Idea: "barebones" Duet3D mainboard, maybe as Pi hat

jumpedwithbothfeet

@o_lampe that is electrickery beyond my knowledge!, I don't know how many of the functions are unloaded to the Pi from the mainboard in SBC mode, does the mainboard just control the steppers and provide sensor/io/power to the connected components? if that's the case why wouldn`t it work?... either way I now have many questions to try and find answers to

o_lampe

@jumpedwithbothfeet AFAIK the Pi can't do AD-conversion, which we'd need for temp-reading and PID-based PWM, but if all that would happen on the toolboards....

jumpedwithbothfeet

@o_lampe well they have their own processors and transmit their io via canbus so....maybe?, would you be able to update/upgrade the expansion boards without a mainboard as such, in reality these are @dc42 or @chrishamm questions! maybe they can put this to bed?

gloomyandy

It might help folks to understand how the major functions are split between the SBC, RRF main board and the CAN board in a setup like this:

SBC:
Handles the web interface (wifi, networking etc.), file I/O, gcode parsing, Optionally it can handle a camera etc.

RRF Main board:
Takes a pre-parsed gcode stream, executes the gcode instructions, performs motion planning (including homing/probing moves and input shaping), handles PID control for local heaters, generates steps for local motor drivers (including pressure advance), generates CAN commands for CAN boards, generates PWM signals for local fans, handles probes, endstops and accelerometers that are attached directly.

CAN boards
Takes commands via CAN, generates steps for drivers (including pressure advance), handles PID control for local heaters, generates PWM signals for fans, handles attached probes, endstops and accelerometers.

o_lampe

@gloomyandy said in Idea: "barebones" Duet3D mainboard, maybe as Pi hat:

RRF Main board:
Takes a pre-parsed gcode stream, executes the gcode instructions, performs motion planning (including homing/probing moves and input shaping), ~~handles PID control for local heaters, generates steps for local motor drivers (including pressure advance)~~, generates CAN commands for CAN boards, ~~generates PWM signals for local fans, handles probes, endstops and accelerometers that are attached directly.~~

A few of these tasks wouldn't happen on the mainboard/PI Hat , if it only has CAN connectivity. That would safe some board space and connectors and a lot of extra copper, making it cheaper and smaller.

Simple Fan-PWM signals could be provided by the RasPi, if they're not too time critical?

jumpedwithbothfeet

@o_lampe the pwm commands would be controlled by the expansion boards via can bus I think the biggest problem would be the motion planning and issuing the can commands surely?

gloomyandy

@o_lampe Just to be clear, my post described how things are done in the current version of the firmware.

Clearly you can move things around (though I'm not sure that moving things like fan control to the rpi makes sense if motion planning remains on the RRF board as this needs to be synchronized with motion. This is particularly true with CNC or laser control).

If you move most of the control logic to the rPi you are effectively describing Klipper...

o_lampe

@gloomyandy
I understood. That's why I only mentioned Fan control. Part-cooling fan, Spindle and Laser control could be done by the toolboards.
I don't want to push RRF towards Klipper, but if it safes us money, I'm in. (I never tried Klipper, so there might be some drawbacks with their setting, too)

jumpedwithbothfeet

I for one, wouldn't want to go the klipper route either, and to get this thread back on its original track I think a stripped down Duet board either with or without an SBC would be a great idea, especially as the maestro/duet 2 is realistically no longer available or a viable choice - just my opinion mind

jay_s_uk

@jumpedwithbothfeet what's wrong with the duet 3 mini?

jay_s_uk

@jumpedwithbothfeet you could always get an SKR3. That's just as powerful as a duet 3 6HC but with a smaller footprint

jumpedwithbothfeet

@jay_s_uk nothing wrong with the mini I would happily buy one, what I`m getting at is the range of boards is effectively limited too just two boards and their variants, and both have limiting factors in use and price, I just believe there is a case for a *stripped down universal duet board that can be tailored/built up to serve either CNC/FDM or any other project by the use of expansion boards by the user, basically a modular system.

I have previously looked at other boards like the SKR but various things like the drivers have always put me off, besides that my 6HC has never let me down despite some of the stupid mistakes I've made, I`d have one in every machine I make, if I could afford it

*edited - added stripped down

sonderzug

Hi all, thank you for the lively discussion, nice to see that this idea sparks some interest.

My idea was inspired for once by all of the already available expansion boards, as well as the uprising of more unconventional machines that are built, be it for the purpose of 3D printing or not. For example, as far as I can tell, people are now also working on implementing robot motion.

I'd think that a robotic arm with 3D printing effector would greatly benefit, in terms of simplified wiring, by having the respective driver boards for each joint very close to the motor, daisy chained, with the effector (1LC toolboard) at the end. An interesting field since people are implementing "true" 3D printing path generation.

In respect to the hardware requirements of this barebone mainboard, as has been discussed above, there has to be a µC on the board but I can imagine it to be a less potent one that the one found on the 6HC or even the mini 5+.

@o_lampe said in Idea: "barebones" Duet3D mainboard, maybe as Pi hat:

@gloomyandy said in Idea: "barebones" Duet3D mainboard, maybe as Pi hat:

RRF Main board:
Takes a pre-parsed gcode stream, executes the gcode instructions, performs motion planning (including homing/probing moves and input shaping), ~~handles PID control for local heaters, generates steps for local motor drivers (including pressure advance)~~, generates CAN commands for CAN boards, ~~generates PWM signals for local fans, handles probes, endstops and accelerometers that are attached directly.~~

A few of these tasks wouldn't happen on the mainboard/PI Hat , if it only has CAN connectivity. That would safe some board space and connectors and a lot of extra copper, making it cheaper and smaller.

Simple Fan-PWM signals could be provided by the RasPi, if they're not too time critical?

o_lampe

@sonderzug said in Idea: "barebones" Duet3D mainboard, maybe as Pi hat:

here has to be a µC on the board but I can imagine it to be a less potent one that the one found on the 6HC or even the mini 5+.

There are often smaller versions of the same MCU available, with less IO pins. As long as it has the same amount of RAM it would be ideal.
The barebone would also need less copper, since there are no drivers onboard.
It probably could be fed from the Raspberry and wouldn't need all the voltage converters?

T3P3Tony

@sonderzug et al

We have been considering a SAME70 CAN-FD control board designed to use CAN-FD expansion for most functions for a long time now, but need to consider the total stock of these processors available to use before adding another product that uses them.

If we did it Pi hat is one form factor that could be used but may not be optimal.