Issues with pressure advance since RRF 3.4

Argo

Yes it’s far from optimal. But at least parts are usable again. Though I had Klipper flashed and it hasn’t the flaws I’m not really into using Klipper. Just a personal preference. But wouldn’t wonder if someone switches because of that.

Heartleander81

@Argo

I will only use it as an emergency backup. Sure if RRF fits again I'll switch back, I think. I'm already a fan of Duet.
But to test whether my hardware fits, I'll try Klippers. The last parts will arrive in the days for the test with me.

jens55

I don't know if this helps but I decided to run some tests. Two printers were used to compare the output. One is a CR10-S5 and one is a Jubilee printer. The CR10 is running a Duet2wifi and a Duex5 expansion card, the Jubilee is running a Duet3-6HC with the extruder being run off a tool board.
In both cases the extruder is a direct drive extruder. Both use firmware 3.4.0.
I used a pressure advance python script that I plugged the correct data into in order for it to generate a gcode file. The file prints a single line with fast and slow segments. Slow segment was 5 mm/sec, fast segment was 100 mm/sec.
The same filament (same roll) was used in both cases.
It probably has been well over a year since I last ran this pressure advance test but it used to show very clearly what the pressure advance should be set to.
I can report that the result was absolutely useless - there was no discernible difference in the layer lines. I ran pressure advance from 0.000 to 1.000 just to cover my bases but did more in-detail testing in the 0.000 to 0.080 range which is the expected range for a direct drive extruder.
There was an occasional abnormality here and there but it was not consistent and certainly was not repeatable.
I have set config.g on both printers to 0.01 as a wild guess. I could have chosen pretty much any figure between 0.00 to 0.08 as the test print showed no difference in the output.
When I was getting close to 1.0, I was seeing some issues but again, there was no clear 'this is good' and 'this is bad'.
I am left with two possible alternative explanations: 1) I don't know what I am doing or 2) PA is completely and utterly borked.
Since these tests have been a good indicator for PA before, I am leaning towards #2.
In all fairness, it did take me some time to tweak the python script to work with a multi extruder printer which initially also caused no change in the printed output. That was caused by me printing with extruder 1 but setting the pressure advance for extruder 0 ... doooohhhh ..... but I did correct that and feel that I have valid gcode files and pressure advance is simply not working. I have run M572 on the active extruder and as far as I can tell, the printer thinks it is set to the right pressure advance.

gloomyandy

@jens55 What was the version of firmware you were using when this test worked? Has anything else changed in your printer setup (hardware or configuration) since then?

If you think this is a problem with 3.4 that did not exist on an earlier version please switch back to that earlier version and publish the results from both. So far I do not think we have any examples that show this is a change between versions of the firmware (when using the same settings and hardware for both new and old versions). If you are using any 3.4 features (like input shaping), you may want to try disabling them and re-run the 3.4 test again before switching back to the older version.

jens55

@gloomyandy, I do not use input shaping. It's been likely a year or more since I last ran these tests. I can not reasonably claim that nothing else has changed. Heck, I wouldn't even know where to start the recreating of old config.g files. I am not in a position to start reverting to old versions. I have neither the time nor the energy to go through that process in a thorough manner. I will likely continue my experimenting for a while but it isn't an exhaustive investigation (and is not meant as such). I am simply throwing my observations into the mix of things.

gloomyandy

@jens55 If you are not using any 3.4 features, I don't think switching to 3.3 would be a big problem, your 3.4 configuration should work I think.

jay_s_uk

@jens55 i've ran a 3.4 config with 3.2 quite happily

Argo

@jay_s_uk

Did you already have the time to print a comparison between RRF and Klipper on your setup?

Adrian52

@jens55 I was stimulated by your post to try again a gcode script I use to calibrate PA, adapted from a previous post. For me, this seems to work as expected:

alt text

It does 4 lines at 20mm/sec, then 4 lines speeding up from 20mm/sec to 100mm/sec and back for each PA setting - I have pictured to speeding up section, where you can clearly see the effect of PA, and confirming the .04 I usually use.

