Stepper Motor thud/hiccup/stutter

[moparx12]

In case anyone else has experienced this, I wanted to post this up here to help me find the problem faster.

As the subject line says, my machine intermittently makes a "thud" noise while running a program. It does not happen every time! I have tried the accel and speed settings all over the place and that does not seem to affect it. I also changed the frequency to 50hz from 100hz which also did not affect it (200hz caused it to not move in any axis). Before I realized it was causing lost steps, I actually cut hinge pockets in a couple of sheets of laminate. The locations in that case were off by 1/4" or more, in the X (short) axis direction only. I had the x axis all apart last week and everything moves smoothly. Any idea what it might be?

Usually, when the thud happens, I lose steps on the X (short) axis. It actually sometimes makes it so that X=0 is thrown off . I have learned that when I hear the thud, I should stop the program and re-zero if possible. It is very frustrating! I have had this happen at 500 IPM and at 300 IPM, always during rapid moves, usually when moving in a diagonal path. It is less severe at the slower speed. It does NOT happen in the same spot every time. Also, sometimes it will do it at a certain place in a program, then it wont do it at all the next time.

Ger says it might be a mechanical problem, and I suppose it could still be. However, I had the belt off that pulley and was able to manually move the Z carriage along the gantry (X axis) freely. I suppose the problem could be mechanical only if it is related to rack/pinion mesh jamming.

Per Ger's recommendation, I changed my buffer size to 0.2 and will test this out ASAP. I will also look at my task manager in my PC to see if I can catch it happening.

I will also add that I have a fairly long ethernet cable, I think 20-25 feet. In case it matters, I'm running an old PC with windows xp on it.

Thanks!

[cncdrive]

It can be many things.
The ones I can think of:

1.) Mechanical problem. Jamming screw, slipping belt/pulley.
2.) Problem with motor drive or motor.
3.) Noise effecting the step/dir signals. Bad grounding or bad power supply or not sufficient power supply buffering causing extra or lost steps on the step/dir lines.
4.) Ground loops, if it is a USB controller and the breakout board has no isolation and if it is grounded in the control box then there is dual grounding, one on the PC and one on the motion controller which is a loop of grounds which can generate noise and can cause lost steps and communication problems.
5.) If they are cheap stepper drives then it is also possible that it is a self resonant frequency problem of the stepper motor + driving mechanism when the motor loosing step when it reaches a stepping frequency which equals the self resonance frequency of the motor with the attached load and so the motor rotates out of syncron. Advanced stepper drives have algorithms against this type of problem while cheap ones usually not.
The solution or test could be to put extra inertia load on the motor, e.g. a disk on the motor shaft or on the ballscrew to see that it shifts the resonance frequency and if it solves the issue or not...

If the UCCNC shows the proper coordinates, but the mechanical coordinates are incorrect then it is not likely that it is a software problem, because the UCCNC reads the coordinates back from the motion controller.

And that you've mentioned that the issue is when you cutting diagonals at high speeds makes me thing that point 3. and/or 4. will be, because at high speeds the back emf which can generate noise is higher than on low speeds and also when more motors moving the same time again the back emf is higher and on diagonal moves more than one motors are moving the same time.

[moparx12]

Ok great. Should my pc case be connected to the same ground as my control panel for the machine? It currently is not.

[moparx12]

Btw, it is possible that it is my drivers, they are marked leadshine DMA860H

[moparx12]

I also noticed I have an extension cord powering my PC laying directly on TOP of the long ethernet cable. Maybe some interference? I'll go ahead and move that out of the way!

[cncdrive]

No, it's not possible, if there were communication error on the ethernet cable then the controller and the software would try to correct it, and if correction is not possible for certain amount of time and amount of data packets then you would receive a connection lost message when you would need to restart the software.
All data packets are CRC error checks, so even one bit of error is detected and then the controller asks for the packet again and again until the packet is correct or until the timout limit which if happens then the controller disconnects and you get an error message.

[cncdrive]

But one thing you can check is the Statistics page on the Profiles page. That graph shows the response time of the controller and it should never go upto the max. 20msec, if it does that is a problem.

[moparx12]

Ill look at that then. I am running the 2017 Screenset and I don't think I have ever looked at the statistics page. I will look tonight and report back. I assume it is a real-time thing only? I will need to watch it while running a program?

[CT63]

Could be a power supply problem. Some switching power supplies require a minimum load to turn on the DC output. If the power supply DC load to the drivers is borderline it could be causing the PS to shut off. i.e. blip.

[cncdrive]

There is no realtime requirement, the data is buffered, but ofcourse there is a time limit for the controller to reply to packets and vica versa, otherwise the system can't work properly if the software has to wait long times for the controller to reply. This time requirement is 20msec which is a relatively high value, because on the ethernet it should not take more than 1msec for a packet to arrive even if it is on a large distance behind routers it should still not take more than 1msec.
So, if it takes more than 20msec for packets to arrive then there is a problem somewhere in the system, with the network card (e.g. drivers problem) or with a router or with network overload etc.