i request the following help with regards to solving ode for the system of equations in the body below?

 function qdot=kinematic_car_better(t,q,u1,u2)
qdot=zeros(4,1);
u1d=polyval(u1,t);
u2d=polyval(u2,t)
l=1;
qdot(1)=u1d*cos(q(3));
qdot(2)=u1d*sin(q(3));
qdot(3)=u1d*tan(q(4))/l;
qdot(4)=u2d;
end

how do i do the following?? 1)set qdot(4) to 0, abs(q(4)) to pi/4 and continue integration if abs(q(4)) exceeds pi/4 2)access and plot variables u1d and u2d in another function