Dynamic Esteps?
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I noticed that when trying to calibrate esteps that I end up with different amounts depending on the speed that I extrude. if im using a slow extrusion say 1mm/sec. its 397 steps but if im trying to extrude at 5mms I need like 410 steps to achieve an accurate 100mm calibration
almost seems like estep should dynamically adjust based on flow/volume speed to compensate.is there a way to accomplish this?
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@adamfilip non linear extrusion is what you're looking for. https://docs.duet3d.com/en/User_manual/Reference/Gcodes#m592-configure-nonlinear-extrusion
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@adamfilip Yes, it's called Non-Linear Extrusion (M592):
https://docs.duet3d.com/en/User_manual/Reference/Gcodes#m592-configure-nonlinear-extrusion
Note that it is only applied to print moves (i.e. ones with XY motion in as well as E), which can complicate tuning a little. General advice is to do equal XY and E moves so all the feedrates are the same.
I think it was more applicable to older style extruders with a single drive gear (i.e. not the dual drive ones that are a bit more popular now), so your mileage may vary.
Also, at 5mm/s with a 1.75mm filament, you are extruding ~12mm3/s, which is right at the top end of what a standard V6 hotend can do (generally 10mm3/s is quoted as the limit, but it varies with nozzle type, size, filament, temp etc). If this is the case, it may be that you are actually losing steps (rather than the filament slipage M592 was meant for), so your results may end up being a bit inconsistent, and you might just want to limit the max volumetric flow in the slicer. I set my slicer profiles for my v6 machines to 10mm3/s as a safety net, so I can then play around with speeds, layer heights, line widths etc without having to worry.
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Generally I'd say it's best to set the esteps at a low feed rate like 1mm/s and then leave it fixed and then find your volumetric flow rate limit to determine your max speed/width/height combination.
I'm of the opinion that if you're using non-linear extrusion to try and compensate for a lack of volumetric flow rate you're probably getting poor extrusion and weak parts.
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Hi,
Just to confirm, did you do the testing with or without nozzle?I did similar testing earlier with absolute vs relative extrusion and found out that absolute extrusion is sometimes causing missed steps with RRF.
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@petriheino Tried it both ways.. with and without nozzle, and with nozzle at different speeds
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@adamfilip You could also try pushing the extruder motor current a wee bit higher, see if that helps. I would try to set the extrusion steps per mm for the extrusion speed you will be using the most. Who cares about 1mm/s and stuff, you wont print with that flow without a tiny tiny nozzle.
But the reality of the situation is such, that there will always be slip, you won't get perfect calibration. Even with the non-linear extrusion, the best you get is dependent on the model (tricky business), but its still open-loop control. Until proper closed loop extrusion control becomes mainstream, we are riding blind.
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@pjl Good points, maybe we should do the testing without filament to see if cause is in firmware (for example measuring motor degrees or step count).
It could be interesting to repeat similar test with other firmware or printers also.
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@petriheino if you have a high micro-stepping value its even easier to skip steps because of decreasing holding torque
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Well, at least measured sent step count seems to be correct (2400steps/mm -> 240k steps for 100mm). Maybe stepper analyzer could be used for skipped microsteps?
