Starting a print fails on Prusa MK3s

zenzenzense

Hardware: Stock Prusa MK3s, Duet 3 Mini 5+ (WiFi)

I am trying to replace the Einsy board on my Prusa with a Mini 5+ using config from https://github.com/CNCKitchen/PrusaDUET. However, I did make some modifications for sensorless homing support using https://duet3d.dozuki.com/Wiki/Stall_detection_and_sensorless_homing.

For the most part homing seems to work when manually triggered from DWC. However, at the start of a print once the bed and nozzle is hot enough, it seems to try to home which fails. Link to the video is: https://www.dropbox.com/s/oejvtjnt360ji5k/printfail.webm?dl=0 (skip to 30s for the failure).

DWC reports the requested speed to be 3mm/s, which I think is not enough for stallguard to work properly. I'm not really sure where to make adjustments, as like I've said, manually homing seems to work ok.

I am trying to print one of the sample gcode files that came with the printer (MK3S_PLA_Batman_200um_18M.gcode). This was of course sliced for the previous board and firmware (Einsy + Marlin). Do these need modification as well?

dc42

@zenzenzense, those files will need modification if they contain any M203 commands.

This is why. M203 was introduced in RepRapFirmware in 2013 and documented at https://reprap.org/wiki/G-code (the master reference for GCode commands for 3D printers). It was standard for speeds in GCode commands to be expressed in mm per minute (e.g. the F parameter of the G1 command), because GCode was developed for CNC machines originally. So M203 was defined a specifying the maximum speeds in mm per minute.

Years later the M203 command was added to Marlin firmware, but unfortunately they broke with convention and existing usage and used mm per second for the M203 parameters. So M203 has a different meaning depending on which firmware you are running. Prusa printers run a variant of Marlin.

There are some other commands that Marlin usurped after they already had defined and documented meanings, but M203 is the one that causes the most trouble. Therefore I suggest you use an editor such as Notepad++ to check whether your GCode files contain any M203 commands. If they do then the simplest option is just to comment them out with a leading semicolon. IMO, M203 is a configuration command that doesn't belong in GCode print files at all.

zenzenzense

@dc42 Thanks! Commenting M203 really did solve the issue. I thought I did something wrong with my sensorless homing setup.