A couple of years back a thread here by the same name, on this very forum.
I'd like to start a similar one, but from a different point of view.
1. I'd like to use an Raspberry pi running a Linux OS as a flight controller for a non-racing drone with commercial purpose.
2. I can't use hats. Solution has to cost-scale, price point needs to be low and... additional reasons (kubernetes) that may require a different thread to explain. Bottom line is no hats like navio2 or even the cheaper PXFmini.
3. I don't want to reinvent the wheel. Ardupilot's (or something equally open-source, linux friendly and feature-rich) is the way to go.
4. I will have sensors - either in the form of an IMU, GPS (and maybe ancillary sensors like ultrasonics) or as a whole el-cheapo flight controller on the side that has sensors and can allow ardupilot running on the raspberry to poll those sensors.
5. The raspberry will also need to control the ESCs - my current rig runs HW30A's - either directly via PWM from the GPIO pins, or via that cheap flight controller.
Any advice on finding cheap&easy-to-interface-with sensors ardupilot can use, and interfacing it with the ESC PWM inputs?