I have build a solution that looks almost like this: The wires that does the communication between the Micro Maestro and the two Jrk's and the RoboClaw are not included, so this is not a perfect drawing but maybe you get an impression on how this looks.
I power my Micro maestro from the battery, and then power my Arduino mega from the Micro Maestro (5V) and also my Jrk's are powered from my micro maestro (this is not shown in the image).
The communication is done by sending commands from Arduino using serial communication (pin 10 and 11 on the Arduino) with the micro maestro and the micro maestro sends commands to the 3 motor controllers (jrk's and RoboClaw). This works ok for some minutes.
When I run this system for a while (3-5 min) I get an error from the Micro Maestro saying
Serial Error 0x0001
At the same time one of my jrk's gets really hot (an IC called MC33926)
I am now wondering if there is a connection between the serial error and the very hot component or whether it is the serial communication between the Arduino and micro maestro is going wrong.