RRF 2.03 pressure advance causes 20% overextrusion

CCS86

@jschall said in RRF 2.03 pressure advance causes 20% overextrusion:

With no pressure advance: https://drive.google.com/file/d/1oFvrJnxZc6fvLlGZqTdCqO7GB4Zfzdy_/view?usp=sharing

Python script output:
fwd_count 1942964
rev_count 961423
net_count 981541
mm 2484.913924

2.48m, dead on what the slicer expected.

Proof positive that PA causes overextrusion and that this is a firmware bug, NOT a mechanical or configuration issue.

Very nice find!

I started a thread recently to brainstorm further PA improvement ideas. Over-extrusion was one of my issues. I am running RRF 3.1.1.

https://forum.duet3d.com/topic/17752/pressure-advance-discussion-for-improvement-in-bowden-printers?_=1598756015603

jschall

Probably going to focus my efforts mostly on scrapping bowden and going to direct...

It is just too painful to deal with.

Edgars Batna

@jschall said in RRF 2.03 pressure advance causes 20% overextrusion:

@Edgars-Batna That's why I went to the logic analyzer, because I knew it would just be constantly dismissed as a mechanical issue if I didn't remove everything mechanical from the equation.

Forgot to mention that my observations also indicated that there's not enough CPU to keep up with tiny moves + PA on the Duet 2. This was also why I stopped debugging.

As for using Bowden, yeah, sort of "forget it". BUT, this issue is not limited to Bowden. As far as I could tell there is no way to completely avoid the issue, but resolution (and in turn the CPU usage) makes it worse.

It is possible that some trivial printers out there sort of work, but, the same way as my prints were dismissed as "not real", I'll just pretend those people don't exist either.

Phaedrux

DC42 has added this to the list to investigate.

dc42

@Phaedrux said in RRF 2.03 pressure advance causes 20% overextrusion:

DC42 has added this to the list to investigate.

I am waiting for the results from @jschall on RRF 3.1.1.

jschall

Oh man, this update process is not working...

There just aren't clear instructions anywhere...

So, I've uploaded Duet2and3Firmware-3.0.zip, and clicked yes when it asked if I want to update. It complained about missing iap4e.bin, but it updated the web control to be very pretty. I searched around for any clear documentation, didn't find any, and assumed that I needed to rename Duet2CombinedIAP.bin to iap4e.bin and upload it. I did that.

Now I still have a very pretty web control, but it just won't update the firmware to 3.0. No error messages whatsoever. What is the actual process to do this?

jschall

Duet Web Control 2.0.4
RepRapFirmware for Duet 2 WiFi/Ethernet version 2.03 running on Duet WiFi 1.02 or later + DueX5
WiFi firmware version 1.23

jschall

Got it. Had to find iap4e.bin from a really old firmware release. Had to find out about this by googling a forum post. I'm sorry, but what the heck? Why not document this in the release notes, or just put the file in the release bundle? Jeez, that's really bad.

dc42

@jschall said in RRF 2.03 pressure advance causes 20% overextrusion:

Got it. Had to find iap4e.bin from a really old firmware release. Had to find out about this by googling a forum post. I'm sorry, but what the heck? Why not document this in the release notes, or just put the file in the release bundle? Jeez, that's really bad.

It is in the release bundle. iap4e.bin is included in the .zip file updates for RRF 2.05.1, 2.05, 2.04, and some earlier releases.

jschall

@dc42 said in RRF 2.03 pressure advance causes 20% overextrusion:

It is in the release bundle. iap4e.bin is included in the .zip file updates for RRF 2.05.1, 2.05, 2.04, and some earlier releases.

It is not in Duet2and3Firmware-3.0.zip

Phaedrux

@Phaedrux said in RRF 2.03 pressure advance causes 20% overextrusion:

Update to 2.05.1 to get on recent code.

Post your config.g.

I did suggest you update to 2.05.1 first.

The issue of missing IAP files does come up and should be better addressed in the documentation. I'll see what I can do about that.

jschall

Currently running the test on RRF3.1.1. It is with x16 microstepping+interpolation, but I'll do a new control test with no PA as well.

jschall

Where the heck in the code are the reverse pins written?

Also my logic analyzer keeps failing.

jschall

Found it.

jschall

Got the logic analyzer to work... It is very picky about USB ports.

fwd_count 10734771
rev_count 8650049
net_count 2084722
mm 2638.888608

3 changes on this one:

RRF 3.1.1, prior tests were at 2.03
x16 microstepping, prior tests were at x8
100% speed, prior tests were at 200% speed
Unplugged the extruder stepper and plugged in an identical stepper so I wouldn't have to listen to the gears make noise.

File is supposed to be 2545.00 mm + 15mm of priming, so this print was within 3% - pretty decent, but there's still a bug.

I am reverting the speed change and testing, and then I'll revert the microstepping change if it doesn't go back up to nasty overextrusion.

jschall

Just a thought, for a next generation path following algorithm, what I would do is:

Segment the toolpath into linestrings in which the angles between the lines are less than some threshold (such as 30 degrees)
Smooth those segments, using maybe a series of cubic splines (long lines may need to be split up into shorter lines first).
Compute the speed curve along the segment such that tangential and radial acceleration is limited and such that the extruder can keep up with pressure advance. Each segment starts at zero speed and pressure and ends at zero speed and pressure.

"Jerk" (bad choice of term) becomes unnecessary. Corners below the angle threshold are rounded smoothly, without ringing or asymmetry. The printer will come to a brief stop at sharp corners above the angle threshold, thus making them as sharp as possible.

A lot of this could be done (and may have to be done) in a preprocessing step.

jschall

RRF 3.1.1, 200% speed, x16 microstepping, 1.0 PA:
fwd_count 12180087
rev_count 10084959
net_count 2095128
mm 2652.060759

jschall

Starting test: RRF 3.1.1, 200% speed, x8 microstepping, 1.0 PA

This one should be apples-to-apples to the tests on RRF 2.03.

jschall

RRF 3.1.1, 200% speed, x8 microstepping, 1.0 PA
fwd_count 6073637
rev_count 5024835
net_count 1048802
mm 2655.194937

So this is not terribly huge overextrusion, I could try printing with this. There's still a bug.

dc42

@jschall said in RRF 2.03 pressure advance causes 20% overextrusion:

Just a thought, for a next generation path following algorithm, what I would do is:

Segment the toolpath into linestrings in which the angles between the lines are less than some threshold (such as 30 degrees)

Smooth those segments, using maybe a series of cubic splines (long lines may need to be split up into shorter lines first).

Compute the speed curve along the segment such that tangential and radial acceleration is limited and such that the extruder can keep up with pressure advance. Each segment starts at zero speed and pressure and ends at zero speed and pressure.

"Jerk" (bad choice of term) becomes unnecessary. Corners below the angle threshold are rounded smoothly, without ringing or asymmetry. The printer will come to a brief stop at sharp corners above the angle threshold, thus making them as sharp as possible.

That's similar to what I have planned. A disadvantage is that the existing effect whereby the perimeters of holes are always under-sized would be made a little worse.