Sensorless homing not working

jujojujo_2003

I have an ender 3 with these stepper motor drivers for X & Y axis https://www.printedsolid.com/products/ldo-nema-17-motor-high-temp-voron-ldo-42sth40-1004mahvrn
(this is a 0.9 stepper) and I am not able to get sensorless homing to work. I have a duet 3 mini 5+ board (with 3.2.2 firmware)

What I gather from https://duet3d.dozuki.com/Wiki/Stall_detection_and_sensorless_homing
there are the following variables that I can play with to get sensorless homing to work

i) The current percentage value for stepper motor in M913 command
ii) The feedrate for G1 command for homing
iii) The sensitivity params (S ) in M915
iv) Stealthchop <-> Spreadcycle cutoff given by V param in M569

From the docs, the only restriction is that feedrate must be lower than Stealthchop <-> Spreadcycle cutoff (which we get from M569 P0.0 command multipled by 60 to convert mm/s to mm/min)

I have tried a bunch of values for these 4 params
i) M913 ranging from 10-100
ii) Feedrate ranging from 2400 to 7500 (capped by stealthchop cutoff)
iii) Sensitivity ranging from -63 to +63
iv) V param for M569 ranging from 1 to 100

For all these cases, the X carriage just seems to move and crash with "Homing failed" message. Given that for all values, high and low I get the same crash, I am not sure how to move or change the parameters.

Also with V < 50, I either get "driver short to ground" error or "high motor temperature" error.
Shouldn't setting sensitivity (S param in M915) to a very low value cause the stall detect to be triggered all the time?
Any idea how I can get this to work?

config.g
homex.g
homey.g
retractprobe.g

homex.g

M98 P"retractprobe.g" 
M913 X70 Y70  		; drop motor currents to 40% 
M915 X S-20 R0 F0 H400; Sensitivity 4, don’t take action, don’t filter, 400steps/sec
G91 				; set relative
;G1 H2 Z5 F1200      ; lift z by 5
G1 H1 X-250 F4500	; move left 250mm, stopping at the endstop
G90 				; back to absolute positioning
M913 X100 Y100 		; motor currents back to 100%
M915 S63 X Y R0	    ; Disable Logging and lower stall detection

o_lampe

@jujojujo_2003 said in Sensorless homing not working:

Shouldn't setting sensitivity (S param in M915) to a very low value cause the stall detect to be triggered all the time?

I'm no expert either, but to me a lower sensitivity leads to harder crashes?

David Green

@jujojujo_2003 said in Sensorless homing not working:

M915 X S-20 R0 F0 H40

I use:
M400
M913 X70 Y70 ; drop motor current to 70%
G91 ; relative positioning
G1 H2 Z10 F6000 ; lift Z relative to current position
G1 H1 X-320 F12000 ; move quickly to X axis endstop and stop there (first pass)
G1 H2 X15 F1800 ; go back a few mm
G1 H1 X-320 F12000 ; 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%
Which works on my CoreXY I don't have the M915 in the homex or y.g

jujojujo_2003

@david-green Tried this one too but it crashes again.

jujojujo_2003

Looking at https://forum.duet3d.com/topic/21108/stall-detection-on-duet-3-mini/4 , I tried updating to V3.3 beta firmware and tried a bunch of S values for M915 from -128 to +127 but still the same crash.

jujojujo_2003

M98 P"retractprobe.g" 
M400                      ; Wait for current moves to finish
M913 X70  		          ; drop motor currents to 50% 
M915 X S-3 R0 F0 H400     ; Sensitivity -3, don’t take action, don’t filter, 400steps/sec
M569 P0.0 V10             ; reduce V parameter so driver operates in stealthChop
G4 P200                   ; wait 200ms
G91 				      ; set relative
G1 H1 X-255 F4000         ; move quickly to X axis endstop and stop there (first pass)
G90 				; back to absolute positioning
M913 X100 Y100 		; motor currents back to 100%
M915 S63 X Y R0		; Disable Logging and lower stall detection

So this is the config that worked for me(On v3.3 beta). It looks like we need to dial M569's V param first such that for that V param, M915 S-63 always triggers a stall and M915 S63 always triggered a crash. Then you binary search on the correct S value

The problem now is that it homing doesn't work when the gantry is towards the end of x axis. But then If I home twice then it works. This seems very hacky. and also I keep getting "Error short-to-ground reported by driver(s) 1"

jujojujo_2003

@jujojujo_2003 said in Sensorless homing not working:

Error short-to-ground reported by driver(s) 1

SO I was able to fix this by reducing the current. My stepper current was set to 900ma . Probably this was too high(even though this is < the rated current of both stepper and driver)

Lowering it to 700ma fixed the issue.