Duet WiFi & dual Z motors

Upgrading my Z1 (Anet A8 clone) with a Duet WiFi, some new steppers and other bits.

So far have got X & Y homing OK but struggling with Z axis, but still working that out myself but may be back for some help if I still struggle.

Main question though is in regards to the dual Z stepper motors, when homing X or Y it moves the Z axis slightly by the motors don't seem to move together, one moves then the other resulting in a very clunky / grindy movement flexing the X axis, when finished however it is back to straight, is this normal?

With the cheapie shipped board they moved together but know the duet runs them in series would this cause that? (Probably a very stupid question but done very little research on the difference)

So far as I know there should be no difference at all in the motor behavior when they are wired in series versus parallel.

Parallel connection is typical for RAMPS boards. The Duet is wired serial, but the same pulses should reach both motors.

Are you running your Duet on 12V? It may be having some trouble getting enough voltage for 2 motors in series.

Solution #1: re-wire the motors in parallel, and increase the Duet's output current.

Solution #2: use the E1 driver as a second Z axis motor driver. (This is actually kind of cool, as it allows you to adjust the motor leveling in software.) I'm doing this.

Solution #3: upgrade your PSU to 24V.

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MBot3D Printer
MakerBot clone Kit from Amazon
Added heated bed.

Leadscrew self-built printer (in progress)
Duet Wifi, Precision Piezo parts

Thanks, certainly didn't look or sound healthy but wanted to double check.

I am running in 12v (24v on the list), it is an uprated power supply though and only 0.9amp motors so supprised it wouldn't be able to power them, but on that note when I set everything up through configurator I did put current down as 900ma, should I have doubled this for the 2 motors?

Don't double the current, that's the advantage to the serial wiring, is that the same current goes to both motors.

That's also the problem with serial wiring. The load (resistance) gets doubled, so 12V might not provide enough push to get both motors moving.

Parallel wiring halves the resistance, but requires double the current. This is why it would probably work well as a solution.

As I said, I'm using the E1 driver to drive the second Z motor. They move in unison (Except right after a certain probe move where they can adjust independently to auto-level the X gantry to the print bed.) It works nicely, and could be a good solution for you, even if you don't use the auto-level function.

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MBot3D Printer
MakerBot clone Kit from Amazon
Added heated bed.

Leadscrew self-built printer (in progress)
Duet Wifi, Precision Piezo parts

This is what is happening... [youtu.be]

Moving down seems OK (but noisy), I'll have a look at using E1 until I can get a 24v supply, leveling the gantry would be a benefit as well.

To use the E1 motor as a second Z:

Reinstall the jumpers on the second Z motor output, and plug the second Z motor into the E1 position.

In your config.g:

...
; Custom Configuration
M584 X0 Y1 Z2:4 E3                 ; Set Z motors on drives 2 and 4
M671 X-43.0:309.0 Y137.5:137.5 S4  ; Set the Z motor relative locations

...

Nothing else should need changing. Note that the X coordinates for the leadscrews has a negative value for the right side lead screw, this is okay, it's used so that the firmware knows how far apart the leadscrews are. the Y coordinate is arbitrary, since it's not actually connected to the bed, so I just used a halfway point on my bed (275mm) for consistency with the bed.g file. This tells the firmware that the screws are at -43,137.5 and at 309,137.5, which is fine even if the X carriage can only go from 0 to 220, it doesn't have to move as far as the actual coordinates.

bed.g looks like:

; bed.g
; called to perform automatic bed compensation via G32
;
; generated by RepRapFirmware Configuration Tool on Tue Jun 26 2018 20:51:43 GMT-0600 (Mountain Daylight Time)
M561 ; clear any bed transform
; Probe the bed at 2 points between the leadscrews
G30 P0 X35.0 Y137.5 H0 Z-99999
G30 P1 X185.0 Y137.5 H0 Z-99999 S2

|The P0/P1 tell the firmware that they're 2 positions used for levelling, and the S2 tells it to adjust the 2 motors. (you would use P0/P1/P2 and S3 if you had 3 Z motors for complete bed levelling.)

I've been told (and experimetation proves it true) that the Duet will make some simplifying assumptions, and it's best to run this a few times, and the correction factor/error should reduce each time. bed.g is run each time you press the "Bed compensation" button in the DWC. I run it 3 times or so when I take the leadscrews or carriage out. Probably a good idea to run it once per time that you power down. Running independant leadscrews like this, the motors will want to stop on a full step, which might get them out of sync. So far, I've been tweaking the hardware on my printer a lot, so it gets run more often than I hope it will eventually need.

This will draw more current from your power supply to power 2 Z motors, but that shouldn't be a problem.

Edited 1 time(s). Last edit at 09/27/2018 05:21PM by SupraGuy.

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MBot3D Printer
MakerBot clone Kit from Amazon
Added heated bed.

Leadscrew self-built printer (in progress)
Duet Wifi, Precision Piezo parts

Cheers will give that a try.

Went to do the changes this morning and as I was editing config.g noticed my steps per MM for Z axis seemed a bit high, looks like I added an extra 0 changed that and moving as they should be Now got to decide what I want more dual extrusion on gantry levelling, but for now that works so on to next thing.

Edited 1 time(s). Last edit at 09/28/2018 06:00AM by Via.

[Edit: being an idiot, ignore this]

Edited 2 time(s). Last edit at 09/28/2018 06:00AM by Via.

Holy crap, thank you for posting this! I was two minutes from wiring my motors in parallel to try and figure it out.

I'd say 4000 steps/mm was a bit high.

400 working much nicer.

Edited 1 time(s). Last edit at 03/17/2019 11:25AM by Gurry87.