x and y motor skip and shifted layers based on print speed

[ml3dprints]

Hi All,

This is an interesting problem. Since S3D doesn't allow for changing the speed of small perimeters, I'm forced to set a lower overall speed for the print. I print PETG and can print larger perimeters and objects at 45mm/s. I cut the speed to 20mm/s. I would get skipping or more like pausing on the X and Y motors causing the print to shift after a few layers. At first I thought it might be my Pololu voyage, which I had at .55v and lowered to .45v. I had the same issue. So for comparison, I used the same parameters in Slic3r. I had no skipping or shifting. In both of these scenarios the x/y travel speed was 150mm/s. So I decided to up my speed to 25mm/s in S3D. No more skipping on the X motor. Now when it moved from the outer perimeter to print the inner perimeters, The Y motor made a lockup sound causing the inner perimeters to start in an offset position. So I dropped the x/y travel speed to 120mm/s. I had the same problem but less of a shift. At 100mm/s, still the same problems but even less of a shift. At 80mm/s the problem went away. I have no problem with 150mm/s travel moves in Slic3r prefer the higher speeds to prevent oozing and stringing with S3D. So far the 25mm/s, 80mm/s combo is not shifting where it already would have in the other situations.

What would cause motors to skip in the g code? I was going to attache the gcode files, but they are too big. Is there any other information I can post from the gcode file?

[CompoundCarl]

It shouldn't matter what speed you set if your printer has the correct acceleration settings. That determines the rate of the speed change, so if that's wrong, it's easy to start skipping steps.

I would try lowering your acceleration settings first before you do anything else.

[ml3dprints]

It's definitely not acceleration. I've done a bunch of different test prints at various speeds and jerk setting and picked the best one. It's definitely an issue with S3D at different print speeds because the problem goes away at certain speed settings as noted. I am not having the issue with Slic3r at the same settings.

[CompoundCarl]

Hmm.. well I'm honestly not sure how it would be possible to skip steps if you had the proper acceleration settings. For example, if you set them very low, then it would ramp up so slowly, it would put almost no force on the motors themselves (besides friction and things like that).

Saying that you use the same speed in another software isn't really a good comparison, since how those speeds are used can be quite different. They are different programs and will make different toolpaths with different behavior.

But anyways, other things to check would be
- motor voltage and stepper driver current settings (usually there's a potentiometer to control this)
- friction or interference on the motion system
- too high of acceleration or jerk settings (there is a gcode command to echo these out from the firmware so that you can verify the settings it is using, instead of assuming, since I've made that mistake before..)