Step-by-Step Setting

The model is the same as in previous pages.

Setting the Model

The model is the same as in previous pages.

The connections could be tricky, especially for the motors. The software I use is based on the project shared by winijenh on the ft:community forum. Thank you winijenh!

The solution relies on a PID controller (reference) and a Kalman filter (reference). Please follow the link for more details, including a ready-to-use Robo Pro project file.

So here's my trial and error process:
  • Accelerometer
    • The accelerometer is the reference.
    • Use a simple program to display i1 X-axis, i2 Y-axis and i3 Z-axis input values. 
    • Move the pendulum: normally, the Y-axis value on i2 port should change.
  • Left and Right Motors
    • Connect the two motors, one on m1 and another on m2, whatever order.
    • Load and run winijenh's WindMill project.
    • Set the values for Kp=50, Ki=0, Kd=0. So the motors will react proportionally / instantly to the position of the pendulum. 
    • Now, move the right side of the pendulum down. Is the motor on the right side = side down running?
    • If not, stop the program and swap m1 and m2.
    • Test again.
  • Going Up or Down?
    • Now, move the right side of the pendulum down. The motor on the right side = side down is running. But is the propeller pushing the right side up?
    • If not, stop the program and swap the red and green plugs for the motor on the right .
    • Test again.
    • Perform the same test with the left side down. The motor on the left side = side down is running. But is the propeller pushing the right side up?
    • If not, stop the program and swap the red and green plugs for the motor on the left.

The model is ready now!

Setting the PID Controller

However, I looked deeper into the PID controller. I used the manual tuning method mentioned here:
  1. Set all value to 0.
  2. Increase Kp till the balance starts to move and oscillate.
  3. Keep half of Kp.
  4. Increase Ki to correct the process.
  5. Increase Kd to improve speed.
It took me 10 minutes to set the values of Kp, Ki and Kd. 

Too high values for Kp, Ki and Kd cause instability. Don't hesitate to decrease them.
Angle = 0,916 °
Angle = -3,77 °
The different sets of values I obtained for a good stability are : 
  • Kp=14, Ki=0, Kd=8 with stabilised angle = 0,916 °
  • Kp=11, Ki=6, Kd=11
  • Kp=11, Ki=1, Kd=9 with stabilised angle = -3,77 °

Play with different sets of values to fully understand 
  • proportional term or gain, 
  • integral term or reset, 
  • and derivative term or rate.

Have fun!

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