Almost certainly your servos wion't like that...
You will need to level shift the PWM signal to match that of the input required for each servo. However you are correct in commonning the 0V lines together.
This could be off the shelf level shifters, or as simple as inverting your PWM output and driving a transistor with a pull up resistor between the output (collector) and your servo power rails.
I suspect, however, that the servos are also quite powerful. You may also want to opto-issolate the servos from your I2C PWM driver:
Code: Select all
5V 3V3 Servo Vcc
| | _____________|
| | | |
| |___________ R (10k) |
| | | |__________ Servo
RPi --> PCA9685_________D K | Where D K is opto transistor Issolator
|_________| |____________ |
0V Servo GND
(Post edited to layout diagram)