Pressure Advance messing with travel moves

JohnOCFII

@gnydick Well, based on my testing, using Pressure Advance together with the experimental "wipe while retract" definitely cause the actual print time to be much longer than the simulated print time when using Slic3r PE version 1.41.2+

Simulated print time: 1:02
Actual print time: 1:37

Same model, no wipe with while retract and no Pressure Advance:

Simulated print time: 1:04
Actual print time: 1:07

I started doing testing with and without PA and with and without the wipe while retract option. I can also test with S3D.

I'm testing with this model: https://www.thingiverse.com/thing:1363023

I'm using the following firmware and DWC:

Firmware Name: RepRapFirmware for Duet 2 WiFi/Ethernet
Firmware Electronics: Duet Ethernet 1.02 or later + DueX5
Firmware Version: 2.02(RTOS) (2018-12-24b1)
Web Interface Version: 1.22.6

gnydick

@johnocfii the reason why it's happening, I'm theorizing, is because the wipe happens at travel speed, so there's a negative extrusion while moving fast, so it thinks it's an extrusion move that needs to be smoothed.

JohnOCFII

@gnydick Could be. It was suggested that I may need to tweak my settings too. In particular, Extruder Jerk. This is on a CoreXY machine:

; Axis and motor configurations
M350 X16 Y16 Z16 E16 I1                             ; Configure 16x microstepping with interpolation
M92 X200.40 Y200.32 Z1600.0 E820.0                  ; Set steps per mm - 1/9/2019 - osh
M566 X1000 Y1000 Z30 E20             			 ; Set maximum instantaneous (jerk) speed changes (mm/min)
M906 X1000 Y1000 Z1000 E800 I50                     ; Set motor currents (mA) and motor idle factor in per cent
M201 X3000 Y3000 Z20 E1000          			; Set accelerations (mm/s^2)
M203 X24000 Y24000 Z900 E3600       			; Set maximum speeds (mm/min)

John

Phaedrux

@johnocfii Yeah the extruder jerk and accel look pretty low.
Try 3000 E Jerk and 8000 E Accel

JohnOCFII

@phaedrux said in Pressure Advance messing with travel moves:

@johnocfii Yeah the extruder jerk and accel look pretty low.
Try 3000 E Jerk and 8000 E Accel

Thanks - I'll raise them up. That seems like quite a leap. Is there some good guidance on settings?

dc42

@gnydick said in Pressure Advance messing with travel moves:

@johnocfii the reason why it's happening, I'm theorizing, is because the wipe happens at travel speed, so there's a negative extrusion while moving fast, so it thinks it's an extrusion move that needs to be smoothed.

Yes, wipe-while-retract might confuse pressure advance. How does it behave if you turn off wipe-while-retract?

Phaedrux

@johnocfii I should mention that those settings are for a Titan Aero. Direct drive 3:1 with slightly larger than pancake motor. So it's a very responsive system. These settings may not be ideal for a bowden tube system, I'm not sure.

From my point of view, the extruder isn't moving much mass at all and it's not traveling very far compared to the other axis, so short quick moves and direction changes aren't as big of an impact as they would be on the other axis. So my settings are high to eliminate any artificial extruder speed limits. It's speed and response will be dictated by the other algorithms at play and the physical limitations of the motor.

If you notice any grinding or skipping with those settings tone them down, but for best responsiveness I think you'd want them on the higher end than the lower end.

It may also be worth mentioning that I'm not using the slic3r wipe on retract function since I'm using firmware retraction.

JohnOCFII

@dc42 I did an actual print last night, and the print time was 1:22. I did a simulation last night, and it was 1:20. But then I did 3 other simulations of the file with and without PA and with and without wipe while retracting, and all had the same 1:20 simulation time. At that point, I shut off the printer (and Duet and went to bed). I just powered up the printer (a RailCore 300ZL) and simulated that file again. Today's simulation showed up at 1:04.

So -- color me confused. Not sure which simulation value is valid. I did not change config.g between simulation runs.

In the mean time, I'm going to increase the extruder jerk and acceleration, which will probably invalidate future tests. For now, I will keep wipe while retracting turned off. I may do some other PA vs. non-PA tests, and will post results if I find the simulation time varies greatly from the actual print time.

Thanks,

John

JohnOCFII

@phaedrux I'm using the Bondtech BMG but my stepper is not a pancake. I'll work my way up on the settings. Appreciate the education!

FYI - here's am image link of my Y-carriage/extruder.

https://imgur.com/Yh9vgY4

deckingman

@johnocfii If it's any help, I'd concur with @Phaedrux that your extruder jerk at 20mm/min is extremely low. I have Bondtech BMGs with Bowden tubes of about 150mm. My E jerk is 3600 mm/min and acceleration is 3,000 mm/sec^2.

JohnOCFII

@deckingman Thanks for the confirmation. Mine is a direct setup (for all intents and purposes -- about 40mm between the BMG and my E3D-v6 hot-end).

I'll start with your settings and see how it goes!

JohnOCFII

I revised my extruder settings as suggested above to the following and also disabled the wipe while retracting setting in Slic3r.

The simulation estimate is now accurate to the actual printing time.
Speed of the print is inline with what I'd expect.

Thanks to all for your guidance.

; Axis and motor configurations
M350 X16 Y16 Z16 E16 I1                                         ; Configure 16x microstepping with interpolation
M566 X1200 Y1200 Z80 E3600                                 ; Set maximum instantaneous (jerk) speed changes (mm/min)
M906 X1000 Y1000 Z1000 E800 I50                         ; Set motor currents (mA) and motor idle factor in per cent 
M201 X3000 Y3000 Z20 E3000                                 ; Set accelerations (mm/s^2)
M203 X24000 Y24000 Z900 E3600                           ; Set maximum speeds (mm/min)

deckingman

@johnocfii Glad it worked out for you.

gnydick

@deckingman

But by @JohnOCFII changing his configuration, the problem is just being avoided, not fixed. The fact that PA makes any changes on a wipe, a move with no extrusion, but may have retraction, is incorrect.

bot

@gnydick said in Pressure Advance messing with travel moves:

@deckingman

But by @JohnOCFII changing his configuration, the problem is just being avoided, not fixed. The fact that PA makes any changes on a wipe, a move with no extrusion, but may have retraction, is incorrect.

PA is not a perfect system. For that matter, wipe-while-retract, and all the other slicer tricks are even FARTHER from perfect... so which do we prioritize? Generalized PA algorithm wins every time for me. Please don't change a thing

deckingman

@gnydick said in Pressure Advance messing with travel moves:

@deckingman

But by @JohnOCFII changing his configuration, the problem is just being avoided, not fixed. The fact that PA makes any changes on a wipe, a move with no extrusion, but may have retraction, is incorrect.

I'm not arguing with the fact that if PA is being applied to non extrusion wipe moves, then it ought not too. Take that up with the firmware author, not me - I'm just an end user like you.

But @JohnOCFII s extruder jerk setting was much too low regardless of whether PA was being used or not.

Having said that, many settings interact with each other. So for example, too low an extruder jerk will have adverse effects when using PA. Also, you may run into problems with too much retraction after enabling PA (because the two things do much the same) and should reduce retraction. That's just the way things interact with each other.

gnydick

@deckingman gotcha, just making sure

dc42

The next firmware release will ensure that pressure advance is not applied to wipe-while-retract moves. I didn't consider them when I wrote the original pressure advance code.

gnydick

@dc42 cool, thanks for clearing it up.

dc42

Should be fixed now in 2.03beta2.