The ArduPilot development team is proud to announce the release of version 3.5.1 of APM:Plane. This is a minor release with primarily small changes.

The changes in this release are:

  • update uavcan to new protocol
  • always exit loiter in AUTO towards next waypoint
  • support more multicopter types in quadplane
  • added support for reverse thrust landings
  • added LAND_THR_SLEW parameter
  • added LAND_THEN_NEUTRL parameter
  • fixed reporting of armed state with safety switch
  • added optional arming check for minimum voltage
  • support motor test for quadplanes
  • added QLAND flight mode (quadplane land mode)
  • added TECS_LAND_SRC (land sink rate change)
  • use throttle slew in quadplane transition
  • added PID tuning for quadplane
  • improved text message queueing to ground stations
  • added LAND_THR_SLEW parameter
  • re-organisation of HAL_Linux bus API
  • improved NMEA parsing in GPS driver
  • changed TECS_LAND_SPDWGT default to -1
  • improved autoconfig of uBlox GPS driver
  • support a wider range of Lightware serial Lidars
  • improved non-GPS performance of EKF2
  • allow for indoor flight of quadplanes
  • improved compass fusion in EKF2
  • improved support for Pixracer board
  • improved NavIO2 support
  • added BATT_WATT_MAX parameter

The reverse thrust landing is particularly exciting as that adds a whole new range of possibilities for landing in restricted areas. Many thanks to Tom for the great work on getting this done.

The uavcan change to the new protocol has been a long time coming, and I'd like to thank Holger for both his great work on this and his patience given how long it has taken to be in a release. This adds support for automatic canbus node assignment which makes setup much easier, and also supports the latest versions of the Zubax canbus GPS.

My apologies if your favourite feature didn't make it into this release! There are a lot more changes pending but we needed to call a halt for the release eventually. This release has had a lot of flight testing and I'm confident it will be a great release.

Happy flying!

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Comment by Claudio on March 21, 2016 at 1:10am
Many thanks!!

Comment by James on March 21, 2016 at 1:22am

Great work guys!!  Thanks for the release notes ,


We tried that last version at a large gas plane, as a testbed and Demo at the same time!!   We used almost all extra features (RPM, Second GPS, PTZ Camera, Companion Comp, Secondary Telem, Nose Gear ...  name it!)

Everything works flawlessly.

Still, we were very excited when you utilized the SBUS out for more outputs..  As you can imagine, we run out them. While we conected our cams  ZOOM, Thermal, retract, nav lights as passthru channels on 9,10,11,12 out.  We can control them via TX as long as we have link, but we cant control them via mavling (Toogle channel X with MP).

One trick was to assign the zoom channel as a camera roll and assign (1 ok 3 to go..).

The question is.. :  can we toggle 9-14 channel out, if they are assigned as passthru function?  Can we use an SBUS converter? 

Comment by Mike Mac on March 21, 2016 at 3:40am

Are there any videos of reverse thrust landings? I would really like to see how that works.


Also all my ESC’s only go one way. Are there any good airplanes ESC’s with reverse capability?




Comment by Jeff Taylor on March 21, 2016 at 7:01am

We use SimonK ESCs which are able to reverse thrust and do allow for quite steep dives of up to 60% gradient on a Skywalker frame. We haven't switched to this firmware yet, Tom Pittenger did a huge update of our internal code (which is public on our github page if you want to try that) to make it more usable for regular DIY Drones users with all different types of planes. Sorry for the marketing materials here but this video shows a reverse thrust landing on the E386, starting at about 25 seconds in.

Keep in mind the E386 also uses a laser rangefinder to flare. APM will have some altitude drift on warm days or after long flights, so it can be a bit tricky getting the right flare altitude. One more big tip for those about to try this, the reverse thrust creates a lot of turbulent air and in our experience it can reduce the elevator's effectiveness quite a bit. We actually turn off the motor just before flaring so the elevator can pull up quickly.

Comment by Ravi on March 21, 2016 at 7:43am

Tridge, you are just amazing. the VTOL planes would be a great sensation as the software becomes more user friendly.

Comment by JB on March 21, 2016 at 8:20am

The software is pretty user friendly already. But I think there is still a fair amount of hardware optimisation that can happen to get each part balanced mechanically, and with those extra parts to tune in code.


I'd also suggest SimonK based ESC or an ESC32 for reverse thrust use. Interesting comment about the loss of elevator control due to turbulence. I suppose a wing won't be affected much though, but I'll keep an eye out for it.

Comment by Tom Pittenger on March 21, 2016 at 11:53am

Hi All,

There is a wiki for the reverse thrust that I plan to add some diagrams to eventually.

Many ESCs that come from the factory as forward-only can have their firmware changed to allow both. BLHeli and SimonK have great options for that.

Comment by MarioSpeedwagon on March 21, 2016 at 1:11pm
Thank you Tridge and all the other contributors for your hard work.
I'm excited to try out the reversible thrust.

Comment by Andrew Tridgell on March 21, 2016 at 1:53pm

@James, the RC_OVERRIDE MAVLink message only covers 8 channels, so you can't use RC_OVERRIDE with channels 9 to 14.

You can set them using the DO_SET_SERVO commands, but you can't setup a channel for both DO_SET_SERVO and for RC pass-thru.

I think we should extend RC_CHANNELS_OVERRIDE in the future to allow for 16 channels.

Comment by Justin on March 21, 2016 at 2:30pm
Great work Dev team. Keep it up


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