Dual Z Steppers - vrefs & is 1 or 2 LV8729 drivers better with 1.7map nema 17s (17HS4401)


First post here… so I guess I should start with a “Hi everyone!”…

tldr: With two 1.7amp nema 17 steppers driving my Z axis, is it better to use 1 or 2 drivers? And should I go for the LV8729s or the TMC2208s I have? If not 2 seperate steppers, how do I calculate the vref?

I’ve recently added a second Z lead screw to my printer, I brought 2 matching nema 17’s that, according to the advert, are rated at 1.7amp their part no is 17hs4401. I was using them with a single TCM2208, and have prepared both a parallel and series connection for them. I started with the parallel connection and confirmed it was working mechanically, and moving smoothly, etc. printed a marvin, wow - the results were soooo much better than my single lead screw…

However, I forgot to tweak the vrefs and, during the next print, the stepper for the Z died. In the process of identifying the cause and working through the rest of the drivers I also managed to short my MKS Gen L board. Now the USB isn’t working and the no matter what combination of drivers and steppers I use I can’t get either of the extruder channels to work.

So I’ve order a replacement board, as the 32bit SKRs v1.3 are only 3/4 “moneys” more than the MKS Gen L, I’ve opted for this. If I’m right I can set the vref using the firmware, and not the potentiometers.

Before I make the same mistake again, what are people’s opinion on the use of Dual Z with 2 steppers, is it better to use a seperate driver for each?

If I only use the one, how do I calculate the vref?

Also, I’ve read some notes on the TMC2208’s specification that state a max current of 1.4 amps. As these “17hs4401” steppers are rated at 1.7 amp, does this mean I shouldn’t use these steppers with the 2208s?

Anything else I should consider when swapping out a board?

I’m planning to use the LVs as I have enough, but I still have a couple of spare 2208’s that have always been good to me, on X & Y at least! So I’m considering using these on X & Y still.

Many thanks, and sorry it’s long!

Hi andrewscott,

Welcome to the forum. When I built my Dolly (mk2 clone), I used TMC2130s for x and y, since they are always running and I wanted to keep the noise down. My dual z-steppers are still running on one A4988. It was just easier to wire. As for the vref, I really didn’t worry too much about it: I kept lowering it until I started to skip steps, then turned it up a little from there.

TMCs current can be set from the firmware; my x and y are both set at 0.8. Keep in mind that your Nemas can draw more than the driver can provide, but it should never reach this level in this use case.

Lastly, if you are going to adjust your drivers with the power on, use a non-metallic screwdriver! :wink: