I've just released ArduPlane 2.73 as a bug fix release for several important bugs in 2.72

The main reasons for this release are:

  • fixed a noise and scaling problem with airspeed sensors
  • fixed a potential flyaway problem with the L1 navigation controller
  • improved handling of poor GPS velocity for attitude correction

This release does not contain the new attitude controllers that I previously said would be in 2.73. Paul and I decided that it would be better to hold those over to the next release, and get this release out with just the above critical bug fixes.

The airspeed problem stemmed from a changed introduced in 2.72 to make ArduPlane automatically scale analog inputs with board voltage. That change was good for voltage and current sensing, but it added a lot of noise to airspeed sensing as the 3DR airspeed sensor is ratiometric (the sensor output scales with the supply voltage). The fix was to add support for ratiometric analog inputs. This release also fixes a bug in the airspeed ratio handling. To confirm the fix I have been driving around in my car with an APM2 and PX4 logging airspeed and GPS speed - that test confirmed the airspeed sensing is now accurate.

The flyaway bug in L1 was caused by an unusual situation where the previous waypoint was equal to the next waypoint, which can happen when a mission is interrupted and restarted. The L1 controller would then level the wings and fly straight ahead until the operator intervened. The bug fix was to make the L1 controller detect this situation and track directly to the next waypoint. I don't think many users would have seen this bug, but it definitely could happen and warranted a bug fix release.

The GPS handling bug was related to the MTK GPS, which can be very slow to report loss of GPS lock, which could lead to very poor attitude from DCM and even a crash if the plane tries to turn while the GPS is reporting incorrect velocity information. The fix was to watch the satellite count, and stop using the GPS velocity for accelerometer correction when it had less than 6 satellites. This is selectable with the new AHRS_GPS_MINSATS option.

Other changes

While this release doesn't have the new attitude controllers I decided to leave in some other smaller changes that have been made since the 2.72 release that I consider to be low risk, including:

  • fix the PX4 barometer driver to run at full rate
  • fixed handling of a saturated compass on PX4
  • added COMPASS_ORIENT option to support external compasses
  • fixed the compass in HIL simulation
  • added GCS messages to flash logs
  • allow 3D accel calibration over MAVLink
  • Added new ELEVON_OUTPUT option
  • removed MANUAL_LEVEL option (manual level is now always on)
  • improved pitch handling when inverted

Of these, perhaps the most useful is the ELEVON_OUTPUT option. That makes it possible to setup your transmitter with normal aileron/elevator and get the APM to do a software elevon mixer on output. That gives better control in FBWA mode than the previous elevon options.

I recommend that all users of 2.72 upgrade to 2.73. Happy flying!

Cheers, Tridge




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Hi Thomas,

The ACRO_PITCH_RATE and ACRO_ROLL_RATE control the rotation rate interpretation of the stick movement. The gains for the roll/pitch servo movement to achieve those rates are the standard ones for stabilized flight, ie. RLL2SRV_* and PTCH2SRV_*. The reason this works is that the new attitude controllers are actually rate controllers underneath, with a thin wrapper for attitude control. I just exposed the underlying rate controllers and hooked them into the ACRO mode.

I did a flight today with my PA AddictionX and ACRO mode. It certainly worked, although it did expose a bug in the handling of the deadzone for attitude lock. I've now pushed a fix for that. I'll fly it again on the weekend and see if it is any better.

Cheers, Tridge

Hi Thomas,

After a few more flights on my AddictionX today in ACRO I did some work with Paul on the ACRO controller, and it should be a lot nicer to use now. We've removed the problem with euler angles on roll, which makes acro loops much smoother.

I've put this in a new 2.74beta4 release, along with a new CRUISE flight mode for FPV flyers.

Cheers, Tridge


I have tried the ACRO mode on my vacation last week. Unfortunately I can not tell anything about the new mode because it did not start.

The funny thing was that the plane did a RTH when I switched to ACRO. But in the mission planer the switch position was set to ACRO...weird!

Maybe I have done something wrong, I will try it again at the next weekend


I notice that your battery voltage is dropping alot when flying...

Your flight is MANUAL only so the APM is out of the story.

 Next time after you take off in a safer environment fly it manual to know it flying habits,  switch to STABILIZED  if possible/all settings are ok.

Sorry if I'm posting in the wrong place, I'm setting up my APM 2.5 and have many questions, the first is about Failsafe
I did the Failsafe setup and it is working ok, when I turn off the radio I can see changing flight modes in MP as expected (first circle after RTH). one thing does not happen as I expected the throttle not going to cruise mode. Even when I start with the throttle stick in the middle and turn off the radio the throttle goes to zero, is this correct? I expected the throttle to maintain cruising speed for the plane back home safely? (I did these tests on land and the GPS locked, I have no airspeed)
(sorry for the mistakes I do not speak English and use the google translator)

The PPM encoder will drop the throttle channel below minimum to indicate to the APM that there is a problem and the RC signal has been lost.  The APM will hold the throttle to maintain  cruise flight.


This failsafe thing is half complicated...

  • Many RC receivers have a built in fail-safe system. All outputs will go to given values if signal is lost. Some use preset values, others just freeze, some even have a combination. This is "receiver fail-safe".
  • Other RC receivers simply stop outputting any signals if radio signal is lost. You have to find out what your system does.
  • If your RC is the type where you pre-set the failsafe values, you can preset an abnormally low throttle value (probably you need to trim unusually low of use sub-trim on the transmitter when setting the receiver failsafe. Afterwards, trim back to normal operation)
  • And if you use the PWM to PPM decoder (meaning: You have a lot of cables from RC receiver to APM, one for each channel), as Craig wrote the PWM to PPM encoder will simulate an abnormally low throttle if all signals from RC go missing.
  • APM can detect this abnormally low throttle value coming in from the RC receiver and use that for detecting signal-lost. You can decide whether it should do circle and RTL when that happens - that is "APM fail-safe". Some people pre-set their mode channel receiver fail-safe to whatever they like (typically AUTO) and turn off APM fail-safe so their planes will continue a mission when getting out of range.
  • If APM is in an automatic mode like AUTO or RTL (it does not matter if it is also in fail-safe or not), then APM will control throttle output to keep flying even if throttle input from the RC is low or abnormally low.

You write "the throttle goes to zero" but is that the receiver's throttle (APM input) or the motor throttle (APM output)? OK I suppose you mean the output.

In RTL, there is another special thing: The altitude is changed as fast as possible, until the RTL altitude is reached. That could be why your motor goes off. It wants the plane to come down. Look at the ALT_HOLD_RTL parameter and set it to something meaningful, maybe 10000 which means 100m above home altitude. Setting it to 0 is not good - the plane will try to crawl home along the ground.




Let me ask. Does speed change works for you in FBWB?

If yes, could you send me your parm file?

(I have attached my)

Please halp me. I have no idea what i am doing wrong... :(



Hey Gabor,

Do you have a tlog to go along with the param file?


Nathaniel ~KD2DEY

Hi Nathaniel,

Thank you for your attention! :)

Unfortunately, i don't use telemetry, as i fly FPV.

I have all the data i need on the video.

This situation i did not think of.

There must be something with my settings. But that i could not find.

It worked before when i have used previous versions of Arduplane FW.

Thx again,



I didn't see anything in your param file that jumped out at me. Admittedly however I don't use FBW-B, I use FBW-A, so I can't confirm your experience. I know you don't have a tlog, but how about a log file?

BTW Off topic, but I'm a big fan of the work you're doing on the Minim-OSD Extra. I'm thinking were getting to the point we need a more resource rich v2.0 board though.


Nathaniel ~KD2DEY


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