Core One+ randomly restarts about 10-15 seconds after starting a new print  

RE: Core One+ randomly restarts about 10-15 seconds after starting a new print

You could search the forum for ESD.

Don't give up with Prusa support, just take a deep breath and get back to them. Their response is not bad - this is a very common failure mode with just about anything electric with detachable power cord. The catch is, it's obvious to some people but not to others. Their checklist serves also the latter 🙂

RE:

If you are printing largish objects, especially with long, fast runs of the print head, static charge build-up on the belt and motors is a problem that has been reported quite often. There is a long thread on this: https://forum.prusa3d.com/forum/postid/752399/   

The underlying issue is that Prusa does not reliably ground the X and Y stepper motors. If the paint layer on the CoreXY mounting frame is "too good", the motors remain electrically insulated and a charge can build up on the moving belts and the motors. Eventually it will discharge through the insulation layer with a minimal arc, causing the printer to crash. In your case the crash happens unusually quickly, so it might be a different issue. But it's easy to check:

You can measure with a multimeter whether your motors are grounded. In resistance mode, measure between any of the four screw heads on top of each stepper motor and a chassis ground point (e.g. the screws in the lower front which hold the Z motors). If you measure high impedance, i.e. more than a few Ohm, the ground connection is missing.

The easiest way to ground the motors is via one of the four screws which hold the motor and its mounting block from below the CoreXY frame. Remove the screw, scrape off a bit of paint in the area below the screw head, reattach the screw. For a secure long-term connection, put in a star washer.

RE: Core One+ randomly restarts about 10-15 seconds after starting a new print

Hi @jurgen-7 - thank you for your memo. This is very helpful, and insightful.

I measured the motors. The X-AXIS motor has an "Open Line" (OL) reading; it does not return any reading across any of the mounting bolts. The Y-AXIS motor has a reading of ~0.433Ω. It seems like it might "be a different issue" requiring more scrutiny. I'm now recording video at the start of every print but have yet to catch the reboot the moment it happens (beyond the video I already shared that shows it at the moment of starting back up). Thanks for your input. I'm really baffled by this issue.

RE: Core One+ randomly restarts about 10-15 seconds after starting a new print

Posted by: @nicknormal

I measured the motors. The X-AXIS motor has an "Open Line" (OL) reading; it does not return any reading across any of the mounting bolts. The Y-AXIS motor has a reading of ~0.433Ω. It seems like it might "be a different issue" requiring more scrutiny. 

Your measurements make sense, but I don't understand your conclusion. The 0.4 Ohm resistance indicates that the Y motor is grounded, but the "open" measurement confirms that the X motor is not. So charge building up on the X drive may very well be the root cause of your crashes.

Please try grounding the X motor. If you don't like the idea of scraping off paint below a mounting screw head, you can also connect a ground wire from the screw head to a suitable chassis ground. For initial tests, just a piece of bare wire clamped below the heads of a motor mounting screw and some chassis assembly screw will do. 

RE: Core One+ randomly restarts about 10-15 seconds after starting a new print

Posted by: @nicknormal

I measured the motors. The X-AXIS motor has an "Open Line" (OL) reading; it does not return any reading across any of the mounting bolts. 

note, it's not "across the motor's mounting bolts", Jürgen gave a reference point on the frame (which is grounded). 

If this would happen on my printer, I'd spend no effort on trying to disprove that there is an ESD problem. Instead, take three M3 washers and a piece of wire. Pull back the insulator with fingernails at appropriate distances, wrap a few times through the washer (for a metal-on-metal connection) and put one on X-stepper, Y stepper and a suitable frame screw. Finally, make sure the washers do have contact with the motor body (risk of insulating paint layer / screw passivation breaking the connection). 

RE: Core One+ randomly restarts about 10-15 seconds after starting a new print

Posted by: @mnentwig

note, it's not "across the motor's mounting bolts", Jürgen gave a reference point on the frame (which is grounded). 

