Confused. Y-Axis Motor Wiring. Reverse Both Or One Coil?

So I’m hoping someone here can clarify something.

I’m turning my old 500mm X-carve into a PNP using a Smoothie board. While wiring the Y-Axis motors, I’ve become confused.

On my other X-carve, one motor has a single pair of wires (one coil) reversed as is shown in the instructions for the older kit here:

BUT all the documentation I see on the Smoothie has BOTH pairs of wires on the Y-Axis motors reversed as is seen in this wiring diagram (it’s a bit of a scroll down, sorry):

I’ve done a fair amount of research and my understanding is you need only switch ONE coil polarity to reverse a stepper. So WHY do the 3D print folk reverse both coils? I’m pretty sure I’m missing something here, but for the life of me I can’t figure it out. Can anyone help?

I don’t think you’re missing something. You want to reverse one pair. Always test with your setup, though.
Can the Smoothie board driver output enough current for the two motors?

But why are all the smoothie diagrams showing BOTH reversed? Hmmm…

That’s a good question. It’s rated at 2A. The configuration allows me to limit the current to the driver, so I’ll be under-driving the Y motors which are rated at 1.4A each. That’s similar to the X-carve which has two 1.6A motors driven by a driver that has a max current of 2.5A so…

The PNP has no cutting head drag so I’m hoping the motors will be fine under -driven.

Got other ones showing the same? Stepper motors won’t work differently because it’s Smoothie.

EDIT: From their docs.

> If when you test it, the two motors turn in reverse, you need to reverse one of the coils of one of the stepper motors, and they will start turning in the same direction.

Thanks for digging deeper. I did see that. I have seen other documentation for the smoothie showing both coils reversed so I don’t think it’s just a single diagram mistake. I’ll look and see if I can re-find those. Most of them were 3D printing diagrams and referring to dual Z-Axes as printers don’t usually have 2 Y-axis motors.

Again, it’s the way steppers work. Smoothie isn’t doing anything magical. If it was a Z axis, they may have been spinning the same way.
I want to see your PNP machine, so just get to it! :wink:

A stepper have minimum two coils which form two pairs, A+/A- and B+/B-
To reverse rotation switch one pair, any will do :slight_smile:

This is typically required in a dual Y-setup where the steppers face opposite direction.
On my dual Y, screwdrive setup both Y´s face the same way and therefore not required.

Show us your PNP-machine if you like to :slight_smile:

Thanks for you help guys. I wired it up today, and indeed, only one coil being reversed was necessary. Not sure why the other diagrams show differently.

Because documentation is an afterthought at most companies?