Can the Servo lib be made to control more than 12 servos per timer? Maybe!

Using Arduino Motors, Mechanics, Power and CNC
14

just let the ISR CYcle through a pre sorted table.

Yep, sounds reasonable.

The next problem is if you have 20 servos at very similar values, Do you stay blocking in the ISR to set all 20 of them ?

What resolution are we talking?

Rob