It was just quickly said in my main post :
Servos vibration : because of the masse attached to the servos (a 18g fin) the servos tend to oscilate if there is no friction to dampen it. You simply need to add friction where you can to stop it.
It’s simply that the PID of the servo can be bad if your fin is heavy AND if there is some play. It gains speed one way, then can’t slow down to stop on the target, overshoots and repeats (this happens inside the servo, and that’s what is moving the flaps in the video I sent, nothing to do with ardupilot because it also happened unarmed). Play plays a big role in this, because the servo shaft can be static with the flaps still moving fast exactly around equilibrium, this is throwing off the PID of the servo.
But the torque of the servo is largely enough. If the servos were powered, and too much force was applied the inner gears broke, I broke a bunch of gears, but never while flying. (having spear servos from which you salvage the shitty plastic gear is helpful)
Sorry, precision of the torque doesn’t mean much. I mean the position of the fins, it’s not a problem of servo resolution, those are surprisingly precise. But the link between servos and flaps can f*ck it up, for example, the servo could move a very little bit to correct, but then because of some play your flap doesn’t move.