I build a drone very similar to the Rotor Riot Cinewhoop, I want to use a Raspberry Pi zero to make the drone fly autonomously. I think that the best idea is to use the Raspberry Pi as a receiver, and to send simple commands: throttle, roll, pitch, yaw, to the flight controller. I am not sure what connection is the best: serial, sbus? I have the T-motor MINI F7 (HD +OSD +VTX SWITCH). I know that I could use another flight controller (Pixhawk, or other autopilot) but I don't have money nor time to buy a new one. Thanks!!!
Yes, a serial communication protocol such as SBUS would be easiest.
There are a number of open source projects that explain how to use it, such as: https://github.com/bolderflight/sbus/blob/main/README.md