@bot regarding the pressure inside the melt chamber:
The new e3d Hermera extruder can push filament with up to 10ish kg (100N).
1,75mm Filament has a cross section of roughly 2,4mm^2.

100N / 2,4mm^2 = 40N/mm^2

Hence the pressure inside the hotend can't exceed 40N/mm^2 = 40MN/m^2 = 40MPa = 400bar

This is the maximum pressure based on the design of the gearing. The NEMA17 Motor can't produce the torque to reach that pressure. There is insufficient information about the real-world pushing force of this extruder.
https://e3d-online.dozuki.com/Document/H4JSEgZEtxEsa5oE/Hemera-Datasheet-(Edition-1).pdf

If the viscocity of molten plastics in the hotend is known one could calculate the pressure needed to uphold a given materialflow through the nozzle. Such calculation can also correct for the nozzle shape and material (friction), making comparison between brass and non-stick coated nozzles possible.

BR, Marius

@bot There are also losses due to friction in the nozzle, especially with "sticky" molten plastics.
The large Volcano nozzles need some extruder torque, even though the nozzle hole is barely smaller than the 1,75mm filament.

Maybe look through data sheets of (bearing) grease. I know that greasing of bearings is done with automated pumps, to select the right pump the grease viscosity has to be known.

Maybe calculating the hotend pressure with the viscosity of thick grease gives results that are in the same ballpark as calculations for molten plastics. Sadly i didn't yet find temperature depended viscosity curves of plastics, making an accurate calculation impossible.

If you do all that in Excel or alike one could quickly change the calculation for different extrusion rates, nozzle sizes (hole and length =>volcano) , nozzle material, ...

@dc42 thanks, that's great to know. Assuming i want to use those 4-Pin IO Headers for other stuff, the PWM pin is therefore switching between a direct connection to ground and being left unconnected or does it use a pull-up? If so, to which voltage and with which resistor?

Thanks so much for the quick help!

Best,

Marius

Hi all,

admittedly, i haven't kept up to date with the forum, but as far as I can tell this issue hasn't yet been answered/solved.
I'm trying to run Noctua fans on an upcoming 3d printer using a 6XD + 3HC setup, however this equally applies to the 6HC.
As per their whitepaper all Noctua fans require the PWM pin to operate at a 5V level.

The convenient 4 pin connectors can't be used because the fan supply voltage is either +12V (internal regulator) or V_FUSED (in my case 24V). Either way the PWM pin won't operate at 5V.

Using the 5-Pin IO Modules isn't any more convenient either, as they seem to supply io[x].out with 3.3V

Additionally i couldn't find the tacho documentation (internal pull up to 3.3V? 5V? 12V? V_FUSED?) and would like to confirm, that the current and voltage is meeting the Noctua spec:

I found that deviating from their requirement with Vcc 5V for their 12V fans seems to work, as long as the current limits are observed. I have used a diode (seen in red) on a custom PCB, as there have been reports of some fan variants having an internal pull-up to ie 12V on the fan side.

I guess the best way forward for me is to consider a custom PCB to switch the +12V PWM from the fan header to +5V and keep the other pins unchanged.

As far as I can tell 5V PWM is the default for PC-fans, so having dedicated fan connectors with this one flaw is very unfortunate.

Best,

Marius

@pcr this is great!
Could you clarify, which Prusaslicer version you are using? I'm running Prusaslicer 2.2.0 and it seems to require later versions.

-Marius

@t3p3tony The LED's are controlled individually and not connected to other outputs. Mounting options for a diy'ed PCB with mosfets is very limited, hence I'll probably use the 24V heater outputs with larger resistors in series to the LEDs. The Duet is mounted directly next to a larger fan, so cooling these resistors shouldn't be a problem. Thanks for your advice!

@t3p3tony then i can't risk plugging the fan PWM directly into the expansion header. The remaining 3 PWM fans (configured to run at 5V) are intended to drive small (5mm) LEDs with around 20mA at 1,2V per LED. (one LED per fan header).

An alternative seems to be, to drive these LEDs from the expansion header at 3,3V (with an adjusted resistor in series of course) to then have available PWM fan outputs for the Noctua fan.

Can the expansion header (or rather the Microcontroller) drive two heater pins (ie heater 3 and 4) with each pin drawing 20mA (40mA in total)?

I could also use the extruder heaters H0 and H1, although I'd need a larger resistor to step down the 24V to 1,2V.
At 20mA that's nearly 0,5W heat disspation per LED, not great, not terrible.

Are there other downsides to either method, and which would you pick?

can i use pin 31 "HEATER7" of the Duet 2 Expansion header for the PWM input of a Noctua fan?
Normally the PWM signal requires 5V signal levels, however Noctua's whitepaper on the matter mentions an internal pullup to "3,3V/5V".
https://noctua.at/pub/media/wysiwyg/Noctua_PWM_specifications_white_paper.pdf
"HEATER7" is conveniently directly next to the PB6 rpm input and I have already used all 3 pwm fan connectors.
Using "HEATER7" for PWM control already works when using the Duet Expansion Breakout Board, but I'm unsure if that expansion board performs any levelshifting.

I'd be connecting directly to the expansion header and the expansion board would obstruct the PB6 rpm pin, so using that board is no option.

Thanks!

@t3p3tony my printer is intended to be a corexy, single Z-axis motor, single extruder. However lot's of addons are "in the works", so I'd tend to future-proof my machine by going with the Duet 3 6HC.
For the 6XD: are we talking 2022, 2023?

Thanks!

@stephen6309 +1
I also use it with duet 2 Ethernet, external drivers (BLDC Servos for X and Y) and as a script in Prusaslicer. I've not done extensive tests, but the prints do look smoother. Never had any issues with it.

I'm comparing the different Duet boards for use in my upcoming 3d printer. So far I've only used the Duet 2, but would be willing to upgrade to Duet 3 (6HC or Mini).
As I will be using external stepper motor drivers, I'm only concerned with the maximum step frequency for those.
afaik the Duet 3 6HC is the fastest, but offers no connections for external drivers, same with the Duet 3 Mini.
Connecting the 1XD Expansion Board limits the step frequency to the 48 MHz chip, so around 50KHz according to the wiki.
Seems like I'm left with the Duet 2 and it's Expansion Breakout Board, although I've not seen any benchmarks for the expansion board.

Am I missing something?

Which would be the best performing Duet for a 3d printer (X,Y,Z,E axis) with four external drivers?

Why is there a 1XD Expansion Board with such a low performance chip, compared to the 6HC? People, that would spend money on a 6HC, external drivers (stepper or servo in my case) surely would take a 10-20€ more expensive 1XD, if it means 5-10x the step rate.

While I'm at it: how about a 3XD to fully utilize faster chips. I'd guess there are many people, that wouldn't need just one external drive in their setup, so a 3XD could offer greater performance with the chips cost increase "spread across" mutiple axis.

Thanks!

Sources:
Benchmarks from another topic
https://forum.duet3d.com/topic/15308/what-is-the-maximum-step-rate-of-duet-3-board/8
1XD benchmarks from wiki
https://duet3d.dozuki.com/Wiki/Duet_3_Expansion_1XD

@janjoh I see. If you can't find a suitable alternative, my solution might be the least bad. You'd of course need more heater blocks, cartridges, thermistors and heatbreaks.
However I found that added cost to be insignificant, given the reliability of my method.
The most important benefit is the ability to have preassembled setups. for example:

high resolution PLA
alu heater block
0.25mm brass nozzle
30W heater
thermistor

Nylon / colorFabb HT
copper heater block
0.4mm copper nozzle
50W heater
PT100 sensor

these hotend assemblies can be mounted with one hand, just use the 7mm hex and the 0.5Nm screwdriver. Most, if not all, coldends will handle the 0.5Nm without needing a second hand.

To clarify my prior statement: the wrench is needed when you only change the nozzle, not if you change the entire hotend.