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Autodriver V13/ steppers not completing large movements and stopping on continuous rotations - SparkFun Electronics

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Hi all.
I have my 4 autodrivers V13 hooked up and working properly with an arduino mega, just a weird problem is occuring :
the steppers never complete large movements or continuous rotations:
If I use mystepper.run(FWD, 300) once for example, it runs for about 2 seconds then stops. If I put the function mystepper.run(FWD, 300), and only this ,in the loop(), it runs, stops, runs, stops etc at regular intervals. The problem is greater with lower speeds (at speeds of about 800, the problem does not occur).
Quite similarly, if I use for example mystepper.goto(5000), the steppers travels for a while and then stops at an apparently random location (the function getPos() works fine). If I ask for small movements (up to about 1500 steps), no problem. Large movements are NEVER completed.
This happens the exact same way on my 4 boards. I tried using just 1, 2 , or 3 of the boards, the problem remains the same.
I know there is something wrong in the way I configure my boards (I dont see any other option...) but do you have any idea what could cause this ?? I have thoroughly read, several times, the hookup guide.

Thanks much !
Thanks for your reply! I don't have much info on my Chinese steppers , just got these values :2.4V, 1.7A ,1.5 ohms resistance and 3.2mH inductance. They should be compatible shouldn't they? I could not find a precise guide explaining how to set the Octhresh, running kval etc to the proper values given the steppers specs. Is there one, or is it more a trial and error procedure ? Thanks much !
Isn't it why the driver uses PWM to drive the steppers, to get the max available torque using a "too high voltage" ? From what I learnt, all steppers have low coil tensions, and the driver must know how much current it "sends" to get the maximum torque without heating too much, and thus uses PWM. Which makes it crucial to calibrate properly the driver (which I'm struggling to do right now :-)). For instance, on my CNC the steppers power supplies are 60V, where the steppers themselves are 6V max. Please correct me if I'm wrong.
According to the datasheet, VSthOff is 6.6V, minimum. If your motor supply voltage is lower than that, the device goes into undervoltage lockout (sec 6.10 in the datasheet). If you are using a motor supply voltage high enough to prevent an undervoltage lockout, your are going to draw too much current if your motor has 1.5 ohm coils.

PWM is used for microstepping.
Thanks again for your reply.
I finally found the solution; PWM modulators are indeed used for voltage compensation (see section 9.1.10 of the datasheet), using the KVAL.
My power supply si 12V, motors have a nominal 2.4V. I set up my acc and run kval at 51 (255 would be 12V, no compensation, 51 is then 2.4V). It works like a charm.