Some questions:
1. Why are you using external stepper drivers at all, when it appears to me that the electronics you are using is capable of driving those motors directly?
2. Why are you driving 1.68A motors at 2.5A? That is a recipe for burning them out. I suggest 1.5A.
3. What power supply voltage are you using for the stepper drivers?
4. Are the two XY motors identical? If you swap them over, does the problem move with the motor?
5. If you swap the drivers over, does the problem move with the driver?
6. Are they 1.8 or 0.9deg/step motors?
In the absence of more information, and assuming no firmware bugs, my best guess is the product of steps/mm and acceleration configured in the firmware is too high for the motors to overcome the rotor inertia.
1. Why are you using external stepper drivers at all, when it appears to me that the electronics you are using is capable of driving those motors directly?
2. Why are you driving 1.68A motors at 2.5A? That is a recipe for burning them out. I suggest 1.5A.
3. What power supply voltage are you using for the stepper drivers?
4. Are the two XY motors identical? If you swap them over, does the problem move with the motor?
5. If you swap the drivers over, does the problem move with the driver?
6. Are they 1.8 or 0.9deg/step motors?
In the absence of more information, and assuming no firmware bugs, my best guess is the product of steps/mm and acceleration configured in the firmware is too high for the motors to overcome the rotor inertia.