问题
So I searched on the net and I'm having some problems imagining how the gimbal-lock occurs. According to what i saw, it occurs when 2 or more axes align losing a degree of freedom but I can't imagine how will the axes even begin to align?
I mean, when i rotate an object around x-axis (for example) doesn't the y and z axes rotate with the X-axis to remain perpendicular? How are they gonna align? Similarly whenever i rotate around Y or Z axis the other 2 axis rotate together and remain perpendicular don't they?
To get a more clear view what I am having problem imagining, check this video. At 5:05 https://youtu.be/Mm8tzzfy1Uw?t=305
You'll see when he rotates around the X axis the green and the blue rings remain there where as according to my imagination the green (Y) and blue (Z) axes should have rotated. I don't understand why the rings are still aligned with the world axis?
回答1:
Gimbal Lock.
Gimbal lock does not lock an axis but rather it locks the action of the gyro to move freely in all three axis.
The gimbal's three axis, yaw outer ring (axis along up/down), pitch next ring in (axis along left/right), and roll the inner ring (axis along front/back). If you rotate the pitch ring 90 deg in either direction it will align the roll axis with the yaw axis and the gyro will act as if they are one.
The following image will help
Left. The Gimbal at start, red axis yaw, blue pitch, green roll. Then rotating around pitch 90deg (blue axis),the roll axis (green) is aligned with the yaw axis (red) and you have gimbal lock.
来源：https://stackoverflow.com/questions/45652366/gimbal-lock-how-does-it-happen