General question about the Duet (off Topic ?)

Hi,
I did a search for Duet on all forums and as Ormerod forum was main area I thought I would as my question here. I am a newbie Ormerod owner (just did my first own design and print yesterday) but I have been playing around with CNC stuff for a few years. Before buying the Ormerod I had been thinking of moving away from a PC base for my other stuff, so I was looking a linuxcnc on BeagleBoneBlack ( I have a BBB plus output board running linuxcnc, again bleeding edge development at present) . However after using the Duet + software for a few days I think I am beginning to prefer it to linuxcnc, because like 3D printing my other stuff uses a very small subset of gcode (unlike linuxcnc which is all encompassing). Also the code base for the firmware is reasonably small and manageable unlike linuxcnc (at least to me ).

I do not want to get into, or start, a which is the best software argument, my question is hardware related. The steppers on my other setup are Nema 23s and I use M325s (now old hat) at 24V max current 2.5 amps to drive them. Will the Duet card handle that loading?. Can someone point me in the direction of a data sheet for the Duet, I looked on the think3dprint3d site but could not see anything in the way of technical documentation. If I bought a Duet could I drive it just from 5v and connect its motor output pins to my M325s would that work or does the card need 12v . If the Duet is thought to be overkill , can the Firmware run either on the BBB or on a Due board connected to some form of breakout board?


All wisdom gratefully accepted.

Alan

(Ormerod 291 )

The Duet uses A4982 stepper drivers, datasheet at [www.farnell.com]. They can handle 2A in theory, but that is probably with better heatsinking than they have on the Duet. 24V is no problem, the Duet board can handle 35V. Duet board details are at [github.com].

---

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

If you want to use your existing drivers, then you would need a board which uses stepper modules like RAMPS or has breakout headers, so you can bypass the onboard drivers. I guess you could find spare pins on the Duet expansion header and change the firmware to use pins those to send signals to the external drivers.

Using external drivers like M325 have other issues, like 3.3V compatibility (they are usually 5V logic) and if they have optos you may need to extend the pulse time for Step signal. It can be done, people use the common TB6560 drivers with RepRap type boards.

Probably any RepRap type board can be made to drive external drivers with some tinkering, there isn't quite an off the shelf solution yet.

If you don't want to get involved in writing firmware It might be a good place to start with exactly what subset of Gcode you need, for example most printer firmwares don't have arc support, which you might expect, as well as coolant, spindle control etc. The GRBL firmware is more oriented towards CNC. Once you have the firmware chosen, find out what it will run on.

---

What is Open Source?
What is Open Source Hardware?
Open Source in a nutshell: the Four Freedoms
CC BY-NC is not an Open Source license

Thanks for the information on extruder expansion boards the EXT4 would fit the bill but not sure what processor board its an expansion too. Am I to assume a standard arduino Due header?

My rose engine is not a standard engineering mill and it is used only to cut patterns on wood, so do not need stuff such as coolant, spindle etc, really just want to control 3 or 4 steppers. I am aiming for a mixed manual / cnc setup where I just use the steppers to control the movement of the headstock so do not even need arc moves or canned cycles, its really quite a simple application thats why a full cnc system is overkill.

I would be happy to use a Due + expansion board and write some firmware or even a Yun but not sure that would be powerful enough. Connecting the drivers directly to the 3.3v gpio outputs I thought would be a bit worrysome so thats why I was looking for some type of expansion card. I am happy soldering simple circuits but do not know anything about pcb layout or manufacture.

Alan

Do you definitely need to run the stepper motors at 2.5A?

---

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

I do not really know as I never put an ammeter on them when they where running but probably not as OT systems such as mine only take very light cuts so I guess I could try them out at 1 amp see if everything worked out ok.

Alan

Stepper motor drivers normally work in constant current mode, so the current will be whatever the stepper driver board is set to. You may be able to run the Duet stepper drivers at 1.5A if you use a small fan to cool the board.

---

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Quote
alanbattersby
Thanks for the information on extruder expansion boards the EXT4 would fit the bill but not sure what processor board its an expansion too. Am I to assume a standard arduino Due header?

My rose engine is not a standard engineering mill and it is used only to cut patterns on wood, so do not need stuff such as coolant, spindle etc, really just want to control 3 or 4 steppers. I am aiming for a mixed manual / cnc setup where I just use the steppers to control the movement of the headstock so do not even need arc moves or canned cycles, its really quite a simple application thats why a full cnc system is overkill.

Sorry, the EXT4 etc is just my standard signature. EXT4 is a general purpose expansion board designed for Pololu stepper drivers, so would not really help you in this case

I think there is a good chance that you can run your Nema23's direct from Duet, if the motors don't need the full 2.5A. I'm not sure what the max current limit on the Due is. My printer has small Nema23's, and runs happily off the same A4982 drivers as the Duet. Powering the Duet from 24V should also help. Adding small heatsinks to the chips helps a little, and fan cooling helps a lot.

I would suggest trying it to see if it works ok, if you can find a friend to borrow one!

If it doesn't work, it will require some hardware/software tinkering to get it to work with the M325s. A safer option might be an Arduino + RAMPS, you can get these very cheaply and several people already use these with external drivers.

---

What is Open Source?
What is Open Source Hardware?
Open Source in a nutshell: the Four Freedoms
CC BY-NC is not an Open Source license

Thanks bobc,

I equipped the enclosures holding the 325's with fans running off 24v, so when I change things over I can use those anyway. I would feel happier not using the duet on my Ormerod for testing, so would the Ormerod firmware work on a due board with a little rewriting of pin assignments etc ?

Alan

The Ormerod firmware should work on the Arduino Due if you add the appropriate extra hardware, or modify the firmware not to need it.

---

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

The Duet software should in principle run on the Due, you might have to chop out stuff to do with SD card, ethernet etc.

If you run on a Due with external drivers though, it would make more sense to use a Due shield like RADDS or RAMPS-FD, as you don't need the drivers, and you can get access to the header pins easily. (Also could be a lot cheaper). You will still need to address the issue of level conversion and pulse timing whether you are using a Due or Duet.

When I get round to it, I will try building the Duet firmware and adapting it for RAMPS-FD. I am also planning an easy header board for external drivers which handles level conversion.

---

What is Open Source?
What is Open Source Hardware?
Open Source in a nutshell: the Four Freedoms
CC BY-NC is not an Open Source license

Hi,
i bought a duet and i'm going to test the pibot 6600 stepper driver. The input is optocoupled so no problem for 3.3 v protection.
Andy