The new screen take less room in the head than the previous one, thus we have the possibility to reduce a bit the size of the head.
Discussing with @Fdepraetre, we slightly modified the I/O board shape to allow a better integration in the Poppy head. Now the board will have these dimensions:
To sum up, ax-18 are servo more reliable than ax-12 with an higher torque.
Practically, the motor is not the same, it is a maxon. But the gear box is in plastic. I already changed one gear when a child sat on my robot…
So the weight is the same.
Concerning noise, it is largely reduced. I really see the difference when the motor is loaded.