Exponential variable for pressure advance?
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guess ill setup a build environment and start messing with it. if i get any positive results ill submit a pull request.
the new linear advance in marlin is interesting, as its based on length of filament compressed.
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@nyt:
the new linear advance in marlin is interesting, as its based on length of filament compressed.
Marlin linear advance is the same algorithm that RepRapFirmware uses; but Marlin implemented it 2 yards later, and the Marlin implementation makes some approximations because it doesn't do precise acceleration.
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@nyt:
the new linear advance in marlin is interesting, as its based on length of filament compressed.
Marlin linear advance is the same algorithm that RepRapFirmware uses; but Marlin implemented it 2 yards later, and the Marlin implementation makes some approximations because it doesn't do precise acceleration.
Did you see the new v1.5 code? They just changed it up
https://github.com/Sebastianv650/Marlin/commits/LIN_ADV_v1.5_final_1.1.x
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it is just my opinion, but i think you missed the point. "missing steps" doesn´t mean only that your stepper misses some steps, it also can mean that the filament slips too much at the extruder gear. When your extruder is pushing hard, the additional E-Jerk introduced by pressure advance can easily overcome the maximum force the extruder gear can handle.
Volcano hot ends require more pressure advance as there's a longer melt zone.
No, only at very low extrusion rates and the difference is not that big to e.g. a e3d v6. If somebody uses a volcano, then normally not to operate in the low extrusion rate area. If a volcano would provide more back pressure at higher extrusion rates, nobody would use it…..
no steps are being skipped. These are 1.7a motors with titan extruders. No signs of skipped steps anywhere, even at much higher speeds and flow rates.
See above. The filament is slipping. I use bondtech extruders with 2.2 A, but that doesn´t mean that the filament is not slipping….
That was PLA printed at 245C. That's pushing it already. The thermistor has been validated accurate as well by external probes, and the tests provided are on two entirely different hot ends/extruders.
In the last appr. half year i have tested > 100 (that is no joke) combinations of nozzles, extruders, and filaments. If you print PLA with 245 °C with a 0.4 at 75/30 mm/s and you see that big difference using a volcano nozzle, your nozzle is really given an extraordinary big amount of back pressure.
Extrusion is consistent between inner and outer layers.
The faster lines are smaller than the slow ones - as far as i can judge. This would be normal when the speed difference would be higher and could be compensated by M592.
you're just guessing here, and again, that's not accurate. At least not for the Olsson model.
That is correct, i don´t really know it, but you will find discussions on youtube and on the web about this issue. The data you have provided shows clearly, that you have a lot of back pressure even at low extrusion rates.
That's great, but this printer, and many others, cannot run high acceleration. Even with high acceleration, you'll still have issues with oozing during moves and lack of filament at line starts when pressure advance is required.
I just wanted to point out, that i did experiment a lot with pressure advance. But because of the E-jerk slipping problem, it is not usable for me.
I cannot reproduce what you have shown and i did play a lot with pressure advance, that´s all. I don´t have any problem at all if an additional tuning parameter is introduced, nobody is forced to use it, but these posts might be useful for others, to maybe find the root cause. -
@nyt\dc42
I haven't tested the latest firmware but one of the biggest issues for me is the behaviour of pressure advance during segmented arcs. Before I went on my 5 week trip "down under" there was an issue with the print head slowing or stopping with high pressure advance when printing circles. IIRC it had something to do with the slicer generating unequal segments which then triggered the Duet pressure advance algorithm. The version of firmware at that time was more sensitive to those unequal segments than previous versions. I need to update the firmware to see if David has managed to "de-sensitise" it.
With multiple extruders, the situation is much worse. I've been trying to get it to work ever since David first introduced it but always have issues doing arcs. It's a real shame because for high speed printing with multiple extruders, it really works well but only with linear moves - segmented arcs have always been a problem for me.
I'm leaning towards the impression that maybe pressure advance has to be implemented in the slicer rather than firmware. The slicer would "know" where an arc is, whereas firmware only "sees" short moves and doesn't look ahead to determine if a series of small moves constitute an arc. David will no doubt correct me if that conjecture has any basis.
I've read that there is a version of Slic3r (Prusa Edition) which implements some form of pressure advance. When I get time, I plan to give that a go.
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I can't contribute to the main topic of this thread as I do not use pressure advance, however…
The faster lines are smaller than the slow ones - as far as i can judge. This would be normal when the speed difference would be higher and could be compensated by M592.
I am using M592 and can verify that (for a v6 with 0.4mm nozzle, PLA), it makes a real difference. Before, I was seeing between 5 and 10% underextrusion at higher print speeds. So if you are not using M592 and have calibrated your extruder at a low extrusion rate, it's almost guaranteed that it will be underextruding at higher extrusion rates.
Edit: I forgot to mention that I am using a Titan extruder.
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PS - it would be really helpful if someone could generate some GCode files for calibrating pressure advance. The test pattern could be linear line segments with speed changes in them, or 90 degree angles. Several layers should be printed to avoid first layer adhesion issues.
