There's a microcontroller on the fenestron that controls two clutches, clamped at 0.4-0.8. The stabilized yaw feeds into that and sends a number that splits in two in the controller.

A positive number simply adds 0.4 to the output, and feeds to the left clutch.
A negative number goes through a switchbox, gets abs treatment and then adds 0.4.

Each output then feeds to either the left or right clutch. Download it and have a look at my solution, it isn't perfect especially at higher engine powers, but it works if you keep the rotor RPS between 40-60.

How did you make a fenstron work I can never actually use it for yaw