[rfresh737]

I have a Benbox DIY Laser machine that uses two A4988 drivers (X and Y axis only) that have 0.1 ohm Resistors.

I've found on the internet two different formulas to calculate the correct Vref values that can I adjust/set using the trim pot. But both formulas give very different values and I don't know which one to use/is correct to use?

The first one:
Vref = motor amps * (8 * Rs)

for my steppers they are rated at 1.3 amps so I get this answer: 1.04 = 1.3* (8 * 0.1)
Which means my Vref values should be around 1.0 volt.

The second formula I found was this one:
Stepper amps/2.5 = Vref
for my steppers:
1.3amps / 2.5 = Vref 0.52 volts.

I have two A4988's and the first one Vref is 0.17 and the second one is 0.417

I set my multimeter to 20 DC scale, power up my controller board with the power supply plug and the USB plug. I put the black lead on ground and the red lead on the trim pot to read the voltage.

Any help and/or clarification would be greatly appreciated.

[Toinvd]

The first formula is a good one which can be used for all of them.
The seccond formula is only for the A4988 with 0.05 ohm resistors. The A4988 comes in different versions with different resistors.
The way you read the voltage is correct. Check the temperature, and apply a small fan to keep them cool, they will smile at you and survive longer.

[rfresh737]

I've come to understand (from the factory) that my two different Vref readings are correct...because one of the A4988's is driving two stepper motors.