Anycubic Kobra neo/go dual Z mod

Required hardware:

1 - NEMA 17 stepper motor (try and get one that's the same height as the original motor 34 mm. if you use one that's too tall it might interfere with the x-end-idler bracket when you try to home the Z)

1 - motor splitter board and cable

1 - 8 mm dia. * 2 mm pitch * 8 mm lead acme lead screw (I think the one you need for full Z height is 350 mm long. Mine looks short because I just used one that I had from an old printer.)

1 - 8 mm dia. * 2 mm pitch * 8 mm lead brass lead nut

1 - 5 mm x 8 mm motor shaft coupler

2 - M5*40 bolts (you can get away with M5*35; that was what i had lying around. but the bolt isn't long enough to engage the nyloc part of the nut.)

6 - M3*10 bolts (4 of these goes in the lead nut, 2 goes in the stepper motor bracket and into the stepper motor)

2 - M3*14 bolts (these goes in the motor bracket)

6 - M3 nuts (4 of these goes on the bolts through the lead nut. 2 of these go inside the motor bracket together with the m3*14 bolts exerts pressure on the gantry post to secure the motor bracket.)

Notes:

"x-end-idler z bracket" prints with 2 spacers. these spacers go on the M5 bolts as seen in the picture.

the way the motor bracket goes into the gantry post is you put the “hooked side” in diagonally with the round corners facing the edges of the rail, then twist the bracket into place so that it is horizontal.

Installation is pretty self explanatory from looking at the pictures.

There's a convenient spot to mount your motor splitter board inside the electronics enclosure, but the cable that comes with it ends up not long enough. I had to improvise and couple two of them together.

Don't forget to give the motors a little more juice by adjusting the Vref on the Z axis.

For reference, before I adjusted the trimpot i measured the stock Z axis Vref to be 0.798 V. I have no idea what the value of Rsense is on this board. I can't find any documentation on this TriGorilla Gen_V3.0.6 so I just played it safe.

Usually, if you double the motors being driven on the driver, you double the current and therefore Vref, but I ended up adjusting it up to 1.093 V (i was trying to get to 1.1) then tested it. it went up and down fine and i didn't observe any skipped steps so i just left it at that. If anyone has a better way of doing it or has information on what drivers are under those heat sinks and what Rsense value these are, please share.

Startup Precautions:

I recommend leaving out the lead screw when first testing the motor. make sure both z motors are turning in the same direction before installing the lead screw and tightening the grub screw in the coupler.

remember to re-level the x-axis against the print bed. it should be easier now as you only need to hold one z coupler still while turning the other by hand to adjust it. after that you'll need to redo the auto-leveling procedure and set your z-offset.

Jan 15 2023 edit: added “* 8 mm lead” to lead screw description. 8 mm lead means for every revolution of the screw the nut goes up/down 8 mm. added "5 mm x 8 mm motor shaft coupler" sorry for the omission. 

Sep 28 2023 edit: uploaded original .dwg file of z-motor-bracket.