Sensorless homing, not working

T3P3Tony

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.