MATLAB: Transfer function, G

Question

I'm doing this transfer function routine but I can't get G, what's wrong?

% servo motor data

% Ra, armor resistance [Ohms]

Ra = 0.34;

% La, armature inductance [H]

La = 0.007;

% Ia, current in the armature [A]

Ia = 8;

% J, motor and load moment of inertia, referring to the motor axis [kg m2]

J = 63.9 * 10 ^ -4;

% C, viscous damping coefficient of the motor and load, referring to the motor shaft [Nms / rad]

C = 18400;

% T, torque developed by the motor [Nm]

T = 1.59;

% kb, generator constant

% [V.s / rad]

kb = 314;

% k, motor constant [Nm / A]

k = 0.19785;

% transfer function calculation:

% motor gain value, km:

Km = k / Ra * C + k * kb

% value of the motor time constant, Tm:

Tm = (Ra * J / (Ra * C + k * kb))

% Transfer function, G (x)

G = Km / (s * (Tm * s +1))

I get this message:

Undefined function or variable 's'.

Error in Untitled2 (line 25)

G = Km / (s * (Tm * s +1))

Answer 1

's' is not defined by default in MATLAB. You need Control system toolbox to create a transfer function. Change the last part of your code to

% Transfer function, G (x)
s = tf('s');
G = Km / (s * (Tm * s +1))