Why are servo motors geting weaker in a few minutes?
So I found the solution. There where 2 problems I found:


The encoders that where in the servo use a PID that is in the
firmware. I accidentally changed the P, I and D values in a way that
all movement of the motors where very inefficient and trembled
internally the motor
Also the DOF 3 motor burned out... maybe because of the
PID changes.


In any case, the PID are programmed correctly now and that one motor has been replaced. It is as good as new now.