The Short Answer
A companion computer is the AI brain on a drone. It sits next to the flight controller and runs the heavy software the controller cannot: computer vision, path planning, object detection. The flight controller keeps the aircraft stable and executes commands; the companion computer decides what those commands should be, based on what its cameras and sensors see.
Why Drones Need One
A flight controller runs on a microcontroller built for real-time stabilization, not for neural networks. To make a drone autonomous — to have it avoid obstacles, follow a target, or map a site — you need a full computer running AI, and that is the companion computer. It connects to the flight controller over a serial UART or CAN link, usually with the MAVLink protocol, sending it waypoints and velocity commands while reading telemetry back.
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Vision Object detection, tracking, and obstacle avoidance from onboard cameras.
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Navigation Path planning and position estimation, often fused with GNSS.
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Links to the flight controller Commands and telemetry over CAN or UART via MAVLink.
On NVIDIA Jetson
NVIDIA Jetson Orin is the usual companion computer because it offers a high ratio of AI performance to weight and power, which is what a drone needs. We build drone companion computers on Jetson and integrate them with the flight controller. See our guide to NVIDIA Jetson for drones for the full picture.