[Solved] Getting layer shifts after switching to direct drive. Can someone help me with acceleration and jerk tuning please?

[bassamanator 1]

The layer shifts are occurring along the Y axis. The following are 3 different prints of the same part. Note, most parts print just fine, this piece in particular is giving me a hard time but there is nothing with the piece/gcode itself, it's simply highlighting the underlying problem. I believe this layer shifting is happening because the printhead is heavier now and getting it moving from a standstill is difficult.

 

I'm going to use Teaching Tech's calibration page but I would appreciate some guidance. In the meantime, I'm going to do a print a reduced Print jerk setting in cura (5 mm/s instead of 10 mm/s).

 

Thanks!

 

Anycubic Mega S.

Knutwurst's firmware based on Marlin 2.0.x.

I used to print at 150 mm/s with my bowden setup, in fact, all the pieces for my direct drive were printed at 100-150 mm/s.

Using Linear Advance 1.5.

Belts are all well tightened (not too tight, of course).

 

 

Edited June 30, 2021 by bassamanator

[GregValiant 1,112]

Greg's Accel and Jerk Tool for Windows.  Unzip and run the Setup file.  It's unsigned (because I'm cheap) so you may have to fool your anti-virus to allow it to install.  When it starts you may have to manually enter the port number.   As a bonus, there is also a utility for printing from the SD card but running things from your PC.

Enter your build plate size in the boxes at the upper left.  Start out SLOW.  At high Accel and Jerk and allowed speeds of up to 400mm/sec - some printers can hurt themselves.

Edited June 29, 2021 by GregValiant

[bassamanator 1]

@GregValiant I'm willing to boot into Windows for this! Thanks!!

 

I will report back my results. Thanks again!

[bassamanator 1]

@GregValiant Unfortunately, I couldn't figure out this tool. I only managed to getting it up and running.

 

In any case, what should I do in theory? I know that the skip always happens along the y-axis, so should I change the Y jerk setting? Or is it something else? I just don't know where to start.

 

Here is the relevant output from M503:

Recv: echo:; Maximum feedrates (units/s):
Recv: echo:  M203 X500.00 Y500.00 Z6.00 E30.00
Recv: echo:; Maximum Acceleration (units/s2):
Recv: echo:  M201 X3000.00 Y2000.00 Z60.00 E10000.00
Recv: echo:; Acceleration (units/s2): P<print_accel> R<retract_accel> T<travel_accel>
Recv: echo:  M204 P1500.00 R1500.00 T3000.00
Recv: echo:; Advanced: B<min_segment_time_us> S<min_feedrate> T<min_travel_feedrate> X<max_x_jerk> Y<max_y_jerk> Z<max_z_jerk> E<max_e_jerk>
Recv: echo:  M205 B20000.00 S0.00 T0.00 X8.00 Y8.00 Z0.40 E5.00

 

[bassamanator 1]

Grrr I thought this issue was solved but not quite. Increasing voltage to the stepper drivers didn't help as much as I thought it did.

Edited June 30, 2021 by bassamanator

[GregValiant 1,112]

On the tool, set a speed and pick a course, then have it run the course.  Change accel and/or jerk, then Prepare and then hit the green flag button to run the course.  You can run up to 200mm/sec at the accel and jerk of your choice.  When you click off the "speed limit" safety, you can run up to 400mm/sec.

Essentially, make changes to the setup, Prepare (sends the accel and jerk to the printer) and Qualify (run the course).

When running the circle courses I found that my Ender was happiest at 500 Accel and 8 Jerk.  The speed didn't matter since with all the starts and stops of a circle the Accel setting holds the speed down and motion is smooth.

 

So start the Accel and Jerk tool.  Set the speed to 150.  Enter your build plate size in the MaxX and MaxY boxes, Prepare, and then hit the green button.  The first course is a diagonal but the Nascar course runs around the periphery of the build plate and gives a better indication of how the starts and stops will be handled.  When the machine is finished moving the average speed is displayed in the boxes at the bottom.  Make changes in Accel and/or Jerk and speed, and Prepare, and then hit the green button to run the course.

Edited June 30, 2021 by GregValiant

[bassamanator 1]

Update: I've upped the voltage for my stepper drivers to 1.15V (which is in fact the voltage that is recommended by users of my printer, it's just that with my bowden setup I was able to keep voltage at 1.0V). I am able to print at 60 mm/s issue free.

 

I've realized that I've been a very silly boy. I somehow equated direct drive with greater print speeds and I don't think that is the case. My printhead is now roughly 140 g heavier and I'm expecting it to print at the same speeds (100-150 mm/s) as when the printhead was lighter. It was very silly of me to think that.

 

@GregValiant Thanks for the detailed explanation and for the tool itself. I will be using it extensively to see if I can increase print speed. It's not so much that I'm a speed junky, it's more that I enjoy tinkering, and getting as much value as is possible out of the things that I own. If I may ask you 2 short questions.

1. Am I correct in my thinking, that with a roughly ~140 g heavier printhead, the theoretical maximum print speed of my printer has been reduced?
2. Do you think that bigger/taller stepper motors would be able to handle greater speeds with this heavier printhead?

