Servodriver in the arm
To have less cables, I mounted a servodriver in the arm. It needs two cables for power, and three for i2c. For power its 6V + GND. In the i2c cable I use 3V3 power + SCL ( clock ) and SDA ( data ). The ground is common and they are connected together in the servodriver.
One of the servo cables goes back into the biceps servo. .