Calculating Cd and Crr coefficient experimentally

On this site I found how to calculate Cd and Crr coefficient from experimantal data:

http://ift.tt/1dw9BCM



I am trying to implement it in a web page and in a smartphone application, so I must "replace" Excel Solver by an algorithm, but I'm very in trouble.

I figured out how to calculate coefficients of fitting polynomial, so I now have the equation which approximates the speed curve, in form of y = ax^2+bx+c



But now how do I correlate this equation to real data to obtain Cd and Crr?



The excel sheet relies on this formula:

v1 = v0 - a*t

where:

a = F/m

and

F = air drag + roll friction

air drag = 0.5 * r *A * Cd * v^2

roll friction = m * g * Crr



so I think it is:



v1 = v0 - 0.5 * r * A * Cd * v0^2 / m - g * Crr



if this is correct, I can "zip" to:



v1 = v0 + K v0^2 + H



and



K v0^2 + H = v1-v0



My idea is to use the next sample to build an equation couple which I can solve for K and H, and get Cd and Crr from them... but it looks like it does not work, what am I doing wrong?



K v0^2 + H = v1-v0

K v1^2 + H = v2-v1