CO2 Laser Interfering with stepper motors

This is where I show it connected to the IEC Socket.

I disconnected the ground for the 24v power supply because it is the one that is connected to its own negative DC.

I would shorten the green grounding wire that goes from the LPS and DC supply to the frame, [that is bundled] unless there is a reason for the extra length.

I donā€™t see anything connected to V- of the 24V supply. Are the DC ground and AC safety ground on that supply connected internally?

How is the DC supply to the Arduino connected and routed?
How is the DC ground on the LPS connected & routed?
Post a picture showing the LPS connectors from the top if possible.
Post pictures of the ANODE wires routing

More detail on what strange is? How is this manifesting in the operation?

I am betting that the interference is not the steppers and their wiring but rather thatā€™s a secondary effect of the controllerā€™s grounding or supply being susceptible to noise.

If the PWM line was being impacted by the noise I donā€™t think this would directly impact the operation of the stepper.

Donā€™t do thatā€¦ You really want that case grounded!

I was wondering whether you had a ground connection somewhere else that was creating a ground loop!

:dart:

This really has to be either

  • The arduino controller itself is glitching from noise from power rails or signal lines ā€” commanding the steppers to do the wrong thing
  • The signals from the arduino controller to the stepper drivers are noisy and introducing unintended transitions on at least one line that arenā€™t commanded by the arduino.

Since Z is moving, at least the Z STEP line has to be glitching for one reason or another. Glitching EN or DIR wouldnā€™t help if Z isnā€™t supposed to be moving at all.

The X artifacts could be glitching any or all of X STEP, EN, or DIR.

I really want to answer all of @donkjr 's questions, but Iā€™m not sure they will be relevant after this post.

OK, a lot has happened this morning. I thought extensively about this on my pillow last night.

Keep these key points of my setup in mind:

  • The LPS is mounted to the frame of the machine.
  • The 24V DC power supply is mounted to the frame of the machine.
  • The 24V DC power supply earth ground, negative (-), and enclosure are all tied together.

Using a multi-meter I found there was continuity between the 24V DC power supply case, negative (-), earth ground and the LPS case.

In my opinion, the DC power supply is junk. I eliminated it from the setup. I unmounted the LPS from the machine and set it on a piece of wood (now there is only one earth ground point). I grabbed my benchtop power supply that has a real earth ground, plugged it into the same outlet as the laser machine (same earth ground), and then connected that to my 24V distribution block that powers the Arduino and CNC shield.

andā€¦ I was able to burn something.

Now, my entire machine is in ruins :slight_smile: I have much nicer 24V DC power supply on order.

After the first successful burn, I wanted to see how far I could push the machine. I upped the speed and acceleration.

X and Y Acceleration: 2000mm/sec2
X and Y Speed: 200 mm/sec

With the higher speed and acceleration values I am seeing a few missed steps here or there. I do not believe I am exceeding the specs of the steppers or the machine. I do think that the Arduino is the cause and noise in the controller is the source, I just donā€™t know how to prove it.

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This is complicated and I think that the earlier questions and suggestions are still relevant.

Clearly, you have a ground(s) loop somewhere. The fact that there are still a few missed steps suggests that although you are making progress you havenā€™t really isolated the source(s).

All of the power supply frames should be tied to the frame of the machine as this is a safety ground. If disconnecting them from the frame creates + results then somehow these circuits are creating a loop that is affecting the logic. Like a shift in the DC supply voltage. Frame ground is for safety and should not be impacting the logic.

Sometimes power supplies have the negative tied to the frame internally. This does not mean that the supply is poorly made. I have seen cases where the logic [power] and frame ground need to be tied together and others where it creates problems.
Check the internals of the supply and see if there is a point to disconnect the two. Most of the time solving the problem by disconnecting these from each other suggests the source is actually elsewhere.

Think of grounding problems as high-frequency perturbations in the supply voltage. Modern chips run in the ns range so high-frequency shifts in the DC supply can dramatically affect the operation and you cannot detect them with common tools.

Recheck your grounding hygiene:

  • Ensure that all power source frames are tied to the frame.
  • Make sure all the extrusion frame sections are actually electrically tied together.
  • Make sure all power supply grounds are tied directly to one point on the frame. One wire from each. Make as short as possible
  • Make sure all loads have both + and - power connections back to their supplies. One set for each.

I am still betting the noise source is the Arduinoā€™s power and grounding.
By chance do you have an ossiloscope?

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@donkjr Yes I have scope.

And here are answers to your other questions:

The V- connection is obstructed in this photo behind my big red arrow. If you look closely you can see the edge of a black wire in the 3rd from top V- lug.

The CNC Shield is connected via the 24v DC V- and V+ that is depicted in the image above. It is routed out of the machine enclosure and into an electronics enclosure that is separate from the machine enclosure. It is grouped with the low voltage logic wiring (x,y, and z endstops).

This post visually represents the strange behavior. In few words, when X is supposed to move left, it moves right, then 2 seconds later it moves left when it should move left, two more seconds it moves right when it should move left. Sometimes stopping altogether when it should be moving. It is erratic behavior.

Iā€™ll ask this question again. How is an Arduino with the CNC shield supposed to be grounded? It only has a negative (-) and positive(+) lug.

This is interesting. I imagine it is OK to have a distribution block located elsewhere and have everything run to thatā€¦ correct me if I am wrong here.

