TMC2130 stallguard2 as touch probe?

Does anyone know just how much force is required to kick in stallguard2 on the TMC2130's? If the force is something that's "safe" for the nozzle to tap on the bed, why not wire up the steppers to act as a touch-probe? I found an old reference to this but it wasn't really fully answered:

[github.com]

I believe dc42 is busy developing such an endstop replacement strategy. The key is to reduce stepper current while homing to reduce forces when the carrier bumps into the frame. If it is precise enough to be used as z-probe is the question.

Sensorless homing is already working on delta printers using the built-in TMC2660 drivers on Duet WiFi/Duet Ethernet electronics. The homing is only accurate to +/- 1 full step at best, however a single round of auto calibration taking about 20 seconds will correct for that inaccuracy. Of course, you need a Z probe for that. See [duet3d.com] for the details.

Stall detection is not a substitute for a Z probe because the resolution is not sufficient.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

It seems that there is a challenge inherent in this, low inductance stepper motors are recommended for better high speed performance with 24v and on a delta if you don't want to go at least a little fast, why build a delta? But high inductance motors trigger stallguard 2 more reliably ie offer a bigger tuning window so you get more reliable detection.

I plan to try it on my next machine which I want to be as experimental as possible, specifying medium inductance motors, I'll home the towers with low motor current set in my homedelta.g file against hard stops,using stall guard.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

Stall detection for sensorless homing isn't difficult, because you can choose the homing speed to be in the optimal range for stall detection, and you can also reduce the motor current during homing. The motors on my delta are rated at 1.68A and have about 4mH inductance. It wasn't difficult to find suitable stall detection parameters.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Encouraging. Thank you I use those same motors currently.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

I tried stall detection on my compact carrier Delta with 1.7A steppers. At first I couldn't find a setting that homes well and later doesn't spit out tons of stall warnings.
I had to modify the homeDelta.g file and add a M915 line in the end to reduce sensitivity and switch filter on. Now it works reliable.

The sensitivity window is pretty small: I had a lucky punch with S5, but then tried S6 and S4 and both failed.

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o_lampe
I tried stall detection on my compact carrier Delta with 1.7A steppers. At first I couldn't find a setting that homes well and later doesn't spit out tons of stall warnings.
I had to modify the homeDelta.g file and add a M915 line in the end to reduce sensitivity and switch filter on. Now it works reliable.

The sensitivity window is pretty small: I had a lucky punch with S5, but then tried S6 and S4 and both failed.

Increasing the minimum speed for stall detection (M915 H parameter) widens the window, but then of course there is a greater risk of missing stalls at low printing speeds.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

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dc42

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o_lampe
I tried stall detection on my compact carrier Delta with 1.7A steppers. At first I couldn't find a setting that homes well and later doesn't spit out tons of stall warnings.
I had to modify the homeDelta.g file and add a M915 line in the end to reduce sensitivity and switch filter on. Now it works reliable.

The sensitivity window is pretty small: I had a lucky punch with S5, but then tried S6 and S4 and both failed.

Increasing the minimum speed for stall detection (M915 H parameter) widens the window, but then of course there is a greater risk of missing stalls at low printing speeds.

Maybe there can be multiple settings depending on how detection needs to work: endstop, bed-level, and obstruction. The sensitivity can be set as needed during the different operations.

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The sensitivity can be set as needed during the different operations.

I tried to set sensitivity while I got so many warnings reported, but sending M915 Sxxx didn't work. I guess, I have to send M915 X Y Z Sxxx instead?
Or would that cause the other parameters to fall back to their default values?

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o_lampe

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The sensitivity can be set as needed during the different operations.

I tried to set sensitivity while I got so many warnings reported, but sending M915 Sxxx didn't work. I guess, I have to send M915 X Y Z Sxxx instead?
Or would that cause the other parameters to fall back to their default values?

You must always provide either axis names or driver numbers in the M915 command so that the firmware knows which motors you are talking about. You can use different parameters for each motor.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].