Can I use a separate power supply to drive large servos by using only the servo control lines and com connection off of the Pixy?
You can use the control and ground signals from the servo connectors on Pixy and then use your own power supply that can source as much current as you need. You’ll need to connect the ground (negative) of your power supply to Pixy’s ground (on the servo connectors, for example), then use your supply as positive. 5-6V is typical for servos.
Just in case, here are the servo connector pinouts (same for Pixy1 and Pixy2):