600mm bowden setup pressure advance calibration

Slzer

Hi All,

I've got a 600mm bowden setup with an E3D chimera on the end. I'm trying to calibrate the pressure advance for PLA material and i have run the calibration test script below. (i followed the tutorial that uses the marlin generator then replaces the marlin gcode with the reprapfirmware M572 command).

To me it looks like a value of 2 is best but wow is the extruder going wild during normal prints - especially small areas of solid infil.

Have i done something wrong here?

pressure advance.jpg

Phaedrux

You may want to try one of the alternative means of tuning pressure advance found here: https://duet3d.dozuki.com/Wiki/Pressure_advance

The more artificial tests such as this one tend to lean towards very high values, but in actual practice the high values don't tend to behave all that well and you can probably get away with a lower value. That said, pressure advance tuning is difficult if not impossible to test and tune in isolation.

owlfab

@Slzer said in 600mm bowden setup pressure advance calibration:

Have i done something wrong here?

That was pretty much my feeling when I set up pressure advance, and I'm still not completely convinced. FWIW I have a similar length bowden (can't measure it because I'm at work). I ended up converging on S1.4 just by printing some square towers and watching the corners. I'm replacing the stepper though, so that could change soon. For background, my extruder is non-geared, 1.75mm, and currently uses a 1.8 degree stepper that is barely strong enough.

I had the same observation that the E stepper kind of goes crazy on small areas. High S values can be demanding. I found that it is very important to dial in E axis current/speed/acceleration/jerk properly. If the stepper can't keep up, the E axis can become the limiting factor for overall print speed, or it can miss steps.

Slzer

What settings have you got for accel and jerks? i feel like it just doesn't do much with my current setup - i did a 1 wall cal cube and at an S value of 2 i looks ok. about to print another with a value of 1 to see if there is any noticable difference.

here are mine

M584 X0 Y1 Z2 E3:4                              ; set drive mapping
M350 X16 Y16 Z16 E16:16 I1                      ; configure microstepping with interpolation
M92 X100.00 Y100.00 Z400.00 E420.00:420.00      ; set steps per mm
M566 X1000.00 Y1000.00 Z50.00 E1000.00:1000.00      ; set maximum instantaneous speed changes (mm/min) X900.00 Y900.00 Z12.00 E120.00:120.00
M203 X10000.00 Y10000.00 Z1500.00 E3000.00:3000.00 ; set maximum speeds (mm/min) X6000.00 Y6000.00 Z250.00 E1200.00:1200.00
M201 X500.00 Y500.00 Z100.00 E850.00:850.00      ; set accelerations (mm/s^2) X500.00 Y500.00 Z20.00 E250.00:250.00

owlfab

One thing I appreciate about the Duet is that you can change most of the motion settings on the fly. If you paste it into the web interface while printing, you can observe the effects immediately without having to start a new print. Then when you have something that works, you can edit config.

I just replaced all of my steppers. Things are still kind of in flux, but the benchy printing right now looks good so far. Here are the relevant lines from my config.g. As you can see, I went down to S1.

M584 X0 Y1 Z2:4 E3                         ; set drive mapping
M350 X256 Y256 Z256 E256 I0                ; configure microstepping without interpolation
M92 X2560.00 Y2560.00 Z25600.00 E4298      ; set steps per mm 
M566 X1000.00 Y1000.00 Z500.00 E1000.00    ; jerk (mm/min)
M203 X18000.00 Y18000.00 Z1000.00 E3000.00 ; max speed (mm/min) 
M201 X2000.00 Y2000.00 Z300.00 E1200.00    ; accelerations (mm/s^2)
M906 X800 Y800 Z1200 E1200 I30             ; set motor currents (mA) and motor idle factor in per cent
M84 S10                                    ; Set idle timeout

; Pressure advance
M572 D0 S1

Edit: I should say that my extruder max speed probably needs to be reduced, since I'm seeing some missed steps.

Phaedrux

@owlfab said in 600mm bowden setup pressure advance calibration:

M350 X256 Y256 Z256 E256 I0 ; configure microstepping without interpolation M92 X2560.00 Y2560.00 Z25600.00 E4298 ; set steps per mm

I'm not surprised you're seeing missed steps/hiccups with x256 microstepping. It's recommended to stick to x16 with interpolation to x256 for this reason.

Slzer

You have much higher extruder accel and a bit higher speeds... i will try it out.

on a side note i tried the hollow cube method... and again i see essentially no difference between the values. i used the M572 command during prints to check and it correctly said extruder 1 was at the values i ran the tests at.

pressure advance3.jpg pressure advance2.jpg

owlfab

@Phaedrux
Thanks for the tip. I will give it a try.

@Slzer
It does seems weird that your towers look the same. When I was printing the hollow towers, the main thing I was watching was the corner where the layer transition happened. On my printer, I was getting a blob there without using advance. Turning it up too high resulted in a gap. If it wasn't for that blob, I probably wouldn't have even bothered.

Slzer

I'm seeing those blobs and they are annoying, they just don't seem to go. Happens most on solid infil layers and then the nozzle catches them on travel moves