New drifting

As noted before I am a rookie so I will understand why this is happening in due time…but not yet. I ran the basic welcome project in Easel and I had an issue come up where each layer was approximately 1/64" over from the previous layer. That is only an approximate. The run had to cut into the material down to a 1/4" depth which became about six passes. After the run the machine returned to the home position that I set at the beginning of the run and it was off by about 1" on the X, 1/2" on the Y, and 1/64" on the Z. I checked the belts and confirmed they were tight. I checked the tightness of the wheels- seemed to match the details in the setup…Thoughts on how to ‘cure’ this drift? Thanks- J.R.



I think this has come to mean that you need to adjust your belt tension, eccentrics, or, motor current (maybe all of the above, too).

I will have to try to adjust the pots for the X and Y drives on the gshield. I could see the z axis being just above the material at the end so it seems reasonable that it is ok. I believe the belts and wheels were good. Certainly worth checking again, but will start with the power adjustment for the next run (perhaps tomorrow).

Had similar isue on just the x axis. Turned out to be the set screw on the pulley. During big movements the pulley slipped. After slip it continued on as normal. Make sure the set screws are tight. If you need more because you sucked them up the vacuum cleaner then go to an RC/Hobby shop, size M3.

So I just had the same issue. It appears I just fell victim to vacuuming up both my set screws for my x axis pulley! Im pretty positive thats going to fix my sudden appearance of the x axis drift! CRAP!

I checked belts, verified wheels, checked set screws, adjusted pots on gshield and this came pretty durn close in my book. 1/32" off on the return after the run. I posted the test pattern at https://www.inventables.com/projects/test-box-circle-diamond

I ran a few more runs with minor tweaks to the pots on the gshield- much better

.

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Replacing my set screws and slightly tweaking the pots did the trick this time. I added a little bit of blue thread lock too.

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Are there voltage test pads near the driver chips so those of you adjusting pots can report the value you find is working? Granted there are different motor options and harness lengths for the 0.5 and 1m rail configs, but would be good to start a data set to help others.

My Xcarve is going to divorce me…still in boxes. I expect to start assembly in July. :frowning:

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Adjust the Y potentiometer by turning it clockwise by a small amount until the Y-axis moves smoothly at rapid speeds (Do it when moving a long distance while Z is retracted on a large job).

WHAT IS WRONG WITH YOU? :grinning:

I was into those boxes less than 5 minutes after I got home!

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@JkWestphal,

Well, I did open the electronics box and poke around and marvel at the excellent packing, but was afraid to scatter things when my installation location isn’t available yet…still finishing a big desk project and have a bunch of wood all over its eventual home…

Desk project is sit or stand (monitor shown is ultrawide 34" in two positions using hydraulic arm, and keyboard tray is going to be Cobra style above or below center desk piece), and since I’m using mesquite for one of the stacks and need 22" layups, but mesquite rarely comes in boards with usable widths beyond 6"…there’s a lot of culling to be done to build them up. I’m mostly done now…another 2 weeks or so to final shape the 3 right side shelves, sand, oil, let oil cure before wiping varnish, then move inside and assemble (I can only work on things on the weekends).

Oh and another note on scale, the bottom left solid is a mid-tower ATX case, above it is my 3D printer, the right side case was going to be.a CaseLabs SMA8 at about 26" tall and deep.

Nevertheless, I remain ashamed… :flushed:
Sorry for temporary threadjack.

At the risk of continuing the thread jack (sorry).

I understand the not wanting to scatter parts in a sawdust strewn woodshop, i had to clean mine up before my machine arrived. Then the night before it showed up the wife wants a new bird feeder, … NOW!

If mama aint happy, aint nobody happy.

Bird feeder is mostly done needs plexiglas yet.

That Desk design is awsome! You are forgiven sir.

End of thread jack.

Is there a more accurate way of setting/tuning the pots on the gshield? Use of an ohm meter?

Not an ohm meter, but you can do it with a volt meter. I have to go to work now, but if you haven’t found out how to do it when I return I can tell you how.

If you could post a general procedure to check the pots using a voltmeter, I’d appreciate it. I’m working on a calibration video and am one of the lucky ones who hasn’t had to adjust the pots, yet. I’d still like to address them in the video though, and will be glad to give you credit for the procedure.

Rob

@RobertA_Rieke

The potentiometers on the grbl board are setting the Vref (Voltage Reference) level on the TI stepper motor driver chips. This determines the current limit for the driver.

You can measure this voltage at one of the potentiometer pins (see photo) and adjust it to obtain a given current limit. Use great care as the potentiometer pins are very close to other components and it is easy to short the pins together with your meter probe. Really bad things happen.

The gShield (version 5) uses a 0.1 ohm current sense resistor so the formula is Vref = 0.8 * I.

The maximum current the driver chip can deliver with appropriate cooling is 2.5 amps. To use this current value you would set the Vref voltage at (0.8 * 2.5 amps) = 2 volts. This is the theoretical current limit.

The NEMA 17 motor (part #25253-01) that Inventables sells has a maximum current rating of 1.68 amps per phase. To set the maximum current limit for this motor you would set the potentiometer to (0.8 * 1.68 amps) = 1.34 volts.

It should be noted that the maximum current a motor can handle is not necessarily the correct setting for the motor. Stepper motors will operate at a lower current than maximum, with a corresponding reduction in torque. You don’t want to exceed the maximum current per phase of stepper motor as doing so will damage the motor.

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That’s excellent information, thank you! I’ve got a couple followup questions:

  1. Should you place the second multimeter probe on the GND screw?
  2. The NEMA 23 motors say they are 2.8A current/phase, so the max voltage for them should be 2.0V due to cooling, not 2.24V. Does that sound correct?
  3. Is there a % you would recommend setting them to, like 90%?

I’m going to recommend that the pots not be tweaked unless poor performance is noted, but it would be nice to give a solid number to tweak up to, rather than just suggesting small pot turns.

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@RobertA_Rieke

  1. Positive lead on the potentiometer pin and negative lead to a ground point. The ground screw terminal where the power wire is connected would be a good place.
  2. Yes and no. The calculation is correct in that a current of 2.8 amps would need a Vref of 2.24 volts, however, that would exceed the capability of the driver chip and it would shutdown due to thermal overload. In fact, without testing, I’m pretty sure that the driver chip will do a thermal overload shutdown even with a Vref of 2.0 volts because the cooling provided for the chips is most likely inadequate. Don’t read that as a criticism toward Inventables because I don’t think that one needs to drive the motors that hard for the X-carve anyway. There are trade-offs associated with the selection of an operating current value some of which are torque, heat, motor life, etc.
  3. No, I haven’t done much testing. I picked an arbitrary point to start with and I’m going to see if I encounter any problems.

The gShield that I received had the potentiometers set for 0.9 amps per phase. Based on the problems many of the forum members reported here, I suspect that’s too low. I have the NEMA 23 motors and I arbitrarily picked 1.6 amps per phase roughly because that is about the maximum for the NEMA 17s which are the standard issue for an X-carve 500mm.

I’m guessing that the stock cooling fan will keep the drivers cool enough to deliver that amount. Only time will tell.

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@LarryM

Great info, thank you! I may recommend starting at 1.4, then bumping up to 1.5 and 1.6 if needed. Be sure to let me know if you start to suspect 1.6 may be too much.