Firmware overview

Dataflow

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

t (float) — 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.
controls (float[]) — user control inputs from the RC, normalized to [-1, 1] range.
motors (float[]) — motor outputs, normalized to [-1, 1] range; reverse rotation is possible.

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 — project's vector and quaternion libraries implementation.
pid.h — generic PID controller implementation.
lpf.h — generic low-pass filter implementation.

See build instructions in build.md.