Pressure advance and Arachne (variable extrusion width)
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Hi,
I have just noticed that PrusaSlicer (and Cura) has implemented arachne based perimeter generation in their new alpha release. Could this variable extrusion width be a problem with pressure advance? (Which, as far as I understand, helps to keep the extrusion width constant) -
Pressure Advance is a "mechanism" to better match the actual extrusion output to the output requested by the control, by means of anticipating the upcoming movements and changing the current extrusion speed before a change in flow is actually requested by the gcode (I hope I'm not totally mangling the actual mathematical model that is working under the hood to calculate PA).
in short, it's not so much a mechanism to keep extrusion constant, but to better match the actual output to the requested/calculated output.
If the extrusion output is varying, e.g. because of Arachne's variable line width, pressure advance should work just the same. I personally haven't had any unexpected results in the combination of both, however there might be edge cases where they might counteract.
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I am using Arachne engine/variable line width since the early Cura betas and it did not suffer from keeping PA configured as before. Cura has other settings that may interact with it (pressure equalization comes to mind), but aren't at the default settings.
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@sonderzug @oliof Thank you guys for your input
. However, I guess I need to think a bit more about this topic to fully understand the relation between Arachne/ variable-extrusion-width and pressure advance.I originally thought about possible issues (not so much in practice but more from a theoretical point of view) as I ran into print speed reductions when using large PA values with low extruder jerk settings in the past. I have also noticed clicking in the extruder (without Arachne) as the extruder constantly changes direction.
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what's a "large PA value" for you? I've not used PA values over 0.3 (with 450mm Bowden) and usually use PA under 0.07 (usually 0.04) with direct extruders.
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@oliof I think I was using .6 or .7 with a long Bowden tube (as recommended on the duet PA website). I have since switched to a direct drive extruder (lgx ace), so this is really no longer an issue for me.
