au_zeus3200,
if you have Mathematica v10 check FrenetSerretSystem[] function in addition to the (very illustrative) suggested demo.
The build-in function can compute all relevant parameters for arbitrary curve:
Clear[a, b, c] ;
res = FrenetSerretSystem[{a[t], b[t], c[t]}, t]
a[t_] = Cos[t];
b[t_] = Sin[t];
c[t_] = t/2 ;
First@Simplify[res]
I.M.
