Stepper Driver REF Settings

Adjusting Stepper Driver Potentiometers

The Generation 4 stepper drivers have four adjustable potentiometers labeled PFD, RC1, REF, and RC2. This allows modularity in the electronics so that stepper motors of all different specs and sizes can be controlled with the same driver. A brief description of what each potentiometer controls can be found on the page about the Stepper Driver v3.3

The pot labeled REF controls current supplied to the motor. This is the most commonly adjusted pot. Do not adjust the others unless you know what you are doing. Conveniently, each pot has a test point for measuring with a multimeter. Put the positive probe on the test point, and the negative probe to ground.

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Note that these values are with the steppers DISABLED, not enabled. 'DISABLED' means that you have not activated your stepper motors in ReplicatorG

If you do not have a multimeter, counter clockwise rotation will decrease the value, and clockwise will increase for REF and PFD — but it's the opposite for RC1 and RC2. There are small indications of the total range for each potentiometer engraved in its case. Suggested values for the stock Thing-O-Matic steppers are:

Stepper Motor REF Voltage (V) Rotation between Max and Min
X & Y 0.600 Between 1/8 - 1/4
Z 0.617 Between 1/8 - 1/4

Note: If you set the current too high, the motor will be eventually get too hot to touch.

If your Z axis stepper motor is making high pitched noises while set to the above REF value, then you will need to change the other potentiometers as well.

Since the motor suppliers have changed over the course of the Thing-O-Matic's lifetime, you first need to identify which motors you have from the image below, and then adjust their respective potentiometers accordingly.

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The suggested pot values for the Z-axis stepper motors ONLY:

Stepper Motor PFD (V) RC1 (V) REF (V) RC2 (V)
Makerbot Leadscrew Nema17 2.311 0.952 0.617 0.963
Moons Leadscrew Nema17 2.311 0.952 0.617 0.963

The suggested pot values for the X&Y-axis stepper motors ONLY:

Stepper Motor PFD (V) RC1 (V) REF (V) RC2 (V)
Makerbot Nema17 1.952 0.953 0.600 0.955
Moons Nema17 1.952 0.953 1.68 0.955

The suggested pot values for the Stepstruder MK7 stepper motor ONLY:

Stepper Motor PFD (V) RC1 (V) REF (V) RC2 (V)
Stepstruder MK7 1.952 0.953 1.68 0.955

The suggested pot values for the Stepstruder MK6 stepper motor ONLY:

Stepper Motor PFD (V) RC1 (V) REF (V) RC2 (V)
Stepstruder MK6 2.31 0.94 1.56 0.94
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