flix/docs/firmware.md

Firmware overview

The firmware is a regular Arduino sketch, and follows the classic Arduino one-threaded design. The initialization code is in the setup() function, and the main loop is in the loop() function. The sketch includes multiple files, each responsible for a specific part of the system.

Dataflow

The main loop is running at 1000 Hz. All the dataflow is happening through global variables (for simplicity):

• t (double) — current step time, s.
• dt (float) — time delta between the current and previous steps, s.
• gyro (Vector) — data from the gyroscope, rad/s.
• acc (Vector) — acceleration data from the accelerometer, m/s².
• rates (Vector) — filtered angular rates, rad/s.
• attitude (Quaternion) — estimated attitude (orientation) of drone.
• controlRoll, controlPitch, ... (float[]) — pilot's control inputs, range [-1, 1].
• motors (float[]) — motor outputs, range [0, 1].

Source files

Firmware source files are located in flix directory. The key files are:

• flix.ino — main entry point, Arduino sketch. Includes global variables definition and the main loop.
• imu.ino — reading data from the IMU sensor (gyroscope and accelerometer), IMU calibration.
• rc.ino — reading data from the RC receiver, RC calibration.
• estimate.ino — drone's attitude estimation, complementary filter.
• control.ino — drone's attitude and rates control, three-dimensional two-level cascade PID controller.
• motors.ino — PWM motor outputs control.

Utility files include:

• vector.h, quaternion.h — vector and quaternion libraries implementation.
• pid.h — generic PID controller implementation.
• lpf.h — generic low-pass filter implementation.

Building

See build instructions in build.md.