Self balancing robot but not balance

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Where do you find these libraries?

#include "I2Cdev.h"
#include <PID_v1.h>
#include "MPU6050_6Axis_MotionApps20.h"

I2Cdev.h seems to be resident in the IDE.
This file: PID_v1.h seems to now be PID_v1_bc.h
MPU6050_6Axis_MotionApps20 does not seem to exist (but you have it, or you could not compile your sketch).

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