BL-Touch - Multiple Probes?

[zemlin]

My BL-Touch is working fine, but I see a little bit of variability in the apparent Z-Height across the bed, so I thought maybe multiple probes would provide a more consistent result.

I tried adding an A3 and S-1 parameter to my M558 in the config.g, but it still only pokes once. I thought that would poke three times and average the readings. I also added two speeds to the F parameter so the second poke would be slower. What am I missing?

M558 P9 C"^zprobe.in" H2 F60:30 T24000 A3 S-1      ; set Z probe type to bltouch and the dive height + speeds
G31 P25 X12.5 Y51.05 Z4.5                          ; set Z probe trigger value, offset and trigger height
M557 X25:275 Y50:300 S50 

[Phaedrux]

What firmware version?

Perhaps part of the problem is that our trigger height is 4.5mm but the dive height is only 2mm.

4.5mm seems very high for a bltouch. The Bltouch documentation says the probe should be mounted so that the probe body is ~8mm above the nozzle tip, which should result in a trigger height of ~2mm.

Regardless, your dive height should be equal to or greater than the trigger height.

Also, for best results with multiple probes with the BLtouch you should try leaving the S value off entirely to leave the default tolerance, and just use a larger value for A. Then it will probe at least twice until two results are within tolerance up to A# of times. Averaging the values should only be used if your probe is truly giving inconsistent results. In which case, something is wrong with the BLTouch.

[zemlin]

RepRapFirmware for Duet 2 WiFi/Ethernet 3.3 (2021-06-15)

It's been a couple years since I set this up, and looking at the CAD models of the print head and bracket I recall the sensor model I downloaded didn't quite match the actual sensor, but I will look into that and see if I need to adjust my bracket.

Initially I did just add the A option, and it did not double-dip with that alone.

[Phaedrux]

@zemlin said in BL-Touch - Multiple Probes?:

Initially I did just add the A option, and it did not double-dip with that alone.

Well I wonder if that's related to the dive height being lower than the trigger height.

[dc42]

@phaedrux said in BL-Touch - Multiple Probes?:

Regardless, your dive height should be equal to or greater than the trigger height.

Actually, that's not necessary. The actual starting height is calculated by adding the trigger height to the configured dive height.

[zemlin]

@phaedrux - I finally got around to modifying my sensor bracket so the height relative to the nozzle is the correct 8mm and adjusted trigger height and dive height accordingly.

The A option on M558 still does not result in repeat probes.

; Z-Probe
M950 S0 C"exp.heater3"                             ; create servo pin 0 for BLTouch
M558 P9 C"^zprobe.in" H2 F20 T24000 A2          ; set Z probe type to bltouch and the dive height + speeds
G31 P25 X12.5 Y51.05 Z2                            ; set Z probe trigger value, offset and trigger height
M557 X25:275 Y50:300 S50 						   ; define mesh grid
M307 H3 A-1 C-1 D-1  

[Phaedrux]

What happens if you leave off the S parameter and set A10?

@zemlin said in BL-Touch - Multiple Probes?:

M307 H3 A-1 C-1 D-1

Also remove that line entirely as it's no longer valid in RRF3.

Can you share your full config.g and homing files? Bed.g as well if it's used? It feels like something is getting altered somewhere that we're just not seeing.

[zemlin]

@phaedrux
Good call - Homing has an A1. Will change that. Thanks.

update: Editing the M588 command in the homeall and homez files resolved the issue. Thanks.