Sensorless homing, not working

StevePS3

I've done a search of the forum and found a couple of related posts but so far I've not found a solution.

Board: Duet 3 Mini 5+ (Mini5plus)
Firmware: RepRapFirmware for Duet 3 Mini 5+ 3.2.2 (2021-02-11)
Duet WiFi Server Version: 1.25

I am trying to setup sensorless homing but no matter what I do, the head simple crashes into the end of the carriage and carries on trying to move.

I've set the parameters for the X and Y

; Endstops - sensorless
M574 X1 S3 ; configure sensorless endstop for low end on X
M574 Y1 S3 ; configure sensorless endstop for low end on Y

; Motor Stall
M915 X Y S5 R0 F0

I then cribbed the homeX from the documentation.
M400
M913 X75 Y75 ; drop motor current to 75%
M400 G91; relative positioning
G1 H2 Z10 F12000 ; lift Z relative to current position
G1 H1 X-320.5 F2000 ; move quickly to X axis endstop and stop there (first pass)
G1 H2 X5 F12000 ; go back a few mm
G1 H1 X-320.5 F1000 ; move slowly to X axis endstop once more (second pass)
G1 H2 Z-10 F6000 ; lower Z again
G90 ; absolute positioning
M400
M913 X100 Y100 ; return current to 100%
M400

So far I've not managed to induce a stall. Can anyone help?

T3P3Tony

@steveps3 have you followed th steps here:
https://duet3d.dozuki.com/Wiki/Stall_detection_and_sensorless_homing#Section_Configuring_Stall_Detection

StevePS3

@t3p3tony Yes, that is the document that I have been using

T3P3Tony

@steveps3

Set the S parameter to the lowest value at which you do not get false stall reports. Typical values for nema 17 motors are between 1 and 3. False stall reports are most likely during fast travel moves, because the acceleration increases the load on the motor. False stall reports are also more likely when the motors are hot.

Have you tried reducing the S parameter until you get a stall?

https://duet3d.dozuki.com/Wiki/M915

Snnn Stall detection threshold (-64 to +63, values below -10 not recommended). Lower values make stall detection more sensitive. S3 is a good starting point for many motors.

At some point there will be an S value that stalls when you reach the end of the axis. For most motors/setups that should be a higher number than what you get when you have it so low that it detects a stall on a normal move.

StevePS3

@t3p3tony I set it to -64 and it still doesn't stall

M915 X Y S-64 R0 F0

dc42

@steveps3 said in Sensorless homing, not working:

Board: Duet 3 Mini 5+ (Mini5plus)
Firmware: RepRapFirmware for Duet 3 Mini 5+ 3.2.2 (2021-02-11)

Upgrade there firmware to 3.3. There is a known issue with sensorless homing on Duet 3 Mini using firmware 3.2.2 and earlier. There is a workaround for it, but it is simpler to upgrade to firmware 3.3.

StevePS3

@dc42 Thanks, I'll give that a try.

StevePS3

OK, I am now on 3.3 and the results are the same. Just lots of belt slipping as the head crashes into the side of the printer.

StevePS3

I have reduced the current to the steppers so that they stall as soon as they start to move. Yet all they do is continue to try to move. I was assuming that they would stop moving as soon as they stall?

jay_s_uk

@steveps3 make sure you have something like D3 V40 on each M569 you want to run sensorless on so they are in stealthchop.
This is a nice bit of test code to make sure your motors are stalling

M915 P0 S-127 H10 R1 ; Set very sensitive stall detect
M574 X1 S3 ; configure endstop for stall detection
G1 X200 H1 ; Should stall pretty much immediately

StevePS3

@jay_s_uk
Yes, that worked. OK, so now maybe I can start to tweak the settings until it works. -127 definitely causes an instant stall

StevePS3

This post is deleted!

StevePS3

A value of about 30 seems to work just fine.