, I've got a Goldenstar RGB3000 that was purchased prior to the pandemic... things got a bit busy for a while so I'm just getting around to getting it going. Right now I've got it hooked up via LaserShowGen & an Etherdream 2, but I'm having some distortion issues. I've attached a few images of what I'm seeing, even after trying to tune things with LaserShowGen's optimization options:

test-img.jpg
3-circles.jpg
circle.jpg

The fact that I'm having getting this distortion, even with every simple tests, is making me think something is up with the galvos. Does this seem correct? If so, are there any idea's on what I can do to try and fix this?

Even slightly more complex tests start to very badly degrade. So as-is it's not really going to work for what I'd like to do - aligned projector/laser visuals. I'm thinking worst case, I'll try and repurpose this laser for a lumia build down the road and purchase a new one for this project.

[buffo]

Right now I've got it hooked up via LaserShowGen & an Etherdream 2, but I'm having some distortion issues. I've attached a few images of what I'm seeing, even after trying to tune things with LaserShowGen's optimization options

I haven't used the LaserShowGen software, but typically you want to turn OFF any optimization options in software before you try adjusting the tuning pots on your scanner amps. This is because some of the points in the ILDA test pattern are positioned such that it should be impossible for the scanners to reach those points, and this fact is accounted for in the tuning process. But if you enable any sort of software optimization, then the software may alter the position of those points (or add additional points) which will invalidate the tuning.

The fact that I'm having getting this distortion, even with every simple tests, is making me think something is up with the galvos. Does this seem correct? If so, are there any idea's on what I can do to try and fix this?

It looks like you're getting a lot of overshoot on both the X and Y; you probably just need to tweak the tuning on your scanners.

Can you post a picture of the ILDA test pattern? Make sure you are scanning it at 30Kpps, with no software optimization, and make sure your scan angle is LESS than 8 degrees. (The length of the sides of the test pattern must be less than 14 cm for every meter of distance between the projector and the display surface.) That image should demonstrate any problems with your scanners quite plainly.

Usually the scanners are properly tuned before a projector is shipped, but every now and then you'll get one that needs a little adjustment. Here's a link to a tutorial on how to tune your scanners.

Adam

[Shasta]

Here's an image of it running with optimizations turned off:

IMG_20220705_145303.jpg

LaserShowGen doesn't seem to let you limit the pps without optimization, but instead runs off fps. This was running at 25fps (flickers, and the cause of the artifact in the photo), but that should put it right near 30Kpps since the test image has 1190 points. Sorry the photo isn't the best, hopefully it gets the idea across though.

[laserist]

Are you sure you've got a good ground?

[Shasta]

The power plug is 3-prong, so it should be grounded fine, I think? I've moved it to a more convenient place for testing and was getting the same results when plugged into both surge protectors.

[buffo]

Here's an image of it running with optimizations turned off:
Sorry the photo isn't the best, hopefully it gets the idea across though.

That photo clearly shows that you need to re-tune your scanners. Not only do you have a great deal of overshoot on both X and Y (see the corners of the inside square), but your servo gain is also very low on both. (Center circle should be touching the walls of the inside square.)

You'll need to open up your projector to gain access to the tuning pots on your scanner amps. Then you'll need to make SURE that you know which pot is which. The ones you will be messing with are SERVO GAIN, LOW FREQUENCY DAMPING, and HIGH FREQUENCY DAMPING. Once you have identified those 3 pots on each scanner amp, you'll have the information you need to re-tune them.

Follow the instructions in the scanner tuning tutorial link I posted above and you should be fine. Obviously you'll need to be very careful - with the lid of the projector open you can be exposed to stray laser reflections, not to mention the danger posed by the exposed mains power wiring! But the tuning process itself isn't too bad.

Also, you'll need to measure your scan angle to be certain that you are below the 8 degree mark. (Use the size adjustment in your software to reduce your scan angle until you are under 8 degrees.) I suggest you actually *measure* this, rather than using the approximation method that is mentioned in the tutorial. As posted above, 8 degrees will give you 14 cm in size (height and width) for every meter between the projector and the wall.

Since your servo gain is already well below where it needs to be, there's probably no need to walk the scanners down (zeroing) any further before starting to tune. Instead, I would start by first adding some low frequency damping to see if you can tame all that overshoot. If that works, then start working your way "up the stairs". (The tutorial explains all this.)

On the other hand, if you can't get rid of the overshoot by adding more low frequency damping, then it's possible that your scanners are over damped. In that case, you should try walking them back several steps first. No need to go all the way to zero, but definitely take them down a couple full turns or so. (NOT ALL AT ONCE THOUGH!)

Good luck!

Adam

[absolom7691]

The power plug is 3-prong, so it should be grounded fine, I think? I've moved it to a more convenient place for testing and was getting the same results when plugged into both surge protectors.

I think what Laserist meant is; there are several ground points in a projector system. Mains ground is important but the amps, PSU output, ILDA connection, and XY inputs should also have a solid ground.

Adam (Buffo) is correct in that your tuning looks way off.

[Shasta]

I think what Laserist meant is; there are several ground points in a projector system. Mains ground is important but the amps, PSU output, ILDA connection, and XY inputs should also have a solid ground.

Ah, yeah then I'm not sure - I haven't cracked open the case to it yet.

Thanks for all the information buffo! I'll give it a go this evening and see where I get.

[laserist]

What I was thinking is: There's a horz jump in the vertical lines of the large square in the ILDA test image - I doubt that's a tuning issue...

[Shasta]

What I was thinking is: There's a horz jump in the vertical lines of the large square in the ILDA test image - I doubt that's a tuning issue...

That's actually an artifact from my phone's camera - I'd set the shutter speed to 1/25s to match the frame rate in an attempt to get a decent picture and my hand must've moved a bit. Thankfully it's not quite that bad... just pretty close lol. I didn't end up having time to mess with it today.

IMG_20220705_153831.jpg