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Channel usage on Controller

Posted by Inq 
Channel usage on Controller
March 25, 2019 02:35PM
Hello RepRap forum. This is my first post and I want to dive in making my own printer. I’ve been printing for about 8 months now on a Prusa i3 Mk3 kit that I assembled and am hooked with the 3D printing. I hope this is the correct sub-forum for these questions.

Background Info – Mainly, I’m wanting to make a large printer and I have some questions. I’ve purchased a MKS Gen-L Controller kit which looks to be similar to that in the Mk3. Although it comes with A4988 drivers, I understand I can swap those out for TMC2130 drivers that will give me the limit feedback like the Mk3 that I think I’ll need.

1 – I know the 5 channels are conventionally set up for X, Y, Z, E0 and E1. Is my assumption correct that these can be allocated differently? In that vein…

2 - The Mk3 has two Z motors and to sync them, the Mk3 drives them to the top until they hit and thus know that the X arm is level. Are they logically driven as 2 channels and each stops based on its own TMC2130 driver feedback OR are they on just 1 common channel and the first motor skips steps once it jams until both are jammed?

3 – If the channels can be allocated differently, can I have, for instance, 4 Z-motors driven off 4 of the 5 available channels? Although I am not married to 4 Z-motors, I don’t really see using 1 motor with belts synchronizing the 4 corners any easier a problem in my case. Manually syncing the 4 corners by loosening the cog on a corner’s shaft isn’t ideal… especially regularly.

4 - What, in general, topic would I need to start researching to achieve the above… modifying the controller board (jumpers or soldering) or what piece of software would I modify? I’m not sure if there is a distinction between Marlin and the controller’s firmware. I think they are synonymous.

5 – Is there some way to link more than one of these controllers? Version A – where they are tightly linked and I can allocate the 10 total channels any way I choose or Version B – a loose linking where I can add some kind of communications USB, Bluetooth or WiFi using say a ESP32 board and then link them through software that I’m willing to write?

Thank you for your time.
Re: Channel usage on Controller
March 25, 2019 06:11PM
I am biased, but IMO you've picked the wrong controller for what you want to do. The Duet WiFi and Duet Ethernet, with an added DueX5 expansion board if you need more stepper drivers, offer those sorts of features as standard: up to 12 stepper drivers, bed levelling using multiple Z motors, motor stall detection, WiFi etc. And you also get the benefit of a 32-bit processor with hardware floating point and 16x more RAM, so you have the performance and memory to do more advanced things in the firmware.

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

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: Channel usage on Controller
March 25, 2019 07:40PM
You may be biased... but you may also be right! thumbs up

I wasn't expecting my first choice to necessarily be the end solution. What I got seemed to be a better board than getting the Mega 2560 and Ramps 1.4 boards and cheap enough that its disposable... $32 for board, display w/ SD reader and five A4988 drivers delivered.

I will definitely check the Duet out, but $275 for both boards is not disposable. I will be way under that for my first full prototype printer.

Also, I am still interested in a more generalized solution of cross board linking. Some of my ideas would use 6 controller boards and all 30 channels. I'm not bashful about digging into Marlin code or home growing my own on Arduino's, ESP32, ESP8266, RapPi or PC's. I'm hoping someone here has either gone down this path before or knows of someone that has... and might know some of the pitfalls. I don't mind learning from anyone's experience. That's what Open Source is all about.

Thanks for responding.
Re: Channel usage on Controller
March 26, 2019 04:15AM
Two things that might be of interest to you:

- Adrian Bowyer recently did an interview, in which he mentioned he was trying out using multiple CPUs in a single 3D printer. See [www.raspberrypi.org].
- Here at Duet3D we previewed the Duet 3 last September. It uses CAN bus to connect multiple expansion boards to the main board. See [youtu.be]. We will release Duet 3 later this year.

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

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: Channel usage on Controller
March 26, 2019 08:40AM
You know... you're right.

I'm such a dweeb sometimes. I've been treating this like some kind of black-box. I only update my Mk3 when Prusa tells me to. Its too expensive and too highly used for it to be down because I experimented too hard. eye rolling smiley Maybe if I had gotten the Mega 2560/Ramps boards it would have slapped me back to my senses.

This is just an Arduino under the covers! I've got Serial, SPI, I2C...

Thanks for the links. I'll check them out.
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