There are a number of errors or questionable items in your code:
1) Inside the for-loop you set theta = 0 so that it will never change.
2) You write sin(theta) and sin(180), and theta and (I suspect) 180 are in degrees, whereas ‘sin’ uses radian measure.
3) In the line
ry=(R*sin(theta))-(L*sin(180))-(R*sin(theta))
the R*sin(theta) terms cancel each other.
4) You set alpha = 0, so why use it in the lines for ax and ay?
5) Why have you defined Md, Id, Mp, Mb, u. They are never used.
