Stardate 98775.72
I connected the ground and 5V buses together around the control boards.
Green: Ground
Red: 5V
I2C uses SDA and SCL connections.
SDA: Serial Data: Data moves here
SCL: Serial Clock: Clock sync here
Mega 2560:
SDA : pin 20
SCL: pin 21
Hero UNO:
SDA: pin A4
SCL: pin A5
I checked each ground and power path with a multimeter to verify wiring. First, I split the power connections of the Arduino devices to separate locations on the boards. 5V is reading 4.99V. Then, I checked for ground loops. Finally, I also wired to limit the connection lengths. The bottom rows are I2C bus. On the control board by the Slave 4, You will notice some extra jumpers.