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    • The standard Hemera motor has a rated motor current of 1.33A.

    • This value is likely to be different from the motor you may have been previously using with your printer.

    • In order to provide the Hemera motor with the correct amount of current, so as to have it's ideal torque level, and not over heat, it is required to make some adjustments to the VREF on your stepper drivers.

    • This guide will provide the information needed for the 3 most common stepper driver types. A4988, DRV8825 and the TMC drivers.

    • A4988 calculation.

    • VREF = Rated Motor Current x 8 x Rsense

    • VREF = 1.33 x 8 x 0.05

    • VREF = 0.532

    • It is advised to add a 10% safety margin to avoid any over heating, decreasing the lifespan of the driver.

    • 0.532 - 0.0532 = 0.4788

    • In order to make the adjustment easier this figure can be rounded up to 0.5v

    • For the A4988 driver, make sure to check the Rsense value on your mainboard or stepstick module. Rsense is not always 0.05 Ohm. Creality regularly uses a Rsense value of 0.10 Ohm on their mainboards for this driver. Using an incorrect Rsense value results in an incorrect current setting.

    • DRV 8825 calculation

    • VREF = Rated Motor Current / 2

    • VREF = 1.33/2

    • VREF = 0.665

    • It is advised to add a 10% safety margin to avoid any over heating, decreasing the lifespan of the driver.

    • 0.665 - 0.0665 = 0.5985

    • In order to make the adjustment easier this value can be rounded up to 0.6v

    • LV 8729 calculation:

    • VREF = Max current / 2

    • VREF = 1.33 / 2

    • VREF = 0.665

    • It is advised to add a 10% safety margin to avoid any over heating, decreasing the lifespan of the driver.

    • 0.665 - 0.0665 = 0.5985

    • In order to make the adjustment easier this value can be rounded up to 0.6

    • Duet settings,

    • In typical use cases the current setting should be 60% - 90% the rated current of the stepper motor.

    • In the case of Hemera that would mean setting the current to between 0.798 A - 1.197 A.

    • for more information please see: https://duet3d.dozuki.com/Wiki/Setting_m...

    • The TMC driver series uses a root mean square (RMS) value for the calculations.

    • RMS = Max rated current / 1.41

    • RMS = 1.33 / 1.41

    • RMS = 0.94

    • TMC 2100 calculation:

    • VREF= (RMS current x 2.5) / 1.77

    • VREF = (0.94 x 2.5) / 1.77

    • VREF = 2.35 / 1.77

    • VREF = 1.33

    • It is advised to add a 10% safety margin to avoid any over heating, decreasing the lifespan of the driver.

    • 1.33 - 0.133 = 1.197

    • VREF = 1.197

    • For more specific information regarding setting current with TMC drivers please refer to the datasheet for your specific step stick/ driver being used.

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7 other people completed this guide.

Dan Rock

Member since: 06/07/2018

21,493 Reputation

40 Guides authored

8 Comments

I don’t understand where to adjust these settings? Arduino?

Sajjad Haider - Reply

It depends on your setup, either physically via the trim pot on the stepper drivers or firmware, there are a lot of different printers on the market so you will have to do a little research on the particulars of your setup.

Dan Rock -

on the sidewinder x1 is this step necessary for the hemera upgrade? I would like to change these values if i can but i’m not sure how to enter these values. I know I can adjust the rms value in the firmware but don’t know hat to do about the Vref. Others tell me that vref must be changed physically and im not ready for that. If I skipped this step would it affect my print quality? If there is a way for me to do this all in my firmware how would I do it? thanks.

*tmc2100 drivers on mks genL btw

Greg Bowes - Reply

ditto ↑ on the Artillery Sidewinder X1 SW-X1

James A Thierer -

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