Issues with pressure advance since RRF 3.4
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Not sure why you seem to be so offended as my comments were not even a reply to your post specifically. I guess that is what the internet has become these days.
I feel it absolutely is on topic. The entire industry right now is using printing and movement speed as a selling point to their machines, and this entire topic is based on software algorithms that are implemented SOLELY to improve printing speed. My Creality 5 Pro is not a Bowden machine, as you assume. It is also only one of four printers that I own. I only use it as an example because it is the one machine that prints consistently with zero corner issues or resonance with zero PA or IS applied and it does this due to the specific reasons that I highlighted.
I have been tuning my Duet-based CoreXY printer for a very long time, using and implementing just about every approach possible, and with each approach, it always comes back to the same basic principle, which I adequately highlighted. Software is not going to make a machine faster when it has specific analog traits and limitations that vary beyond the capability of the software. Yes, it is fun to try, and yes, I can find one or two prints and apply a limited amount of IS and PA and eventually get them perfect... But when I go from a .6 to .8 nozzle and an entirely different material viscosity, or even filament brand... guess what... I need spend another 6 hours tuning IS, flow rate, PA, ect. to get that next print perfect, or I can just slow down and print it in 4 hours instead of 2 or 3 and already have been done with the print. Perhaps my view from a business owner standpoint is different because time to me is money.
You can try and speak for Duet all you want and become offended over some words. Quite the contrary to a defeatist attitude; my sole point is that one should be well aware of the limits of their machine and manage their expectations accordingly. The Bambu comment was because I actually am on loan with one right now to test and study. I am not a fan of proprietary machines, and never have been. The requirements of my business are well beyond the size capabilities of a Bambu. I do feel like they have gotten a few things right because this machine indeed uses feedback to adjust for changing analogous conditions per print and per material and the results are quite evident.
I can assure you the Duet engineers are studying the same technology as well and doing their best to determine future implementation. The bigger burden is on the Duet engineers to design an open source software that works across any machine, which of course is a much greater challenge, and I have nothing but commendation for Duet, Dave Crocker, and the hard work they have put in to meet customer expectations to date. I would not be in a Duet forum with over a thousand dollars invested in numerous Duet boards if I was not a huge fan of both their product and their work.
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https://forum.duet3d.com/topic/33803/unable-to-stop-severe-bulging-in-corners-with-new-print-head/29
The same issue in above link too.
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Most likely it is obvious on CoreXY machine. When there is a corner, and moving before arrived the end of corner, both A motor and B motor, need to slow down, severe bulging will come before arriving the corner. If it is the machine like UM, it will be only severe bulging after corner but never before corner, as there is only one aixs motor for each aixs. However this is the inherent feature for CoreXY, due to it needs both A motor an B motor keep moving.
This is the first time I am using CoreXY machine, the E3D ToolChanger.
No clue how to fix it...
What I guess, PA can't fix this, as it is XY movement related, not extrusion related. However the Input shaping is the direction. RRF Input shaping is still the blackbox, a long way need to go.
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Adjust the belt tension can not fix the problem.
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Someone shared me that, he has the same issue on RRF, however It comes to be fixed after he using the Klipper. Really no idea what's the diff.
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This problem can be replicated on Hbot and other similar Cartesian designs. Its only more obvious because CoreXY tends to have higher speeds thus requiring higher flow rates. Overall, its almost entirely a flow control issue instead of a kinematic issue.
Klipper has a feature called smoothing time which works with their pressure advance - My current belief is that this smoothing time is the key to fixing this issue. I am currently building a test machine that will use klipper for an apples to apples comparison between RRF and Klippers implementation. But ill be having to do it after SMRRF as time constraints are tight right now.
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@PCR so do I (actually capable of triple play -- Marlin, RRF, and Klipper). I can't say I have these issues with bulging corners but I run quite high extruder jerk and acceleration (https://forum.duet3d.com/topic/33964/e-acceleration-has-to-be-limited-to-to-e-jerk-pa?_=1700602309451). I wonder what e jerk and acceleration the people heavily affected run; if jerk and accel aren't high enough I can see that PA may kick in "late" and not have (any) effect, especially at higher speeds.
<>RatRig V-Minion Fly Super5Pro RRF<> V-Core 3.1 IDEX k*****r <> RatRig V-Minion SKR 2 Marlin<>
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@oliof said in Issues with pressure advance since RRF 3.4:
@PCR so do I (actually capable of triple play -- Marlin, RRF, and Klipper). I can't say I have these issues with bulging corners but I run quite high extruder jerk and acceleration (https://forum.duet3d.com/topic/33964/e-acceleration-has-to-be-limited-to-to-e-jerk-pa?_=1700602309451). I wonder what e jerk and acceleration the people heavily affected run; if jerk and accel aren't high enough I can see that PA may kick in "late" and not have (any) effect, especially at higher speeds.
