How to disable extruder stepper during mesh bed probe

Luke_D3D

I'm getting false triggering issues with my (clone) BL Touch sensor. I've tried twisting the extruder stepper wire pairs for each coil, and moving the touch sensor wires further away from all other cabling (except within the cable harness going to the extruder).

I thought a quick win might be to turn off the extruder motor current during bed probing, I tried adding M18 to the bed.g but it doesn't seem to work, and suggestions as to why?

M561 ; clear any bed transform
M18 E0 ; disable extruder stepper to reduce noise
G29  ; probe the bed and enable compensation

Also, for the probe connection, I am using a length of USB cable stripped from a mouse, and wired the screen wires as the ground connection. This seemed like a sensible approach, but I'm no expert. Any comments on that?

From the config.g:

M307 H3 A-1 C-1 D-1
M558 P9 X0 Y0 Z1 H5 F500 T3000 A6 S0.04 B1 ; Configure probe A=max 6 times, S0.04m = tol, B1 disables heaters for probe
G31 X-66 Y0 Z0.54 P25			;was z1.92 (larger value moves nozzle closer to bed)
M557 X1:182 Y4:156 S29                ; define mesh grid

Phaedrux

@Luke_D3D said in How to disable extruder stepper during mesh bed probe:

M558 P9 X0 Y0 Z1 H5 F500 T3000 A6 S0.04 B1

Your command isn't quite right. Try this:

M558 P9 H5 F60 T3000 R0.5 A6 S0.03 B1

S0.04 is less sensitive than even the default. 0.03 is the default. The BLTouch should be capable of 0.003

@Luke_D3D said in How to disable extruder stepper during mesh bed probe:

I am using a length of USB cable stripped from a mouse

I think the twisted wires in there may be your issue. I would suggest making your own cable harness.

https://duet3d.dozuki.com/Guide/Ender+3+Pro+and+Duet+Maestro+Guide+Part+5:+Upgrades/54#s224

Are you sure that M18 E0 is not disabling the motor? If the hotend is up to temp will it still extrude?

Luke_D3D

Thanks, I'll give that M558 change a try and double check on the extruder disable. Then re-evaluate the wiring if there are still issues.

Luke_D3D

Following up on this: the M18 does work, of course. I had my Slicer calling G29 directly, not bed.g, so M18 never got run.

On the subject of the interference, I ordered some ribbon cable and JST connectors and crimped a new cable for the probe. I also made some stand-offs to separate the stepper cables from the others in the cable harness. (photo below.) The probe does not do the instantaneous false triggers it was occasionally doing before. Unfortunately, its still not performing well. Strangely, the number of repeat probe events does change that much between S0.01 and S0.03, so I feel certain it is some kind of pick-up rather than the noise floor of the system.

If I separate the probe wire from the harness completely and suspend it off to the side, I can get a really good mesh probe. For now I'm just reloading the saved mesh from file and only probing the center before each print.

I'm wondering whether this is just shoddy performance of the Trianglelab clone BLTouch, I haven't had the same problem with the genuine BLTouch on my other printer. I'm thinking of getting the differential IR probe instead, and giving that a try.

Phaedrux

@Luke_D3D said in How to disable extruder stepper during mesh bed probe:

I'm wondering whether this is just shoddy performance of the Trianglelab clone BLTouch, I haven't had the same problem with the genuine BLTouch on my other printer.

Hard to say with clones, but it wouldn't surprise me.