Issues with pressure advance since RRF 3.4

Argo

I see.

I know from another Klipper user that he also only could get nice corners by playing around with the smooth time setting. Pressure advance alone did not help much.

Maybe extruders / hotends are so particular nowadays that we need this setting to get nice corners?

Here is the example from the user I'm talking about:

He has a bowden setup and needed to increase the smooth time in order to get nice corners. PA alone did not the trick.

@dc42
How high are the chances we might get this feature for RRF? I think this might very much help those who are having problems with PA at the moment.

Heartleander81

@Argo ok. Nice test from him. I find for my Hevort 0.02 smooth time and 0.044 PA. Worked nice. I hope my Info can help Duet.

CR3D

@dc42 Hi David,

I have to join this conversation because through my contact to @Heartleander81 i noticed this effect with "round corners" at some of our machines to.

I think this comes with newer firmware and if you made some changes into PA there would be an issue. But how can we test it that it would be helpfull for you?

one of our customers has now contacted us explicitly about this effect and is looking for a solution. I can't compensate for it by increasing the PA value. We've tested a lot here.

Thank you Regards Christian from @CR3D

dc42

@CR3D said in Issues with pressure advance since RRF 3.4:

But how can we test it that it would be helpfull for you?

Find a print where there is a clear visible difference between the effect of pressure advance (e.g. on corners or infill) between RRF3.3 and RRF3.4.4 with the same configuration for both, and no input shaping when running RRF 3.4.4.
Edit the GCode file to reduce it to a short print, preferably just 1 or 2 layers.
Post that file along with your config.g and other relevant macro files.

gnydick

@dc42 why don't you just generate the move list from a 3.3 system and from a 3.4 system for the same gcode and output it to text files and diff them?

dc42

@gnydick said in Issues with pressure advance since RRF 3.4:

@dc42 why don't you just generate the move list from a 3.3 system and from a 3.4 system for the same gcode and output it to text files and diff them?

Because none of the prints I and others have tried show any difference between 3.3 and 3.4. Nobody has produced a print and machine settings that shows a difference. If somebody ever does, then I will be able to use the method you suggested or another method to see what has changed.

oliof

I personally believe that the changes must have happened before 3.3 ... or that the observed issue isnt due to a change in firmware but a change in perception of acceptable corner bulging due to the performance of non-RRF systems.

A decent way to bisect this is to take a Duet2 board, and go back all the way to RRF 2.0.3, and then work through at least 3.0, 3.1.1, 3.2.2, 3.3 to see whether my hypothesis holds.

But I wouldn't ask anyone to lose a week of their life to do this...

dc42

@oliof I think you are likely correct. Pressure advance is not a compete solution to corner bulging because there are other factors at play. I have to compensate for one of those other factors separately from PA.

Accuracy of perimeters in general (including reduced corner bulging) is better if you select "External perimeters first" in the slicer. Doing so might make printing steep overhangs more difficult, but I am not aware of any other disadvantages. I have been printing external perimeters first for years.

gnydick

@dc42 why wait? I would do what I'm suggesting over and over with lots of different gcode files.

In fact, I would make that part of the release process to validate.

jay_s_uk

I've printed test files with 3.2.2, 3.3 and 3.4.4 and have no been able to see a difference

oliof

@dc42 thanks for the additional insight! It may also be a bit slicer dependent. I remember KISS Slicer for example is doing a slight inwards bend before steep angles; other slicers may not do this.

Argo

I already tested different slicers and settings also different RRF versions.

Only thing that helped with my machine was connecting Klipper (Pi).
I suspect that PA smooth time is the factor (feature) that is RRF missing to improve this.

But the reasons why my bedslinger (also RRF with Duet 3 Mini) produces better corners? I don't know. My Voron (printer with the issues) uses a different kind of hotend which is also not compatible with the PID algorithm RRF uses as PID tuning only works when calibrating the hotend as heater and not as a tool But that's another issue I already reported in another thread.

gnydick

I can conclusively report that Input Shaping interferes with Pressure Advance. Didn't know if anyone else has been able to confirm on their prints.

evan38109

@gnydick I've also seen issues with input shaping + pressure advance, though I'm always open to having done something wrong on my end. At the risk of hijacking a closely-related-but-not-quite-the-same thread, you can see the artifact show up as an indentation before and after turns in the photo below. I wasn't able to remove it with any amount of tuning.

gcode here.
Ringing tower model here.
Config files for the machine when the above was printed in this commit. (Newer repo state is a bit different; I'm converting to closed loop.)
If you want to re-slice for your machine, the PrusaSlicer layer change script, designed for 0.25mm layer height, is:

{if layer_num== 1}
M593 P"none"                           ; no input shaping
M572 D0 S0                             ; no PA
{elsif layer_num== 60}
M593 P"ei3" F42 S0.1                   ; enable input shaping
M572 D0 S0                             ; no PA
{elsif layer_num== 120}
M593 P"none"                           ; no input shaping
M572 D0 S0.09                          ; enable PA
{elsif layer_num== 180}
M593 P"ei3" F42 0.1                    ; enable input shaping
M572 D0 S0.09                          ; enable PA
{endif}

droftarts

@gnydick said in Issues with pressure advance since RRF 3.4:

I can conclusively report that Input Shaping interferes with Pressure Advance. Didn't know if anyone else has been able to confirm on their prints.

… which is why we recommend tuning pressure advance AFTER tuning input shaping.

Ian

evan38109

@droftarts Yes, I've heard this before and followed this instruction.

First, I tuned IS with PA off, arriving at M593 P"ei3" F42.

Second, I printed this calibration print with input shaping held constant and PA values varied from 0.00 at the far right (bottom of the print) to 0.14 at the far left, incrementing every 5mm.

Note how the pre- and post-seam artifact is not present when PA is zero on the right-hand side when PA is off. The artifact I am referring to the horizontal line / thin section that measures around 4mm before and after the seam, and the corners. It's present for any PA values from way too low to way too high as long as IS is enabled, and absent if PA is off. Apologies for my photography.

Did I misunderstand something? What else could I have done?

gnydick

@droftarts, makes no difference.

Monteaup

I had this issue for nearly two years... No problem with marlin firmware.

Tried everything. Changed Steppers, different extruders, hotends, bowden tubes.... I had to use a PA value of 0.4 with a 5cm bowden.

New Year, new (last) try. Had already a bambu lab printer in the basket. Instead, I ordered an Malow NF Sunrise extruder. Thought, this has to work. It's a all in one solution.

First print yesterday without calibration a PA value of 0.04 with perfect corners.

Argo

@Monteaup

It seems some extruder / hotends cause issues with the PA implemenation we have atm with RRF.
With Klipper you also would need to play around with "PA smooth time" so PA does work properly. Maybe we'll see such implementation in RRF anytime soon.

dc42

@Monteaup, you show two cubes in your photo. What is the difference in print settings between the two?

Can you post a more detailed close up photo of the seam that you say is present for any PA values?

PA doesn't fully address the problem of over-extrusion in corners. I am looking to address this separately.