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flix/docs/firmware.md
Oleg Kalachev 52819e403b Major rework of rc subsystem 
Implement channels mapping calibration.
Store mapping in parameters.
Get rid of `controls` array and store control inputs in `controlRoll`, `controlPitch`, ... variables.
Move `channels` variable to rc.ino, channels are not involved when controled using mavlink.
'Neutral' values are renamed to 'zero' - more precise naming.
`controlsTime` is renamed to `controlTime`.
Use unsigned values for channels.
Make channel values in simulation more alike to real world: unsigned values in range [1000, 2000].
Send RC_CHANNELS_RAW instead of RC_CHANNELS_SCALED via mavlink
Don't send channels data via mavlink if rc is not used
2025-07-14 12:01:29 +03:00

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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

Firmware dataflow diagram

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 — project's 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.