Selecting the right electronics for my project

Hello everyone,

I am planning to start making a 3D printer very soon and I was wondering if more experienced users could help me deciding on the right Electronics for my project.

Basically the idea is
1/ making a powder bed binder jetting type of printer,
2/ using 5 steppers for the axis: 2x Nema17 and 2x Nema23, + 1x Nema14 + possibly a servo or other small stepper.
3/ There would be 2 heated beds to reach T° between 40°C and 150°C, one for the build plate and one underneath the powder feeding platform.
4/ with a 500watts IR heat lamp passing over the powder bed to cure the binder
5/ and some kind of inkjetting system to selectively deposit droplets of binder.

Would anyone recommend a specific microcontroller for such a 3D printer given the type of voltage/power requirements that come with using Nema23s and inkjetting and the flash memory needed for the jetting part? I am having a hard time trying to figure out what would be the best/most straightforward choice between a Taurino Power with RAMPS (which is rated for up to 35V), or a Smoothieboard, a Mega/Ultratronics, or a Arduino Due with RADDS shield which have the advantage of being 32bits...

Any suggestions appreciated!!
cheers

You left the Duet WiFi and Duet Ethernet out of your list of possible electronics - which surprises me, because they are more suitable for driving Nema 23 motors directly than the boards you did list, on account of using higher-current stepper drivers.

The requirements you list sound fairly straightforward except for the inkjetting system. Most firmwares don't support multiple bed heaters, but many support both a bed heater and a chamber heater, which covers your controlled heaters. The 500W lamp can be controlled from a fan or GPIO output via a SSR.

Are you planning to write the firmware to control the inkjetting yourself, or is there some existing firmware with this functionality that you want to use?

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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].

Thank you dc42 for your quick reply!

I didn't really know about the Duet Wifi, it seems like a good choice, but I don't really see the difference with an Arduino Due with a RADDS shield, except that Arduino Due is maybe more flexible and can be programmed within Arduino IDE while Duet does not (or can it?)

Yes I was planning to write the firmware for the inkjetting myself, with the help of more experienced users I know. So I guess I would need to make sure there is enough available pins on the controller board for hooking up the additional circuitry for the jetting...

Quote
yala
Thank you dc42 for your quick reply!

I didn't really know about the Duet Wifi, it seems like a good choice, but I don't really see the difference with an Arduino Due with a RADDS shield, except that Arduino Due is maybe more flexible and can be programmed within Arduino IDE while Duet does not (or can it?)

The main differences are:

- Duet WiFi/Ethernet have 5 properly-cooled (via the PC TMC2660 drivers on board, with up to x256 microstepping, in theory rated at 4A peak but we currently limit them to 2.4A in firmware. RADDS has 6 sockets for plug-in drivers, but you won't find plug-in drivers that can handle 2.4A.
- Duet WiFi/Ethernet give you software control of motor currents and microstepping (and even the chopper control register of the driver if you want).
- Duet WiFi/Ethernet provide the awesome Duet Web Control web interface, see [reprap.org]. Due/RADDS has no web interface.
- Duet WiFi/Ethernet use a SAM4 processor with 128K RAM and hardware single-precision floating point, running at 120MHz. Arduino Due has 96K RAM, no hardware floating point and runs at 84MHz. Both have 512kb flash.
- Duet WiFi/Ethernet has a few extra features, such as a power monitor and expandability to a total of 12 stepper drivers.
- Duet WiFi/Ethernet runs only RepRapFirmware - probably the most advanced firmware available for 3D printers. Due/RADDS can run a few different firmwares (including RepRapFirmware).

Arduino IDE is OK for novices getting started with small projects, but truly awful when it comes to serious firmware development. We use Eclipse for firmware development. See [github.com] for the source code.

HTH David

Edited 1 time(s). Last edit at 08/23/2017 11:27AM by dc42.

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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].

Hi David,

Alright you convinced me that Duet Wifi is better I don't quite need 12 stepper drivers though haha

I was told by someone else also today to forget IDE and use Gcode-based firmware such as Grbl and Marlin instead. I understand that RepRapFirmware is similar, but designed for ARM processors while grbl/Marlin are for AVR chips.
How straightforward would it be for someone knowing grbl to use Marlin or RepRapFirmware?

