On a printer which uses two or more Z motors to raise/lower the bed or gantry, you can have the firmware probe the bed and adjust the motors individually to eliminate tilt. This feature is implemented in RepRapFirmware version 1.19 and later.
A valid M671 command enables auto calibration of the Z motors. When you run G32 to perform bed probing, the final G30 command (the one with the S parameter) in bed.g will then cause auto calibration to be performed. The auto calibration uses a least squares algorithm that minimises the sum of the height errors. The deviation before and expected deviation after calibration is reported.
If you have two Z motors, the calibration process adjusts the bed tilt along a line between the two leadscrew positions, on the assumption that the tilt at right angles to this will not change. With three motors, it adjusts the tilt in both directions. With four motors, it adjusts the tilt in both directions and also the twist. You should not use 4 leadscrews with a bed that is rigid enough to resist twisting strongly.
You can run G32 again to repeat the process if you wish.
If your bed is not perfectly flat or the gantry sags a little when the head is over the middle of the bed, the process will cause a small shift in the Z=0 position. To correct this, if you are using the Z probe to do Z homing, you can just re-home Z at the end of your bed.g file.
... M584 X0 Y1 Z2:4 E3; two Z motors connected to driver 2 (left motor) and driver 4 (right motor) M671 X-20:220 Y0:0 S0.5 ; position of leadscrew/bed pivot point at left and right of X axis M208 X-5:205 Y0:200 ; X carriage moves from -5 to 205, Y bed goes from 0 to 200 ...
G28 ; home G30 P0 X20 Y100 Z-99999 ; probe near a leadscrew, half way along Y axis G30 P1 X180 Y100 Z-99999 S2 ; probe near a leadscrew and calibrate 2 motors
... M584 X0 Y1 Z2:5:6 E4; three Z motors connected to driver 2 (front left), driver 5 (rear middle) and driver 6 (front right) M671 X-15:100:215 Y-10:190:-10 S0.5 ; position of leadscrew/bed pivot point at front left, rear middle and front right M208 X-5:205 Y0:200 ; X carriage moves from -5 to 205, Y bed goes from 0 to 200 ...
G28 ; home G30 P0 X20 Y20 Z-99999 ; probe near a leadscrew G30 P1 X100 Y180 Z-99999 ; probe near a leadscrew G30 P2 X180 Y20 Z-99999 S3 ; probe near a leadscrew and calibrate 3 motors
... M584 X0 Y1 Z2:3:4:5 E6; four Z motors connected to driver 2 (front left), driver 3 (rear left), driver 4 (rear right) and driver 5 (front right) M671 X-15:-15:215:215 Y-10:190:190:-10 S0.5 ; position of leadscrew/bed pivot point at front left, rear left, rear right and front right M208 X-5:205 Y0:200 ; X carriage moves from -5 to 205, Y bed goes from 0 to 200 ...
G28 ; home G30 P0 X20 Y20 Z-99999 ; probe near a leadscrew G30 P1 X20 Y180 Z-99999 ; probe near a leadscrew G30 P2 X180 Y180 Z-99999 ; probe near a leadscrew G30 P3 X180 Y20 Z-99999 S4 ; probe near a leadscrew and calibrate 4 motors
VERY IMPORTANT! Assigning a drive using M584 does not remove its old assignment. Therefore, if you assign a drive that defaults to being an extruder drive, you should also assign the extruder drives explicitly as in the above example. Failure to do so may result in unexpected behaviour.
See Gcode wiki entry for M584.
If you have an axis with more than one motor (doesn't have to be Z, can be X, Y or any other multi-motor axis), with each motor connected to a separate motor driver on the Duet, and each motor has an associated endstop, you can home each motor individually to level the axis.
In RepRapFirmware 3, you do not need to split the axes to level them, as you do in RRF2. The firmware understands if you define the axis endstops correctly. For example, if you have a dual motor Z axis, with endstops at the axis minimum, define the Z endstop in config.g as follows:
M574 Z1 S1 P"zstop+e1stop" ; configure active-high endstops for low end on Z via pins zstop and e1stop
Make sure that the two endstops are defined in the same order in the M574 command as the corresponding Z motors in your M584 command. For the example above, M584 Z2:4 would be correct, assuming one Z motor is plugged into driver 2 (Z driver on Duet 2) and its endstop is plugged into zstop, while the second Z motor is plugged into driver 4 (E1 driver on Duet 2) and its endstop is plugged into the E1 endstop pins.
When homing, RRF3 will home both axes, and stop each motor when each endstop is triggered. Note that DWC and M119 will only show one endstop per axis, but will show the axis endstop as triggered if either switch is triggered. So you can test them by triggering one at a time.
See below for an example of Z axis levelling in RepRapFirmware 2.x, on Duet 2. This can be applied to other axes, if necessary.
See the wiring diagram for your Duet board for motor connections.
; Relative positioning G91 ; Lift Z without endstop protection G1 S2 Z2 F6000 ; Course home X and Y G1 X-215 Y-215 F4200 S1 ; Move away from the endstops G1 X5 Y5 F6000 ; Fine home X and Y G1 X-215 Y-215 F360 S1 M98 Phomez.g
M208 X0 Y0 Z0 U0 S1 ; Set axis minima M208 X210 Y210 Z200 U200 S0 ; Set axis maxima ;DUAL Z M584 X0 Y1 Z2:3 U3 E4 P3 ; Endstops M574 X1 Y1 Z1 U1 S0 ; Set active low endstops M558 P0 X0 Y0 Z0 H2 F60 T6000 ; Set Z probe type to switch, the axes for which it is used and the dive height + speeds G31 P600 X0 Y0 Z0 ; Set Z probe trigger value, offset and trigger height M557 X15:195 Y15:195 S20 ; Define mesh grid ; Drives M569 P0 S1 ; Drive 0 goes forwards M569 P1 S0 ; Drive 1 goes backwards M569 P2 S1 ; Drive 2 goes forwards M569 P3 S1 ; Drive 3 goes forwards M569 P4 S1 ; Drive 4 goes forwards M350 X64 Y64 Z64 U64 E16:16 I1 ; Configure microstepping with interpolation M92 X320 Y320 Z1600 U1600 E92.6; Set steps per mm M566 X600 Y600 Z12:12 U12 E300:300 ; Set maximum instantaneous speed changes (mm/min) M203 X30000 Y30000 Z1200 U1200 E1800:1800 ; Set maximum speeds (mm/min) M201 X2500 Y2500 Z500 U500 E3000:3000 ; Set accelerations (mm/s^2) M906 X1000 Y1000 Z800 U800 E1000:1000 I50 ; Set motor currents (mA) and motor idle factor in per cent M84 S2 ; Set idle timeout
; Lift Z relatively to current position G91 G1 S2 Z2 F6000 ; split Z motor control to Z and U ; for it to work we have to show U (param P4) in the UI M584 Z2 U3 P4 ; Move Z and U down until the switches triggers G1 S1 Z-205 U-205 F1000 ; back to combined axes and hidden U M584 Z2:3 P3 ; Back to absolute positioning G90 ; Tell the firmware where we are G92 Z0 ; lift Z after probing, without endstop protection G91 G1 S2 Z10 F1000 G90