i want to know the formula for calculating the degree of freedom & center of gravity of a rover....
If you have a link like eg. an elbow, that will rotate(/bend) in one plane, it is 1 DOF. If it can rotate in another plane as well, it's 2 DOF and so on - no formula, just plain old counting.
The center of gravity can be found (for a 2D representation) by placing the ROVer with each wheel on a weight (or one wheel at one weight and the other wheels levelled to match in a pinch, if you are short of weighing equipment).
If you need a 3D representation, it gets a bit more complicated to find on the kitchen table.