So first of all we need to stop tuninig anything but testing the capability of the E motor.
Btw, any steps or details shown how to find out the value? -
@hestiahuang I simply increased extrusion speed into thin air until the extruder skipped, then backed off of that 20%, after that did firmware retrac/unretract with increased acceleration until the extruder screamed, and then backed that off 20%
There is a case to be made that you may need to redo this for PETG due to its difference in backpressure behavior, but I never bothered and it seems to work well enough.
In direct drive, my PA value is 0.02 to 0.03 and that seems to be good enough.
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@oliof What extruder jerk are you currently running? After reading your other thread I tried increasing mine to the 3000 range (previously it was 300), but with that setting I started getting various odd noises at sharp corners and seemed to be losing extrusion.
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@gloomyandy jerk in the 300 to 600 range, acceleration in the 3600 to 6000 range
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@oliof Thanks, what sort of jerk and acceleration are you running on X, Y, Z? I must say I do find the entire jerk/acceleration thing very confusing having spent some time yesterday searching the forums it seems that values anywhere from high jerk/lowish acceleration to low jerk/high acceleration seem to be in use! There also seems to be some (unresolved) confusion as to when jerk is actually applied with some comments indicating it is only used between moves while others say it is applied (in mode 1) as an initial speed for moves that start at zero.
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@gloomyandy jerk is a bit of black magic, I spent a weekend with a friend trying to read and understand how its applied in RRF, but I forgot all about it since then.
my jerk/accel on the IDEX are
M566 X360.00 Y210.00 Z18 E300.00 P1 ; Set maximum instantaneous speed changes (mm/min) M201 X7500.00 Y4000.00 U7500.00 Z100.00 E6000.00 ; Set accelerations (mm/s^2)(this is an i3 style portal printer with a prusa bear like frame with a 220^3 print volume)
On the V-Minion my values are
M566 X900.00 Y900.00 Z60.00 E300.00 ; set maximum instantaneous speed changes (mm/min) M201 X3000.00 Y3000.00 Z200.00 E6000.00 ; set accelerations (mm/s^2)(this is an Ormerod style cartesian cantilever printer with a 180^3 print volume)
Just a note that the accelerations on the V-Minion are quite low compared to the klipper config for it, it is on record with 6 minute speed benchies, but I haven't pushed that far yet.
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@oliof Thanks! It's interesting that your two printers have such a big difference between them! I'm currently using something similar to your first example on my toolchanger with a jerk of 300 and acceleration of 15000, I do get a lot of ringing though so I'll probably be reducing the acceleration somewhat.
Don't want to disrupt this thread, but I wish there was a good way to determine good values for jerk and acceleration with RRF.
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@gloomyandy the first printer isna glorified ender3 with a terrible y motion system that's dragging it down (also 6mm belts). The second is a very compact machine with 9mm belts designed for rigidity and speed.
To be fair, I haven't even started really tuning the V Minion for fast printing simply for lack of time, or the differences would be even more striking.
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@oliof Can't resist taking this thread slightly more off topic! How did you select the Jerk speed for the V-Minion? Did you use any test prints to help? I seem to remember it has a big impact on how curves get printed...
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@oliof
I currently am running a jerk of 1000mm/min with accelerations of 4000 mm/s/s Using a Hemera XS with a volcano style hotend.I used to run by the theory of low jerk high acceleration (J of 500mm/min and 7000mm/s/s) but im now just trying everything in order to isolate the issue
Edit: I should say I am only experiencing this issue on larger nozzles. On a 0.4mm nozzle the issue is imperceptible enough to not be an issue, but on a 0.6mm nozzle the issue is exceptionally bad.
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I think everyone should learn to use one of these
You apply pressure at one end which forces a viscous fluid out of a restricted orifice. Just like a 3D printer extruder. You'll learn a lot about how the flow of a viscous fluid out of a small orifice reacts (or rather hardly reacts) to changes in pressure on the input and how difficult it is to get that flow rate to match the rate to change of movement of the nozzle through space.
Personally, I get best results by keeping the filament flow rate as near constant as possible which essentially means low(ish) acceleration and high(ish) jerk and using pretty much the same speed for all move types.
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@gloomyandy re:jerk -- I increased it until I got skipping on the motion system, then backed off by 20%. It seems to be a good approach that gets me into a "usable, not too low" range.
@deckingman I had issues with too low acceleration causing print head inertia to be a factor on corner performance. So I tend to aim for low-ish jerk and higher acceleration.
