Cant set the correct Vref for stepper motors

Hey everyone,

First of all I want to say that I'm new and not good at this stuff but I still try. So my friend and I are currently making a chess computer that moves pieces in real life with an elektromagnet. The magnet is moved by stepper motors. These steppers are plugged in a cnc shield with an Arduino uno, however when we first tried out the steppers we didn't realise setting the Vref was a thing, so we didn't and the motors ran way too hot. After googling this we came to the conclusion that it was a normal thing but after the steppers melted the plastic of our 3d-printed holders we knew something was up. We stupidly didn't set the correct Vref values on neither of the 3 steppers, and now we can't seem to. We use nema 17 motors and drv8825 drivers so with the formula Vref = Imax / 2 we calculated we only needed about 0.35 V, we were getting 19.25 to 19.08 and it wouldn't go any lower than that. So after using a different power supply it could run at about 3.5V. However the steppers weren't responding to our code, only when we cranked it up to 12V was the stepper actually moving, but also getting too hot. So our questions are: Did we ruin our drivers? Is it still possible to set the correct Vref or are we just too late? And what specifically do you think broke? Any help would be greatly appreciated.

Vref can be set down to 500mV (lesser is possible but its very close to the trimmer pot's end of travel) corresponding to a current of 1A. On the DRV8825 board clockwise reduces Vref and anti clockwise increases Vref.

Nema17 tells about the mechanics, the face, the mounting holes, and tells nothing about suitable current.
Post the schematics for the unfortunate setup.

The Vref setting depends on the current sense resistor in the motor driver, and different manufacturers use different sense resistors.

In order to correctly set the current limit, you MUST know that sense resistor value. Pololu gives reliable instructions for setting their drivers, but those don't necessarily apply to the many clones.

What you wrote...makes no sense.

Here is the easiest way to adjust:

  1. turn pot to lowest current
  2. run the motor at 40 rpm or so
  3. turn pot to increase current until the motor starts running roughly.
  4. turn pot back a little bit

You should use a non-conductive tool to adjust the tiny trimpot.

For the DRV8825 board this is when you turn the trimpot all the way CW. Do not connect the motor at this time (disconnect Vmot) and measure the voltage at the trimpot centre and ground to verify that the voltage is indeed zero or close to it. Then either connect the motor and advance it slowly or if you are sure of the voltage advance the trimmer till you reach that.

I think you have the cheap clone DRV8825 boards with the test-point pad on the wrong trace. The rotating metal part of the trim-pot is the point to measure for those.

Its so pathetic they couldn't even clone a circuit that's well documented correctly...

Alternatively buy the genuine Pololu DRV8825 boards.

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