Serious issue with Firmware and Errors  

Serious issue with Firmware and Errors

I just got my MMU3 up and running and I'm seeing what I consider a serious flaw in the firmware for error handling - I've already encountered it multiple times.

One example: Tonight I tried printing the multi-color sheep from Printables, one of the samples that Prusa has put on the site for testing an MMU. It got to 87% done, which is most of a 9 hour print. I got back to my shop and looked and one filament wasn't loading. My options? None. I could hit "retry." I appreciate that, it's quite helpful and I know it took a lot of work, but it doesn't help if I need to manually fix something on the MMU, then resume the print. At this point, almost 8 1/2 hours of a 9 3/5 hour print had gone by. If I could, I would seriously prefer to be able to resume the print, rather than start a new one.

I forgot the exact error code, but it was something about the filament not loading. I could pick "RETRY," and that is IT.

What I needed to do was to pause the print, check out the MMU and the filament, and, if I could have (at the time) just paused the print, I would have moved the selector over so I could see what was going on with the idler and pulley. If I could have done that, I would have seen an issue with the filament, manually unloaded it by pulling it out, then reloading it. Once all that was done, I could have resumed the print without WASTING 8 1/2 hours of printing. (Note: I did try to pause the print with Prusa Connect. I paused it, but on the printer itself, all I could do was still hit RETRY. Somehow, pausing it, then hitting retry to look more closely at what was happening resulted in the print being stopped.)

I admit, I've been spoiled by Prusa. Their tech support is excellent! (I've needed it several times while working on my MMU3, since I had to deal with a few unusual situations - like how I positioned my filament in a tight space.) The guides are usually top notch for assembling any Prusa product. In my experience, my MK3S+ worked perfectly once I assembled it and finished checking everything out (of course it requires proper maintenance, but so do all machines). When I upgraded to an MK3.5, again, the guide was excellent and, once assembled and checked out, it has worked flawlessly.

The MMU3 - well, there are serious issues with it, starting with the one I brought up: I COULD HAVE SALVAGED THIS PRINT. If I could have just paused the print, so I could have had manual control over the MMU to move the selector out of the way, then to unload the filament and reload it, then restart the print, I would not have to start from the beginning. I'm surprised by this, since it seems so unlike my previous experiences with Prusa equipment. I hope that the newness of the product is the excuse - that the software is still in evolution, and that Prusa is going to put in options to pause the print so we can get manual control if a print is interrupted.

I have had multiple times, while testing, and once things were supposedly working, where, during a print, this happened. I couldn't pause it and fix something or pull stuck filament out of the selector or the main part of the MMU3. I couldn't pause the print so I could double-check things like the pulleys to be sure they were fastened down, or to unload and reload filament. As best I can see, if there is ANY error in the MMU, a print is dead. Deep sixed. It is an ex-print and has shuffled off its mortal coil and joined the choir invisible. It's a dead print.

The MMU is a complex machine and it is not just a foreseeable condition that filament might get stuck, or may need to be reloaded manually, or that a person might need to take over manual control if there's an error, then, when the situation is resolved, resume the print. It's not just foreseeable, it's something a good programmer (and I speak from experience) should KNOW is going to happen and should allow for it.

(In the past I've used OctoPrint, which lets me pause a print. I don't know if that would have worked here. First, the MMU plugin has issues right now and doesn't even recognize the MMU, and, second, even though I tried pausing through Prusa Connect, that still left me with ONLY the "RETRY" option on the printer itself.)

So here are what I consider serious issues with the MMU3:
1) This issue - that when it throws an error, the ONLY option is "RETRY." Pausing the print should be an option, and that includes a pause mode that allows the human full manual control of the MMU to remove, load, unload, or clean out filament, as well as to do any other troubleshooting or maintenance that might let a print continue.

2) The guide has issues. For example, it's the only Prusa guide I've seen that has NO parts list so when you get the kit, you can check to be sure you have all the parts. I get that there are many variations - which printer is it for, is it an upgrade for an MMU2? I get that, but the parts list can be broken down into sections.

3) There are other cases within the MMU3 guide where I found incomplete information. For instance, when first loading filament in the MMU, nothing is said about what to do, manually. I wasn't sure if I should push the filament through the PTFE until there's resistance, or push a bit more to force it into the pulley on the MMU, or even through the pulley.

I really like Prusa and their products. Ever single interaction I've had with any Prusa employee has been helpful and often enjoyable. (Well, when things are bad, even when they're helpful, it may be still be frustrating because of what the issue means in terms of downtime or needed work or parts.) The guides have been great and the forum - people on this forum have been wonderful and I rate it as one of the best help forums I've seen on the internet. (And I've been on the internet, asking for and giving help, since before those of us on Usenet had to deal with AOL and Eternal September.)

But the MMU - the issues with the guides and the lack of options (especially a simple pause option) on errors are seriously concerning. I really hope someone responds to this by saying, "Oh, you dimwit! If you just do this, you can pause it and these other issues are easily solved and you just didn't look in the right place." However, the inability to pause the print from the printer control panel is a serious problem.