Motor stall detection as Z probe
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I'm going to try on my 1.5m delta as well, I will probably probe each print since so far most of my prints take forever anyway so why not.
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I have implemented this as Z probe type 10 in the latest build of firmware 2.0alpha. I've a few more things to test and at least one thing to fix before I do another 2.0alpha release.
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This would probably not work very well on deltas. If you use 5mm pitch screw with 0.9 degree stepper on Z axis, each full step is only 0.0125mm.
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@shen said in Motor stall detection as Z probe:
This would probably not work very well on deltas. If you use 5mm pitch screw with 0.9 degree stepper on Z axis, each full step is only 0.0125mm.
That's right, it will only work when the Z steps/mm is high enough so that one full step provides sufficient resolution, but low enough that the motor stall can be detected before too much force is applied between the nozzle and the bed.
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Oops must have followed a link and forgot, was referring to endstop not probe. Have smart Effector for probing.
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It works fine for endstops, but because it is not very accurate, and I can confirm this having an endstop-less delta running, you need to auto-calibrate after each homing or you will not have an accurate enough calibration to print. Not a particularly big problem, but it highlights that it won't work for most deltas as a z-probe. My cylinder delta is 400steps/mm as it is leadscrew driven on XYZ but this is still only a 40-microns-accuracy z probe which is a good factor of 4-8 out on a smart effector or piezo probe.
Simon. Precision Piezo Z-Probe Technology
www.precisionpiezo.co.uk
PT1000 cartridge sensors NOW IN, just attach to your Duet board directly! -
@djdemond said in Motor stall detection as Z probe:
It works fine for endstops, but because it is not very accurate, and I can confirm this having an endstop-less delta running, you need to auto-calibrate after each homing or you will not have an accurate enough calibration to print. Not a particularly big problem, but it highlights that it won't work for most deltas as a z-probe. My cylinder delta is 400steps/mm as it is leadscrew driven on XYZ but this is still only a 40-microns-accuracy z probe which is a good factor of 4-8 out on a smart effector or piezo probe.
Yeah I'm excited to try out the smart effector, my arms finally arriving today. 500mm from Haydn. Do you have your calibrate script for endstop less? I definitely don't mind probing each print.
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@mysta said in Motor stall detection as Z probe:
Yeah I'm excited to try out the smart effector, my arms finally arriving today. 500mm from Haydn. Do you have your calibrate script for endstop less? I definitely don't mind probing each print.
For a script to home a delta without endstops, see the example macro file towards the end of https://duet3d.dozuki.com/Wiki/Stall_detection_and_sensorless_homing#Section_Configuring_sensorless_homing. This file is for testing homing without endstops. For actual use as a homing file you could simplify it. For example, you don't need the M574 commands to change the endstop type because you can just set stall detect endstops in config.g if that's the only type of endstop you ever use.
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Thanks, I'll start from there. I left the endstops on my frame just in case but I'm really interested in using some of the new functionality of the 2660
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In firmware 2.0beta 1 you can now set Z probe type 10 in the M558 command, which selects a Z motor stall-detect probe. As I explained previously, this will only work if your Z steps/mm is high enough for 1 motor full step to provide sufficient resolution, and if you can find a combination of M915 stall detect settings and motor current that you can detect the stall before the Z motor drives the nozzle too hard into the bed.
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M80 ;PSU ON
; Homing file for RepRapFirmware on Large Kossel
; Sensorless Homing test file for RepRapFirmware on Kossel
M915 X Y Z S2 F1 R0 ;set stall detect drives, S-threshold (-64 to 63), F1 filtered, R-log only
M400 ; make sure everything has stopped before we make changes
M574 X2 Y2 Z2 S3 ; set endstops to use motor stall
M913 X30 Y30 Z30 ; reduce motor current to 50% to prevent belts slipping
G91 ; use relative positioning
G1 S1 X700 Y700 Z700 F2000 ; move all carriages up 700mm, stopping at the endstops
G1 Z-5 F2000 ; down a few mm so that we can centre the head
G90 ; back to absolute positioning
M400 ; make sure everything has stopped before we reset the motor currents
M913 X100 Y100 Z100 ; motor currents back to normal
G1 X0 Y0 F2000 ; centre the head and set a reasonable feed rate
M574 X2 Y2 Z2 S1 ; set endstops back to normal so that homedelta.g worksYou just need to experiment with M915 R to get the threshold right.
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I like experimenting and would like to give this a go. I am building a corexy, with 3200steps/mm on Z with1/16th microstepping. I could also go for a 0.9 stepper motor and get 6400 steps/mm at 1/16th or 3200 at 1/8th, or 1600 at 1/4 and so on.
With a 1.8 stepper, accuracy would be 0.005
With a 0.9 stepper, accuracy would be 0.0025What would be the best choice?
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Well for Z positional accuracy at 10 microns would be fairly good, 5 microns even better, 2.5 microns is probably excessive, but then I cannot see a reason to choose 1.8 deg motor for Z, it never has to move fast.
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How about steps/mm with a 0.9degree. Is 6400 doable for the duet or should I then use 1/8th microstepping, or does this have no effect at all? And then, are there any downsides to 1/8th microstepping?
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6400 steps/mm is doable and given the very small amount of movement required in z it won't overly tax the processor. However in terms of stall detect only full steps count so 0.9 degree is preferable.
1/8th is noisier. But try it, its very interesting to see the differences in noise, speed and (if you look really hard) print quality between different microstepping modes.
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Cool, thanks!
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Hi @dc42!
I have been able to successfully autohome X, Y and Z using sensorless homing (I am working with a coreXY).
Currently I am experimenting with manual bed levelling assistant using StallGuard but I don't know how to correctly input StallGuard parameters into probing. My code is as shown below. Am I missing something?
config.g file
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M671 X111:11:211 Y14.2:194:193 P0.7
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M558 P10 X0 Y0 Z0
...bed.g file
G28
M915 Z H200 S3 F0 R1
G30 P0 X111 Y14.2 Z-99999
G30 P1 X11 Y194 Z-99999
G30 P2 X211 Y193 Z-99999 S3I have uploaded firmware 2.0 beta 2
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That looks correct to me, although you may need to adjust the probing speed (F parameter in M558) and you may also wish to adjust the travel speed between probe points (T parameter).
Getting the Z motors to stall without applying excessive force to the nozzle will be a delicate balance. You will probably need to use M913 to reduce the Z motor current temporarily.
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Thank you @dc42
The manual bed levelling assistant is working smoothly now! Great stuff!
We are looking onto the possibility of implementing fully automated bed levelling using 5V servomotors. Is it possible to connect them to the original duet wifi board. If so, where should we connect them?
Thanks, good job
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If the servomotors have stepper motor style step/dir/enable inputs then you can connect them to the expansion connector.
