[BUG] FT_MOTION breaks sensorless homing

[vovodroid]

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

Yes, and the problem still exists.

Bug Description

With FT_MOTION enabled (no both old and new IS) it's impossible to find good value for sensorless sensitivity. For instance there is false triggering with 88, but no bump detection with 87.

BTT SKR 3, TMC2209, homing current 100mA

Bug Timeline

No response

Expected behavior

No response

Actual behavior

No response

Steps to Reproduce

No response

Version of Marlin Firmware

bugfix-2.1.x 2024-08-07

Printer model

No response

Electronics

No response

LCD/Controller

No response

Other add-ons

No response

Bed Leveling

ABL Bilinear mesh

Your Slicer

None

Host Software

None

Don't forget to include

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

Additional information & file uploads

Marlin.zip

[thisiskeithb]

homing current 100mA

That's pretty low. Try bumping that up in 100mA increments. I typically run 1/2 X/Y_CURRENT for X/Y_CURRENT_HOME with sensorless homing.

You can also try increasing HOMING_FEEDRATE_MM_M. I have to home slowly on some machines, while others have to home quickly for sensorless to work.

[vovodroid]

Question is why FTM affects these parameters? Isn't it internal driver function?

[thisiskeithb]

Question is why FTM affects these parameters? Isn't it internal driver function?

It's a whole new motion system & still quite buggy / experimental.

edit: cc'ing @ulendoalex & @narno2202 as they may have some tips.

[narno2202]

I have the same problem when I set sensorless homing for the fisrt time in the standard motion system. I have to decrease the X and Y motor current to get reliable homing. For the X axis nominal current is 800 and 400 for homing, for Y axis nominal current is 1000 and 800 for homing.
With FT_MOTION I need to change the stallguard sensiitivty : X senssitivity 55 no change, Y sensitivity 45 instead of 55.

[vovodroid]

I played with current in range 200-400, but didn't succeeded to get it working.

I saw proposition to disable FTM during homing, why not to do it?

[narno2202]

I forgot to mention that with my settings, sensorless homing works both with standard motion and FTM. What kind of failure do you have? : no motion or grinding on stop.

[vovodroid]

grinding on stop.

This one or false triggering.

[thinkyhead]

I saw proposition to disable FTM during homing, why not to do it?

If homing doesn't work with FT Motion then this is a broken aspect of FT Motion that we want to fix, especially if FTM is going to be the only motion system enabled for some builds. Eventually we'll get it working reliably.

I'm not sure if Ulendo has sensorless homing setups they can use for testing and debugging, but I sure do, and as I get into deeper testing along with Ulendo over the coming days I'm sure we'll find and fix the cause of the unreliability.

[narno2202]

I have found sensorless homing difficult to tune with standard motion. Once tuned, It works fine also with FTM with minor changes but seems to be relatively hardware dependant.
@thinkyhead, Ulendo tested FTM on an Ender 3 style printer (as mentioned in their scientific papers). In previous talks with @ulendoalex, I've understood that FTM was not tested with sensorless homing and diffrent kind of probe. This was fixed after merging into Marlin.

[vovodroid]

Could sensorless homing issue be related to sound? Actually strange sound is caused by current waves, probably affecting bump detection.

[narno2202]

I don't think so.
I have a look at your Configuration.h file. Homing speed is 20mm/s (X and Y axis). Sensorless homing also relies on speed, mine is Marlin default (50mm/s). The 3 parameters are speed (not too low not to high), motor current and stallguard sensitivity. You need to tweak them to find the good combination but in my experience It's a little bit tricky. The best will be a wizard.

[vovodroid]

Homing speed is 20mm/s (X and Y axis).

That's Klipper recommendation https://www.klipper3d.org/TMC_Drivers.html#choose-homing-speed

A good starting point for the homing speed is for the stepper motor to make a full rotation every two seconds.
For many axes this will be the rotation_distance divided by two. For example:

[stepper_x]
rotation_distance: 40
homing_speed: 20

You need to tweak them to find the good combination but in my experience It's a little bit tricky.

I had no problem with tuning standard motion. Speed and current affect sensitivity, but there is always range 50 or more where detection works.

[vovodroid]

Ok, I've tested with increased speed - 40-50 mm/s. Now I succeeded to to home X/Y, though sensitivity range is still more narrow than for "classic" motion.