Servo motor grounding issue

Hello everyone, I would like to ask a question.
I need to power 5 servo motor by LiPo Battery through two 9A buck converter. I use star grounding method to ground all the servo motor together at the negative terminal of LiPo battery with the GND of Arduino where the PWM pins of Arduino is connected to the servo motor and the Arduino have return current path to the LiPo battery. The Arduino is powered by USB. Is it possible to do so or is it dangerous to do so ?

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Whow! I'm impressed by Your post having even the schematics!
No, You can safely power the Arduino from the USB, comouter, charger etc.

Any voltage drop or disturbance by e.g. by the buck converters between the LiPo- and Servo- affect the PWM signals. This should not be a problem with digital (PWM...) signals.

With few exceptions, you want all grounds connected together.
You don't say which buck converter you are using, but the input and output grounds are normally connected together on the PCB.

pololu

Not just "normally", but simply an inevitable consequence of how the circuit operates. (You might imagine an inverted version where the positive rail would instead be commoned. Has anyone seen one?)

The point is however that the control line to the servo must travel along with the ground, so in the OP's diagram above, each control line goes back along that negative line to the LiPo battery, then along with the negative alongside each buck converter and from there along with the regulated power to its respective servo.

And PWM pins are generally not relevant to servo control.

I had to say "normally" because invariably someone would find the single exception and call me out on it.

Absolutely, isolated converters are definitely available, as standard components.

Most certainly they are, but they are not the "buck converter" which we are discussing here, which is a particular configuration using a single inductor, series switch and shunt commutation diode.