Just to help anyone having a problem getting controllers to work with FPVFreerider, I present my experience:
I've had a problem getting my Taranis Plus working in FPVFreerider. Basically, Windows sees the controller as a joystick device, and I can see the inputs changing the bars and so on in the Windows Joystick properties smoothly, so the controller works ok.
In FPVFreerider, the controller sticks were being seen either full off or full on, i.e. as if they were a switch. no amount of tinkering with gains of offsets helped.
However, I noticed that I also had another joystick device connected, in this case a 3DConnexion 3D Mouse, so I disabled it in device manager. Now my Taranis works flawlessly in FPVFreerider, with the controller calibration now showing the circles changing smoothly instead of either at the bottom or at the top.
I hope this helps someone else.