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Auto-TakeOff problem - not enough pitch?

PX4 Autopilot Airplanes (Fixed Wing)
#1

Hey there,

we are using the PX4 autopilot for our “Searchwing” project:
https://www.searchwing.org/en/
We are the branch of the University Of Applied Sciences Augsburg:
http://www.hs-augsburg.de/homes/beckmanf/dokuwiki/doku.php?id=searchwing

We use a Mini Talon and Pixracer and so far the flights have been working out very well!
Flying missions and even landing works like a charm!

The main thing we are struggling at the moment is the take off:
We want to hand launch the model. Using manual control this works good.
If we try this in mission mode, the take off is detected and the motor starts spinning. it goes to 100% throttle, but it seems there is not enough pitch - so the plane crashes after 2 seconds.

What parameters can be used to tune the take off?

thanks
Gregor

1 Like
#2

@KingBBQ unfortunately there is not a parameter for auto-takeoff pitch (yet! fyi @dagar and I have been discussing adding one for a while now, just hasn’t been prioritized yet). However, you can influence takeoff pitch using the Takeoff Waypoint in Qgroundcontrol. There is a “pitch” entry field in the Takeoff waypoint editor. PX4 looks at the waypoint, and if it is a Takeoff type waypoint, then it looks for the Pitch value and will use it. Also, I believe there is a bug in PX4 where if you do not have a proper Takeoff waypoint and try an autotakoff in Mission mode to a normal waypoint the pitch command gets very screwed up internally and does bad things.

For now just be sure you are using a Takeoff type waypoint

Keep an eye out for if a new takeoff pitch parameter ever comes around, then you can just permently set it and now have to worry about planning a special Takeoff waypoint with the pitch set right for your vehicle…

#3

@Antiheavy thanks for your your detailed reply.

Just before your message we did detailed testing of the model together with a experienced RC pilot. he managed to take off manually and gave us the crucial tip, that helped us getting the auto take off working with PX4:

He said that the auto pilot would turn the engine on to late. So we changed the parameter fw_thr_idle to 0.3 / 0.4 - and this did the trick!

More details can be found here: http://www.hs-augsburg.de/homes/beckmanf/dokuwiki/doku.php?id=searchwing-flug-20180520

We will try also with the “pitch” field as you suggested, maybe this can make the take off even more stable…

cherrs
Gregor

#4

I love your videos. It seems your flying speed is is faster than your throwing speed which is also part of the reason for the slow climbs. Of course, you must fly a safe speed above stall, but depending on how heavy your vehicle is, you might be able to slow down slightly and climb faster. Great airplane, looks a little like this old one: https://en.wikipedia.org/wiki/Lockheed_Martin_Desert_Hawk :wink: