Pressure advance sounds like a machine gun

Lo-Fi

Hello!

I thought I'd have a play with pressure advance. I have a printer with a belt reduction extruder and .5m bowden, so it seemed high-time to investigate.

2 problems: firstly, the extruder sounds like a small machine gun half the time. Sounds like a motor missing steps.

Secondly, it fails the print all the time as the MFM calls out too little movement (which I believe is probably correct). Particularly for small features like infill.

I'm running M572 D0 S0.4

I can smooth it out by setting extruder instantaneous speed changes super low (50), but it's slowed things down hugely as your might expect. The extruder is bombproof otherwise - I can't remember the last time I had a movement warning from the MFM.

What, if anything, am I doing wrong? Apologies for the hiatus - usual life stuff, I'm afraid!

Thanks in advance

; Configuration file for Duet WiFi (firmware version 3.3)
; executed by the firmware on start-up
;
; generated by RepRapFirmware Configuration Tool v3.3.10 on Mon Jan 10 2022 00:22:29 GMT+0000 (Greenwich Mean Time)

; General preferences
G90                                            ; send absolute coordinates...
M83                                            ; ...but relative extruder moves
M550 P"Ender 5 Plus"                           ; set printer name

; Network
M552 S1                                      ; enable network
M586 P0 S1                                     ; enable HTTP
M586 P1 S0                                     ; disable FTP
M586 P2 S0                                     ; disable Telnet

; Drives
M569 P0 S1                                     ; physical drive 0 goes forwards
M569 P1 S1                                     ; physical drive 1 goes forwards
M569 P2 S0                                     ; physical drive 2 goes backwards
M569 P3 S0                                     ; physical drive 3 goes forwards
M584 X0 Y1 Z2 E3                               ; set drive mapping
M350 X16 Y16 Z16 E16 I1                        ; configure microstepping with interpolation
M92 X80.00 Y80.00 Z800.00 E1000.00              ; set steps per mm
M566 X1000.00 Y1000.00 Z100.00 E50.00        ; set maximum instantaneous speed changes (mm/min)
M203 X12000.00 Y12000.00 Z400.00 E1000.00        ; set maximum speeds (mm/min)
M201 X1200.00 Y1200.00 Z200.00 E1000.00       ; set accelerations (mm/s^2)
M906 X800 Y800 Z800 E800 I30                  ; set motor currents (mA) and motor idle factor in per cent
M84 S30                                        ; Set idle timeout

; Axis Limits
M208 X0 Y0 Z0 S1                               ; set axis minima
M208 X350 Y360 Z400 S0                         ; set axis maxima

; Endstops
M574 X1 S1 P"xstop"                            ; configure switch-type (e.g. microswitch) endstop for low end on X via pin xstop
M574 Y1 S1 P"ystop"                            ; configure switch-type (e.g. microswitch) endstop for low end on Y via pin ystop
M574 Z1 S2                                     ; configure Z-probe endstop for low end on Z

; Filament Monitor
M591 D0 P3 C"e0_stop" S1 R70:130 L26.67 E6.0; Duet3D rotating magnet sensor for extruder drive 0 is connected to E0 endstop input, enabled, sensitivity 24.8mm.rev, 70% to 130% tolerance, 3mm detection length
M591 D0 ; display filament sensor parameters for extruder drive 0

; Z-Probe
M950 S0 C"exp.heater3"                         ; create servo pin 0 for BLTouch
M558 P9 C"^zprobe.in" H1 F120 T9000            ; set Z probe type to bltouch and the dive height + speeds
G31 P500 X45 Y0 Z2.399                         ; set Z probe trigger value, offset and trigger height
M557 X45:345 Y25:325 S100                      ; define mesh grid

; Heaters
M308 S0 P"bedtemp" Y"thermistor" A"Bed" T100000 B4138 ; configure sensor 0 as thermistor on pin bedtemp
M950 H0 C"bedheat" T0                          ; create bed heater output on bedheat and map it to sensor 0
M307 H0 B0 S1 P19.56 I0.71 D134.26             ; disable bang-bang mode for the bed heater and set PWM limit
M140 H0                                        ; map heated bed to heater 0
M143 H0 S100                                   ; set temperature limit for heater 0 to 100C
M308 S1 P"e0temp" Y"thermistor" A"Nozzle" T100000 B4138  ; configure sensor 1 as thermistor on pin e0temp
M950 H1 C"e0heat" T1                           ; create nozzle heater output on e0heat and map it to sensor 1
M307 H1 R2.624 K0.576:0.000 D6.17 E1.35 S1.00 B0 V24.2 ;
;M307 H1 B0 R2.451 C156.9 D6.32 S1.00           ; disable bang-bang mode for heater and set PWM limit
M143 H1 S280                                   ; set temperature limit for heater 1 to 280C

;Sensors
M308 S2 P"exp.thermistor6" Y"thermistor" A"Heat Sink" T100000 B3950 

; Fans
M950 F0 C"fan0" Q25                           ; create fan 0 on pin fan0 and set its frequency
M106 P0 C"Part" S0 H-1                         ; set fan 0 name and value. Thermostatic control is turned off
M950 F1 C"fan1" Q500                           ; create fan 1 on pin fan1 and set its frequency
M106 P1 C"Tool" S255 H1 T65                      ; set fan 1 name and value. Thermostatic control is turned on

; Tools
M563 P0 S"Extruder 0" D0 H1 F0                 ; define tool 0
G10 P0 X0 Y0 Z0                                ; set tool 0 axis offsets
G10 P0 R0 S0                                   ; set initial tool 0 active and standby temperatures to 0C

Phaedrux

@Lo-Fi said in Pressure advance sounds like a machine gun:

I'm running M572 D0 S0.4

How did you determine that value?

Max extruder speed of 1000mm/min seems pretty low. How fast are you retracting and what is your retraction distance?

Here are some settings that I would start testing with.

M572 D0 S0.05
M566 E1500
M203 E6000
M201 E3000

You may need to redo your retraction tuning even before you try to experiment with PA. And then again when you have determined a good PA value.

Lo-Fi

@Phaedrux said in Pressure advance sounds like a machine gun:

M572 D0 S0.05
M566 E1500
M203 E6000
M201 E3000

Thanks for the reply. It was a starting point suggestion from the documentation based on the bowden length. My Pulley ratio is 3.75:1, so I have to be a little careful about speeds and accelerations, as I'm pretty sure those settings all specify conditions at the filament after the gearing, not the motor? I'm running 6mm, 40mm/s retract currently.

Phaedrux

@Lo-Fi said in Pressure advance sounds like a machine gun:

I'm running 6mm, 40mm/s retract currently.

I don't think you're reaching this speed. 40mm/s is 2400mm/min, but you've got your extruder limited to 1000mm/min

Lo-Fi

@Phaedrux I think I probably muddied the water by posting the config after I'd been messing with it! You're right, of course.

I'm going to strip it right back and start again - I'll keep the thread updated.

Lo-Fi

@Phaedrux

Going back over my notes, I originally had extruder max speed at 3600, then subsequently fiddled with it. I've just rebuilt my config entirely and all seems well.

I do still have an issue with the MFM reporting too little movement (<40%) with pressure advance on, though I'm homing in on whether it's slipping itself or whether there is actually some under extrusion going on. My feeling so far is it's struggling to react to rapid moves, but only some slow motion footage will be able to confirm that. I can't hear any skipping and the filament feels like its movement matches the extruder. My prints usually run around the 80-110% mark and I've had the MFM set 70% - 120% for as long as I can remember.