The APM dev team is delighted to announce the release of APM:Plane 2.74, a major new release with a lot of new features. This release is recommended for anyone flying fixed wing aircraft with an APM2 or PX4.

There are a lot of changes in this release, but some of the highlights are:

  • new APM_Control attitude controllers.
  • new TECS speed/height controller from Paul Riseborough.
  • two new flight modes, ACRO and CRUISE
  • new camera trigger by distance system, for better aerial mapping
  • dozens of small fixes and improvements from two months of development
  • lots more documentation, including tuning guides for all the new parameters

Scroll down for a more complete list of changes, but before that I'd like to give you a bit more detail on the highlights above.

New Attitude Controllers

The new "APM_Control" attitude controllers have been in development for a long time. Originally developed by Jon Challinger last year, they were extended by Paul Riseborough and made compatible with the existing parameter names. The key advantage of these new controllers is their improved handling of noise, and much better ability to tune for your aircraft. There is a new tuning guide in the wiki which gives detailed instructions on how to make the most of the new capabilities.

One of the big effects you will see with the new attitude controllers is better handling of pitch compensation in turns. The new PTCH2SRV_RLL parameter makes tuning for flat turns much easier, which has been a major source of frustration in the past.

The new controllers also handle sensor noise much better, especially if you use any D term in your roll or pitch controllers.

New Speed/Height Controller

The new TECS speed/height controller is the second major controller change in this release, and will make a world of difference for aircraft with an airspeed sensor. After a lot of testing I decided to make TECS the default in this release, although you can switch back to the old controllers using the ALT_CTRL_ALG parameter if need be. If for some reason you find you do need these old controllers then please let me know, as I am planning on removing the old controllers in the next release.

The previous airspeed controller for speed/height suffered from a major problem that it gave absolute priority to airspeed. If the aircraft could not achieve the target airspeed you had set then it would dive to gain speed, even to the point of diving into the ground. This made it quite fragile, and you had to be very sure of your airspeed configuration.

The new controller operates over a range of airspeed values, set using the ARSPD_FBW_MIN and ARSPD_FBW_MAX parameters. That controller will try to meet both the airspeed and altitude demands of the mission, but if it can't reach the target speed it will happily fly a bit slower, as long as it doesn't get below ARSPD_FBW_MIN. You can control the relative priorities of speed versus height using the TECS_SPDWEIGHT parameter. See the full tuning guide for details.

New ACRO flight mode

After a suggestion from Thomas in the 2.73 release thread, we have added a new ACRO flight mode.

This modes brings rate controlled stabilization to APM:Plane, and should help give you an "on rails" manual flight experience. It is a lot of fun to fly, but it is not for beginners!

We're planning on expanding the ACRO mode in future releases. Right now it is great for "locked in" flying, and also good for loops and handles inverted flight very nicely. It doesn't yet handle knife-edge or prop-hanging.

New CRUISE flight mode

After a suggestion from Hein, we now have a new CRUISE flight mode. This mode is ideal for longer distance flying without a pre-programmed mission. It is like FBWB, but also does ground track heading hold, with heading update via aileron or rudder.

I've been testing CRUISE at my local flying field, and it is the easiest mode to fly in APM. Just steer the plane around the sky, and when you stop steering it locks onto a ground track and holds it. It isn't a good mode for takeoff and landing, but once you are in the air it is great.

New camera trigger system

When using APM for aerial mapping where you want photos taken at regular distances, the previous system was to setup a grid mission with a "camera trigger" mission item at regular intervals within the mission. That worked, but led to overly large and complex missions. You can now just set a single parameter CAM_TRIGG_DIST to the number of meters of flight between photos, and the APM will take care of when to trigger the camera. This makes for much simpler missions, and also works in other flight modes, including FBWB and CRUISE.

Lots of smaller changes

As is usual with a new release after a couple of months of development there were a lot of smaller improvements based on feedback from users. Many thanks to everyone who gave feedback and contributed patches!

Here is a partial list of the changes:

  • added new GND_ALT_OFFSET parameter for ground station barometric correction
  • made it possible to set the failsafe battery voltage and battery level at runtime via parameters
  • added MIXING_GAIN parameter for controlling the elevon and v-tail mixers
  • fixed stick mixing range in AUTO modes  (thanks Soren!)
  • fixed mode logging in dataflash
  • added support for the EagleTree I2C airspeed sensor on PX4
  • added new RCMAP_* parameters for re-mapping control channels (good for DSM and SBUS receivers on PX4)
  • made it possible to configure board orientation at runtime, to make setup easier without rebooting
  • switched to new task scheduler for more accurate internal timing
  • added a new RELAY_PIN parameter for setting up camera trigger via a digital pin
  • added secondary rudder support, useful for when a separate servo is used for a nosewheel and the rudder, or for v-tail planes with nosewheels
  • fixed RTL glide slope when starting above the target RTL altitude. Descent should now be smooth over long distances. Many thanks to Kitsen13 for raising this.
  • fixed a bug with FBWB airspeed control. Many thanks to Gabor for reporting this
  • Added FS_LONG_TIMEOUT and FS_SHORT_TIMEOUT parameters. Many thanks for the suggestion by Aleck
  • fixed handling of deadzone parameters on RC channels. Many thanks to Soren for reporting this
  • many small C++ fixes from NeuroCopter. This sort of detailed review of our code is much appreciated!
  • fixed analog in handling with some unusual devices - thanks to Andi for noticing this!
  • added support for apparent versus true airspeed calculations based on pressure altitude, for better flight control at higher altitudes
  • avoid writing unchanged bytes to EEPROM, for faster updates and less wear on the chip
  • cope better with large yaw changes in the AHRS code
  • improved the reliability of USB connections on PX4
  • added PX4 support for RELAY (thanks to Marco Bauer)
  • fixed handling of high spin rates in AHRS (thanks Jurgen!)
  • removed support for the old APM1 1280 based boards.

