bug: pressure advance causes overextrusion

jschall · 29 Aug 2020, 04:31

See also https://forum.duet3d.com/topic/18412/rrf-2-03-pressure-advance-causes-20-overextrusion/21

Steps as counted by logic analyzer connected to step and direction pins:

Without pressure advance:
fwd_count 1942964
rev_count 961423
net_count 981541
mm 2484.913924

Same file with pressure advance set to 1.0:
fwd_count 6334445
rev_count 5157566
net_count 1176879
mm 2979.440506

Logic analyzer output, no pressure advance
Logic analyzer output, pressure advance 1.0
Python script to count steps

jschall · 29 Aug 2020, 05:45

For now this is confirmed only on 2.03, will do an upgrade to at least 2.05 and probably 3.1.1 soon.

dc42 · 30 Aug 2020, 07:25

Thanks, I'll wait for your results with 2.05.1 and 3.1.1.

bot · 30 Aug 2020, 15:45

@jschall It seems like you've lost interest, based on the other thread. What model of logic analyzer were you using? Do you have any tips on how to get quickly up and running measuring step pulses in the way you did?

I'd love to test 2.05.1 and eventually rrf 3 myself, but I have no clue where to start other than googling "logic analyzer."

jschall · 31 Aug 2020, 15:25

@bot said in bug: pressure advance causes overextrusion:

@jschall It seems like you've lost interest, based on the other thread. What model of logic analyzer were you using? Do you have any tips on how to get quickly up and running measuring step pulses in the way you did?

I used a Saleae.

I will still test 3.1.1...

Stephen6309 · 2 Sept 2020, 13:22

Was the microstepping set to use microstep interpolation mode in M350?

jschall · 2 Sept 2020, 18:03

@Stephen6309 No, it was set to 8 with no interpolation.

jschall · 2 Sept 2020, 18:05

@Stephen6309 Also, my understanding is that interpolation means the stepper driver (which is receiving the steps) interpolates between them, not that the microcontroller sends a different number of steps?

Phaedrux · 2 Sept 2020, 18:22

@jschall correct.

x16 with interpolation is the gold standard with the Duet boards because it's sufficient resolution for most 3D printing applications, it has a manageable step pulse generation load for the CPU, and the interpolation results in smoother, quieter operation.

Stephen6309 · 3 Sept 2020, 13:43

@jschall I wasn't sure if that would affect the measured step count.

bot · 3 Sept 2020, 15:23

So now that we have confirmation that there seems to be an error in PA, even in 3.x firmware, can we have this item put back on the magical list of items to investigate in RRF?

CCS86 · 28 Dec 2020, 15:33

Has this issue progressed at all?