How to set bowden length on MMU2s with MMU3 firmware  

RE: How to set bowden length on MMU2s with MMU3 firmware

Posted by: @juan-puchol

Hello,

I'm using a Caribou 320 MK3S printer with my MMU2S (now with firmware 3.0.0) and my bowden tube is very large, so to load filament is very slow because it stops in the middle and search the extruder slowly.

I have changed the "minimumBowdenLength" variable from 341 to 490 and compiled the MMU3 firmware, so now the load is faster. My bowden tube is 505mm, so play with it to achieve your correct value.

 

The full changed code I have changed is on the src/config/config.h file:

87 static constexpr U_mm defaultBowdenLength = 700.0_mm; ///< ~427.0_mm - Default Bowden length. TODO Should be stored in EEPROM. 392 a 784

88 static constexpr U_mm minimumBowdenLength = 490.0_mm; ///< ~341.0_mm - Minimum bowden length. TODO Should be stored in EEPROM.

89 static constexpr U_mm maximumBowdenLength = 850.0_mm; ///< ~792.0_mm - Maximum bowden length. TODO Should be stored in EEPROM.

 

NOTE: the firmware is on any MK4 firmware (folder lib/Prusa-Firmware-MMU)

 

Good Luck and Happy Multimaterial Printing

 

How did you make the changes to the src/config/config.h file?  What software did you use (arduino ide, pronterface?)  And how did you connect to the mmu? did you connect to the MK4s main board or the MMU board?  I have the same issue with my new set up and need to change the Bowden tube length in firmware too. 

I installed self-retracting spool holders in the dry box to eliminate the need for a buffer chamber.  the set up works very well and reduced all the excess Bowden tubes running everywhere.

thanks for any help

RE: How to set bowden length on MMU2s with MMU3 firmware

This may be the simplest way to change Bowden Length.
https://forum.prusa3d.com/forum/postid/741818/

RE: How to set bowden length on MMU2s with MMU3 firmware

Hi,

Getting back on this, I tried to do the exact same, and I can set it correctly (If I send M707 A0x22 it reports "384" which is hexadecimal for my 900mm bowden length. but, when loading it does about 300mm quickly and then still continues slowly??

More details here on github

Any tips?

RE:

Your 384 returned by the M707 A0x22 command is really your about 300mm (exactly 384mm) of fast charging, and not any hexadecimal 900mm! You have to enter the 900mm value there in decimal, i.e. M708 A0x22 X900. The length must be between 341 and 1000mm, otherwise it will not be saved.

RE: How to set bowden length on MMU2s with MMU3 firmware

 Huh, I just came from 2 other posts stating "REMEMBER TO CONVERT THE BOWDEN TUBE LENGTH TO HEXIDECIMAL!!!"

I tried writing the decimal and it indeed works now!

Thanks!

Posted by: @carlmmii

Since it doesn't seem to be explicitly explained/documented anywhere yet for what to do to set it, I'll leave this here.

FW 3.0.1 added the register. From the registers.cpp file:

| 0x22h 34 | uint16 | Bowden length | 341-1000 | 168h 360 | unit mm

The register is at 0x22h and has a default value of 168h (360mm).

This page describes the register system and vaguely how to modify them using M707 (read) and M708 (write) codes via PuTTy/Arduino IDE/Octoprint Terminal. If using Octoprint, make sure you add the M707 and M708 codes to the capitalization blacklist (OctoPrint -> Settings -> Features -> Features -> Terminal Auto Uppercase Blacklist).

This page describes exactly how the M707 and M708 codes work.

To read the Bowden Tube Length register:

M708 A0x22

To change the Bowden Tube Length register:

M708 A0x22 X[###]

REMEMBER TO CONVERT THE BOWDEN TUBE LENGTH TO HEXIDECIMAL!!!

The allow range is between 341mm (155h) and 1000mm (3E8h).

From the release notes, the bowden length value represents the "actual" length of the bowden tube itself. I would assume this is based on stock setup hardware (festo connection at both the selector and the hotend top mount). If you've modified either of these for any push-through connectors (i.e. a pushthrough modification to extruder gears), the calculated tube length needs to be lowered by the amount of extra passthrough length that exists.