Anyone using servo motors with custom controller?

Two years ago when I pre-ordered the 1F I didn’t know much about CNC. I still don’t. But I spent the last two years of my life building a system to be as perfect as I can.

In my job, I am forced to do things “good enough.” I need to have something in my life I can try to make perfect.

So I find out that the Buildbotics controller converts arcs to line segments. In another thread I learned there is a max deviations setting that must be set every time you boot the CNC. This may solve the issue? I don’t know.

I understand that 1F builds this to be a hobby machine and has to keep the price reasonable. When I bought it I researched the hardware and that is what sold me. It never occured to me that the controller would be so… well, limited. I just wished they offered an upgrade to the controller to begin with… I would have gladly paid the extra. But I was ignorant and didn’t discover this somewhat disheartening limitation until I spent countless hours over two years. Live and learn. I did end up with a nice size work-bench if I move the gantry to the back. (wink)

So I am trying to learn from my purchase mistake and get sound advice… if I decide to sink more money and time into this thing and upgrade.

I have read about people using the Acorn controllers. Has anyone gone the extra step and added the servo motors?

Also, it seems that these controllers use physical limit switches for homing. Do they not work with - I think it is called - “stall homing” like the 1F? That is one thing I do like about the current setup; no physical switches.

Thanks… and please forgive my ignorance.

I believe Jason Stewart on the FB group has the Acorn and a while back purchased Teknic servos.
I am not sure how far he has gotten in the build - he has not posted updates in a while so probably busy with work.
I am happy with my Masso controller. I am using steppers, although I had upgraded those from the stock 1F. I will be sharing my progress soon for those interested, as I am nearly finished my ATC upgrade.


Excellent! I would love to read about your upgrade!

Maybe JS will post here. (No FB for me.)

Hey Ziggy,

you asked about using servo motors with custom controllers, however I know something about using them with the Buildbotics controller. The new Buildbotics Controller version has an additional 15-pin auxiliary I/O port which provides access to the motor enable, step, and direction inputs to the motor drivers. These lines provide the ability to bypass the internal motor drivers and control external drivers.

There was one user interested in using third-party servo drivers who reported having done that and used these external Closed-loop Stepper Drivers on the Buildbotics controller. For this, it was needed to modify the Buildbotics controller to lead the points mentioned above (step{X,Y,Z,A}, dir{X,Y,Z,A}, motor enable, fault) in the circuit out. A description of the project that user made can be found here. Finally the new Buildbotics Controller has the onboard connectors J1 and J2 on pcb / J1 and J2 on the schematics now which lead the circuit points out to the 15-pin auxiliary I/O port for connection of external stepper drivers.

You may ask, will this work with the Onefinity Controller, which is a hardware fork of the Buildbotics controller? Well the points in the circuit are there, at the inputs of the internal DRV8711 stepper drivers, however unlike on the Buildbotics, they are not led out. If you have the confidence to solder with an SMD soldering tip and to wire your own 15-pin auxiliary I/O port, like the user mentioned above did with the Buildbotics controller, then it would work. Note that the pcb layout of the Onefinity Controller (v4 (power rocker switch version), v5 (power push-button, self-powering off version)) differs from the Buildbotics controller’s pcb layout.

Further video watching

Precision motion control: ODrive Servo? Trinamic Stepper? Chinese Hybrid?

I always enjoy Marco R’s mix of offbeat humour and technical savvy. Thank you for the link :smiley:

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Aiph5u… Thanks! It is late now but I plan on going through your links tomorrow.

I might still be a newbie at CNC but I am a veteran at SMD soldering and have even just bought a new precision hot air system. (This is part of what I do for a living.)

Again, I haven’t read the links… but would making these changes to the BB controller somehow mitigate the Arc to line segment bugaboo that has me so bummed?

(I ruined a piece of wood I have been saving for a long time because of this.)

I upgraded from a Chinese CNC controller (which in and of itself wasn’t bad at all), to an Acorn, and really love it. I was originally hesitant to have a PC in the shop, but I’m really happy with the setup now.

It is not configured for stall homing (neither was my previous controller), but I manually home it and it works well for me. So far I’m not motivated enough to install limit switches.

I also recently looked into Clearpath servo motors. It’s tempting, but it’s also a huge cost justification and I’m not completely convinced it would really do that much for me. My machine is already as accurate as I need it to be with the steppers & very conservative feedrates.


Thanks Bill! Nice setup! When you mean you manually home does it just mean that you manually move X,Y, and Z to the 0 position?