In any case, I'm considering this issue resolved.

[GregValiant 1,112]

#1.  No.  The speed will not be reduced but it cannot accelerate or decelerate as quickly.  Consider that at 100mm/sec and 5000mm/sec² accel it takes 1mm to get up to speed and 1mm to stop.  At 100mm/sec and 500mm/sec² accel it takes 10mm to get up to speed and 10mm to stop.  That is where the weight is going to show up - in your acceleration setting.  Jerk is in mm/sec and an inexact analogy is "minimum speed going around a corner".  That won't play into things as much as your Accel setting.  If you try to accelerate that extra 140g like you did without it - then you could very well start skipping teeth on your X belt.

 

#2.  Maybe.  That is an answer to the question "Can the stepper motorr handle it?" but the question needs to be broader "Can the printer frame, wheel bearings, steppers, belts, etc. handle it?".  I had a buddy that dropped a high performance V8 into a Simca.  The first run down the track and the little uni-frame body had twisted so badly that when it came back it was only able to put three wheels on the ground at a time.

 

The real advantage to DD is printing certain materials (like TPU) that can take advantage of the short filament path.  I did a test with my printer and I can print large flat areas at 175mm/sec.  I kept increasing the Acceleration during the print and at about 1200 the extruder could no longer keep up at the start of any extrusion.  In that test it wasn't the XY steppers that were the problem, it was the E motor.  Everything affects everything.

[bassamanator 1]

18 hours ago, GregValiant said:

...

 

@GregValiant So, I got this tool working now with your instructions, and what can I say, this tool is like magic. The thing is, I'm not sure what data I should be gathering from it. For example, I set Accel to 500/500, Jerk to 10/10, speed to 150mm/s, and did the Nascar race (after qualifying). The printhead moved around smoothly. Is that the test? Should I be listening for strange sounds/skipping belts?

 

If that is the case, and I find that anything over 500/500 and 10/10 cause the belts to skip, would I then do a

M204 P500.00 R500.00 T500.00
M205 X10 Y10

My current acceleration settings are:

M201 X3000.00 Y2000.00 Z60.00 E10000.00
M204 P1500.00 R1500.00 T3000.00

 

Thanks again!

[GregValiant 1,112]

OK - 150mm/sec for speed and start moving the Accel up.  As the quickness of the starts and stops increases, you will come to a point where the machine can no longer handle the motion.  You will notice that it goes from "quick" starts and stops to "violent" starts and stops.  Yes, it may result in skipped teeth on the belt.  You can turn off the safety and run the printer at 400mm/sec but start with the Accel at 250 and move up from there.

You can uncheck the "sync" boxes and enter different values for X axis and Y axis.  That would allow you to run the X axis at say an Accel of 1000 and the Y axis at an Accel of 500.

 

The circle courses in the program are generated with G2 and G3 commands.  You want smooth motion around the circles as any stuttering will leave little blobs on a curve in a print.

Once you get the settings the way you want them with the tool, use the "Send current Accel and Jerk and Save" button.  It's rose colored and below the Com Port button.  It will update the printer to the new settings.

The Accel will become the printer MAX accel setting (M201).  When you slice something, you can enter whatever accel you want and Cura will add an M204 line to the gcode, but the printer will limit it to the M201 Max Accel numbers.  M201 is like a speed limit for Accel.

 Jerk is different as there is no Max so whatever you enter in Cura gets added to a gcode file as M205 X?? Y?? and the printer will use it.  There is no "Max Jerk" gcode command (although the firmware will have Max Jerk values hard coded in). 

 

Edited July 1, 2021 by GregValiant

[GregValiant 1,112]

I went back and looked at your first photos.  Did you get around to calibrating the E-steps?  Along with the layer shift I thought it looked like it might be under-extruding as well.

[bassamanator 1]

5 hours ago, GregValiant said:

I went back and looked at your first photos.  Did you get around to calibrating the E-steps?  Along with the layer shift I thought it looked like it might be under-extruding as well.

I, too, noticed the under-extrusion that you're talking about. The e-steps are calibrated but the flow rate could have been off. It was a frustrating time for me and this particular STL became my goto test piece, it would fail 100% of the time, and it's possible I might have rushed through some settings.

 

I'm far from perfect/good calibration, which I'll be doing using your tool and Teaching Tech's acceleration tuning gcode generator. But in the meantime, I remembered what another MK4 user had told, he halved his X axis acceleration. I've done the same (M201 X3000.00 >> M201 X1500.00) and have printed several pieces at 100+mm/s, completely issue free.

 

One thing I still don't get is why the layer shifts were happening along the Y axis.  I would have expected them to happen along the X axis because the heavier printhead moves along this axis. Upping the Y stepper motor driver did not help at all, as I mentioned earlier.

 

I have to say this direct drive upgrade (I call it an upgrade because it's cleared up room on my work desk and has made the filament changing process so much quicker) has been an enormous learning experience for me. I remember seeing the MK4 back in late March, when I first started printing, and it was an impossible upgrade; the thing came with a 5 page instruction PDF (which I now see as a god send). Now I feel confident that I could put together a Voron, using the many guides out there of course.