how to regolate vref for clone axis

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how to regolate vref for clone axis

Post by soanlu » Sun Oct 27, 2019 8:16 pm

I'm Andrea from Rome and I'm building my first laser cnc with arduino uno, cnc shield, drivers dvr 8825 and nema 17 with 1,7A (to calculate the vref I have considerated 1.5 A and I have set each vref 0.750 mV)

For the X axis the motor is driven by a sigle driver (X) while for the Y axis I have two motors driven by two drivers (I have cloned the A axis with jumpers on the cnc shield ).

My question is :
when I move only the X axis the amperometer reads about 1.2 A, also when I move only two motors for the y axis the amperometer reads about 1.2 A (in this case I thought that it was about 2.4/3 A).
Is it normal 1.2A for the Y axis with two motors and two drivers(each vref is set 0.75mv)?
For Y axis have I to raise the vref until i got 2.4/3 A?

Sorry for my English and thank you in advance.


Bertus Kruger
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Re: how to regolate vref for clone axis

Post by Bertus Kruger » Sun Nov 03, 2019 6:15 pm

Best to follow Pololu instructions : ... r-carriers

I am assuming you measured the current on your power supply. If so, this is in put current.

The current setting set on the stepper driver are output current and are at a different voltage. (Lower voltage but higher current)

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Re: how to regolate vref for clone axis

Post by StuartB » Mon Nov 04, 2019 3:21 pm

Hi Andrea.
Because it a Laser engraver you dont need to set either of the drivers that high. A CNC machine needs higher current because it has to move a tool against the workpiece. So it needs high torque, the laser engraver only has to move the laser and the Y axis gantry, and because there are 2 motors on the Y it's easier for them to move it, and does'nt touch the workpiece. So it does'nt need that much torque and so less current.

I have a laser engraver with the same setup, 1 X motor and 2 Y motors with the same DRV8825 drivers.
I set my current to between 250 and 300mv. The motors run absolutely fine and also stay a lot cooler.
Also the 8852 drivers also stay cool.
If it struggles to move you can always set it a bit higher.

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