Raspberry pi zero-based UAV RC using XboxOne controller and FrSky DHT transmitter module
Other hardware controllers and transmitter modules (e.g, Orange) may be compatible, but I haven't tested them.
The XboxOne controller transmits joystick and button data over a USB connection to the pi. Raspbian provides the xpad linux kernel module to parse the serial stream from the controller. The xpad module mounts the controller as a device, which can be accessed using its api and enumerations.
Stick commands and buttons are mapped to specific actions. Since there are no switches an internal state machine manages the active mode and submode (ch 5 and 6). The stick commands are mapped to the normal commands for manual / altitude assist / position assist modes. Buttons are mapped as follows:
dpad_up: manual dpad_right: altitude assist dpad_down: position assist dpad_left: auto
left button: return (requires mods in px4) right button: failsafe (requires mods in px4) X: launch (requires mods in px4) Y: land (requires mods in px4) B: offboard
Note that some of these mods must be mapped internally in the px4 firmware. The dpad modes are supported directly by px4 already, but there aren't currently any ways to map launch, land and failsafe modes to RC inputs without some modifications in px4. This work is still in progress.
The FrSky DHT transmitter module expects a CPPM signal from the pi with a 27ms frame length. This allows us to combine the 8 channels with 1ms minimums, 2ms maximums and 100 microsecond gaps. The remaining frame time is allocated for the sync pulse. You can read more about how CPPM signals work here and [here](https://sourceforge.net/p/arduinorclib/ ... %20Signal/). To generate the CPPM signal, we use the pigpio library. Thanks to Joan for the support.
Try installing the joystick project from apt-get, and then run
joytest /dev/input/js0
You should see a stream of commands printing to the terminal.