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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Thx Paul,

I have come to the same point. :)

But when TKOFF_THR_DELAY, is available, i will use it. ;)

It is not the only plane we plan to use this function on.

Like my friend has a flying wing.

The best way to trow that plane to the air, is to hold it on your hand and positioning your fingers on its firewall. Sounds a bit scary, right? I :) 

I did trust my friend when i did this, that he will not aply throttle too soon. :D

But at the moment i can't rely on APM on this. Should not.... :)

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Do you have an idea on pitching down when throttle is aplied?

Is there a parameter that compensates this?

Thx,

Gábor

Hi Gabor,

I have also noticed that my OSD has a kind of latency now. Did datatransfer got slower?

yes, it is a bit slower. The 2.74 release includes the new task scheduler library which is much stricter about timing, and gives top priority to the flight code (stabilization, navigation etc). The new TECS altitude controller and the new attitude controllers are more CPU intensive than the old ones, and the task scheduler now strictly enforces the core code running at the desired rates which leaves less time for MAVLink processing. The result is that you often get MAVLink messages sent at a bit lower rate than you ask for.

One of the issues is that the time it takes to assemble and send a MAVLink message is a somewhat variable. In the task scheduler we have to list the worst case time a task may take. The scheduler then determines if there is enough time to perform that lower priority task before the next IMU 50Hz "tick". If there isn't enough time then it defers the MAVLink message send until after the tick.

I am planning on having a look at the timing to see if I can improve it but I don't yet know how much more room there is to squeeze in more work on the AVR2560.

btw, one thing you can do is change the relative rates of each type of MAVLink message stream. Which messages are the ones that need to be updated more quickly for typical OSD usage?

Cheers, Tridge

I have made the switch today to 2.74b and I must say the new attitude controllers are a big improvement over the old ones.
To make automatic flight perform about the same as the old altitude controller I had to increase the pitch gain and I added 0,1 to the TECS pitch damper. After that it flew allright, without oscillations. I can see the new controller can benefit A LOT from an airspeed sensor, so I ordered the kit when I got home. (TECS almost stalled the plane a couple of times, old controller never did that with the same settings. I had to reduce PITCH MAX)

Just a couple of questions:
1: When I increase the I gain of the pitch and roll2srv controller, nothing seems to happen. I put it in fbwa mode and lay it tilted on the ground. I would expect the control surfaces deflecting an extra 15 degrees over time to compensate for the tilted position of the craft, but they stayed right where they were.  is there something wrong with my settings?

2: When I have an airspeed sensor installed, And I fly in windy conditions where the wind == airspeed_cruise with the plane downwind and at target altitude, The ground speed will be zero. Meaning the plane can't fly back to me when I switch to RTL.
Is there some compensation built in that makes sure the ground speed cannot be zero or negative?

Hi Pieter,

TECS almost stalled the plane a couple of times, old controller never did that with the same settings. I had to reduce PITCH MAX

Can you post a tlog for us to look at?

1: When I increase the I gain of the pitch and roll2srv controller, nothing seems to happen. I put it in fbwa mode and lay it tilted on the ground. I would expect the control surfaces deflecting an extra 15 degrees over time to compensate for the tilted position of the craft, but they stayed right where they were.  is there something wrong with my settings?

I'd need to see your settings to know :-)

Is there some compensation built in that makes sure the ground speed cannot be zero or negative?

you can set MIN_GNDSPD_CM to the minimum ground speed you want in cm/second. That will ask the controller to push things faster if you drop below that ground speed.

Cheers, Tridge

Here is my onboard log with tuning logging enabled.
I still have some fine tuning to do, don't get me wrong the TECS controller was doing a great job once I got the setting right.
It only has me wondering about that pitch and roll integrator gain. It does not deflect the control surfaces when I leave the plane tilted.

Attachments:

Hi Pieter,

It only has me wondering about that pitch and roll integrator gain. It does not deflect the control surfaces when I leave the plane tilted.

The new attitude controllers have protection against integrator buildup when the plane is on the ground and not flying, or in the initial stages of takeoff. It will only start to use integrator once the aircraft reaches ARSPD_FBW_MIN (which is 6 m/s in your log).

This prevents integrator buildup from causing a crash on takeoff.

Cheers, Tridge

that explains it!
Thanks a lot Tridge, I did not know the attitude controllers have an integrator buildup protection.

hello Tridge. I will review the flashlog to be sure. Only when I saw the photos taken, some pictures were very near each other. seemed not to be equidistant. only a visual perception. I'll have to check the flashlog.

thanks

jim

I have amy APM2.0 in an X5  flying wing that worked great with 2.73, yesterday the same plane in the same field suddenly lost its GPS position in the middle of a auto flight and according to the MP it was flying backwards for a few seconds, the only thing that changed was the update to 2.74b. the Sat count dropped from 12 to 6 in the midlle of a 45-50degreee banked turn to the north. it recovered after several seconds and continued the mission then it did the same again and went into circle mode then then recovered again, I landed safely and everything seems OK.

Is 2.74b handling the GPS differently or did I just have a bad day? or could the high angle of bank have caused the issue.

thanks 

Curious, which GPS module are you using?  Not sure I have a fix, just wondering if you are MediaTek vs uBlox

its the original one that came with the APM 2 module, its fixed on the APM not a seperate unit. I do not know the make, it was purchased Jan 2012. it never had any issues of failures before.

I think I might have found a bug in acro mode.
When I move the elevator stick about 10% up or down away from neutral, I get full deflection of the elevator resulting in very nervous pitch behaviour.
Aileron and rudder servos respond normal to stick input ( Full range of the stick proportional to servo output)

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