PID tuning for a small Flying Wing (~47 cm wingspan)

PX4 Autopilot
3

Airspeed Scaling

Actually, I often noticed that vehicle was wobbling after “few seconds of flight after takeoff”, and after close examination of the log, I found that most likely it is suffering from PID not being scaled with respect to the airspeed.

image
image1647×998 165 KB

Log link: https://logs.px4.io/plot_app?log=e7f3aa9c-9321-4286-a877-90a54d687f92

As I plotted vxy (ground speed) here, you can clearly tell that as the vehicle crosses around 6 m/s mark (as I remove the throttle and let it glide), the vibration goes away.

Therefore, I am planning on:

  • Enabling the Airspeed selector module
  • Setting ASPD_PRIMARY to “Groundspeed minus windspeed”

This I believe should then provide the estimated airspeed data from the ground speed and allow PID scaling, I will have to test this!

PID gains

As you said, FF of 0.2 or higher often resulted in overshoot, so in the flight linked above, I actually removed the FF gains, and only relied on P and I gains.

However, it seems like probably airspeed scaling would help remove the wobble, then I will definitely also tune the PID gains again (and perhaps put FF back in).

Btw is having FF gain very crucial?