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Introduction

When changing the extruder motor to a compact but powerful motor (recommended for the Titan and Titan Aero) or Slimline motor (still useable but may require slower printing speeds) you will most likely require a slight adjustment to the stepper driver to ensure that you are not over or under powering the motor. Not over or underpowering is important in order to provide the ideal amount of torque for the extruder to run without skipping steps or overheating and damaging the motor.

For the Compact but powerful motor, the Maximum rated current that you should set the stepper driver to output is 1.68A.

For the Slimline motor, the maximum rated current that you should set the stepper driver to output is 1.4A.

  1. In order to get an accurate result from the calculation you need to work out what resistors your A4988 uses. Different manufacturers use different resistors which affects the final settable figure.
    • In order to get an accurate result from the calculation you need to work out what resistors your A4988 uses. Different manufacturers use different resistors which affects the final settable figure.

    • In terms of Pololu A4988's, boards made before Jan 2017 used an Rsense value of 0.050, boards made after Jan 2017 use a value of 0.068

    • Other reprap boards may use different values so make sure you refer to the data sheet.

    • The A4988 boards that we sell are based on the Pololu board and therefore use a resense value of 0.05.

    • VREF = Rated motor current x 8 x Rsense

    • VREF = 1.68 x 8 x 0.05

    • VREF = 0.672

    • it's always a good idea to provide a 10% safety margin to make sure your not running components at the maximum rating.

    • VREF with a 10% safety margin = 0.6

  2. To work out what your current VREF is you need to use a multi-meter
    • To work out what your current VREF is you need to use a multi-meter

    • We are dealing with DC voltage so select the 2V DC option.

    • Make sure the printer board is fully powered, ie it must be powered by the power supply not just over USB to get a correct reading.

  3. Use the red probe on the potentiometer, Use the Black probe on the Ground Pin.
    • Use the red probe on the potentiometer,

    • Use the Black probe on the Ground Pin.

  4. In order to rotate the potentiometer you will need a ceramic screw driver to prevent shorting out any of the components whilst performing the adjustment.
    • In order to rotate the potentiometer you will need a ceramic screw driver to prevent shorting out any of the components whilst performing the adjustment.

  5. From the first reading the VREF was set to 0.845v this is too high and will lead to the motor over heating and may loose torque and begin under extruding. By rotating the potentiometer anticlockwise you can decrease the VREF.
    • From the first reading the VREF was set to 0.845v this is too high and will lead to the motor over heating and may loose torque and begin under extruding.

    • By rotating the potentiometer anticlockwise you can decrease the VREF.

    • The second image shows the correct 0.6v set, being exactly on the dot isn't vital in this case as we are below the maximum rating of the motor.

    • Depending on the manufacturer of the board the direct of rotation may be different so check before turning it too far.

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Dan Rock

Member since: 06/07/2018

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