Tom is correct. The "control rod" in these pocket type hinges is actually a torsion rod. The control force is transmitted from the servo as a torque or twist in the rod. We can hit some hefty control surface forces in our jets and need a very stiff control set up. The pocket type systems that I have personally seen did not, in my opinion, have a beefy enough torsion member for our use. That is not to say it can not be done (it can), just that the ones I've seen were inadequate due primarily to too much torsional flexsure.

(rocket structural analyst for 22.5 years)