Slow down before endstop?

theKM

So I've tried to chase down what straight probing can do for me...

I made a setup with a breadboard to emulate the analog signal, and confirmed that with buttons I could trigger a value of around 515, and 1000 (confirmed in DWC probe interface)... to correspond with the docco of what the IR probe does. Set the probe value with G31, also verified in the UI.

Regardless of what I send through 32.8, it only ever moves at the second feedrate from 558, nothing I tried got it to move at the initial faster rate.

The move itself accelerates and decelerates if not interrupted, and the stop is still a hard stop (it's only moving at the second slower feedrate, so I guess that's expected).

There is an ominous line in the gcode docco:

"When doing a plain G30 command, an additional probe will be done using the first speed to establish the approximate bed position, before one or more additional probes are done using the second speed. The first speed will not be used when probing at a defined point or when mesh bed probing.".

I've tried to find any config examples of something I may have missed to get it to honor the initial feedrate, but, not finding any.

M558 P1 C"zprobe.in" H0 F10000:300 T500
G31 P500 X0 Y0 Z0

; following line is actually pretty handy
G38.2 X{move.axes[0].userPosition-25}

Phaedrux

@thekm said in Slow down before endstop?:

There is an ominous line in the gcode docco:

"When doing a plain G30 command, an additional probe will be done using the first speed to establish the approximate bed position, before one or more additional probes are done using the second speed. The first speed will not be used when probing at a defined point or when mesh bed probing.".

This refers to using the A parameter to do multiple probings. That's when the second probe speed is used.

theKM

@phaedrux ...I don't know what's left to try then, I'm not setting any "A" parameter anywhere and it's only ever moving at the slower feedrate.

The M558 and G31 lines above configure the probe, when the G38.2 runs the probe input certainly stops the move, but nothing I've tried gets the probe to move at the initial 1000 to allow it to slow to the second feedrate.

M558's P1 sets the analog input, and G31 sets that threshold, and it does indeed trigger based on G31's P value

Phaedrux

You're trying to use two different features together.

The M558 P1 analog input allows for the slow down as part of the ir probe functionality. I'm not sure if that will actually work with a non-ir probe at all.

And defining the two speed probing is only used when A is set. If you set A2, the first probe would be fast, it would then trigger, back off to the dive height, and then probe again at the slower speed.

theKM

@phaedrux

I'm not sure if that will actually work with a non-ir probe at all.

...the IR probe just sets a voltage on the input pin for however close it thinks something is. I've replicated the voltage with a couple of resistors as a voltage divider, the controller thinks it's an IR probe. The DWC UI says its emulation of analog probing is working fine.

And defining the two speed probing is only used when A is set. If you set A2, the first probe would be fast, it would then trigger, back off to the dive height, and then probe again at the slower speed.

Yup, certainly seems that way.

Annnnnyways... would be nice if there was an option for G1 to receive an interrupt in order to slow down ahead of an end stop.

fcwilt

@thekm said in Slow down before endstop?:

And defining the two speed probing is only used when A is set. If you set A2, the first probe would be fast, it would then trigger, back off to the dive height, and then probe again at the slower speed.

So even having two speeds doesn't solve the problem of the abrupt stop?

Frederick

theKM

@sinned6915 ...the voltage divider worked just fine, values in DWC showed it, could set the threshold to trigger and such, it showed it triggering, not a problem.

What didn't work though, was the "G38.2" working as you said it would. It only ever moves at the slower configured feedrate and is stopped dead by the probe.

theKM

@fcwilt ...From phaedrux's confirmation, it will slow for subsequent probes, but that's only after the first probe at the faster rate... which is move, trigger, dead stop, back up a little, go slow until trigger. It looks like it's just what the normal endstop homing does but it's all just baked into one gcode like with a specified probe count.

From everything I've seen, the duet only knows how to interrupt a move with a hard stop... I'd love to be proven otherwise

Think I'll just move on. I'm hacking up the UI so the movement panel is more configurable so it's easier to get to custom macro buttons that can park the machine in known places, near home, etc. Then it can just be homed slowly, as well as handy buttons for fixtures and such.

Phaedrux

@thekm said in Slow down before endstop?:

From everything I've seen, the duet only knows how to interrupt a move with a hard stop... I'd love to be proven otherwise

You're not wrong. It would be a feature request. It has been discussed before for CNCs, so this isn't the first time it's come up. From what I understand it's not trivial. But it is on the wishlist.

droftarts

@thekm The slow down when using an analogue probe (like the IR probe) no longer happens in RRF 3.3 and later (and only works with Z probing afaik). Instead M558 allows the fast then slow probing. See under 'New features' here https://github.com/Duet3D/RepRapFirmware/wiki/Changelog-RRF-3.x#reprapfirmware-33

• M558 now accepts either one or two F values, e.g. F1000:300. If two values are provided, then when executing a G30 command with no P parameter an additional probe using the first speed will first be done to establish the approximate Z=0 position, followed by one or more probes (controlled by the A parameter) to establish Z=0 more precisely.
• When using an analog Z probe, the probing speed is no longer reduced when the probe is close to triggering. Use the new M558 facility to do fast-then-slow probing instead, if necessary.

Also, not relevant here, but the IR probe is always in digital mode on Duet 3, because of the permanent pullup resistor. On Duet 2 it can be run in analog mode.

Ian