@acer 
Thanks for the tip with unapply, it worked!

@tomleslie
I defined the functions befor, I just showed you the part for the coordinates calculation because its a pretty big text.

Thanks for your help mates!

Thanks for your answer!
I just tried it with this code:

Rb:=13;
X(phi[0]):=(Rb+s[0](phi[0]))*cos(phi[0])-Ds[0]*sin(phi[0]);

Y(phi[0]):=(Rb+s[0](phi[0]))*sin(phi[0])+Ds[0]*cos(phi[0]);

t:=evalf(Pi);

seq(X(phi[0]),phi[0]=0..t,0.1);
seq(Y(phi[0]),phi[0]=0..t,0.1);

sadly it wont work and give me these results:

X(0), X(0.1), X(0.2), X(0.3), X(0.4), X(0.5), X(0.6), X(0.7), 

  X(0.8), X(0.9), X(1.0), X(1.1), X(1.2), X(1.3), X(1.4), X(1.5), 

  X(1.6), X(1.7), X(1.8), X(1.9), X(2.0), X(2.1), X(2.2), X(2.3), 

  X(2.4), X(2.5), X(2.6), X(2.7), X(2.8), X(2.9), X(3.0), X(3.1)
Y(0), Y(0.1), Y(0.2), Y(0.3), Y(0.4), Y(0.5), Y(0.6), Y(0.7), 

  Y(0.8), Y(0.9), Y(1.0), Y(1.1), Y(1.2), Y(1.3), Y(1.4), Y(1.5), 

  Y(1.6), Y(1.7), Y(1.8), Y(1.9), Y(2.0), Y(2.1), Y(2.2), Y(2.3), 

  Y(2.4), Y(2.5), Y(2.6), Y(2.7), Y(2.8), Y(2.9), Y(3.0), Y(3.1)