Introduction¶

Quadcopter (X-Mode) using RTOS.

Insert picture of build

Control loop: PI-PI.

D Gain will not be used as data is noisy and caused instability shortly after liftoff.

Progress:

1. Code now utilises threads and ticker.

• Highest priority given to inner loop and plant output. Next priority given to outer loop. Lowest priority given to telemetry.
• Time critical routine given to command input.

1. Code uses semaphores and mutexes.

• Threads are triggered periodically and optimised to run within a bound guarantee.
• Bus resource protected by mutex to ensure no corruption of data.

1. Code is now ran at maximum speed for every task.

• 400Hz pulse, update and loop.
• 200Hz loop
• 50Hz time-guaranteed for command input
• 50Hz lowest priority telemetry.

1. Code uses non-blocking I2C

• Will need to monitor state machine improvements.
• So far, RTOS has not entered deadlock for > 8 hours of continuous operation! Code is stress testing by having it simulate the worst flying conditions it may be subjected to.
• MPU DMP quirks for setup are overcome by creating a separate class for non-blocking implementation, and adding a destructor to the original library for house-keeping purposes.

1. Control loop now solid.

• PID gains now fully tuned.
• PID control theory, especially for early warning disturbance rejection almost compliant. There is no motivation to achieve compliance as even with flashed ESCs, the max input update rate is 400Hz. A naive Nyqist analysis would suggest that running the ESC at the same speed as a control loop would have ill consequences with aliasing.

Loop will soon incorporate altitude hold. Debating whether to use APM, Ardu- or Aeroquad approach. Algorithm will be posted here, no code until licencing and citation issues are pursuant.

Implementation¶

RTOS¶

4 main threads:

• Thread1: Output telemetry.
  • Outputs: YPR, Gyro, Altitude, Voltage, RC Input, RC Command, PID output, ESC Power
  • Thread frequency: 50Hz.

• Thread 2-Master: YPR sample, PI Master/Outer control loop. Attitude control.
  • Subfunction: Sample MPU6050 and calculate Yaw Pitch Roll angles from DMP quaternion.
    • Settings: 50Hz sampling rate (Attitude), 100Hz output FIFO buffer.
  • Settings: Input limits: -500.0, 500.0; Output limits: -200.0, 200.0; Output bias: 0.0, Automatic mode
  • Settings: KP: 0.5, TI: 1.0, TD = 0.0
  • Thread frequency: 200Hz

• Thread 2-Slave: Gyro sample, PI Slave/Inner control loop. Rate control.
  • Settings: Input limits: -500.0, 500.0; Output limits: -200.0, 200.0; Output bias: 0.0, Automatic mode
  • Settings: KP: 7.0, TI:2.0, TD = 0.0
  • Thread frequency: 400Hz

• Thread 3: RC & Bluetooth Command
  • Settings: Default quadcopter is unarmed
  • Thread frequency: 50Hz

• Thread 4: Update ESC pulsewidth
  • Note: My ESCs can apparently handle refresh rates of up to 400Hz. This means that the ESC should handle a 400Hz PWM pulse. This is distinguished from how fast I update the actual pulsewidth/duty cycle of my pulse!!!
  • Settings: PWM frequency: 400Hz
  • Thread frequency: 400Hz.

AHRS Sampling¶

Thread frequency: 200Hz

MPU6050 Sampling rate: 100Hz

FIFO Buffer Output rate: 100Hz

To be completed

Gyro Sampling & PID calculations¶

Master PID Loop¶

Thread frequency: 200Hz Control: PI

To be completed

Slave PID Loop¶

Thread frequency: 400Hz Control: PI

To be completed

RC & Bluetooth Command¶

Thread frequency: 50Hz

To be completed

Update ESC¶

Thread frequency: 400Hz

Pulse period: 400HZ

Pulse update rate = Thread frequency = 400Hz

To be completed