Pi as Co-Pilot

Overview

The Raspberry Pi serves as an auxiliary flight control unit that interacts with the main flight controller. It sends RC commands and reads telemetry data using MSP over a serial interface. Depending on the flight mode selected via the Betaflight AUX3 channel, the Pi executes different behaviors.

There are two main operational modes:

• Stable Hover & Object Detection Mode (AUX3: 1300–1800):
  In this mode, the Pi takes control of the flight sticks to maintain a stable and level hover. It continuously sends neutral RC values to keep the drone steady in the air. At the same time, it scans for red objects using the onboard camera, as described in Red Object Detection. If a red object is detected, the Pi rotates the drone either to the left or right to align with the object. Since the Pi Cam is downward-facing, this turning motion can help position the drone precisely over the target — for example, to pick up a package using the attached magnet.

• Forward Flying Mode (AUX3: 1800–2100):
  In this mode, the Pi commands a slight forward motion by adjusting the pitch input. This enables the drone to move ahead while still maintaining stability.

Hardware Setup

To establish communication between the Raspberry Pi and the flight controller, connect the two devices via a UART interface:

• Raspberry Pi TX → Flight Controller RX (e.g., UART3)

• Raspberry Pi RX → Flight Controller TX

Ensure the Pi is properly powered from the drone's power system.

Software Architecture

A custom Python script runs on the Raspberry Pi to handle MSP communication. This script acts as a bridge between the Pi and the Betaflight flight controller, issuing control commands and reading telemetry over a serial connection.

MSP Communication Module

The MSP class abstracts the protocol details and provides high-level methods for:

• Sending RC input (send_rc)

• Reading current RC channel values (read_rc)

• Sending flight control commands with pitch, roll, yaw, and throttle inputs while maintaining AUX values (send_flight_control)

This module encodes MSP packets with proper binary formatting and checksum validation to ensure robust communication. It typically operates over /dev/serial0 (Linux) or COMx ports (Windows).

Through this abstraction, the Raspberry Pi can behave like a secondary flight controller that only overrides inputs when allowed by the MSP Override switch.

If send_rc is used, only the four primary flight control inputs — roll, pitch, yaw, and throttle — can be manipulated. This is because in the Betaflight Setup, we set the msp_override_channels_mask to 15, which corresponds to the binary value 0000000000001111. Each bit in this 16-bit mask represents one RC channel, starting with bit 0 = roll, bit 1 = pitch, bit 2 = yaw, bit 3 = throttle, and so on up to channel 15 (e.g., AUX channels).

Setting the mask to 15 (0b1111) enables override control only for these first four channels. If you want to override additional channels — for example, AUX3 — you need to set the corresponding bit to 1 as well. In this case, the mask would become 79 (0b01001111), allowing control over roll, pitch, yaw, throttle and AUX3.

To summarize: 15 (binary 0000000000001111) → Only channels 0–3 (roll, pitch, yaw, throttle) are overridden. 79 (binary 0000000001001111) → Channels 0–3 and channel 6 (AUX3) are overridden.

You can customize the msp_override_channels_mask by setting the corresponding bits for each channel you want to control from the Pi.

Co-Pilot Flight Logic