OBAL acts as a simple board with necessary sensors that can be upgraded easily. The board is built over Raspberry Pi. It can use Raspberry Pi 2,3,4 & zero.
Current Linux-based Ardupilot flight controllers that run on Raspberry Pi usually consist of a shield with built-in sensors on it. That cannot be removed or replaced easily. However OPAL is more like a test or development board where you can remove sensors and replace sensors easily.
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