The phrase "forget IDE and use Gcode based firmware such as Grbl or Marlin instead" makes no sense. All the 3D printer firmwares are Gcode based. Whether an IDE is used to develop a particular firmware or not is a personal choice. I use Eclipse IDE to develop RepRapFirmware, but one of my associates uses Vim editor and a makefile to work on the same firmware.

Grbl was designed for CNC applications, not 3D printing. Grbl, Marlin and RepRapFirmware all work in much the same way, although the details are different. For example, RepRapFirmware generates the stepper motor pulses in a smooth train, whereas Marlin and Grbl use an approximation that causes pulses to be generated at irregular intervals.

Edited 1 time(s). Last edit at 08/24/2017 02:10AM by dc42.

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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].

Alright, got it! sorry for mixing things up I understand much better now thank you.
One last question on this topic: How easy would it be for a colleague who knows Grbl language perfectly to work with Marlin or RepRapfirmware?

That depends on what you mean by "Grbl language". Do you mean the gcode CNC language that Grbl accepts as input, or the programming language that Grbl is written in?

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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].

Yes the programming language it is written in, i believe it's called C sharp.

Grbl is written in C, not C#. Both RepRapFirmware and Marlin are written in C++, which is a more advanced programming language that grew out of C.

If you want to use Grbl, that's fine if your project resembles a CNC machine more than a FDM 3D printer, and you should look for a platform that runs Grbl. But if it resembles a FDM 3D printer more than a CNC machine or you need 32-bit processing power, pick a good 3D printer firmware instead. For 32-bit platforms that means RepRapFirmware or Smoothieware.

Edited 1 time(s). Last edit at 08/24/2017 06:27PM by dc42.

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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].

Alright, got it! Thank you very much Sir.

Hi, are there any ADC pin that are not assigned on the Duet Wifi or expansion boards and that I could use to connect my own circuitry?

If it's just one ADC pin you need, the simplest option is to use the ADC input on the Z probe connector. You can connect a Z probe (if you have one) to the E0 endstop connector instead.

The other ADC pins are mostly allocated to thermistor inputs, including 5 on the expansion connector. If you will be modifying the firmware then you could re-allocate them. You may need to remove the corresponding 4.7K pullup resistors.

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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].

Hi dc42, if you still have time for my questions

1) If I need a very small heated bed to reach ~100°C, something like 5x5cm for instance, powered from a 24V psu, then a 25W silicone or polyimide heater would draw only 1A at 1W/cm2 and a 100W one would draw 4A at 4W/cm2 (although that may be excessive?) So for such low power requirement I can connect the heated bed directly to the corresponding heated bed pin right?

2) You suggested earlier to wire the 500W 230V IR lamp to a fan output pin through a DC-AC SSR (e.g. Crydom D2425 I suppose, SSR-10DA is enough..) The fact that fan pins are rated for 1.5A wouldn't be an issue right?

3) If I also need a pump that runs on a 24V DC motor to run a couple of seconds when needed, can I connect it directly to another fan pin as well? Or would I be better off using a pump with a stepper and connect it to one of the extruder drivers?

Cheers!

1. Yes. I normally suggest 0.4W per sq cm, but a small bed like that one may need more.

2. Not an issue. SSR-10DA would be adequate, I use one for the bed heater on my delta printer.

3. Yes you can drive the pump from a fan output as long as the current requirement is no more than 1.5A (2A when starting is ok). Current production Duet WiFi and Duet Ethernet boards (PCB revision 1.02) have built in flyback diodes on the fan outputs so they are ok to use with brushed DC motors. If for any reason you use an older version then you need to add an external flyback diode.

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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].

Thank you!
I have a Nema 23 with holding torque 1.5 Nm rated at 3.25A can I use it with the TMC2660? I just need to set the driver to 2.4 (potentially 2.8A if it doesnt get too hot??) and that would work fine but I wouldn't get full torque right?
So if I set the drive at 2.4A, that is 2.4A / 3.25A = 74% of the motor's rated current, which gives approx. 0.74*0.707= 52% of the specified holding torque (using your method to calculate that from here)
If I could set the driver at 2.8A then I would be at 86% of the motor's rated current and thus 61% of the holding torque. Is it possible?

The current is limited in firmware to 2.4A at present, although we'll increase it some more when we have implemented standstill current reduction independently for each motor.

Stepper motors in 3D printers are normally run at between 50% and 85% of their rated current. They get very hot if you run them at full rated current.

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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].