My MPCNC is following it’s gcode instructions, but it occasionally seems to pause between instructions, creating a jerky motion. I could capture a video if that would be helpful. I searched the forums, and @forcerouge (“Dui, ni shuo de dui” - my poor translation would be “Yes, you speak truly”) suggested it might be to do with it updating the display. I don’t have the display connected, since it didn’t appear to be working.
I don’t think it’s relevant to the Serial interface, because I’ve run it successfully with both Repetier Server and CNC.js, and both experienced the jerky effect. I think it might be a firmware issue. I’m using Marlin, set up according to the instructions.
Please ask any clarifying questions you can think of
Are you sure it’s pausing between instructions and not within instructions? Make a long slow move with a single G-code command and see if it is jerky during the move.
If the current is too high, the drivers might go briefly into thermal shutdown which could produce apparent pauses. This can be checked by seeing if the machine is losing position. Or you can feel the drivers and see if they feel hot. Or you can lower the current and see if the jerky behavior stops or becomes less frequent.
If you move just X back and forth, and if you move just Y back and forth, do you see jerks in both cases? This could eliminate wiring issues, because it’s extremely unlikely that both X and Y have exactly the same wiring problems.
On a whim, I tried cutting from gcode on an SD card. It worked perfectly. There might be some kind of queuing issue with the instructions, perhaps the Raspberry Pi 3 A isn’t up to the task (though, I doubt that very much).
There don’t seem to be issues while running in straight lines, even long ones. The problems seem to occur during curves. I’ll try to work out what the cause is by running the experiments you described later, and I’ll report back here. For the moment though, I will consider this solved.
FYI think I am having the same issue on my low rider on cnc.js and raspberry pi 3a,
This is also a known issue on octoprint for 3d printing… lots of segments in the gcode curves will cause it to max out the serial communications and start stuttering. Apparently she did some experiments with support for wifi SD cards in octoprint to get around the issues.
Not looking forward to doing the SD card shuffle
I’m generating my gcode in fusion not sure if there are any ways to resolve it there. I changed the tolerance in the post processor to 0.05mm from 0.001 and my file size dropped from 2300K to 650K so it might help.
I had the same thing happen twice this week, the machine went from drilling a hole to taking off in one direction cutting through the stock ruining the material.
Glad to hear I’m not alone. I’ll come back to this issue later, for the moment it’s working, and I’ll just have to learn to enjoy the SD card shuffle, as you put it.
I did several cuts with the new tolerance setting and the jerkiness is gone for me with no visible change in quality. So if your software gives some control over the amount of gcode created for curves it might be worth looking into.
Thank you both for this. Changing the Tolerance and Smoothing in Fusion makes a big difference in how cleanly (no stutter/jerk) with fusion on curves (even with no tool load).
