This is in reference to the query here: https://forum.duet3d.com/topic/31427/moving-an-actuator-as-a-zprobe-instead-of-the-entire-axis?_=1678019622288

When attempting to implement the aforementioned, on changing the assignment for the z-axis the motors de-energize which results in the gantry (80+ Kgs) falling.
Is there any way to keep the drivers enabled when the motor assignment for the Z axis is changed?
If I were using external drivers this could easily have been done using the enable pin, is there a way to control the enable of the driver and not the axis?

@dc42 Setting Z=0, mesh probing, and bed leveling.
I tried the mentioned flow but the motors de-energize when changing assignments which results in lost steps.

@o_lampe Oo that's neat and would solve the issue. Thanks.
I just checked the schematics. All the enable inputs seem to be tied to a single pulled-up line from the MCU.

I'll try this out as soon as I get a chance. Thanks again.

@deckingman I apologize if my description was confusing.
I will fix the gantry falling by replacing the gearboxes so the gantry falling when power is lost isn't an issue.

The problem is only when reassigning the axes while the machine is powered on do the motors lose energy. Now the axis won't fall when that happens even if the motors are not energized, but since it'll be probing the weight is going to be shifting and I would like to have no lost steps.
And since it's an industrial environment I can't rely purely on the worm gears when probing hence it's important that the motors are energized.

TL;DR: What happens when power is lost is not the concern here, but keeping the motors energized while probing is.

@deckingman I'm not using leadscrews, I've made a custom chain + sprocket assembly that the gantry runs up and down on.
There's a 10:1 worm gearbox between the sprocket and motor. I figured a worm gearbox would not be back-driven but I seem to have selected a lower ratio than required. My current solution to that is to switch the sprockets to smaller-diameter ones or switch the gearboxes to a higher ratio.
I'm leaning toward the latter.

Even still assuming the gantry doesn't fall down, I'd like for it to be rock solid in place when the entire actuator-based leveling happens which takes us back to the previous issues.

P.S.: The mounts are only printed to test and will be CNC'd later on.

@Phaedrux It would be very expensive for me to swap the motors or attach brakes to the same. As a last resort, I'd much rather move to external drivers since an enable pin would solve all my issues, but to do that I'd have to buy a 6XD or 4 1XD boards which would result in about the same price so yeah still quite expensive. And either way would result in more points of failure.

And since this is something that possibly could be done in software, I'd much rather do that.

@o_lampe @deckingman The post-processing solution might just work but will need to figure out how variables work here better.
I've tried out the 3-way swap and ran into an issue, I'll walk through the current flow:

1. Home the printer with Z motors assigned to Z
2. Assign all the Z motors to U and do a relative G1 H2 U0.1 move right after to energize the motors.
3. Assign the actuator to Z and probe the bed.

The problems with the current flow are as follows:

1. When doing the G1 H2 U0.1 move after the reassignment to energize the motors there's a slight period where the motors are not energized and the gantry falls just a bit before they are. The falling is a problem, to begin with, but energizing the motors while it's falling would result in massive back emf.
2. Right now I'm without the actuator logic this is what I'm using to level the bed:

G30 P0 X180 Y310 Z-99999 ; probe near a leadscrew fl
G30 P1 X180 Y1160 Z-99999 ; probe near a leadscrew
G30 P2 X1190 Y310 Z-99999 ; probe near a leadscrew 
G30 P3 X1190 Y1160 Z-99999 S4; probe near a leadscrew and calibrate 4 motors

The issue is with the last line, since executing the gantry leveling is automatic at the last line which does not give me a chance to remap the 4 Z motors to Z.
Is there any way to split the execution of the leveling from the last line (S4)

@deckingman That's interesting and I'll certainly give it a try just to mess around, but it's not applicable here because assuming it works it'd move all the motors simultaneously or none at all whereas the purpose is to move 4 motors for Z when printing and otherwise and use an actuator on the extruder for leveling.
So mapping 4 motors for Z and mapping actuator for Z and U probably will result in the entire axis moving with the actuator on any Z command.

This is in reference to the query here: https://forum.duet3d.com/topic/31427/moving-an-actuator-as-a-zprobe-instead-of-the-entire-axis?_=1678019622288

When attempting to implement the aforementioned, on changing the assignment for the z-axis the motors de-energize which results in the gantry (80+ Kgs) falling.
Is there any way to keep the drivers enabled when the motor assignment for the Z axis is changed?
If I were using external drivers this could easily have been done using the enable pin, is there a way to control the enable of the driver and not the axis?

@DrDFlo @o_lampe
"I am upgrading to a 12 mm high-helix lead screw for faster travels at lower RPMs, but I am limited here by the c-beam aluminum extrusion profile"

Why not go with a rack and pinion setup?
I am coincidentally making a very similar printer with the same extruder.
The differences are as follows:

1. Integrated servos instead of steppers for X and Y (Stepperonline iSV-T motors)
2. Using chains and custom sprockets for Z.
3. Modded the MDPH2 with a RTD pt1000 as a failsafe for the terrible grounded thermocouple on the extruder (Probably going to replace that too )
4. the X and Y motors use a 1:5 Planetary gearbox and connect to 1.5 module pinions that travel on racks. There's no backlash, it's smooth and it's really fast.
5. It's bigger.

Hello,
Would it be possible to map an actuator with a stepper as the Z probe with a switch on end rather than only deploying the Z probe and moving the entire Gantry up and down?
My gantry weighs almost 100 Kg so I'd like to minimize the Z motion as much as possible.
I was thinking something along the lines of:

1. Map the actuator as a separate axis and home the actuator zero with an end-stop on the actuator.
2. Move the extruder to the probe point and remap the Z to the actuator.
3. Retract the actuator till another switch or sensor (which is mapped as a Z probe) at the bottom end of it touches the bed and the actuator moves back up again.
4. Remap the Z back to the Z motors.

This seems doable as an alternative, but is there any inbuilt functionality in the Z probing setup that I could use here?