Dis-similarity in transfer function of DC motor

I calculated the transfer function of a DC motor using this equation

J = 0.01;

b = 0.1;

K = 0.01;

R = 1;

L = 0.5;

s = tf('s');

syt = K/((J*s+b)*(L*s+R))

Output:

syt =

0.01

------------------------

0.005 s^2 + 0.06 s + 0.1

I even calculated the state space model of Dc motor:

A=[-b/J K/J;-K/L -R/L]

B=[0 ; 1/L];

C=[1 0];

D=[0];

when I converted the state space to transfer function

[a1 b1]=ss2tf(A,B,C,D)

OUTPUT

a1 =

0 0 2

b1 =

1.0000 12.0000 20.0200

Please help me to understand why are they different.Thank you.

Answer 1

[And_Or]

I assume that you want the transfer function that has the the armature voltage as the input and the rotational speed as the output. You should check the transfer function. The transfer function of the DC motor is:

syt= K/((J*s+b)*(L*s+R) + K^2)

With this transfer function, you will get the following answer, which is equivalent to ss2tf

             0.01
  ---------------------------
  0.005 s^2 + 0.06 s + 0.1001