Stabilized start and Auto Takeoff

#1

Hi,

I’ve mounted a Pixhawk with px4 stack on a Bixler 3. Now, I’m having a really hard time getting this thing into the sky using manual mode and all this equipment (Without it flew just like a dream), as the trims are just too poorly set. Therefore I’ve crashed it already many times right 1-2 seconds after start.
Is there a way using a stabilized mode right from the start? I’m pretty sure, after it is in the sky I will get the chance to set the trims just right.
Second question is about the auto takeoff. Somehow it just won’t start, Can someone explain how to us this mode? What I did for auto takeoff:

  1. Set the auto takeoff point on Qgroundcontrol mission about 150 Meter away from home
  2. configured pitch angle and heading ° (I’m not sure, what heading this is - flight direction after auto takeoff point reached?)
  3. Set the Bix3 in direction of auto takeoff
  4. Switched to auto takeoff - then command gets rejected and it switches automatically to altitude flight mode, where it doesn’t seem to react at any input given (throttle, pitch etc) It’s just stands there.
#2

Hi Camperinho,
I always takeoff in stabilized mode. I have a switch on my transmitter that mixes some elevator up. I use it during takeoff and turn it off afterwards. In stabilized mode it is important to throw your plane almost straight. Otherwise if you throw it with the nose up, your Pixhawk will countersteer and try to get the nose down, which will propably end up in the ground. With the elevator up switch, takeoff in stabilized mode works very well on my Bixler 2.
I can’t answer you auto takeoff question, because I never used it. Maybe someone else?

#3

Hi timoski,

Thanks! I’ve just realized that the px4 stack offers also the fly-by-wire mode. I oversaw this completely. Also your tip using an elevator switch sounds good.
Is this stabilized mode on px4 stabilizing like on multi rotors? Meaning it levels the plane completely? I think the APM plane stack has the FBWA(stablized) mode, which is more like a trim set.

#4

Push: Nobody knows how to configure the auto takeoff mode?

#5

Following this thread as I am playing with auto takeoff my self without that much luck. Although, I get the plane to 100% throttle and fly in the lauch direction. However, I can’t seem to get it to proceed to the takeoff point.

#6

It will only proceed once it reached the climb out altitude. So if your pitch control loop is badly tuned it might take a while to get there. Without a log file its impossible to tell though.

#7

Hey Lorenz,

Thanks for your reply, I will have a closer look at the pitch control.

#8

If you’re doing an auto takeoff with a bixler you’ll probably want to enable runway takeoff (https://pixhawk.org/firmware/parameters#runway_takeoff). This will give you throttle right away.

#9

Thanks for your link, very helpful!

#10

Successful auto-takeoff with the PX4 firmware.