I assume Nick has made the right measurement. Measuring the resistance between any pair of the four mounting screws on a motor should always show a connection, so that can't be how he measured the open circuit. (The screws are always connected to each other via the motor chassis. They may just all be isolated vs. the CoreXY frame if Prusa did too good a job on the powder coating.)

Thanks for elaborating on the wiring to ground both motors! I understand that Nick is running a makerspace at CUNY, so this should be pretty straightforward for him or the electronics-guy-in-residence. 😎 

RE:

I just don't understand one thing: It has been proven hundreds of times here that grounding the motors solves this problem, but there are still "experts" who, instead of popping into the local hardware store to buy a few toothed washers for a few cents, unscrewed one of the screws holding the motor, used a screwdriver to scratch the paint around the hole where the screw was, put the purchased toothed washer on the screw, put the screw back and tightened it properly, and thus solved the problem according to the description of @jurgen-7, are "fumbling" here with a multimeter, and yet it is clear from the description that they don't even know how and what to measure! On both motors, one of the mounting screws is quite easily accessible and there are plenty of photos that show it. Working on this repair is faster than writing meaningless litanies about meaningless measurements!

RE: Core One+ randomly restarts about 10-15 seconds after starting a new print

IMO, it's always better to make a measurement to establish what the problem is for certain, and make it again after the fix, to be certain it's fixed. If the measurement itself is a problem, it's better offer some advice on how to correctly make it. Too often I've been 100% certain I knew exactly what the problem was, only to find a case of something different. I'd quote Lord Kelvin on measurements but I'm too lazy. In this case though, odds are darn good it's grounding! IMO again, all that said, the grounding should really be taken care of in the assembled units by Prusa, and the above-mentioned star washers included with the kits and described in the instructions. There should also be lugs and a wire harness for the Z motors, which are inherently insulated. I've caused a full reset by accidently touching the rear Z screw with the build plate.

RE: Core One+ randomly restarts about 10-15 seconds after starting a new print

Here it is also a question of whether you yourself introduced the static charge into the printer, for example with clothing made of synthetic fibers. It is quite common for such fibers to charge themselves, especially when it is dry around you. But this is only an assumption and one of the possibilities, and of course it is impossible to judge the case from a distance.

RE: Core One+ randomly restarts about 10-15 seconds after starting a new print

Thanks again, @jurgen-7, others. Apologies I've been slow to respond, I've been sick with a cold, and only got to my studio today since my last post; I was reminded of this thread when the machine rebooted today. In the past, the machine typically reboots ~15 seconds after starting. Today, it happened ~15 *minutes* after starting - you can see in this video that the print is halfway through the 4th layer (floor) when the printer rebooted. I just completed a ~45-minute print and tested the motors immediately after the print finished, and the Y-AXIS motor is now measuring around 20-25Ω, so I'm guessing that's the culprit. I have some days off next week for our "Spring Break" and will attempt to find the culprit mounting hole.

RE: Core One+ randomly restarts about 10-15 seconds after starting a new print

All you need to do is to remove one screw from each of the motors (X and Y) and install a "Star" washer underneath it. Simple fix, which doesn't come with the risk of running a wire in some area that impedes the extruder movement.

RE: Core One+ randomly restarts about 10-15 seconds after starting a new print

X & Y motors only need a toothed washer and/or a bit of paint scraping. Z motors probably need a wire as I don't think there's any path to get them to ground because they mount on plastic parts. Caveat emptor- I haven't looked under the printer in a while.

RE: Core One+ randomly restarts about 10-15 seconds after starting a new print

I don't think the z-axis motors have an issue.  X and Y have those long rubber belts attached that build up charge.  The Z motors don't.

RE: Core One+ randomly restarts about 10-15 seconds after starting a new print

No, but I've accidently touched the rear Z screw with the build plate and the printer shut down and rebooted! I wasn't even wearing my wool socks, but it was winter and low humidity.