APM:Plane 2.74 released

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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  • @Paul and Andrew, thanks guys I will take these settings and suggestions to the field today.

    Again sorry I can't find anything in this thread so I apologise for not responding to the original tree branch...

    Are you guys also active on the arduplane forum?

  • @Paul, sorry I cant find that original thread... this forum really is not good for any sort of discussion... it's painful in fact :)

    Anyway I reverted back to previous firmware to ensure I had a good working machine, now that I am on the latest download I will try to play with the TECS as per your sugesstion.

    Will TECS work well without an airspeed sensor? I just don't want the added complexity etc of it.... but if I have to do it I will.

    Great work btw guys this AP has come a really long way since I tried it a few years ago.


  • Hi,
    I saw somewhere instructions to update the ATMEGA32U2 (PPM encoder), really need to do this update?


  • Hi all,

    I have asked this before, but noone seamed to know the answer.

    I give it another try. :)

    Can someone explain how KFF_THR2PTCH works?

    This is all wiki tells me:


    Throttle to Pitch Mix (ArduPlane:KFF_THR2PTCH)

    Note: This parameter is for advanced users

    Throttle to pitch feed-forward gain.
    Range: 0 5
    Increment: 0.01


    Is it that when APM aplyes throttle than it also ads some elevator?


  • hi again guys, wow this "forum" is extreemly difficult to follow, I had to unsubscribe because of the flood of emails.

    Is there a better place to discuss issues etc?

    Anyway I downgraded my firmware then re-tested and all my pitching and throttling issues went away... not sure why.

    I tuned the X5 so it was flying quite well but now I realise that the distance photo trigger is only available on the latest firmware....

    Now I have upgraded to the latest firmware (have to start tuning over again I guess) and notice that "Level" is gone and there is now a button saying "calibrate acc" which we can not press.... why? how do we calibrate our acc's now?

    I assume we have to use the level command in the CLI to set level... so is that now where we also have to calibrate the acc? if so that's not good becuase I have to connect via usb to do this.



  • Paul,
    I got it to work. Yesterday I received my airspeed kit and I installed and calibrated it. Set the min and max speed accordingly and I flew it.
    Now my plane flies beautiful again. Much more accurate then with the old controllers.
    Great work, thanks!

  • Moderator

    Is failsafe broken again?

    When I turn my radio off in AUTO, (short and long failsafe checked) the failsafe triggers RTL but when I turn the radio on again the mode returns to AUTO setting up a potentially dangerous endless loop.

    Really bad! It should only return to AUTO if the mode switch is toggled. Or is APM inadvertently detecting the mode switch when the signal returns?

  • Moderator

    I'm trying to garner some support for assignable mission buttons in the Mission Planner. This is particularly applicable to ArduPlane:

    If you think this is a good idea please +1

  • Moderator

    @Paul Riseborough: please could you post your X8 wing parameter file here? It would really help to have an X8 setup that we knows works very well.

  • Hello, Still tweaking and tuning. Yes, it's sort of fun but sometimes unexplainable things happen. Today, just for the heck of it, I went up to about 650 ft altitude in FBWA mode and then switched to RTL. My RTL altitude is set at 200ft. Well, the plane came down in a spiral fashion at zero amps (no motor) but then it surprised me be deciding the RTL altitude was around 265ft and began to add power and circle there. During prior flights it homed in on the 200ft quite nicely. It would appear that if the altitude difference is lower or only slightly higher than RTL Alt. it does fine.

    Anyone have suggestions or an explanation?



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