The behaviour you are seeing may be caused by the “yaw controller”, which moves the motors left and right to make sure that the robot keeps pointing in the same direction. Here are some steps you can try to solve the problem:
 
1. Turn off the yaw controller on lines 102-103 by setting the turning parameters to 0

float Tp = 0;
float Td = 0;

2. Check that the robot is using the correct sensor axis; do this by uncommenting line 704 of the code. This will allow you to see the current angle being recorded by the sensor in the serial monitor of the Arduino IDE. The angle should be 0 when the robot it vertically upright, and change to +-90 degrees as the robot is tilted horizontally.
3. One of the motors may be wired backwards, meaning that it rotates in the wrong direction and is causing the robot to turn.

好吧，两个电机都转了，但是更奇怪到事情发生了，为什么他们不是同时运行？前倾时，左边的运行，后倾时，右边运行。
Google translate: Ok, both motors are turning, but it’s even stranger that something happened, why aren’t they running at the same time? When leaning forward, it runs on the left, and when leaning backward, it runs on the right.

Google translate: Hello, I don’t know why, I go to the balancing car. With your program, only one motor works and the other doesn’t work. Very strange

It’s really difficult to help you out as your description of the problem is very vague! Have you tried testing the components separately with the Galileo? Are the components wired properly? Is the power plugged in… 🙂

I included it as I planned to use it later to be able to steer and drive the robot around with a wireless controller. I also found that it helps to keep the robot facing the same direction, even if the motors are slightly mismatched.

I implement your code and schematic but im not sure what happen, only one motor is working, i tested two motor with a DC power supply and they’re fine or my problem can be by my switches could be damaged?