M558 - questions in regards to A parameter

[garyd9]

The M558 gcode command is documented (for the duet board) here:

https://duet3d.dozuki.com/Wiki/Gcode#Section_M558_Set_Z_probe_type

The "A" parameter offers a multi-probe functionality, with it defaulting to "1" (single tap.) If A is >1, it's the "maximum number of times to probe…" Being a maximum, it implies that less than A probes might occur. However, nothing explains that. Does it always probe the max times? Under what circumstances would it probe less than the max times?

The "S" parameter is documented as "tolerance when probing multiple times." However, there's no default value shown. What is the default tolerance? (It appears it's 0.03 based on the source. I've submitted an edit to the wiki to show that.)

How do the A and S parameters influence each other?

From the latest RC builts, I think that a probe will occur UP TO "A" times unless 'x' probes are within a specific tolerance of each other. I'm not sure what 'x' is. (2? 2 consecutive?) In builds prior to RC2, if 'x' probes weren't within the specific tolerance, the probe would be reported as a failure, but in RC2, it was changed so that the probe would just return an average? If this "average" fallback is used, is anything reported to the console log?

Thanks
Gary

[mortn]

Thank YOU! I have just been wondering about the same thing for an hour! It would be great if someone can tell a bit more about the exact behaviour of M558 in conjunction with parameters A and S.

[dc42]

I have expanded the description of M558 on the GCodes wiki page. Let me know if it isn't clear.

[Dougal1957]

David

The A Param is still not clear when it says maximum number of probes at what point does the Firmware stop probing early I assume it is once a certain number of probes are within the tolerance range but a bit more clarity may be in order here?

[dc42]

@dougal1957, see the new paragraph that I added at the end.

[Nxt-1]

@dc42 said in M558 - questions in regards to A parameter:

I have expanded the description of M558 on the GCodes wiki page. Let me know if it isn't clear.

This explanation helped me as well, thanks

[Phaedrux]

@dc42 Will P10 probe type for stall detection be added to the documentation? Or is it a little too experimental for broad distribution?

[dc42]

@phaedrux said in M558 - questions in regards to A parameter:

@dc42 Will P10 probe type for stall detection be added to the documentation? Or is it a little too experimental for broad distribution?

Good point, I will add it.

[T3P3Tony]

@dc42 I have added it here too:

https://duet3d.dozuki.com/Wiki/Connecting_a_Z_probe#Section_Mode_Num_10

[Phaedrux]

@t3p3tony would it be a good idea to link to the forum thread discussing implementation of z stall probing?

[T3P3Tony]

@phaedrux yes - which one is it?

[Phaedrux]

@t3p3tony I'd say this one

https://forum.duet3d.com/topic/4772/motor-stall-detection-as-z-probe

[T3P3Tony]

@phaedrux thanks, done.