X-axis stuttering/jittering with loud noise (FIXED)

CNC Machines Shapeoko 3
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I’ve seen some other posts which mention this problem I’m having, but nothing with a definitive solution so I’m starting a new thread to add my details, in the hopes that it’ll help someone in the future.

Problem: Despite my S3 having worked fine the previous day, upon powering on and hitting the Initialize Machine button, the X-axis motor is emitting a loud racket and moving the toolhead left and right short distances very rapidly (like a mm or two either direction). The Y and Z axes are fine.

About 6 months ago, the machine exhibited this X-axis jitter/stutter behavior for some time (days) and then it went back to behaving normally, as suddenly and magically as the stutter appeared. I haven’t used the machine much in the past 6 months but over the past couple of days got the machine set up for a new project and now the jitter state is back and it doesn’t seem to want to leave.

Things I’ve discovered:

powered-off, the X axis moves easily and smoothly.

I have a spare Carbide3d motor. Plugging that motor to the connector near the toolhead (ie, on the other side of the long cable from the controller board) results in the jittery/stutter-y movement and lots of vibration of the motor.

Plugging the spare motor directly to the controller/Grbl board (no long cable) yields a smoothly moving motor.

Progress! So, now I’m looking at the cable as the culprit and I’m thinking that perhaps over time, one of the wires has degraded because of the many bending cycles. That could also explain why this behavior is intermittent, if the wires are degraded but not totally separated. All that said, it just doesn’t seem very high probability. Why does it work so repeatably when it’s working, before it magically flips to the “bad” state, where it’s equally repeatably bad until it suddenly flips states again?

I pulled the X-motor cable out and inspected it and visually it’s fine but of course I’m going to replace it. While I wait for a replacement cable to try it out, is there something else I should be looking at?

I’m hoping someone has seen this behavior before and can save me some time!

thanks all -

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The behavior you are describing is being caused by one of the coils in the stepper motor not getting properly energized. From the sounds of it your cable has a break in one of the conductors that intermittently making contact. As the cable moves around it might make contact for a while then disconnect. It could also be related to temperature. As the cable warms up and cools off it could make intermittent contact. I would recommend getting a multimeter. Use it in continuity mode and put the probes on either end of each wire in the cable then move the cable around. If the cable shows continuity in one position but it breaks in another you have your culprit.

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Thank you for the quick reply. I was just putting a battery in the multimeter! I’ll report back.

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Yep, one wire open. So much for my “low probability” comment. Now I need to find some replacement wire.

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Well, the saga continues! I repaired the cable with some 22AWG, re-tested and all lines are good now, yet it’s still doing it!

So I thought maybe I damaged the motor with all that vibration, but the spare motor also vibrates.

Any other ideas? I can put the multimeter probes on the leads while the machine is operating: are there some tests I can do to try to figure out what’s going on?

All I’ve done so far is to check the impedance of the coils - they were both 1.7ohms.

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amazingly, fixing the broken lead didn’t fix it! could I have damaged the Grbl board?

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It is possible. An intermittent connection when power is applied is one of the things which will damage a stepper driver.

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Thanks, Will. Would you please advise on cost and availability of a new control board? Thanks

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Go to:

https://my.carbide3d.com/

click on “Shapeko 3”

https://my.carbide3d.com/gettingstarted/shapeoko3/

click on “Spare Parts”

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Thank you!

Can anyone guide me as to how I can test my current board? Between the multimeter and an o-scope, I can take some data if only I knew more about how to verify output of stepper drivers.

thanks much -

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I haven’t used one of those in 50 years.

Go for it if it helps

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Now that you mention it, I say o-scope but really it’s a logic analyzer, with a couple of analog input pins with o-scope functionality.

So, I guess I should say, to someone who might be inclined to lend me their wisdom in the ways of stepper drivers: I can scope digital signals, analog voltages and DC voltages. How might I test my C3D controller board (specifically the X stepper driver).

thanks all -

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First verify that your stepper motor is good. Check continuity on the motor wires. There should be two pairs of connected wires. Next switch into resistance mode and check that the two pairs measure roughly the same. I had a stepper motor on a 3D printer where one pair measured 2 ohms and another measured 12 ohms. Both showed continuity but the difference in current flow would cause problems.

If the stepper checks good attach the repaired cable to the motor and repeat the test from the controller end connector while moving the wire around. I have seen it where there were multiple intermittent breaks in the wires before. Again you also want to make sure the resistance is roughly the same between the coils.

If the cable and the motor both check good it pretty much leaves the controller.

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Thanks! I’m in the middle of writing down the resistance values for each lane along the cable. It seems that the resistance can change quite a bit while I move the wires at the connectors. I have the probes in a gap between the header connector and the receptacle connector so I can test through the pin-to-terminal connection and, at first glance, there’s a lot of variation with wire movement. So, I suspect my board is fine and I need to upgrade the cables and connections from stock.

Mine is a pretty old S3 with original cables. I’m guessing the pin-to-terminal contact surfaces have degraded, perhaps the spring force of the terminals have gone down.

I’ll update with some resistance numbers and if the variation is more than you’d expect, I’ll have to pull those terminals out of the plastic housings and clean and reshape the contact springs, as a near-term fix.

I really need this machine up and running today!

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Yeah it sounds like your cable is bad. The resistance of the wire will change slightly as it moves around, but if it is significant it means that individual strands in the stranded wire have breaks in them and are losing contact with each other.

Obviously replacing it with a proper wire from C3D is the best option.

That said you need the machine up ASAP. The “quick” and dirty option is to make your own. When I moved my SO3 into an enclosure I had to lengthen all of the wires. I chopped the connectors off with about 4 inches of the original wires and then soldered a length of stranded led cable in the middle. I used this stuff:

https://www.amazon.com/gp/product/B01KWBPC7M/

but Home Depot sells 22 gauge 4 conductor stranded wire for security systems.

You will want to make sure the connections at the connector are good. You can try carefully removing the terminal connectors from the terminal block and verify that the crimp on the connector is good. When splicing the wire look up the NASA approved lineman method. Make sure the splice is not in an area of the cable that needs to move around. Make sure to put your heat shrink tubing on BEFORE soldering the wire (ask me how I know to do that :stuck_out_tongue: ).

DO NOT use these things:

They use a very low melting solder that does not wick into the solder joint well making a weak connection (again ask me how I know).

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Well everyone, the problem was solved by replacing the connector which mates to the Grbl control board. I had inspected that previously, but not closely enough. There was corrosion on one header pin and (at least) one of the terminals in the cable connector was moving around quite a bit, making for an intermittent connection.

Combine this with the one wire which was a no-connect and it appears the motor cable end-of-life for my aging S3 is rapidly approaching. I’ll be looking for some nice shielded-wire cabling to make replacements. I’ll update this or start a new thread with that info when I find a good option.

Many thanks to @WillAdams and @CthulhuLabs for all the help and encouragement!

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