Just in case you were experiencing the same problem as I was having: my FlightVelocity trim wheel was hardly usable with FS2020 because it responded too slow: turning the wheel had very little effect.
The FV trim wheel uses ‘joystick’ button up/down events (so it’s not an axis) which can be assigned to the Elevator trim up/down events in FS2020. When you touch the wheel, these button events are fired in rapid succession after each other, but apparently not rapid enough!
To solve this problem, you need to install FSUIPC 7 (currently free in beta while the FS2020 SDK is being worked on, but definitely worth buying when it gets fully released). Now, the standard FSUIPC user interface does not allow you to solve the problem directly however, since you can assign a FS2020 event to the trim wheel events/buttons, but you cannot add key/event repeats. What you need to do is edit the FSUIPC7.ini file and add the repeats manually.
So after downloading FSUIPC 7, run the FSUIPC7.exe as administrator (right-click, ‘Run as administrator’). An icon is added to the Windows tray at the bottom right. You can either click that and select ‘Show’ or press Alt+F to display the FSUIPC user interface. In the user interface, select ‘Assignments’ from the menu and select ‘Buttons & Switches’.
Roll the FV wheel down (for elevator trim up). You should see some information at the top of the dialog referencing the Button 0 (remember, the FV sends button presses when you roll the wheel). Now select the button at the right ‘Select for FS control’. Then underneath that, press the box titled ‘Control sent when button pressed’ and select the event ‘Elev Trim Up’. To save you lots of scrolling, you can press ‘e’ on the keyboard so that it jumps directly to the first action starting with ‘E’. Repeat the same for ‘Control sent when button released’.
Now that elevator trim up is done, roll the FV wheel up (you should see Button 1 becoming active) and repeat the same steps, but now select ‘Elev Trim Down’ for the two events.
Press OK and select Exit from the File menu. Now in the directory you have downloaded FSUIPC7 to, you should find a file called FSUIPC7.ini. Double-click that and open it with Notepad. Scroll to the section named [Buttons]. You should see 4 entries there, like:
The idea now is to repeat the RD entries 1 and 3 such that on a ‘button’ down event from the trim wheel, a number of trim commands are sent to FS2020. I use 5 entries, but adjust to taste. You need to change the numbering so you cannot just copy the lines. Mine looks like:
So you only have to repeat the RD actions. I am not allowed to upload an .ini file here, so you have to do some manual editing. I hope this information helps someone here!