Inconsistent Z distance movement

[RaymondS]

Hi All,

VID_20211026_225032.mp4

Just upgraded my CR-10S Pro v2 with the Duet 3 mini 5+ and linear rails. So, new to the Duet game.

My Z movement is not consistent and cannot figure out why. New lead Screws, backlash Nuts, everything is tight.

https://youtu.be/sXt5mdn_cKc (Just in case video is not viewable)

Any suggestions as to where to start looking

[PCR]

@raymonds please Post your config.g

[RaymondS]

@pcr

config.g

Hope I am doing this correctly

[PCR]

@raymonds your M906 Z current is only 500 amps

please increase it to 1000

[PCR]

@raymonds and there is a Typo

M584 X0.0 Y0.1 Z0.2:3 E0.4

Should Look Like this

M584 X0.0 Y0.1 Z0.2:0.3 E0.4

[RaymondS]

@pcr

Will try again at 1000, but last time it was this high I could fry eggs on it...

Will make correction on M584 as well. Thanks

[PCR]

@raymonds you can Play with the M906. Think your Main Problem was the M584

[PCR]

@pcr keep in mind that 1000ma in RRF are 707ma in Marlin or Klipper

[RaymondS]

@pcr
Made the changes, still not consistent. Motors are very hot on the touch.

But think I will replace the lead screws first as I think this Teflon coat could possibly be a problem in that I don't know if it is consistent (I bent the originals by mistake and ordered these) I don't have confidence in them as I had to remove some of the coatings just to get them into the coupler... (as you can see in the pic) So coating might also not be consistent up to the top of the screw.

Even though the picture might make the spacing look wrong, the spacing is correct and doesn't bind when moving up or down. But they are tighter through the backlash nuts than in comparison with the normal lead screw.

Thanks for the help. But think I should just go back.... Too many parts upgraded in a single move makes it hard to troubleshoot.

[engikeneer]

@raymonds I haven't downloaded your config (on mobile), but maybe your Z accel and jerk settings or speeds are a bit too high for your setup? Might be worth reducing them a bit and seeing if it helps.

I assume you've checked the grub screws etc for any mechanical slippage

Also, might be worth removing the antibacklash nut. Unless your z accel is greater than 9810mm/s, you won't be outrunning gravity so the antibacklash won't get you much other than extra friction!

[RaymondS]

@engikeneer Thanks for the input. Appreciated.

I did not think the acceleration and jerk would affect the absolute positioning of the Z, only the quality of the filament had been layed down in a specific movement. So expected 100% same movement distance all the time. All settings for M566 and M201 are standard (as per the online configuration tool - don't recall changing anything here). As for M203, I did up the max speeds but did not know this could change the absolute position, I will reduce this again and see what happens.

As for grub screws, I have triple checked this including alignment (making sure of no binding). This was my initial thought of the problem.

I think the next item post slowing down max speed is to remove the backlash nuts and run another set of tests. Going to follow a very slow and iterative change now so that I can see what is causing which issue (have another but first trying to get E-Steps dialed in correctly).

I have noticed that when changing direction (down to up and also up to down movements), that within the first 1mm you always seem to lose +/- 0.20. Is this normal?

; Drives
M569 P0.0 S0                                 ; physical drive 0.0 goes backwards
M569 P0.1 S0                                 ; physical drive 0.1 goes backwards
M569 P0.2 S1                                 ; physical drive 0.2 goes backwards
M569 P0.3 S1                                 ; physical drive 0.3 goes backwards
M569 P0.4 S0                                 ; physical drive 0.4 goes backwards
M584 X0.0 Y0.1 Z0.2:0.3 E0.4                 ; set drive mapping
M350 X16 Y16 Z16 E16 I1                      ; configure microstepping with interpolation
M92 X80.15 Y80.15 Z400.00 E387.10            ; set steps per mm
M566 X900.00 Y900.00 Z60.00 E120.00          ; set maximum instantaneous speed changes (mm/min)
M203 X16000.00 Y16000.00 Z6000.00 E1200.00   ; set maximum speeds (mm/min)
M201 X500.00 Y500.00 Z20.00 E250.00          ; set accelerations (mm/s^2)
M906 X800 Y800 Z1000 E800 I30                ; set motor currents (mA) and motor idle factor in per cent
M84 S30                                      ; Set idle timeout

[engikeneer]

@raymonds that sounds like you are losing steps when the axis is accelerating and changing direction (I.e. because your acceleration/jerk is too high). If you command it to accelerate too fast and it doesn't have enough torque/power the motor will lose steps. It will think it had moved 100mm, but will have actually moves less. In direction changes you have to do double the amount of acceleration (I.e. decelerate, then accelerate again) so you are more likely to see missed steps than in a normal move

[rjenkinsgb]

Looking at the photo, could the spacer pillars that link the ballnut mount to the linear slide be flexing slightly?

The near spacer in the photo looks to have a twist in it.

I'd try it with power off and the digital vernier over one screw, turning the motor very slowly each way by hand and see if the motion follows exactly or not.

The spacers may work better as tall blocks rather than just tubes, so it's impossible for them to rock.