More stepper motors

Im learning about CNC and ran across an question I cant find an answer to… What is the maximum number of stepper motors you can independently control? From what Ive seen, the SKR Pro can control 6, but that seems to be the limit.

Is there a way to chain controllers together? Expand them somehow?

Im mostly asking just for general information, but I have seen things already that use 7+ motors…like a cross gantry 3D Printer that uses 4 to drive the X and Y (similar to the mpcnc) and then 3 more for the table (Z Axis).

Thanks for helping me learn!


In theory, the limit is the limit of your processing power. Ignoring infrastructure issues, pitch the SKR Pro, get yourself a nice, beefy linux box with a couple of multi-port ethernet cards in it, then hook those up to some Mesa Enternet breakout boards, and connect them up with standalone stepper/servo drivers. Drive the whole shebang with LinuxCNC and you’ve got an N-Axis, industrial grade CNC controller. It’ll even slave different motors together for you and everything.

But that’s not really what you’re asking, is it? :wink:

You can chain at least two, if not three motors together in series from one driver. They aren’t driven independently, but if you’re using them both for the same axis, it’s not that big of a deal, as long as you have a hard stop available to always start your machine from. That’s what V1 users were doing (and still do, for the most part) before dual endstops became possible. As far as chaining controllers, I don’t know how much, if any, work has been done along those lines. Maybe some custom software…

The printer you describe could (and probably is) driven with no more than 5 drivers. I expect the X and Y are squared via hard stops at start-up and the three Z motors are used for bed leveling. And it might be run with just three drivers, with all three Z motors in series (or parallel [ugh!]).

Many of those many driver printers are driven by a duet. There is a duet expansion board with more drivers and there is a higher level comms protocol between them.

Biqu/BigTreeTech/whatever the actual company is has also come out with a board called the GTR that is very similar to the Duet with the expansion

Wow I just did a search in the Marlin code and the BTT GTR that Heath mentioned is the only one to support 11 axes: X, Y, Z, and 8 extruders E0 through E7. Looking into it, I have to say it’s pretty interesting in the huge number of peripherals.

In principle any of the RAMPS pins could be devoted to extra axes, by defining the pins (3 pins per axis). I don’t know what would actually happen if you plugged in 5 drivers on RAMPS and wired up 6 more externally, but it could probably be made to work. Beyond 8 extruders (E0-E7) would need more extensive changes to Marlin.

I think you can also do many axis with klipper. You can essentially add ramps boards on different usb ports.

Your point about “any RAMPS pin could be devoted to extra axes” has always intrigued me. I’ve really wanted to set up a multi color printer inexpensively (like basically not going prusa with an MMU2 unit, more like kraken or diamond head). Half motivated for the fun of figuring it out and half because I really really want to print a 3D Settlers of Catan board (it’s on thingiverse and it looks amazeballs).

The GTR board started to make me think I could do it with 4 colors fairly inexpensively, like not jumping to duet basically. But the thought of taking a cheap ramps board and just starting to re-assign pins until it did what I wanted was very intriguing to me. I always felt like it should be reasonable, as far as I can tell from the circuitry diagrams and actual examination of the board most of the pins for the motor controls in a ramps board aren’t much different than any of the auxiliary pins in the board. You could always just wire those pins over to a breakout “cnc” board and it should work in theory. Never got there, and now I have purchased a cheap 3 into 1 type nozzle that I really want to get started on (I procured a cheap Geeetech printer that I think I want to fix up and get this setup going on).

Also seriously considering starting a YouTube channel to document that journey because there seems to be so little info out there on how to get to multi-color (more than 2 really) printing. I think it might be interesting to a lot of people especially if I can get there fairly inexpensively.

More extruders need more than just more drives. They also need mosfets for heaters and thermistors for temp sensing. Ok. Just two more, so 5 pins per extruder. But they need to be PWM capable.

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That’s a good point, I had forgotten about the heaters and thermistors. I guess it depends what style of multi-material extruder. There is definitely a limitation on mosfets and maybe a limitation on analog-capable pins.

I’m still waiting for someone (else) to do a true mixing extruder with the six base colors needed, CYMKWT (Cyan, Yellow, Magenta, Black, White and Transparent)… I believe it’d not be too hard to fire up a board with the 9 needed drivers.

Pia Taubert is mentioned by name on the page for Marlin’s 6-channel mixing feature
And his dissertation contains a design (although it’s not a product) for a 6-channel mixer

I’ve always thought that design could be improved by putting the throats at an angle to the mixing chamber instead of perpendicular. With the design shown the process of pushing the filament doesn’t help much in generating the pressure to move molten plastic out of the nozzle. The design as is is a lot easier to create since you don’t have to have a fifth axis to CNC the part out.

Agreed that you need more than just extruder stepper control, thermistors mosfets and such are also important, so like you said PWM needed. You would need to make sure you are pinned up enough in PWM to make it all happen. Never did make it far enough to actually get going on trying it all but it always intrigued me.

If you’re running 1 nozzle with multiple inputs like a mixer though the need for heat control is reduced to what all boards are capable of. 3 into 1’s seem to be plentiful and are fairly cheap (I think I paid like $40 for the on sitting on my shelf), but it isn’t super common in the community really or at least it isn’t super well documented. My opinion there for sure, but tutorials and stuff aren’t super easy to come by.

i know this is an old post but i thought it might be relevant that now there is the BTT GTR board, with expander it has 11 stepper drivers including 8 heat pins and 8 fan pins. so get to designing the full color mod i would love to try it out!

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Forget about BTT GTR. All termal ports on M5 expansion board have terrible filtering and therefore that much jittering, that there´s no way to have additional extruders on that extension board - it´s useable only for 2 to 4 Z motors and 1 to 2 x motors.

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Interesting to know that, sad because it is really the only alternative to the Duet and expansion.

Maybe they will get a software update to move the PID to the expansion board and then the loop will be tighter.