Thanks for the reply. To my knowledge I have already uninstalled both vJoy and SmartPropoPluss.
Inwas wondering now if the problem is that I'm sending a 16bit value from my current Arduino receiver, instead of the more usual 8bit signal. Any ideas?
[Fixed]
I can confirm that joystick values in 8-bit format works with FPV Freerider! I'm using a Joystick library from Heironimus, he has two versions, the older one works with this simulator. However, the channels "Throttle" and "Rudder" do not register in the calibration menu. Using for example Z-axis and X-rotation for throttle and yaw works.