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Everything slows down when X axis changes direction.

geofox784geofox784
in General
So I have an interesting problem where everything slows down, as if hitting a sharp vertex, when X changes direction by any amount. This results in noticeable scars in the print. 

I created this random shape to test this. It is only one wall thick and using vase mode, so it is not stopping to raise Z for the next layer. I have confirmed that Z is raising continuously throughout the print. This problem is still noticeable when printing normally and not in vase mode, but it is harder to photograph.
The arrows point to where there is an artifact as a result of everything briefly slowing down. Notice that it is only where X changes direction. There are sharp points where X changes direction as well, but I ignored those as it would not be noticeable at an edge anyway. 


Here is a side view.


A close up:
 

And a slow motion video. You should be able to clearly see the slow down here.: 
https://www.youtube.com/watch?v=ofv1BpCF-Jc&feature=youtu.be

I am using 1.0.0 dev. 
Y does not affect anything when changing direction, only X. 

I have looked through the Gcode, specifically where X is at it highest and lowest value, and it is just normal G1 code. Nothing out of the ordinary. 

This happens on the smallest curves or the largest curves. 

Maybe this has something to do with jerk or acceleration?

Comments

  • geofox784geofox784
    Better quality video:
  • RepetierRepetier
    Clearly nothing I'm used to see. Only reason I know where this might happen is if you have backlash enabled in your firmware. Then changing x direction makes a pure x move to compensate backlash which slows down movement to 141% jerk I think. So please check if backlash is enabled for you and try disabling it.
  • geofox784geofox784
    Repetier said:
    Clearly nothing I'm used to see. Only reason I know where this might happen is if you have backlash enabled in your firmware. Then changing x direction makes a pure x move to compensate backlash which slows down movement to 141% jerk I think. So please check if backlash is enabled for you and try disabling it.
    I know for a fact that it is enabled. In fact it is only enabled on X and Z, not Y. That would explain why Y does not have the same effect. I'll try disabling it. Is there any way to fix this while keeping backlash enabled? Could I adjust jerk? 
  • geofox784geofox784
    Just disabled that and it fixed the problem. I really like having backlashed enabled.  Is there any way to fix this while keeping backlash enabled? Could I adjust jerk? 
  • RepetierRepetier
    Jerk is the variable determining the slowdown, but a jerk set too high will cause loosing steps sooner or later. So be carefull on how high you go. Also higher accelerations might reduce the time spend while switching directions and reduce the visible effect.
  • geofox784geofox784
    I think I will just have to go with disabling it. While running this test I had jerk set to the default 20. I've since reduced it to 8. I certainly dont want to set it higher. It would be nice if in a future version of the firmware backlash could be ignored in regards to jerk. 
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