What happens if there is a programming error and something tells an axis to go past its limit? Does it just grind against the end stop? Is there some sort of current sensing that will stop the program?

I have learned a bit from this thread already! For instance, I now understand that there are closed loop stepper motors that would be a nice compromise between the stock 1F motors and Servo motors.

I think the 1F motors are NEMA 23 so I did a bit of looking.

I found these: I have no idea if they would be the right “horsepower.”

Amazon link - Stepper Motors

Here is the Centroid Acorn controller. Is this the one that you use?

Acorn CNC controller

Finally, here is another question stemming from my ignorance: This controller is 4 axis. The 1F is 3 axis but uses 4 motors. Would I have to use all 4 axis of the CNC controller for each motor? Or could one axis from the controller drive two motor drivers leaving one axis free for future expansion?

Thanks again for all your help. I may start putting a shopping list together. I have invested too much to be stymied at this point.

I will first try the settings in the BB controller… but the explanation above about being underpowered and making compromises doesn’t sound like the BB controller will be a good long term fit. I get that I am just a beginner and should learn on what I have… but frankly I am getting old and wood is expensive. I don’t want to waste too much more time or wood.

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Oh… I forgot to ask…

Are you using the stock motors with the Acorn? Are you able to buy just motor drivers for these?

I see that closed loop would require a lot more wiring and this would probably mean my drag chain system wouldn’t be big enough.

I know that @Aiph5u, who is a skilled and devoted curator of information on this site, will be able to provide links to the various threads discussing this. I know there are pros and cons to doing this.

I specifically purchased the 5 axis version of the Masso controller to leave a dedicated axis ‘A’ axis for my planned rotary upgrades. I made a tangential knife and it worked for that prototype. I needed both Y axes to have their own driver and proximity sensor to take advantage of my controllers auto squaring feature. I am not sure how that would work on the BB or Acorn if you were relying on one driver to output the same Step/Dir signals simultaneously to two connected steppers.

There are also electrical issues to consider, as was noted in another topic:

Towards the end of the reading you will find reference to the BB manual that discusses wiring and stepper/driver amperage considerations.

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Hey Ziggy, hey Tom, hey all,

Gladly at your service :slight_smile:


The Acorn can work with servo drivers, but is not servo aware. This means the drivers do the compensation, with controller unaware of it happening. That can allow for discrepancies to creep into motion until the problem is corrected. A closed loop servo based controller is another step up from an Acorn controller.

Acorn is itself a huge step up from buildbotics, the arc processing being a big one. I am assembling an Acorn for my onefinity, and also upgraded my steppers to much more powerful models. The new drivers run at 48 volts vs the 36 of the stock controller, which increases available torque on each stepper. My non-air conditioned shop is limiting progress, along with being down with COVID for a few weeks. I will share more info on Facebook group in time.

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No, the step and direction signals would continue to be lines, not arcs. That is a function of the control software. I don’t think the Pi has the horsepower to keep up.

On my Acorn which is a 4 axis controller I wires one axis to two drivers for Y axis, leaving the 4th for a rotary A axis. This config means I must use manual squaring, but that is simple with the Onefinity. If someone has no desire to add an A axis, then each Y driver could be on its own axis and the Acorn could be configured to self square.

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I look forward to reading about your experience with Masso vs. the stock controller and especially your ATC upgrade.

Thank you. I have only read about the stock controller from users here in the forum, but am very pleased with the Masso controller and the team behind it. I am just installing the retractable tool rack cover I built, and will share my build update soon for those interested.


I will be very interested.

Hey Ziggy! Please forgive my slow response to these questions, I just now saw them.

I’ve actually got a recent update on how I home the machine with the Acorn. I used to move it close to home, kill motor power, then manually move the machine to the stops. Then power motors on and set home. However, I’ve discovered that I can actually do my own stall homing. Now, instead of killing motor power, I toggle the jog mode to slow (turtle/hare icon in the center of the jog arrow cluster) then just bump the machine up to the stops & set home.

The Acorn (as well as the DDCS controller) have soft limits, so once home is set the soft limits will dutifully keep the machine from hitting any hard stops. Like the Buildbotics controller, I have to rehome after a power cycle with the Acorn. This was not the case with the DDCS controller, it would store both machine & work coordinates when powered down. Of course if the machine was manually moved from it’s last power-on position, these coordinates would no longer be any good.

I recently stumbled upon the topic of servo motors with battery backed up encoders so even when powered off any movement would be recorded, yet another rabbit hole for me to go explore :wink:


That sounds very interesting! :sunglasses: