I'm having a hard time understanding how a circuit can have multiple power sources and have them all tied to the same ground. See the following schematic as an example:
Here's my current thought process, which is probably fundamentally flawed. The large Voltage source pumps current through the curcuit to drive the motors. That same current comes back through the servos and hits the ground wire. As it goes through the ground wire, how does it know to go back to the battery and not the ground on the Arduino chip?