Scanning offset question



I just switched from GRBL to AWC708C on my homemade laser and am now having the scanning offset problem. It seems fixed with the Lightburn software option for the 100mm/s and 300mm/s but as shown in the images, the 200mm/s rectangle is skewed in both. Any ideas? Also, why would the laser not have this issue at all with GRBL (on 8 bit controller) and have the issue on a nicer controller, I believe the 708c is 32bit? Thanks for the help.

This image didn’t load in the OP, this is the 100 and 300mm/s rectangles fixed with scanning offset option enabled.

Your motor drivers might be expecting ‘rising edge’ step signals, while your controller is outputting ‘falling edge’, or vice versa. That could explain the skew in the 200 version, but it doesn’t explain why you aren’t getting that in the other two. You could also just have a bad motor driver, or have it improperly wired or grounded. Try swapping the X & Y drivers to see if the problem goes away.

I already tried the rising and falling edge and when I did the opposite it made the skew worse. I will try swapping X and Y drivers tomorrow though and make sure everything is grounded properly.

I just swapped drivers and the same exact problem. Is it possible that it is a software bug? I never had the skewed rectangle until I started messing with the scan offset.

Here are my offset settings, when the rectangle is skewed, I didn’t have a value for 200mm/s but I just added this negative value and the rectangle is no longer skewed but the offset is still present, only on the 200mm/s though not the other two speeds.

If you change the line shift of 200 to be .365 does it still skew?

I’ll give it a try later today and let you know

Try deleting the ‘200’ line altogether as well, and see if that has an effect. Having the negative value in the middle there is very odd - the offsets are usually ascending and close to linear (like, 0.1, 0.3, 0.5, … )

It skews at 200 on everything I’ve tried except the negative value. I changed the acceleration on my DSP controller from 3,000 to 5,000mm/s2 and that now takes the skew away. The offset is still present so now I will recalculate all those values. Do you have any idea why my GRBL machine never had the offset problem but this 708c has the problem?

The AWC machine is running several orders of magnitude faster, and uses external components (the motor drivers) which themselves can sometimes be problematic. Without using a logic analyzer and seeing your exact settings, no I couldn’t say. Most people who purchase these controllers are buying them installed in a machine, set up by a manufacturer, not the end user, and they are somewhat geared that way - the non-Chinese documentation isn’t fabulous, and there are more things to go wrong.

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