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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Yes you're right. I've just looked at this latest episode and FAILSAFE does flash up on the HUD, and the mode switches to RTL right before the twitching starts.

I've attached a screen shot showing the tuning graph. ch1out moves but I'm surprised that ch1in moves too. Isn't that a trace of the input from the RC receiver?

I'm setup with GCS failsafe enabled, and throttle failsafe disabled. RSSI is 217 and the signal strength in the top right of the HUD shows 90% at the time FAILSAFE flashed up on the HUD so I'm surprised to get a GCS failsafe event occurring. Any ideas?

(Boy I'm pleased that the motor didn't start up, I'll re-read the notes about that to make sure I'm aware how that works.)


The manual explains how important airspeed sensor calibration is then doesn't mention how to do it!

There is an ugly but easy way:

Wind direction is usually precise enough even if AS sensor is not calibrated that well.

So fly like wind is from 90° or 270° relative to your plane, than AS = GS if it is calibrated right.

If you use Minimosd-Extra there is a wind panel that gives you the wind direction.

This is how i did it.


WoW! Great new features. Can't wait to try it on my scratch build test tank :) Thanks all the developers and suggesters of new features!

Thanks Paul!

I've also created a wiki page describing the process in more detail

Cheers, Tridge

Maybe I will finally reinstall my 2 year old diydrones airspeed sensor. First time I used it, things went nuts and I never had the chance to discover the problem. From reading the changes, it seems that was the problem I was having with it.

Hi Paul,


Sure, if the wind is strong or gusty than this does not works right.

A small wind is not a problem. Quite precise.

The thing is that i don't have telemetry. :)

But basically i do the same.

I did not have a better idea, when i had to calibrate it. Now i think it is precise.

But if you are experienced, you can see if AS is wrong, only by watching back a regular flight.

Like in this vid my AS reads a bit high:



I have used the TRIM_AUTO feature before as it sounded like a good idea. What are the developer's thoughts on this?



Hi Steven,

I use TRIM_AUTO all the time, unless I am teaching someone to fly with a buddy box. If I'm using a buddy box then its potentially bad, as if I give the student MANUAL control, and then flick to FBWA to recover quickly while they have lots of stick deflection then it will get very bad trims. It is tricky to remember to always let go of the trainer switch before switching modes (especially when the student is diving the plane towards the ground!).

Cheers, Tridge

Is it true, that even if i don't use auto trim, trims reset on boot?


Thanks. I assume it's 1=enabled and 0= disabled.

You may be thinking of level. Trim is what you adjust your plane's control surfaces to for straight and level flight.

Well done!

I went flying today with 2.74b and I have to say that it works perfect. I had a strong wind but the plane managed to fly as precisely as it never did before. The new TECS control allows to make rapid climbs without overshooting or oscillating.

I flew mostly with the standard parameters and did no fine tuning. Even in turns the plane kept its given altitude.

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