Feature request - Stallguard on extruder_stepper sections

Features
1

In a printer with a single print head and multiple extruder-steppers feeding different materials to that print head one at a time through a 4 to 1 funnel, it would be very advantageous to be able to detect a stall when parking one filament and unparking the next to be printed. Occasionally the previous filament parking fails to completely clear the path sufficiently to allow the next filament to get through that funnel, and the unpark action fails. If Klipper could detect this, it could be handled the same way as a filament runout with a pause for operator intervention, thus saving the print.

Using the same configuration syntax as is used for sensor-less homing of X and Y axis motors but applying it to extruder_stepper motors (and the corresponding tmc2209 extruder_stepper section), and either simply detecting that configured level of resistance during any movement or only during a unparking move (which might also require a new movement command syntax, so it might be easier to simply do it any time). Then use this stall detection as a filament movement failure equivalent to a filament_motion_sensor section.

Most of the code required to support this should already exist.

2

FWIW, I would suggest spending some time to get the stallguard measurements.

The thing is, that your motor can just spin too slow, or just be too small, to generate enough back emf for stallguard to even detect something.
Not the thing that you are describing, but literally anything.

And then, if it can detect something, if you can reliably detect the stall in the graphs.
It could possibly be implemented.

Hope that helps.

3

Those are good things to know. With that in mind - these extruders are using NEMA 17 steppers, and based on that input I would expect to run them at a reasonably high step rate when unparking the filaments. Perhaps it would not work when normal extrusion was taking place, so that could be removed from the request. At that point the more normal sensors can be used.

4

You can manually set it without too much difficulty.

[tmc2209 extruder]
#stealthchop_threshold: 999999 ; StealthChop always enabled. (TPWMTHRS = 0)
#coolstep_threshold: 0.002 ; Coolstep almost always enabled
driver_SGTHRS: 1 ; 0 means disabled.
# DIAG is pulsed by StallGuard when SGTHRS * 2 > SG_RESULT. It is only enabled in StealthChop mode, and when TCOOLTHRS ≥ TSTEP > TPWMTHRS

[gcode_button MOTOR_DIAG]
pin: ...
press_gcode:
  M118 Extruder Stall!

However, as @nefelim4ag noted it’s probably not going to work correctly. I tried, and saw too many false triggers.

Beyond that StallGuard4 only works when in StealthChop mode, and there’s some potential issues with that.

However, “stealthChop” mode may produce lower motor torque and/or produce higher motor heat. It may or may not be an adequate mode for your particular printer.