X-Axis Jitter

Mostly Printed CNC - MPCNC Troubleshooting
#1

I have weird jitter in only one axis that I cannot seem to figure out. I have spent hours trying various solutions and isolating possible culprits, but still no luck. Starting to get a little frustrated.

I’ve swapped outputs on the RAMPS using the “smooth” y-axis, but no luck. So its not the driver or how the driver is tuned.

I’ve squared the frame many, many, many times. I’ve also loosened and tightened all of the “long” bolts that affect bearing preloads. Also tried belts tight and loose…no difference.

Also tried moving motors to see if maybe it was a bad stepper, but nothing. Still stays true to only this axis.

Here is a video of what I’m talking about. Very odd. It almost seems like the deceleration in the firmware is causing an issue, yet that doesn’t explain why one axis is perfect and the other is most certainly not.

#2

Mine does that when I try to move it too fast.

#3

That should be controlled in the firmware though through max travel speed. Have you reduced yours?

#4

Sounds like you have moved everything but the wires? switched drivers? What drivers are you using? What are they set at?
What are your steppers rated for?

Lots of variables and your haven’t given many details.

#5

I believe they are pololu DRV8825. I did try swapping the driver, as well as using the y-axis output for the x-axis. Tried turning the driver up and down. Enough to where the motor was severely torque limited by current. And over enough to where I could hear it whining. Around 0.7v…whatever that current limit ends up being. Forgot the equation for the DRV8825.

I also rewired the motors a few times to verify it wasn’t a bad connection. And again when moving around the motors.

Pulled the motors and verified they are turning opposite of each other, obviously.

These are the Kysan steppers rated at 76.4 oz-in. Plenty of torque.

#6

So you have swapped motors, wires, drivers.

The only thing left is physical, or speed related. Are you moving that with the screen, gcode, or repetier?

I am willing to guess you are using the screen, it is not tuned very well for large manual movements. use repetier and make sure your speed setting are slow enough.
The best way to test it is with gcode or a test script. I have a torture test script here in the forums. those things are set by default for tiny little 3d printers, not a relatively massive thing like the mpcnc.

I think if you run some actual gcode you will have no issues. Strap a pen on that thing and follow the estlcam walkthrough.

#7

Oh and best not to set the drivers by feel, they are extremely sensitive. Find your steppers rated amps divide that by 2, then use 90% of that number as the desired voltage for the pot. No higher than .7v unless you have active cooling. If it is a DRV8825, that will not work for the a49’s.

#8

Thanks for the quick replies! I’ll try this tomorrow. I’ve been using commands of 50 steps directly through repetier. I don’t have a standalone LCD controller.

It’s possible it’s too fast. Yet I find that odd because the y-axis loves it. Smooth as silk.

#9

Just thought I’d toss in a quick update. I finally solved the issue, which was a mistake on my part. I had borrowed motors from my printer, including one of the gears. So while 3 of my motors have 16T gears, one on the x-axis had a 20T. Doh! Problem solved. :slight_smile: