L6470 Different angular speed on stepper motors using RUN command

[tomasikpe]

Hi, i have a issue when trying to synchronize 2 and more stepper motors.

Issue:
The issue is that when software send RUN command with the same argument (speed value), after several revolutions motors tend to spin with some offset which is growing really slowly but is visible.

Context:
There are 2 devices with custom PCB, L6470 (1 per device) and stepper motor. I send some UDP packet in order to engage sending command to L6470, therefore all motors start on the same time. All electronic parts on devices are the same (including MCUs), software is also the same, even stepper motors are the same. I use 128 microstepping, other config values are on default. Command are sent successfully, so SPI communication is fine.

Question:
Where could be the problem? Is this voltage varation on L6470, stepper motor imperfection or any other factor i am not aware of?

Thank you in advance

Tomek

[Cristiana SCARAMEL · Accepted solution]

Hello @tomasikpe and welcome to the ST Community.

The difference observed is due to the fact that the same clock is not used for the two devices. I can propose two solutions:

1. use an external clock for both devices (or use an extremely precise quartz for each)
2. use OSCOUT of one device as OSCIN for the other so as to synchronize them

Let me know if if these info are useful to you.