X Axis Stuttering  

RE: X Axis Stuttering

It's simply printing the infill as fast as it can, and some places it isn't printing and it moves to the next spot.  Just happens fast enough it's hard to track.  For grins, you can use the Tune/Speed adjust to slow down from 100% to 25% to see what is happening.  

RE: X Axis Stuttering

Hey Tim, thanks for looking at this.

This is the same behavior happening on layer 1 of a print. Its printing supports on the left and right of the bed. This only started happening after adding the MMU2s

RE: X Axis Stuttering

One last video, layer one, doesn't look normal.   But there isn't any one thing that's going to be an obvious source of non-uniform motion, especially if it's repeating.   The obvious sources are belt hop or drive gear spin, but these have other obvious artifacts (layer shifts).  The other common problem is bearing drag caused by pinching the bearing shell.  MK3S extruder housings have been shown to cause layer shifts until the screws near the bearings are loosened.  Also a belt that was tensioned to get that magic 240 LCD reading is possible.  My belt numbers are 295 and 296, and belts more than tight - the LCD numbers are based on motor torque, not belt tension - and IMNSHO shouldn't be used as such. 

Try setting print speed from 100% to 30% and see if the effect changes. 

Also - try manually moving the extruder left and right - if you feel sticky spots, if confirms it isn't normal.

ps: in that first video, the infill pattern and angle can make the extruder do some odd things. Patterns like gyroid that don't align with a part, the printer will hop around to print sections down the length of the part, zip to the next place where it aligns to print, etc.  That's what the first video looked like was happening.

As for an MMU causing it?  Unless a power supply limitation, I can't really see any reason for it. Some wildly unlikely thoughts come to mind, but I have no knowledge of the MMU to printer interface, so would be speculating.

RE: X Axis Stuttering

I'm starting to think this is a power supply limitation. 

Over the past few days I've been playing around with belt tension and print speeds. I also started using a kill-a-watt to measure power consumption from the wall.

Decreasing the print speed to 50% eliminates the stuttering. As you increase the speed to 60% the stuttering comes back and gets worse the faster it goes. I figured out that my x-axis belt was a little too tight so I loosened it to something more reasonable but it didn't help the stuttering.

Paying attention to the kill-a-watt the printer is drawing 2.6A from the wall when it stutters. The power supply is rated for 2.5A max. I mentioned the MMU2 because since upgrading I noticed the PSU runs much much hotter. Is this something Prusa knows about?

I'm going to try buying a new higher wattage PSU and see if that helps my situation.

RE: X Axis Stuttering

You need to be careful with the meter; it can mislead if you don't have a good grasp of what it is telling you.  2.6a may or may not be meaningful. Power factor, crest factor, voltage vs current phase, is it reading RMS or an average, etc.  If power in watts is lower than 80% of the power supply label, you're probably not overloading it.  And you can use the LCD to monitor the DC output of 24v: if you see it dropping >10% when the machine stutters, maybe you've discovered something.  

Since slowing speed has an effect - I'd suspect bearings being too tight before anything else.   You also need to understand the printer has a few parameters like max speed, acceleration, and deceleration: even volumetric flow limits can do odd things to print speeds.  Depending on how you slice the model you can get some strange combinations.