My system is pretty basic - duet2wifi with no SBC running 3.4.4, with mzv IS, single nozzle, direct drive orbiter 2.

Adrian52

@Adrian52 should add that the script is adapted from that posted by DonStauffer (https://forum.duet3d.com/user/donstauffer) here

https://forum.duet3d.com/post/250961

I found it quicker without a raft, so made an anchor piece to start the test strips . Apologies to DonStauffer for mangling your script.

;	set variables

var StartX = -70
var StartY = -25
var LinesPerTest = 4
var LinesBetweenTests = 4
var AnchorLines = 10
var TempBed = 60
var TempTool = 195
var ToolNum = 0
var Ext1 = 0
var Ext2 = 1
var Width = 0.55
var Height = 0.2
var ExFactor = 1.0
var Retract = 1.0
var Prime = 0	;	Before Raft

var PALow = 0.0
var PAHigh = 0.07
var PAIncrement = 0.01

var SpeedRaft = 400
var SpeedSlow = 1200
var SpeedFast = 6000
var SpeedTravelXY = 9000
var SpeedTravelZ = 1200
var SpeedRetract = 7200

;	Calculated and Utility Variables

var TestCount = 1 + floor((var.PAHigh - var.PALow) / var.PAIncrement + 0.5)

var FilFactor = var.ExFactor * var.Width * var.Height / (pi * 1.75 * 1.75 / 4)

var PA = var.PALow - var.PAIncrement

var Dist = 0

;	PREPARE

T{var.ToolNum}

M82	;	Extruder Absolute Mode

;	Heat Bed and set Hot Ends to Standby

M400

M117 "Heat"

M140 S{var.TempBed}				;	set Bed Temp

M568 P{var.ToolNum} S{var.TempTool} A2	;	set Tool Temp

M116 H{var.ToolNum + 1} S1			;	Wait for temp

G4 S12					;	Delay to Allow for Overshoot

M116 H{var.ToolNum + 1} S1		;	Wait for Recovery

M116 H0 S1					;	Wait for Bed

M400

M117 "Home"


G1 Z30 F3000
G30

M400

;M117 "Anchor"

;	Go to StartX - Width *5, StartY

G90	;	Absolute

G92 E0

G0 E{-var.Retract} F{var.SpeedRetract}

G1 X{var.StartX - var.Width * (var.AnchorLines-4) } Y{var.StartY} F{var.SpeedTravelXY}

G1 Z{var.Height} F{var.SpeedTravelZ}

G91	;	Relative


set var.Dist = (2 * var.TestCount * var.LinesPerTest + var.LinesBetweenTests * (var.TestCount - 1)) * var.Width

M221 S110 ;set extrusion factor to 110% for anchor

while iterations < var.AnchorLines

	;	Draw anchor Line

	G0 Y{var.Dist} E{abs(var.Dist) * var.FilFactor} F{var.SpeedRaft}

	G92 E0

	;	Break here if last time

	if iterations + 1 >= var.AnchorLines

		break



	;	Move Over



	G0 X{var.Width} E{var.Width * var.FilFactor} F{var.SpeedRaft}

	G92 E0



	set var.Dist = -var.Dist



G0 E{-var.Retract} F{var.SpeedRetract}	;	Retract



;	BEGIN TEST PATTERN


M400

M117 "Test Pattern"



