Why is the stepper skipping

X axis stepper is skipping! And possibly Y axis as well.

I’ve removed the belts to isolate the issue. In the video you will the x axis stepper skip at certain points… not the acceleration moves but you will actually see it skip. The black marks helps see the movement. The background noise is the y axis and it does something similar but more subtle. There is only one single y axis motor with a torque tube type shaft on each end to turn the belts on the Y.

Any ideas what is causing this, how to confirm and further isolate the issue. Things to try?

RUIDA DSP, 500x300 Chinese blue and white 50w. You know the type.

Steppers are of type: 23HD450Y
Drivers are of type: 2DM542-N

Video of the issue: https://youtu.be/6RrYdA_fIZk

That doesn’t look like skipping, it looks like backlash compensation.

With no backlash compensation, moves are sent to the steppers “pure”, with no adjustments. With backlash compensation enabled, each time the stepper reverses, the system sends a rapid sequence of steps to pull up the backlash (slack) and then continues.

I could be wrong, and this could be something else, but an unloaded stepper doesn’t usually skip by itself.

I’m confused. This behaviour occurred before I removed the belts. Prior to removing the belts I could visibly see the laser head jerk at the moment the stepper jerked and made the clunk sound. I removed the belts after to isolate the issue and sound to see if this was caused by the belts, friction, pulleys, etc.

The video shows that at certain moments the stepper exhibits that clunk and jerk motion.

I’m not sure where to turn next to test things. All wiring to power supply and drivers appear to not be loose.

If this is backlash compensation, it would happen regardless of whether you had the belts connected or not. It’s literally the controller executing some number of extra steps with each direction change to compensate for slack in the mechanical system.

I can’t say for certain that’s what this is, but it’s what it looks like.

@LightBurn Just so we are talking about the same thing in the video look at 0:14s mark. That sudden twitch/jerk motion is what I’m talking about. You think that is backlash compensation?

After watching your video more closely, the jumps don’t just happen on direction changes, and they don’t happen with every direction change, so you might just have a broken stepper.

And for the record, backlash is not wiring - it’s mechanical. This is what backlash looks like - the inner arrow would be your stepper, and the outer ring is the mechanical system being driven. The two little dots represent the slop in the system, causing backlash:

Thanks for that. I will try replacing the motor to see if that helps. Others have suggested I try swapping the power supply.

You could swap for nearly any motor (and adjust the current on the driver accordingly) just to see if the new motor exhibits the same behavior.

When it skips it produces cuts with these skips.

That does not look like skipping to me, I don’t think an unloaded motor can skip - and if it did it would make more noise than a single “clunk”.

Could be a bad motor, bad driver or (hopefully) a loose wire somewhere. I would check all the wiring connections and make sure they are secure.

Then you could swap the wiring over for the motors (at the drivers) to test them. Use the X axis driver to run the Y axis motor and see if the behavior follows. If the Y axis motor also behaves badly then you know it is not the X axis motor or the wiring from the driver to the motor. It would point to the driver or a wiring problem from the control board to the driver.

Speaking of skipping steps, when I got my machine (80W CO2 “red and black” chinese clone, Rudia controller) a few months ago, my Y axis motor wouldn’t move at all. I traced it down to a poor connection in a plug that connects the stepper motor wire to the wire from the mother board where it transfers through sheet metal in the framework of the machine. There was too much tension on the wire from the stepper, so the wire would partially disconnect from this “transfer” plug. I simply unscrewed the plug from the framework to release tension from the wiring. The machine has been working fine ever since, with the exception of one instance when the Y axis motor quit again, but resumed after I fiddled with this connection again. The other exception is apparent skipping or minor misalignment of some lines in my cuts. Could this misalignment be traced to this apparently fixed, but possibly intermittent wiring in this plug?


Never hurts to check that you are well grounded.