103 Compiled Firmware - HefnySco/OBAL GitHub Wiki
PLEASE DOWNLOAD BINARIES FROM https://firmware.ardupilot.org/
e.g.: https://firmware.ardupilot.org/Copter/stable-4.2.3/obal/
For OBAL that uses GY-91 Sensor or PPM-RX
you need to build the code as described in details in WIKI.