This new release has a lot of new features that should improve the flying experience for all APM users. The APM dev teams wishes all APM users many enjoyable flights, and we hope you have as much fun flying this release as we had making it.

Happy flying!

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Hi Martin,

yes, it logs latitude, longitude, altitude, roll, pitch and yaw, along with the GPS timestamp

Cheers, Tridge

I too think that a mix value of 1 would give me all the authority I need but unfortunately that makes flying in stabilized mode impossible because roll authority is really really massive and pitch authority is about right.... 

I do think that having a parameter to allow for more elevator control in the mix is needed. If you have elevons that are far out on the wings they are going to give more response than say ones further in. I may cut my elevon length down a bit to mitigate this but I should not have to and this will in turn cut down my elevator response unless I extend them in towards the body (the have been shortened a few inces out from the body)

I will also turn on the control tuning as suggested and hope to test again tomorrow... 

Hi Al,

Also is there another parameter that we are not seeing that could give more elevator authority (pitch p is maxed at 1.0 and mix gain is 0.8, and have increased max pitch angles)

You can set PTCH2SRV_P to more than 1.0 if you like. There are some planes that need more than 1.0 if they have relatively small natural pitch control (for example, I found that a SkyWalker 1900 I was tuning needed a value of 1.5). I've just fixed the auto-generated docs so they it shows a allowable range of 0.1 to 2.0 instead of 0.1 to 1.0. That should propagate to mission planner soon.

Have you posted a tlog somewhere for us to look at?

Cheers, Tridge

Hi Steve,

We could add asymmetric mixing to the ELEVON_OUTPUT mixer, but it would be equivalent to reducing the aileron rate in your transmitter, so I'd prefer to use that method as it more closely aligns with how people normally setup an RC plane.

When you changed from using the old elevon system for APM and switched to using ELEVON_OUTPUT you would have needed to change your transmitter settings to send aileron/elevator separately and no longer do mixing in the transmitter. That means you are really starting from scratch with your transmitter gains. It is quite normal to have to get those gains setup right for the characteristics of your model.

I usually use the rate control of the roll and pitch channels rather than the adjusting the endpoints directly, as it is much easier to do in my transmitter menus.

Note that you need to re-do the radio calibration if you change rates.

Cheers, Tridge


The activity seems high so I will ask a question I had about 3 months ago. Is there a way to check RTL operation on the ground? When I originally asked it was because I had "twitching" my rudder (3 Ch plane) in the RTL mode while on the ground. It was almost like some kind of Morse Code, a couple of short and some long twitches. I had GPS lock and HDOP was below 2.0. Before I could test it in the air, there was another release of firmware and the twitching went away. I didn't look back. However, with 2.74, the twitching has reappeared. Any help appreciated.



Thank you. I was thinking the same thing but since the twitching went away several firmware revisions ago and then reappeared, I was concerned there may be more to it.
Thanks again!

You guys ROCK. I can hardly wait to fly it! Thank you so much.

Andrew, Paul

Thanks so much for the excellent explanations and all your work to get this out to us. I am heading out tomorrow to do further tuning based on your suggestions.

Thanks again


I've had a very disconcerting Morse Code type twitch on the ground too. See video.

It's the aileron AND rudder (and I think elevator too) moving to the same twitching pattern (the rudder only moves slightly, perhaps about the same proportion as my rudder mix setting). Each time it has happened I've reset by reconnecting the battery and I've flown without issue. But it's very disconcerting.

It's only ever happened on the ground while setting up at the airfield. I've tried leaving it turned on at home for an hour or so and it's never done it.

I've checked my log file for the aileron output (and input in case it was my transmitter), but I was unable to find anything. The mode was manual. (My phone clock and APM/GCS clock aren't very well synced so I can't be sure I'm checking the right spot).

I'm still using 2.73.

Thanks for the info, so what are the maximum values in these fields? Is this documented somewhere?

Excuse my ignorance here as it is late but it looks like your pitch p is .5 and roll p is .4 on the x5. So what I am missing is how that is 2.5 times roll gain? What am I not understanding :)

Thanks Again for taking the time to respond!!! Out testing again tomorrow.


I see,

Thank you.

I have another question.

Is wind fixed now?

I mean in 2.73 when i started to dive windsped showed extreamly high values!

I think that it is because it does not calculates with pitch angle. Or might be even better the angle the plane really is going (up down)

So while let's say there is absolutely no wind, and i dive hard. 

AS is lets say 10 m/s than GS is much less than AS. It can even be 0m/s.  But this would give us a 10 m/s windspeed. 

Not sure if this is the problem, I don't quite understand APMs code, but this can case this.


Hi Guys,


may someone explain to me the right procedure to calibrate the airspeed sensor?

I looked in the guide but I've not found anything.


Thanks a lot!

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