Which Duet for a CNC?

Nightowl

I'm patiently(!) awaiting delivery of my RatRig KillerBee 1075 CNC machine and, after some research, have come to the conclusion the Duet control system is probably the best for my needs - but which one? I originally asked this question of Ooznest, when I was looking at their WorkBee, but they seemed to think the Duet 2 was perfectly adequate.

Essentially, I'm trying to decide between the Duet 2 Ethernet and the Duet 3 6HC, but I wonder if the 6HC is much more than I need. I was leaning towards this one as it's their latest board and appears to be eminently more upgradeable/configurable, but is this really necessary for a relatively standard CNC machine with an AMB milling motor that has a digital interface (Like this one here)?

As I understand it, the Duet 2 requires a PWM to voltage 0-10V converter to control on/speed/off functions of the milling motor, but is this also the case for the Duet 3?

Looking to future plans, the only advancements I might consider would be the addition of a laser and/or a 4th axis.

Oops, I forgot to add I'm using Nema 23, High Torque, 1.8degree/step, 345oz-in stepper motors and my MacBook, not a Raspberry Pi.

Thanks in advance

dc42

@nightowl999 there are a few considerations:

Duet 2 supports a maximum of 2.5A peak motor current, and needs to be well-cooled to handle that current. Duet 3 MB6HC supports a maximum of 6.3A peak.
Duet 2 has only 512kb of flash memory and RepRapFirmware 3.4 almost fills it entirely. This means that in future, Duet 2 will not be getting some of the firmware enhancements that Duet 3 gets. These enhancements are likely to include support for additional CNC-specific GCode commands.

To control the spindle motor, if it has 0-10V analog control then you will need an isolated PWM to 0-10V converter for either board. There are two designs of converter widely available on eBay, Amazon etc. but only one of them provides isolation.

Duet 3 has an output with a 5V-level PWM signal that is intended to drive a laser or PWM to 0-10V converter. With Duet 2 you can normally use a heater or fan output to drive the converter instead; however if you want to drive a laser that needs a 5V PWM signal from Duet 2 then you will probably need to add a level shifter.

HTH David

Nightowl

@dc42

Thank you, David, this helps enormously!

It looks like the Duet 3 then and an isolated PWM to 0-10V converter!

droftarts

@nightowl999 for CNC setup and notes on the 0-10V PWM board, see https://docs.duet3d.com/User_manual/Machine_configuration/Configuration_CNC

Ian

markz

@nightowl999 From someone who's done this twice...

On my Taig milling machine I built the motor system from scratch and used 4A 250oz-in motors and run it with a 6HC. This limits me to ~32VDC to drive the motors which reduces available torque (they could handle 50VDC). I'm ok with that but run my mill at slower feeds/rapids than some people. I like the all-in-one solution of the 6HC and barely use the capabilities.

On my 12sqft CNC router I did a conversion from the commercial controller (which would have cost $1,000 to upgrade to Win10) to a Duet2 Wifi. Here I used the extender card and drove the existing motor drivers from that. So it's a duet controller with 5 external drivers (2 Y and a rotary). Again it works awesomely but here I get the full torque of the 120VDC drivers. I do lose some pulse speed with the Duet2 (and ended up only 5-ustepping the screw-driven Z axis) but don't seem to miss it.

So, external drivers->Duet2, internal drivers (<=6A, 32VDC) Duet3 6HC. My 2c.

Also, I wouldn't use Ethernet nowadays. One more cable. Because the controller caches the job Wifi isn't nearly the issue as with dumb (mach3-type) controllers.

Mark

Nightowl

@markz
Ah, interesting comment about WiFi over Ethernet.

My workshop (read "garden shed") is only where the machine is ru (MS Surface Pro) and not where the design takes place (in the house on my Mac), and the wired network is extended with PowerLine adapters - which also provides an extension to my WiFi, but I hadn't really considered WiFi because of the distance. What's important is both machines can connect to my NAS drive, which is where all the design and g-code files are stored.

If this is no longer an issue I would consider WiFi, as long as I still had shared access to the NAS, but I'm not sure what benefit there would be for me.

Nightowl

@droftarts

Thank you. I've not seen that specific page before, but it certainly helps explain things for me.

I'm assuming the Duet is by default a printer controller - I wasn't aware there was any difference in the control system - so I definitely need to use the M453 command!

Is this a once-only command, or would I need to do every time I power up the controller?

Thanks

dc42

@nightowl999 said in Which Duet for a CNC?:

Is this a once-only command, or would I need to do every time I power up the controller?

You would put that command in your config.g file on the SD card, then it will be executed automatically at power up.

Nightowl

@dc42 Thank you

chernogorsky

Sorry for asking in an existing thread, but it looks like fitted (delete it otherwise)
@dc42, same question - whats the best Duet for CNC
Im starting a new project (printnc), and one of the option I'd like to check is d3.
My time estimate is in +- 2-3 months from now I'll have the mechanics, so by then I need to have some controller

Any chance that MB6XD (if I understand it correctly) be available, or its better for aiming to 6HC + 1HCL in case I want closed loop ? or even just 6HC + external drivers.

dc42

@chernogorsky if you want to use closed loop drivers then either use the 6XD and use external step-servo drivers, or you can use a Duet 3 Mini and EXP1HCL boards. Neither is completely ready yet: the 6XD won't be in production for about 2 months or more, and the EXP1HCL firmware is still in the beta test phase (but we hope to have the first stable release soon).

chernogorsky

@dc42 thanks for the reply
May i signed for alpha/beta for 6xd
I have all the experience with d2/d3 and really wanna try it. Willing to test only recommended cl drivers
Dont want put 4x1hcl and waist all internal ports

dc42

@chernogorsky I've asked for you to be added to the queue for the 6XD.

zsc100

@dc42 Is there any update to this. I also want to look at a retrofit CNC application and I need step/direction output. I really wish there were at least pads on the PCB for this even if no headers. I'm an EE so I assume I can scope/find them on the input side of the stepper drivers, but that's a PITA. Is there no one board solution as of now? If not I'll go ahead and grab the Duet3 Mini and just break out the Step/Dir myself.

jay_s_uk

@zsc100 the Duet 3 6XD is already on sale.
Other option would be an SKR3 or Fly-Super8Pro. They have standard stepstick sockets and support CAN-FD

T3P3Tony

@zsc100 I will make a forum announcement about availability through our resellers in the next few days. We are shipping out back orders this week.