[BUG] M221 / Flow Rate setting lower then 100 sets the flow way too low

[EvgenyD]

Did you test the latest bugfix-2.1.x code?

Yes, and the problem still exists.

Bug Description

Setting flow rate value (via M221 or LCD interface) lower then 100 results in the extrusion rate being extremely slow.
Flow rate higher then 100 work correctly.

Bug Timeline

No response

Expected behavior

Setting flow rate to 99 should not produce noticible change in flow rate.

Actual behavior

Setting flow rate to 99 result in a flow rate way too low, with extrusion motor nearly not moving.
it feels like the flow rate is set to 0.99% instead of 99%.

Steps to Reproduce

1. start print with flow rate set to 100
2. while printing set flow rate to a vlau lower then 100 (e.g. 99) through the menu or via M221 command
3. almost no material coming out of nozzle and the extruder motor not moving.

Version of Marlin Firmware

bugfix-2.1.x

Printer model

Kossel Delta

Electronics

Trigorilla upgraded for TMC drivers

LCD/Controller

default, REPRAP_DISCOUNT_SMART_CONTROLLER

Other add-ons

TMC2208 drivers (Hybrid Mode) for all the motors. UART control.

Bed Leveling

MBL Manual Bed Leveling

Your Slicer

Prusa Slicer

Host Software

Pronterface

Don't forget to include

• A ZIP file containing your Configuration.h and Configuration_adv.h.

Additional information & file uploads

Marlin.zip

[ellensp]

As a start provided config has a few issues,

has #define MANUAL_PROBE_START_Z 0.5 and #define MANUAL_PROBE_START_Z 0.8
causing thousands of redefinition errors

change #define MANUAL_PROBE_START_Z 0.5 to

  #ifndef MANUAL_PROBE_START_Z
    #define MANUAL_PROBE_START_Z 0.5  // (mm) Comment out to use the last-measured height
  #endif

This line is invalid as HOMING_FEEDRATE_Z is not defined.
#define Z_PROBE_FEEDRATE_FAST (HOMING_FEEDRATE_Z / 2) //(4*60)

this is wrong

// #if PROBE_SELECTED && !IS_KINEMATIC
  #define PROBING_MARGIN_LEFT 50//PROBING_MARGIN
  #define PROBING_MARGIN_RIGHT 10//PROBING_MARGIN
  #define PROBING_MARGIN_FRONT 10//PROBING_MARGIN
  #define PROBING_MARGIN_BACK 10//PROBING_MARGIN
// #endif

Since this Machine is IS_KINEMATIC these defines are also removed by marlin in https://github.com/MarlinFirmware/Marlin/blob/bugfix-2.1.x/Marlin/src/inc/Conditionals-5-post.h#L3265-L3269

There is no need disable the additional axis stuff, with the driver disabled it is just ignored.

Here are updated and cleaned configs
Cleaned Configuration.zip

[ellensp]

"Setting flow rate value (via M221 or LCD interface) "

There is no way to set flow rate on this lcd with these settings.

edit:

You can in the Tune menu, which only shows if printer gets into printing mode by printing from sdcard or M75

[ellensp]

I setup a test rig, used the cleaned up config as much as possible (only changed motherboard to BOARD_RAMPS_14_EFB (same chipset) and change steps/mm for my hardware)

I made a simple bash script to generate test gcode

E_VALUE=200
flowrate=100
echo "M302 S0; Allow cold extrusion"
echo "M75; Start print timer"
echo "G28; Home all axes"
echo "G1 Z180 F1000; Move nozzle to 180mm above bed"
for i in {1..200}
  # disable for lcd test of flow.
  #echo "M117 Flow set to $flowrate"
  #echo "M221 S$flowrate"
do
  for j in {1..1}
  do
    echo "G1 X50 Y50 E$E_VALUE  F1000"
    E_VALUE=$((E_VALUE + 200))
    echo "G1 X-50 Y-50 E$E_VALUE F1000"
    E_VALUE=$((E_VALUE + 200))
  done
  echo "G92 E0; Reset extruder position"
  E_VALUE=200
  flowrate=$((RANDOM % 101 + 50))
done

It generated lots of gcode like this but longer (DO NOT RUN THIS ON A REAL PRINTER)

M302 S0; Allow cold extrusion
M75; Start print timer
G28; Home all axes
G1 Z180 F1000; Move nozzle to 180mm above bed
G1 X50 Y50 E200  F1000
G1 X-50 Y-50 E400 F1000
G92 E0; Reset extruder position
G1 X50 Y50 E200  F1000
G1 X-50 Y-50 E400 F1000
G92 E0; Reset extruder position
G1 X50 Y50 E200  F1000
G1 X-50 Y-50 E400 F1000
G92 E0; Reset extruder position
G1 X50 Y50 E200  F1000
G1 X-50 Y-50 E400 F1000
G92 E0; Reset extruder position
G1 X50 Y50 E200  F1000
G1 X-50 Y-50 E400 F1000
G92 E0; Reset extruder position
G1 X50 Y50 E200  F1000
G1 X-50 Y-50 E400 F1000

And M221 does just what it was meant to, it adjusted the extruder flow rate to the percentage.

I cannot see any issue

[EvgenyD]

Thank you for looking into the issue.
I am still working on configuration files - i'm trying to upgrade from 1.9 version to 2.1 - so there are still some junk left here and there, and I appreciate the help with the config files.
for the flow rate issue here is the video comparison of the extruder motor speed setting 99-100-101% from LCD menu:
https://github.com/user-attachments/assets/f4b95cef-bac5-4ebd-9f20-e2dfe2abedc0

I am not sure which variable exactrly is set through the menu, it is called "Flow" and the same behaviour occures using M221 command (M221 S99 and so on), so i assumed it is the flow rate:

[ellensp]

Ok that one mystery solved

The tune menu is only available while printing.
Need to add M75 to my test gcode to enable that or print from sdcard or it doesn't get into printing mode

Tested on my test rig using Flow menu item still works as expected.

I still cannot replicate this issue, not even from the flow menu