4 Z Motor Gantry levelling

Adamfilip

I have a custom machine that has similar motion to that of a Voron 2, fixed bed with XY Gantry moving in Z
I have 4 Z motors one for each corner

I am doing Gantry tramming using "Bed levelling using multiple independant Z motors"
https://docs.duet3d.com/User_manual/Connecting_hardware/Z_probe_auto_levelling

It works but Im finding that I need to run it 3-4 times before its really gets level.
was hoping to tune it to get it closer on the first shot.

the Pivit points where the Z belts are, are fairly far away from.
Also the Pivot is raised up higher in Z from the top of the nozzle

M558 P8 C"!^zprobe.in" H10 F200 60 T5000 A1 S0.05    ; K0 for probe 0, P5 for NC switch, C for input pin,
G31 K0 P500 X0 Y0 Z-2.4      		; CHECK for LOOSE things first! set Z probe trigger tap
M671 x-65:-65:375:375 Y-105:435:435:-105 S40  ;tap

bed sequence

G90
;G4 P250

;M561			; Clear any bed transform
G30 P0 X25 Y15 Z-99999 ; probe near a leadscrew
G30 P1 X25 Y250 Z-99999 ; probe near a leadscrew
G30 P2 X265 Y250 Z-99999 ; probe near a leadscrew
G30 P3 X265 Y15 Z-99999 S4 ; probe near a leadscrew and calibrate 4 motors

Video of my printer probing
https://www.youtube.com/watch?v=Oj3F1VG-WbY

TLAS

@Adamfilip
When I was looking at the design for my latest printer, I read in the documentation that 4 z-motors are not recommended. Something about a twisting motion for calibration causing errors and not being reliable. 3 motors is greater than 4 when it comes to calibration.

I highly recommend taking a look at the z-motors page.

Adamfilip

@TLAS Yes I also read/heard that 3 points of articulation is better (delta) but with Moving Gantry its more difficult to achieve.. a moving bed on three points is easier as bed is rigid. it would be a major redesign of the machine. not something im motivated to do

Phaedrux

4 endstops in a set position to get it very close in one move? Make them optical so they can be passed through and easily tweaked.

jay_s_uk

@Adamfilip if its anything like the voron then gantry may drop more in one corner than the others.
Best is to use the iteration feature to probe the bed as many times as required to get it level.
We have an example using iteration here https://teamgloomy.github.io/useful_macros.html

oliof

Also, the frame (including bed mount) and the gantry need to be square to avoid skew errors from either the belt runs or the gantry.

Your drawings don't show how the bed is installed either, I will assume it's a fixed bed mount (no springs etc).

Adamfilip

@oliof Bed is hard mounted and very ridgid, no flex, frame is very stiff with reinforced steel corners,
verticals are 40x40 Extrusion and rest is a mix of 20x40 and 20x20. Using Exoslides for motion on XYZ. its very solid.

@jay_s_uk Z motor are Exoslide Worm gears, so gantry does not drop when power is off.

@Phaedrux the idea of an endstop per is a good one and im considering it if i have enough ports remaining

Here is a video showing the build/setup of my machine,.ignore the background noise.. my laundry dryer is running lol

https://www.youtube.com/watch?v=Lxkx0YHlETc

dc42

@Adamfilip said in 4 Z Motor Gantry levelling:

Bed is hard mounted and very ridgid, no flex, frame is very stiff with reinforced steel corners,

The combination of 4 leadscrews and a very rigid bed is over-constrained, because it only takes 3 points to define a plane. The use of 4 leadscrew bed levelling is appropriate when the bed is less rigid so that it can twist a little.

Adamfilip

@dc42 bed is not moving. just XY gantry received the levelling. and the gantry is not that ridgid

Adamfilip

@Phaedrux now I need to figure out how to Home Z the Gantry to 4 endstops first and then still use Z probe for general Z homing and Mesh generation

dc42

@Adamfilip said in 4 Z Motor Gantry levelling:

@dc42 bed is not moving. just XY gantry received the levelling. and the gantry is not that ridgid

OK, then 4-leadscrew levelling should be usable. Can you try running G32 several times in succession and posting the output here? I would like to see how the corrections change with repeated runs.

Adamfilip

@dc42 i run a macro for gantry levelling
this is the code

G90
G30 P0 X25 Y15 Z-99999 ; probe near a leadscrew
G30 P1 X25 Y250 Z-99999 ; probe near a leadscrew
G30 P2 X265 Y250 Z-99999 ; probe near a leadscrew
G30 P3 X265 Y15 Z-99999 S4 ; probe near a leadscrew and calibrate 4 motors

this is the result

Adamfilip

When I run G32 nothing happens

jumpedwithbothfeet

@Adamfilip you need to put your macro into bed.g for G32 to run I believe

dc42

@Adamfilip G32 runs file bed.g. It's OK to run a different macro explicitly instead.

It looks to me that your macro converges well after two iterations, because the corrections made the in third iteration are small. So I suggest you use a while-loop to execute those G30 commands twice. No need to mess with multiple endstops.

Phaedrux

@Adamfilip said in 4 Z Motor Gantry levelling:

@Phaedrux now I need to figure out how to Home Z the Gantry to 4 endstops first and then still use Z probe for general Z homing and Mesh generation

If you have the endstops available, you need to use M574 to create a Z endstop and use all 4 pins with + between them. Make sure the order of the endstops matches the order of the drivers in M584. Then home Z normally with a G1 H1 Z move. Each motor will move until its corresponding endstop is triggered.

Example here: https://docs.duet3d.com/en/User_manual/Connecting_hardware/Z_probe_auto_levelling#axis-levelling-using-endstops

You can then follow that up with a G32 to use the probe to do any fine correction if you think that is needed.