Originally Posted by Ether

You pick a point, usually the center of geometry of the wheels¹, and then any motion of the vehicle can be described in terms of these 3 "degrees of freedom":

1) rotation of the vehicle around that point, and

2) translation (motion) of that point in the forward/reverse direction (with respect to the vehicle), and

3) translation (motion) of that point in the left/right direction (with respect to the vehicle).


Some examples:

a) a car driving forward in a straight line. The forward translation is non-zero, and the rotation and sideways translation are both zero.

b) the moon going around the Earth. Call the "front" of the moon the part that is facing the Earth. The forward translation is zero, the sideways translation is non-zero, and the rotation is non-zero (it is equal, in radians per second, to the sideways translation speed divided by the length of the radius of the moon's orbit).

Here are some example diagrams of how Ackermann, rotary, "moon", and "dosado" motions can be described in terms of the 3 degrees of freedom.


¹this usually makes the inverse kinematics easier