Vassilis’ Projects

I was able to do a test flight with the airspeed sensor and the modified airspeed and altitude control loops. Some further tuning is required, but I am fairly happy with the results I got so far. First a brief description of the modifications made.

Besides the drivers for the EagleTree airspeed sensor, I had to modify the vertical control loops to make use of the airspeed. Since the actual airspeed is now known, I decided to try separating the altitude and airspeed loops as shown in the diagram below. Basically the throttle and pitch are now controlled independently and are not coupled in the control loops (of course one affects the other but the control loops are independent). The airspeed is controlled by two cascaded PI loops, the first is used to regulate the ground speed and the second the airspeed. This is needed to ensure that if the ground speed drops below a certain value the airspeed will be increased to compensate (in order to maintain a valid GPS heading).

I did some basic testing on the simulator (using airspeed = ground speed) and it worked well enough to fly test and tune. The following two plots are from an actual test flight after spending some time setting the loop gains (the real-time tuning through the GCS is a time saver!). The plane was flying circles at a constant altitude (except in the end). The wind was about 5 m/s, judging from the ground speed variations. In the middle there is an example of what happens when the ground speed falls below the setpoint. Finally the altitude setpoint was changed to verify that the airspeed will be maintained while climbing.

The altitude gains were the easiest to tune. Altitude is maintained fairly decently, at the end the altitude setpoint was changed (aggressive climb mode was disabled). This is still using the GPS altitude, barometric altitude has been implemented but not tested yet (Kalman parameters may need some tuning)

Considering this is the first flight test I am fairly happy with the results. I would like to see if I can get the airspeed to hold closer to the setpoint, the reading is inherently noisy so either some additional filtering or further tuning of the gains might help. As soon as everything is tested I will submit to SVN. Remaining items that need testing:

• Aggressive climb mode
• Altitude control using barometric sensor
• Test airspeed and barometric sensors in 3rd party mode (in the default mode the sensors will output raw values where in the 3rd party mode they will output converted values)

This entry was posted on Friday, October 2nd, 2009 at 11:00 pm and is filed under Paparazzi. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.