Lazy auto take off with APM

by on February 29, 2016

I know that APM supports automatic takeoff, but from my reading on the matter, it wants you to program the takeoff as a mission from the ground control station.

This is way too much work, I fly all my APM craft without a GCS at all, I want to just go somewhere and fly. As such, when I got my new Zephyr II flying wing, I wanted a simple and easy way to automate hand-launching that takes advantage of the APM’s autopilot.

Enter my Taranis!

I set up a switch on the Taranis which is set to ‘Replace’ 3 channels – mode, elevator, throttle.

It changes the mode to FBWA, sends full ‘up’ elevator, and sends 100% throttle with a ‘Slow Up’ of 8 seconds – meaning it goes from 0 to 100 over 8 sec.

FBWA is the ideal mode for a hand launch, as it converts stick inputs into degrees and climb rates, relative to the airframe’s current position.

This means that full ‘up’ elevator results in a nice smooth climb at around 2meters per second, and the wings are kept level for the duration. The FC is constantly analyzing the altitude of the plane, and as such it only gives enough elevator to maintain a climb.

You should note however, that the FBWA throttle is capped by the THR_MAX parameter, so be aware of what this is set to before you try a launch – you want to have plenty of power!

Here’s the resulting launch video:


I keep returning to this effortless video. This looks like a great approach, one that’s becoming more popular. Thank you for sharing (although I wouldn’t mind an .eepe dump of the model setup from OpenTX Companion, hint hint).

Are you sure you are using FBWA, and not FBWB? Reading the docs, FBWB is the one that has the FBWB_CLIMB_RATE parameter that defaults to 2 meters/second maximum.

If you are indeed using FBWA, and not FBWB, then the reason for pitch being limited might be the LIM_PITCH_MIN and LIM_PITCH_MAX settings.



Again, not trying to argue with great results, just trying to get absolutely clear how the results were obtained.

Hi Stew, glad you found some use in my post 🙂

I am definitely using FBWA and you are right that it is pitch angle and not climb rate. With this in mind, you may have better results with FBWB, however it does rely on an accurate Baro reading, and since you are going from stationary to ‘flight speed’ very suddenly, you may find that the Baro reading is affected.

I’ll see if I can get a model dump for you too.

Your method looks really interesting. I would love to use this method with my heavy Drak.
I would really appreciate if you could share your Taranis model settings (I get some trouble to set this right).

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