;	Go to StartX, StartY

G90	;	Absolute

G1 Z{var.Height} F{var.SpeedTravelZ}

G1 X{var.StartX} Y{var.StartY} F{var.SpeedTravelXY}

G91	;	Relative

while iterations < var.TestCount

	;	set PA

	set var.PA = var.PA + var.PAIncrement

	M572 D{var.Ext1} S{var.PA}
	M572 D{var.Ext2} S{var.PA}

	echo "PA=",{var.PA}

	;	Draw Reference Lines

	while iterations < var.LinesPerTest

		G0 E0 F{var.SpeedRetract}		;	Unretract

		G0 X140 F{var.SpeedSlow} E{140 * var.FilFactor}

		G92 E0

		G0 E{-var.Retract} F{var.SpeedRetract}	;	Retract

		G1 Y{var.Width} F{var.SpeedTravelXY}

		G1 X-140 F{var.SpeedTravelXY}



	;	Draw Test Lines

	while iterations < var.LinesPerTest

		G0 E0 F{var.SpeedRetract}		;	Unretract

		G0 X35 F{var.SpeedSlow} E{35 * var.FilFactor}

		G0 X70 F{var.SpeedFast} E{105 * var.FilFactor}

		G0 X35 F{var.SpeedSlow} E{140 * var.FilFactor}

		G92 E0

		G0 E{-var.Retract} F{var.SpeedRetract}	;	Retract


		G1 Y{var.Width} F{var.SpeedTravelXY}

		G1 X-140 F{var.SpeedTravelXY}



	;	Move to start of next comparison



	G1 Y{var.LinesBetweenTests * var.Width} F{var.SpeedTravelXY}



;	Finish up



M400

M117 "Done"

G10 P0 S0 ; turn off temperature
M140 S0  ;turn off bed heater
G28  ; home

jay_s_uk

@Argo I have but I'm awaiting some feedback for I post anything

jens55

@Adrian52, thanks for posting the script and the results. I will see if I can get that working here!

jens55

I went back to the original script posted by DonStauffer with the raft and I did see the ever so subtle change in the printout. Interpretation of the test print is difficult but it works better than what my previous script was able to do.
I kept the raft so I could remove the finished print in one piece and examine it clearly. I did have adhesion problems because it's a single line and I am working on adjusting my bed temperature to fix that.
Final verdict: I didn't know what I was doing and pressure advance does in fact work on the CR10 printer. I have not yet tried this on the Jubilee where the extruder is driven off a tool board. Note that this only speaks to PA changing and not necessarily to how effective the PA is in an actual print.
Tests are ongoing ......

gnydick

This post is deleted!

Heartleander81

Update on my conversion to Klipper.
At first the corners didn't look any better than with RRF until I came across a post today that refers to extruder smooth time.
The standard is with Klipper 0.04, which I also use.
Switched to 0.01 and the corners look awesome.
In the article it was said that some extruders can not cope with the smooth time and then you have to get smaller. see my pictures.

With smooth time 0.04

With smooth time 0.01

R4ffers

@Heartleander81 wow mate what a difference

Heartleander81

@R4ffers oh yes.

@dc42 is there also something like pressure advance smooth time under RRF? A few clippers have the problem with the high smooth time, but those who have problems are mostly DirectDrive extruder users. Maybe that's an approach you can follow.

Phaedrux

@Heartleander81 Can you link that article you mention?

sebkritikel

@Phaedrux I see some discussions on it at the bottom of Klipper's Kinematics page
https://www.klipper3d.org/Kinematics.html

Some other pages of interest
https://klipper.discourse.group/t/pressure-advance-smooth-time-on-direct-extruders-with-short-filament-path/1971
https://github.com/Klipper3d/klipper/issues/4442

richfelker created this issue in Klipper3d/klipper

closed Pressure advance smoothing induces e-axis position swings that scale with acceleration #4442

dc42

@Heartleander81 said in Issues with pressure advance since RRF 3.4:

@R4ffers oh yes.

@dc42 is there also something like pressure advance smooth time under RRF? A few clippers have the problem with the high smooth time, but those who have problems are mostly DirectDrive extruder users. Maybe that's an approach you can follow.

No, there isn't anything similar. I will look into that Klipper feature.

The reason I have made no progress on this is that while a number of users seem to think that pressure advance doesn't work as well in RRF 3.4 as it did in 3.3, and I am prepared to believe that there may be a difference because the relevant code had to be rewritten to accommodate input shaping, nobody has been able to provide a simple GCode script and machine settings that demonstrate a difference when input shaping is disabled. That includes me - I have compared RRF 3.3 and RRF 3.4 prints.