Question: Help getting rid of a recursive assignment message

I am trying to write out a code to solve for current in a LRC circuit. I have written a code that I think is capable of doing this but keep getting a recursive assignment message in my for loop. I have looked it over about a hundred times and can't see where I have defined a variable in terms of itself. Any help on this would be greatly appreciated. A copy of my code so far is listed below.

> with(plots);
> u := proc (t, Q, dQdt) options operator, arrow; 0.15e-2*cos(omega*t)/0.25e-2+(-1)*1.5*dQdt/0.25e-2+(-100000/7)*Q/0.25e-2 end proc;
> omega[R] := 1/sqrt((0.25e-2*70)*10^(-6));
> ti := 0; tf := 10*(2*Pi/omega[R]); omega := omega[R]-1.5/(0.25e-2); num := 20; e := (tf-ti)/num;
> t[0] := ti;
> for i to num do t[i] := e*i+ti; dQdt := dQdt[i-1]+e*u(t[i-1], Q[i-1], dQdt[i-1]); Q[i] := Q[i-1]+e*dQdt[i] end do;
%;
Error, recursive assignment
NULL;