I did not use the differential equations technique. My Evaluation page looks like this:

a =-g*Math.sin(q)/L;
q -= w*dt - 0.5 * a * dt*dt;
a = -g*Math.sin(q)/L;
w-= a*dt;
t +=dt;
x = L*Math.sin(q);
y = -L*Math.cos(q);
PE = m*9.8*(L+y);
KE = 0.5*m*L*L*w*w;