1 Topic by CarstenBe (edited by CarstenBe 2014-03-16 10:07:03)

  • CarstenBe
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  • Registered: 2014-02-11
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Topic: Vref?

Hi.

I have adjusted the extruder Vref by turning the trimpot all the way down, and then slowly back up just before the motor started pulsing.

This puts the Vref at 1.4v ??

I have also adjusted the x Vref from .51 to .42 as per the sollidodle website. This resulted in an extremely hot x motor (nearly melting the belt)

It seems to me that going from .51 to .42 increased the amps instead of going down.

This dosent make sense when looking at the numbers on the solidoodle website:

    ▪    Extruder: 0.192V (note: for Rev E Motherboards, the extruder voltage should be 0.770V)
    ▪    X-Axis: 0.443V
    ▪    Y-Axis: 0.520V
    ▪    Z-Axis: 0.500V

This would put the smaller x motor under more load than the y and z motors.

This is on a one week old SD4 with the Rev E board.

Any ideas on this…?


Kind regards
Carsten

Solidoodle 4. Glass bed. E3D v6

2 Reply by grob

  • grob
  • grob
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Re: Vref?

How are you measuring Vref exactly? Using this article? http://wiki.solidoodle.com/multimeter-testing
I personally have just tuned the motors by ear and left it at that. Nothing's running particularly hot, I did have to wind the extruder and x motors down a bit to reduce pulsing (no skips yet, but keeping an eye on it...).

SD3. Mk2b + glass, heated enclosure, GT2 belts, direct drive y shaft, linear bearings, bowden-feed E3D v5 w/ 0.9° stepper
Smoothieboard via Octoprint on RPi

3 Reply by knowack (edited by knowack 2014-03-17 14:32:07)

  • knowack
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Re: Vref?

A few weeks ago, I tried adjusting my SD4 to the VREF values posted, and X Y Z axis stalled out (the extruder too, as I recall).  Fortunately, I had written down the values before I began, so I just set them back to the original voltages.

I did reduce the extruder VREF by .2 volts, which completely eliminated the moire effect.  (Original voltage was .821, posted procedure recommended .400, I set mine to ~.620)

4 Reply by adrian (edited by adrian 2014-03-17 14:41:55)

  • adrian
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Re: Vref?

knowack wrote:

A few weeks ago, I tried adjusting my SD4 to the VREF values posted, and X Y Z axis stalled out (the extruder too, as I recall).  Fortunately, I had written down the values before I began, so I just set them back to the original voltages.

I did reduce the extruder VREF by .2 volts, which completely eliminated the moire effect.  (Original voltage was .821, posted procedure recommended .400, I set mine to ~.620)

So VREF is determined by two things essentially;
The sense resistor used (this can change between manufacturers, and why A4988 StepSticks have different VREF values to Pololous. The value of the resistor determines the VREF values you adjust against...)

Or the Driver Chip itself is different (DRV8825's from Ti use different values to the Allegro A49XX's) .

Now, I can't see Solidoodle changing to the Ti chips - so I'm just going to *guess* (thats all I can do, because I wont believe for a moment the printrboard schematics on the solidoodle website are the same as what they ship today given the firmware is now different and thus violating GPL.... but I digress...) that they have changed the sense resistor.

If someone can take a high resolution, clear, closeup picture of the printrboard for me, I will try and identify whats changed. But I'm going to just guess they have switched sense resistor values...

PM me a URL, or PM me for an email address if you don't want to post it publicly (I'd like the full res, huge original file, so I can get in close and try and read the tiny values on the resistors on the circuit near the stepper drivers).