Issues with pressure advance since RRF 3.4

Tinchus

I will add a little comment here based on my past experience tunning PA: it works very well whilw the requested speed ks close to the real speed. The further you go and the results starts to be less effective. In yor slicer config i can see a perimeter speed of 120mm s, and your infill has 260 mm s. In your pictures i see what it looks like a test cube .
If that cube is small, you will never reach 120, that would be the requested speed. Firmware will give so ething smaller.
But later in tbe infill the requested 260 speed will never be reached either but the difference between requeste and real speed will be muuuuuch bigger, so probably you wont bave very good results.
I would suggest to retune PA with a model that let you reach real values closer to the requested speed and retest to see if there is any difference

jackantubis

I have same kind of issues since 3.4.
Maybe the Pressure Advance don't have a 3rd order compensation for speed variation, could be a good update.
Made 4 measurements at different speed, make the equation in excel.
Can we add this with "Duet programming Gcode" ?

Argo

@tinchus

Thanks for your theory but requested speeds are reached.

CCS86

This is very interesting. I had noticed some of these artifacts too but hadn't pinned it down to PA changes in the 3.4 releases. Good job zeroing in on this!

gnydick

same experience, lurking for update

CCS86

Well, that sucked... I tried to downgrade to 3.3 for a back to back print test and that almost destroyed my Mosquito hot end. The hot end fan spooled up with its normal blip, but then slowly wound down to zero at my normal PWM setting. The entire heat sink ended up packed with molten filament and had to be drilled out. The hot end fan won't stay running at any other PWM value than 255.

Off topic, but what changed between 3.3 and 3.4 on this? I'm back on 3.4 and it runs fine again.

Phaedrux

@ccs86 How did you have it configured?

When a fan is configured as thermostatic using M106, the S parameter is now ignored. If a single T value is given, then when the temperature is above the T parameter the fan will run at the PWM specified by the X (maximum PWM) parameter (default 1.0).

From the 3.4 notes.

Argo

@jackantubis @gnydick @CCS86

Could you also please provide some examples? So we can be sure we are having the same issue.

gnydick

@argo https://forum.duet3d.com/post/289116

jumpedwithbothfeet

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

@ccs86 How did you have it configured?

When a fan is configured as thermostatic using M106, the S parameter is now ignored. If a single T value is given, then when the temperature is above the T parameter the fan will run at the PWM specified by the X (maximum PWM) parameter (default 1.0).

From the 3.4 notes.

Apologies for going off topic, but by that statement M106 in GCode dictionary could very much do with a rewrite

gloomyandy

@gnydick Can I just check, I think in the your other thread you reported that going back to 3.3 did not make any difference to the results you are seeing? Is that correct or was the regression test you did just to 3.4?

Argo

@dc42
Have you already had time to look into this or can I provide you with more data/examples...?

Argo

@paanjii2

All details are in this thread and in this one: https://forum.duet3d.com/topic/26062/3-4-0beta7-new-input-shaper-disturb-pressure-advance

If you want any specific information please ask.

gnydick

@gloomyandy that is correct, didn't see a difference.

dc42

@argo this is close to the top of my list to look into. What's a good print to test this on - is a hollow square tube sufficient?

Argo

@dc42

You could just create a shape box in Prusa Slicer (or similar slicer that can generate shapes) with the following measurements:

X: 50mm
y: 20mm
Z: 5mm

Perimeters: 3
Top Layer: 0
Bottom Layer: 4
Infill: Grid 20%
Layer time goal: 0s (so it does not slow down the print)

My speed settings: https://forum.duet3d.com/post/288649

If you are using a direct drive extruder with PLA a PA value around 0.055 is usually a good value.
I would not print it hollow so you can compare the quality of infill lines and corners.
The issue I'm having is healthy infill lines and bulging corners or sharp(ish) corners but starving infill lines (example in this posting: https://forum.duet3d.com/post/288686).

dc42

I confirm there is an issue with pressure advance in RRF 3.4. It works better in 3.3 but I think it is still not quite right. We'll issue another 3.4.2rc release when we have fixed it.

dc42

Further to my previous message: I made a mistake in my test program. Currently I can't see any difference in how PA behaves between 3.3 and 3.4 with input shaping disabled. I will investigate further next week.

ctilley79

@dc42 Try it with input shaping enabled. A problem people are having is tuning PA after enabling IS.

dc42

@ctilley79 before I look into the interaction of IS and PA, I need to understand why some users are reporting that even with IS disabled, PA behaves differently in 3.4 compared to 3.3.