I am mobile so my posts for the next few days may be ugly.

This is a hard question to answer accurately. If all the loads come to a single block and then a single wire goes to the supply that could be a culprit especially if the wire is to small a gauge.

I just realized that we jumped into a grounding problem and didnā€™t rule out a bad Arduino, shield or code?

Please post pictures and manuf. info of the Arduino, shield and itā€™s local wiring.

James Harding via Maker Forums Monday, September 5, 1:36 PM
Iā€™ll ask this question again. How is an Arduino with the CNC shield supposed to be grounded? It only has a negative (-) and positive(+) lug.

I can better answer this when I see the board and shield setup.

I would get a buss or connection to as many ground connections as possible.

Look at the Arduino power with your scope while this problem happens.

Make it a good day!
Don

@donkjr
Here is the legit Arduino Uno board, prontoneer CNC shield, and I snip of the scope connected to a coil pair from the scope on the x axis. Iā€™ll connect the scope to the power supply of the Arduino and upload shortly. :




We need to see how the Arduino power and ground are connected and from what.

Edit: I think I see it connected to a screw terminal at the lower right of the shield?

Provide pictures of its location, mounting and power wiring.

If I recall you have a 24v supply how are you getting 12v for the Arduino.

Stepper coil traces probably wonā€™t be easy to decifer.

Yes, itā€™s the lower right. The CNC shield has an allowable voltage range input from 12-36v. I have attached a photo of just the Ardunio and CNC shield without any wiring so you can get a better view.

Currently the Arduino isnā€™t mounted to anything because Iā€™ve had to dump the guts of my control box out onto the table to do all of this testing. I will get a photo of how itā€™s connected once I get it reconnected.

The Arduino canā€™t run on 24v so there must be a regulator/converter on that shield.
Do you have a schematic or can you point me to the manuf web site for that shield.

The reason I am poking at this is converters are notoriously noisy if not done right.

So the Arduino is in a separate box from the laser frame? How long is the wiring into the frame.

Incidentally, when the laser fires do you hear any cracking or hissing?

Isnā€™t the Arduino getting its 5V from the USB interface and the 12-36V is just on the CNC shield for the output driver of the stepper motors?

Here is the current layout:

Here is the website for the CNC Shield: https://blog.protoneer.co.nz/arduino-cnc-shield/

@dougl yes, the 5v could come from the usb port or the barrel jack or the CNC shield does have a 5v breakout pin that goes straight into the arduino header.

Just being clear here, the 5V pin on the protoneer is just a pass through, thereā€™s no buck converting on the protoneer supplying 5V to the arduino, right?

Can you try swapping out your USB cable? Try not passing it through the plug in the case; just use a high quality USB cable straight from your computer to the arduino, keeping it away from all other wires.

The number of laser problems that have been resolved by replacing the USB cable is amazingā€¦

That is correct, the protoneer is just a passthrough, You can see the separate buck converter in the image I posted.

Yes, Iā€™ll swap the USB cable out now. Iā€™m currently testing stuff right nowā€¦

Yes the Arduino is in a separate box from the laser frame.

The stepper motor wires are at least a yard long. The end stop wiring is roughly as long as their corresponding stepper motor wires. The 24v power leads are 24 inches or so.

In this photo you can kinda see how far the separate electronics enclosure is from the laser power supply.

Crackling, why yes. This is a relatively new symptom too. Here is a very short video of it happening.

Thanks for photos I think we now have a full picture.

BTW: nice build. Many makers do not pay attention to wiring design and electronics packaging and it makes solving this kind of problem all the harder.

Just as FYI, is the blue mounting plate on the floor of the box with the bosses purchased?

Ok then. There are two common problems we see that were synonymous with arching and may be manifesting here.

  1. Poor quality USB cables. I donā€™t know for sure but I suspect poor grounding and shielding.
  2. Ground loops in the controller to PC connection. Some USB driver boards were the culprit.
  3. HV arching causing electronics to go wack-a-doddle [technical term].
  4. A combination of the above.

We have helped in multiple of these scenarios and in most the arching had to be stopped. In these cases we never really isolated where and how it was injected into the electronics. The energy dumped with these lasers is crazy high so think of an Arduino running in the middle of a lightning storm.

Did I observe correctly in the video that the stepper noise was synonymous with the arc?

So letā€™s find out why the HV is arching.

Be cautious the LPS lightning can be lethal.

Set up the machine to run in the dark. Turn out the lights, start the job and watch for the source of arch. They may be very bright lightening strikes or less obvious showers of sparks (corona).
Arcs also can be from bad tubes but letā€™s not get ahead of ourselves.

My guess is that somewhere the anode lead is too close to ground or there is a sharp edge in a connection. Also check that the FG pin on the LPS and the cathode is at safety ground.

If you have a laser current meter you should be able to see a jump in current when it arcs.

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Thank you! Itā€™s been a long time in the making.

I designed and 3D printed it to mount all of my electronics to. As of now itā€™s looking like itā€™s going to need to be redesigned though.

In that video it does appear as thought the arc coincides with the stepper stopping. I must say though this crackling/popping was not happening until very recently. I changed the 24v power supply for a different one.

Tonight when it gets dark out, I will run the test to see where the arcing is coming from. Iā€™ll let you know the results!

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