Blogs

The ardupilot development team is proud to announce the release of version 3.2.0 of APM:Plane. This is a major release with a lot of new features.

The changes span a lot of different areas of the code, but arguably the most important changes are:

• automatic stall prevention code
• PX4IO based RC override code on FMU failure
• I2C crash bugfix
• new autoland code from Michael Day
• compass independent auto takeoff

I'll go into each of these changes in a bit more detail.

Automatic Stall Prevention

The automatic stall prevention code is code that uses the aerodynamic load factor (calculated from demanded bank angle) to adjust both the maximum roll angle and the minimum airspeed. You can enable/disable this code with the STALL_PREVENTION parameter which defaults to enabled.

When in stabilised manual throttle modes this option has the effect of limiting how much bank angle you can demand when close to the configured minimum airspeed (from ARSPD_FBW_MIN). That means when in FBWA mode if you try to turn hard while close to ARSPD_FBW_MIN it will limit the bank angle to an amount that will keep the speed above ARSPD_FBW_MIN times the aerodynamic load factor. It will always allow you at bank at least 25 degrees however, to ensure you keep some maneuverability if the airspeed estimate is incorrect.

When in auto-throttle modes (such as AUTO, RTL, CRUISE etc) it will additionally raise the minimum airspeed in proportion to the aerodynamic load factor. That means if a mission demands a sharp turn
at low speed then initially the turn will be less sharp, and the TECS controller will add power to bring the airspeed up to a level that can handle the demanded turn. After the turn is complete the minimum airspeed will drop back to the normal level.

This change won't completely eliminate stalls of course, but it should make them less likely if you properly configure ARSPD_FBW_MIN for your aircraft.

PX4IO based RC override code

This releases adds support for PX4IO based RC override. This is a safety feature where the stm32 IO co-processor on the PX4 and Pixhawk will give the pilot manual control if the main ArduPilot micro-controller fails (or the autopilot code crashes). This is particularly useful when testing new code that may not be stable.

As part of this new RC override support we also have a new OVERRIDE_CHAN parameter, which allows you to specify a RC input channel which can be used to test the RC override support. See the documentation on OVERRIDE_CHAN for details.

I2C bugfix

This release fixes another I2C bug in NuttX which could cause the Pixhawk to lock up under high I2C load with noise on I2C cables. This bug has caused at least two aircraft to crash, so it is an important fix. I hope this will be the last I2C crash bug we find in NuttX! An audit of the code was done to try to confirm that no more bugs of this type are present.

New Autoland code

This release incorporates some new autoland capabilities contributed by Michael Day. The key new feature is the ability to trigger an automatic landing when a RTL completes, which for the first time allows a user to setup their aircraft to land using only transmitter control.

The way it works is there is a new parameter RTL_AUTOLAND. If that is set to 1 and the aircraft reaches its target location in an RTL it will look for DO_LAND_START mission item in the mission. If that is found then the aircraft will switch to AUTO starting at that section of the mission. The user sets up their land mission commands starting with a DO_LAND_START mission item.

There is more to do in this autoland support. We have been discussing more advanced go-around capabilities and also better path planning for landing. The code in this release is an important first step though, and will be a good basis for future work.

Compass independent takeoff code

The auto-takeoff code has been changed to make it more independent of compass settings, allowing for reliable takeoff down a runway with poor compass offsets. The new takeoff code uses the gyroscope as the
primary heading control for the first part of the takeoff, until the aircraft gains enough speed for a GPS heading to be reliable.

Many thanks to all the contributors, especially:

• Paul and Jon for EKF and TECS updates
• Bret and Grant for stall prevention testing
• Michael for all his autoland work
• all the work on NavIO, PXF and Zynq by John, Victor, George and Siddarth
• The PX4 team for all the PX4 updates
• Flaperon updates from Kirill

More complete list of changes:

• allow GCS to enable/disable PX4 safety switch
• make auto-takeoff independent of compass errors
• report gyro unhealthy if calibration failed
• added support for MAV_CMD_DO_LAND_START
• added RTL_AUTOLAND parameter
• disable CLI by default in build
• new InertialSensor implementation
• added landing go around support
• enable PX4 failsafe RC override
• added OVERRIDE_CHAN parameter
• changed default AUTOTUNE level to 6
• changed default I value for roll/pitch controllers
• added CAMERA_FEEDBACK mavlink messages
• use airspeed temperature for baro calibration if possible
• added STALL_PREVENTION parameter
• fixed handling of TKOFF_THR_MAX parameter
• added ARSPD_SKIP_CAL parameter
• fixed flaperon trim handling (WARNING: may need to retrim flaperons)
• EKF robustness improvements, especially for MAG handling
• lots of HAL_Linux updates
• support wider range of I2C Lidars
• fixed fallback to DCM in AHRS
• fixed I2C crash bug in NuttX
• TECS prevent throttle undershoot after a climb
• AP_Mount: added lead filter to improve servo gimbals
• Zynq and NavIO updates
• fixed preflight calibration to prevent losing 3D accel cal
• perform a gyro calibration when doing 3D accel cal
• added DO_CONTINUE_AND_CHANGE_ALT mission command
• added support for DO_FENCE_ENABLE mission command
• allow gyro calibration to take up to 30 seconds
• improved health checks in the EKF for DCM fallback

Note: If you use flaperons you may need to re-trim them before you
fly due to the change in flaperon trim handling.

I hope that everyone enjoys flying this new APM:Plane release as much as we enjoyed producing it!

Happy flying!