Centroid Community CNC Support Forum

Hi All,

I’m really running out of ideas here. My Acorn works fine on its own driving 4 stepper motors using Geckodrive GR214V. Now, when I connect VFD 0-10V with manufacturer recommended capacitor (it is worse without the capacitor and RPM is incorrect), all the stepper motors behave erratically and moves around randomly. It seemed like a ground issue and I’ve made sure that I’m doing the star grounding with shielded cables. So, after much of troubleshooting, if I ground VFD Common then erratic behavior pretty much goes away and everything works as expected. However, mainly X and Z axis stepper motor lose their position slowly and quietly. I can feel the step is being triggered when I touch the motors. I thought I’ve fixed the erratic behavior issue, but found out this slowly losing position issue while doing circle diamond square test when it seemed like gcode is doing layer shift. I really have no more ideas and not sure why VFD would affect stepper motors in such a weird way. I’d really appreciate if anybody has an idea to explain this issue. Thanks!

Regards,
Eric

Does the position loss only happen while the spindle is running? If so, I think that would indicate the spindle is putting out electrical noise that is getting through the shielding on the stepper cables or possibly to the stepper drive inputs. The solution to that would be to improve the filtering on the VFD input and maybe better cable on the VFD output.

To get the best recommendations, we will need some pictures of the cabinet and all the relevant wiring.

Are you using VFD specific cable and have everything grounded properly? I'm guessing no as this is definitely a noise issue from the VFD. I have used Fuling VFD's in the past and they work great.

Your step and direction cables should also be shielded twisted pairs to maximize noise rejection.

Thank you all for your responses!

@centroid647
It happens when machine is in idle and doing nothing. I’ve also attached the picture of my setup, so let me know if you spot anything odd or unclear.

@ShawnM
Yes, I’m using one of these proper VFD cable: https://www.ebay.com/itm/145871539791?m ... media=COPY

As for the grounding, it is grounded on both side and should I check anything else in terms of grounding?

@tblough
I’m using shielded cable as you can see from the picture and for the time being I’ve disconnected shield grounding to see if it makes any difference. Also, my understanding is that the GR214Vs are wired according to https://www.centroidcnc.com/dealersuppo ... 113.r2.pdf. So, since all the inputs are optically isolated and VFD connection is only one 0-10V cable, I’m thinking it shouldn’t be a problem. I also tried getting them far apart as well.

UPDATE
After thinking about this for a while, I’ve tried separating the Acorn power supply AC circuit from 60V stepper drive power supply as AC and DC GND on Acorn power supply is connected together. It seem to make the situation little better, but I can still hear and feel that the Z axis is occasionally stepping and slowly moving up over time. Looking forward to your responses. Thanks!

Regards,
Eric

You should try grounding the shield on the VFD cable at the end closest to Acorn. Sometimes grounding it at both ends makes things worse. This also applies to your step/direction signal wires. They should only be grounded at one end, not both.

Do you have a common ground bus bar in the system? I don't see one. All grounds need to go to ONE bus bar.

That ribbon cable from Acorn to the DB25 board isn't helping things either, It's totally unshielded with many cables running near it.

Is your backplane plastic or metal?

@ShawnM
Ah, OK. I’ll try changing the grounding on the VFD cable. As for the signal wires, they are grounded at one side.

Regarding the common ground bus bar, I don’t have one and everything that needs to be grounded bonded together with the wire nut at the top right corner.

Also, ribbon cable is a good point and I wonder why I didn’t think about it before. I’ll change that to shielded DB25 cable.

The backplane and the enclosure are plastic. I got it because it was cheaper, and had enclosure fan with power supply and temperature sensor that you see next to the Acorn power supply.

I’ll make those changes and will report back. Thanks a lot!

Regards,
Eric

UPDATE

OK, grounding doesn’t seem to make a difference. Also, I think isolating AC circuit between 24V and 5V power supply and 60V power supply didn’t resolve the issue.

Next, I’m going to replace the breakout terminal with ribbon cable with metal DB25 breakout connector as it seems that it is going to be crammed after a cable with two DB25 connectors on both ends.

I’m also wondering if I should supply 5V from a different power supply in order for the optical isolation on GR214V to be effective. It sounds like optical isolation works for a separate grounds and I’m guessing that steps being triggered means definitely something is affecting step/direction signal. Otherwise, I can’t think of any scenario that could cause step motors to jog on their own on the output side.

Every ground needs to be at the same location on a common bus bar so it would be impossible to have what needs to be grounded in a single wire nut. If it spiders all over the cabinet that's not a common ground point.

Back plane has to be metal, plain galvanized steel is the best choice but never plastic. Plastic and wood back planes are terrible to use. This is another cause for noise.

I understand everyone is on a budget but you cannot short yourself in critical areas when building a CNC. This is not a cheap hobby and when you buy cheaper components to save a few dollars you pay for it in the long run by wasting countless hours troubleshooting all the issues that come up because you are using said components.

There's no need for a temperature sensor for the fan. It should be running all the time and "pressurizing" the cabinet. Do not have it pushing or blowing air out of the cabinet. Not sure how you have it wired but correct this if you have it backwards.

@ShawnM
I do understand what you’re saying and as far as I can tell it is a star grounding. It is just few wires including 4 wires to stepper drivers, VFD common, HomeAll, and eStop. So, I feel like I could be missing something when you say impossible.

Sorry if it did upset you and I do appreciate you taking your time and responding. I’ll definitely switch out the enclosure for a proper one. I had this enclosure a long time ago and it made sense to make use of it. I just thought it is quite odd that the issue appears only when I connect VFD and felt like a some type of grounding issue than noise. Of course I could be wrong and as you can see I’m switching them out one by one.

As for the fan, it suck air on one side and blows on the other side. I hope this is not related to this issue. If it turns out to be then will be resolved with metal enclosure. Thanks!

Regards,
Eric