Feel free to look at code and implement your own. This article will be updated slowly, whenever I get a break from rock climbing, university and work commitments. Feel free to comment or ask me questions as need be.

Trung Tin Ian HUA - pHysiX Coding May 2014

Code is currently undergoing major changes to improve loop speed and implement stable cascaded control. Currently testing stability of PI-P vs P-PI for attitude, and P vs PI control for rate mode.

Introduction¶

Quadcopter (X-Mode) using RTOS.

Insert picture of build

Partslist¶

Sensors¶

• TiltyQuad
  • InvenSense MPU6050
  • HMC5883L
  • MPL3115A2
  • Onboard voltage divider for voltage sensing

Frame¶

• Hobbyking SK450
• Custom 3D printed motor mounts
• 5.5mm thickness vibration-absorbing foam

Propulsion¶

• 4x Hobbyking Blue 30A ESC, flashed with SimonK firmware
• 4x Turnigy D2826/950kV motors
• 2x LH 10x4.5 props
• 2x RH 10x4.5 props

Electrical¶

• 1x Turnigy 1000mAh 20C Lipo (Entire control logic uses 300mA peak)
• 1x Zippy 5000mAh 30C Lipo
• 1x Turnigy 5A max Low RF Noise BEC

Radio¶

• 1x HC-05 Bluetooth (TiltyQuad IMU)
• 1x Turnigy 9x v2 9 channel receiver
• 1x Turnigy 9x v2 9 channel transmitter, flash with OpenTX and running lipo pack

Implementation¶

RTOS¶

4 main threads:

• Thread1: Output YPR telemetry.
  • Subfunction: Sample MPU6050 and calculate Yaw Pitch Roll angles from DMP quaternion.
  • Settings: 100Hz sampling rate, 100Hz output FIFO buffer.
  • Thread frequency: 100Hz.

• Thread 2-Master: YPR sample, PI Master/Outer control loop. Attitude control.
  • 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, and Telemetry control
  • Settings: Default quadcopter is unarmed, and no telemetry is outputted.
  • 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: 100Hz

MPU6050 Sampling rate: 100Hz

FIFO Buffer Output rate: 100Hz

To be completed

Gyro Sampling & PID calculations¶

Master PID Loop¶

Thread frequency: 200Hz

To be completed

Slave PID Loop¶

Thread frequency: 400Hz

To be completed

RC & Bluetooth Command, and Telemetry¶

Thread frequency: 50Hz

To be completed

Update ESC¶

Thread frequency: 400Hz

Pulse period: 400HZ

Pulse update rate = Thread frequency = 400Hz

To be completed

Results/Demonstrations¶

Link to youtube video

To do/discussions (respective order of priority)¶

1. Implement Integral control (P-PI or PI-P);
2. Improve Control loop (remove slight oscillations, investigate D gain)
3. Add support for EEPROM to store tuned gains outside of default
4. Remove Bluetooth arming dependency
5. Remap keyboard input for intuitive Telemetry/control
6. Add in LCD output for offline setting/debugging
7. Add in voltage sensing alarm
8. Build GUI using Processing for Multiwii-like control
9. Finish this article!