There are lots of transitters/gamepads that work with Freerider on Android.
It will differ on different devices though. Your device needs to support USB OTG. (Not sure if Android 7 makes any difference, I have no experience with that version myself).
Many people are using their Taranis, Flysky, Devo, xbox360, ps3, or universal usb RC transmitters on android for example.You can search for "freerider android" on youtube and you will probably find some tips.