Grbl clone axis

Hi, I’m sure I’m not dreaming this but I’m sure I read somewhere that it is possible to basically clone an axis to enable two stepper motors to run on separate drivers on the same axis.

Essentially I have a 3 axis grbl controller with 1 driver for each axis. I would like to use this on a cnc laser with just an X axis and two Y axis with two separate motors on the Y.

Is there a way in Grbl to alter config.h to enable this?

many thanks.

Have you read through the configuration file comments for anything about setting up the Z axis as a 2nd Y axis output? They tend to document that configuration quite well.

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Never thought of that Doug, I find GitHub a difficult place to navigate :wink:

I found these two lines in the latest Grbl issue.
// #define ENABLE_DUAL_AXIS // Default disabled. Uncomment to enable.

#define DUAL_AXIS_SELECT X_AXIS // Must be either X_AXIS or Y_AXIS

I’m guessing if I uncomment the UNABLE_DUAL_AXIS and then change DUAL_AXIS_SELECT X_AXIS to:

DUAL_AXIS_SELECT Y_AXIS then when I plug my second Y axis motor into the Z axis everything will synchronise properly?

That is what I would think is meant by dual axis but I’m surprised it does not mention anywhere what the dual axis was going to drive for the 2nd axis. ie it should have stated if X_AXIS then the X and Y axis motors will drive as X, if Y_AXIS then the Y and Z axis will drive as Y.

BTW, I would not be messing with github to look at the configuration file. Didn’t you clone the repository to your local system… That is where I’d be looking through the config file for hints in the comments.

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Hi Doug, I understand what you mean but I couldn’t find anything more explicit in it’s directions.

I never mess about with anyone’s stuff, I downloaded the latest build to my laptop and will alter it there before loading up through Arduino IDE.


If you use separate stepper drivers, you can just connect two drivers to the step/dir pins of one axes.


Hi Caludio, doesn’t that involve soldering though? I was looking for a simpler solution, for me at any rate (zero soldering skills).

It depends what board you have, but yes, mostly it needs soldering or some prototyping cables.

@dougl I like to encourage everyone to be kind here. I agree soldering isn’t a hugely difficult skill for most folks to pick up, but no real need to laugh out loud at those who don’t know that yet… :confused:

will delete. My Richard comes out when people want others to do more for them than they will do for themselves.

Guess I must have missed something. Wasn’t expecting anyone to do anything for me other than confirm or comment on what I thought was an acceptable solution for someone with no soldering skills, who has tried repeatedly to master it, and still cannot.
Never mind.

Understood, not everyone finds the same skills easy. Sorry this conversation went a little off the rails. :grin:

It doesn’t have to include soldering. Usually you don’t want to solder cables to pin header connectors anyway; crimping is better. Additionally, if you are using external drivers, many of them have screw connectors and you can daisy-chain them. If you are using screw connectors, you want to protect the wires with “bootlace ferrules” to protect the delicate wire strands from being cut by the screws. I bought this:

It’s also possible to drive two motors with one stepper driver, though there are tradeoffs. Do you know about the possibility and the tradeoffs?

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Hi Michael and thanks for the reply. Large paws and arthritis disqualify me from delicate work, such is life.
I wondered regarding the ‘stacking’ of driver modules, i.e. the ones that slot into a conventional control board, whether or not there was enough pin sticking up to attach anything to as my first thought was to use an ‘intermediate strip’ (can’t remember the exact definition, header pin connector?) between them.
I’m looking at using integral drivers as regards the standalone variety to use on say a cnc with two Y axis motors, or a cnc laser with a heavy carriage on the same axis requiring a fair chunk of current that one driver will not provide.

Now if my understanding of the situation is incorrect then someone please correct me, that’s why I’m asking the questions.

Regards, laurence

No, you can’t just stack them; at least, as I understand your question. I don’t know what board you are using though.

With arthritis causing trouble soldering, unlikely that the delicate work of cutting and bodging traces would work. Slaving axes in software is clearly better for you!

Are you aware of the new work being done on grblHAL? I haven’t checked whether they have implemented slaving axes there, but it’s where the future of grbl seems to be happening right now, as far as I can tell.

Hi Michael. As Dirty Harry once said “A man has to know his limitations”, hence the coding approach :wink:

I haven’t examined GrblHal, tbh the board(s) I was looking at are only 16 bit and my understanding is Grbl Hal is 32 bit so wasn’t sure they were compatible.

I’ll still check it out though, thank you.

32-bit boards are cheap these days. I’d suggest taking another look, because they really open up so many more options. This is especially true when it comes to solving problems in software instead of hardware. It’s not just grblHAL; most of the interesting firmware development today is happening on 32-bit controllers, most of which are based on ARM.

Hi Michael, yes I’ve been considering the 32 bit boards although since Brexit/Covid we in the UK are having shortages and prices seem to be increasing exponentially!
Definitely on the list of things to buy though!

many thanks.

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