@Rongzhong Li Thanks for your help. The problem has been solved with your instruction.

@Rongzhong Li As shown in the video. After typing "kbalance", I cannot send any other commands anymore.

@Rongzhong Li But when I upload Writeinstinct.ino, everything works well while upload Opencat.ino, the problem occured.

Thanks for your reply. Maybe the reason is shown in the images. When uploaded the Writeinstinct.ino 34 skill addressed and while uploaded the Opencat.ino, only 3 skill addressed. I uploaded several times with the same results.

Thanks for your concern, such issues have been solved by reconnecting the wire and adjusting the voltage. Another issue is that when I uploaded Opencat.ino to the mainboard, everything works well, but when I try the serial commands in the serial monitor, the first command was ok, and then following commands did not have a response. I need to power the cat again. I was confused.

Yes, four servos are MG09 and I download the code two month ago. What is the meaning of semi-tranparent case?

Yes, I first calibrated the motor and then installed the leg and head. Sometimes the motor went to the right position and sometimes went to the wrong position. Sometimes, the head even rotated more than 360 degree. Another issue is that the motor suddenly rotated to an wrong position and then rotate to the right position smoothly when I input a command.

Thanks for your reply. I have solve this problem with your help. However, another issue is that servos sometimes has a wrong position feedback. As shown in the figure, when I press "c", sometimes the position of one hing leg is wrong, and when I press "j", serial monitor shows that all the position is zero.