If the test pattern is printed as a grid, then the pressure advance can be varied along one axis and the speed along the other. That should provide a good visual indication of how pressure advance should be changed with speed, giving me a basis on which to implement nonlinear pressure advance.
As most users of Cartesian and CoreXY printers choose the origin to be at one corner of the bed instead of the middle, test patterns should be provided for both delta printers and Cartesian/CoreXY, or a single test pattern provided that assumes the origin is at the centre but that has an adjustable tool offset at the start.
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PS - it would be really helpful if someone could generate some GCode files for calibrating pressure advance. The test pattern could be linear line segments with speed changes in them, or 90 degree angles. Several layers should be printed to avoid first layer adhesion issues.
Did you see this? https://somei3deas.wordpress.com/2018/01/15/an-attempt-to-investigate-pressure-in-the-extrusion-system-with-a-diamond-hot-end/
The gcode file is dead simple and it worked well. You do need to be able to lay filament down straight onto the bed at high speed though. The advantage is that it's very quick to print and easy to spot what's going. I guess it'd be easy enough to make a basic rectangle printed at slow speed for the first few layers, then tack that high speed gcode on the end of it. Thinking about it, I also guess that most people won't be able to get up to 300mm/sec so it'd need to be limited to (say 100mm/sec).
If you think that would serve, I'll give it a go when I get time.
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@vp:
it is just my opinion, but i think you missed the point. "missing steps" doesn´t mean only that your stepper misses some steps, it also can mean that the filament slips too much at the extruder gear. When your extruder is pushing hard, the additional E-Jerk introduced by pressure advance can easily overcome the maximum force the extruder gear can handle.
It's not slipping at these speeds. This isn't even fast. IIRC, it behaved pretty much the same even when doubling the layer height. I'll test this more at some point, but I have a long print running currently.
@vp:
Volcano hot ends require more pressure advance as there's a longer melt zone.
No, only at very low extrusion rates and the difference is not that big to e.g. a e3d v6. If somebody uses a volcano, then normally not to operate in the low extrusion rate area. If a volcano would provide more back pressure at higher extrusion rates, nobody would use it…..
so you're confirming what I said. There's a difference between lower and higher speeds.
@vp:
That was PLA printed at 245C. That's pushing it already. The thermistor has been validated accurate as well by external probes, and the tests provided are on two entirely different hot ends/extruders.
In the last appr. half year i have tested > 100 (that is no joke) combinations of nozzles, extruders, and filaments. If you print PLA with 245 °C with a 0.4 at 75/30 mm/s and you see that big difference using a volcano nozzle, your nozzle is really given an extraordinary big amount of back pressure.
Yes, it's a nuisance. It would be less of one if I was using a brass nozzle, but that doesn't work so great with abrasives as we all know.
@vp:
Extrusion is consistent between inner and outer layers.
The faster lines are smaller than the slow ones - as far as i can judge. This would be normal when the speed difference would be higher and could be compensated by M592.
The tip of the nozzle going over the lines and the lighting skews this. The lines are the same width when printed separately as measured by calipers.
@vp:
you're just guessing here, and again, that's not accurate. At least not for the Olsson model.
That is correct, i don´t really know it, but you will find discussions on youtube and on the web about this issue. The data you have provided shows clearly, that you have a lot of back pressure even at low extrusion rates.
The issue isn't all about massive back pressure. It's a large melt zone, and when heated, filament expands as it has a moisture content.
EDIT: after reading other posts about nonlinear extrusion, that looks like the issue. Going to plot out a graph with my setup in a few hours when this print is done.
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I can't contribute to the main topic of this thread as I do not use pressure advance, however…
The faster lines are smaller than the slow ones - as far as i can judge. This would be normal when the speed difference would be higher and could be compensated by M592.
I am using M592 and can verify that (for a v6 with 0.4mm nozzle, PLA), it makes a real difference. Before, I was seeing between 5 and 10% underextrusion at higher print speeds. So if you are not using M592 and have calibrated your extruder at a low extrusion rate, it's almost guaranteed that it will be underextruding at higher extrusion rates.
Edit: I forgot to mention that I am using a Titan extruder.
What settings are you using for this? I've been cranking up the temperature to reduce pressure and slipping.
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What settings are you using for this? I've been cranking up the temperature to reduce pressure and slipping.
For a v6 with 0.4mm nozzle, bowden, titan, 1.75mm PLA @ 200deg I am using M592 D0 A0.010 B0
This gives me reasonably linear extrusion between 1mm/S and 5mm/S extrusion rate.
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What settings are you using for this? I've been cranking up the temperature to reduce pressure and slipping.
For a v6 with 0.4mm nozzle, bowden, titan, 1.75mm PLA @ 200deg I am using M592 D0 A0.010 B0
This gives me reasonably linear extrusion between 1mm/S and 5mm/S extrusion rate.
Thanks, will experiment with this a bit once my print finishes. Currently pushing around 14mm/s at with 0.6mm nozzle 0.4 layer heights at 100mm/s speeds. Hopefully this is the solution along with pressure advance.
