zero output continuously in closed loop

Hi I am getting zero output continuously in closed loop in the following simlink model. I gave step inputs of magnitude 1 at t=1 sec. The matlab function code is:

function [q_v_dot, q4_dot,w_bi_dot] = sc_dyn(q_v,q4,w_bi,tau)

I=[0.0027 0 0;0 0.0107 0;0 0 0.0101];

w_bi_dot = inv(I)*(tau - Smtrx(w_bi)*(I*w_bi));

q_v_dot =(1/2)*(q4*eye(3)+Smtrx(q_v))*w_bi;

q4_dot = -(1/2)*q_v'*w_bi;

end

function S=Smtrx(i)

S = [0 -i(3) i(2);i(3) 0 -i(1);-i(2) i(1) 0];

end

Please let me know why I am getting zero, even if I give step input?

Regards

valli