add WIP linearization to quadrotor

docs/src/examples/quad.md

@@ -179,3 +179,21 @@ nothing # hide
 ![quadrotor animation](quadrotor.gif)
 
 The green arrows in the animation indicate the force applied by the thrusters.
+
+```@example QUAD
+quad = RotorCraft(closed_loop=false, addload=false)
+quad = complete(quad)
+inputs = [quad.thruster1.u; quad.thruster2.u; quad.thruster3.u; quad.thruster4.u]
+outputs = [quad.y_alt, quad.y_roll, quad.y_pitch]
+
+op = [
+ vec(ori(quad.freemotion.Rrel_f).R .=> I(3));
+ vec(D.(ori(quad.freemotion.Rrel_f).R) .=> 0*I(3));
+ quad.world.g => 9.81;
+ inputs .=> 1; 
+] |> Dict
+ssys = structural_simplify(IRSystem(quad), (inputs, outputs))
+
+lr = linearize(IRSystem(quad), inputs, outputs; op)
+
+```