Copter-3.5.2-rc1 is ready for beta testing

Copter-3.5.2-rc1 will be available through the MP’s “beta firmwares” link (and perhaps through other GCSs as well) about 5hrs after the timing of this posting (it takes a while to get through the autotester and builder).

This is a relatively minor release which includes these changes over 3.5.1 (Release Notes):

  1. GPS glitch arming check and notification (flashing blue-yellow LED, message on HUD)
  2. Arming check for minimum voltage (see ARMING_VOLT_MIN parameter)
  3. Landing Gear startup behaviour now configurable (see LGR_STARTUP parameter)
  4. Solo LED fix when using “boat” mode
  5. Bug fixes:
  • resolve barometer floating point exception when ground pressure set to be negative
  • resolve freeze if SERVOx_FUNCTION is set above 80
  • Intel Aero I2C bus fixes

Any testing people can do, would be greatly appreciated, thanks!

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Just a note that a) it’s Intel Aero RTF not Aero and b) those are not really fixes… It’s the addition of 1 more i2c bus so people can connect useful sensors without interfering with the mag

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Hi all,
I have recently uploaded 3.5.1rc1 into a Pixhawk controlled Quad. Much alarm when I switched to Alt Hold the Yaw and Aileron sticks were reversed. The throttle and forward/back remained OK. I fly mode 2 so left-hand yaw and throttle and right hand forward/back and left/right. I switched to stabilize and headed for the deck, took off again in stabilise mode and the quad handled well then switched to Alt Hold, when I was one mistake high, just to convince my self I was not going ga ga and the same thing happened.
I also get a mode change error from mission planner when I try and engage Auto Tune and it does not start to auto tune.
I haven’t flown at all for about two years but when last flying, don’t ask which version of Aurdupilot firmware I was using as I can not remember, this Quad flew OK.
Any ideas I am a little short of playing time so I will be unable to flash the the older version 3.5.1 for at least 3 day in order to try again.



Did a flight test of a couple of the added features: minimum voltage and landing gear. I like the min voltage pre arm, seems to work as expected. Not sure what to expect with the landing gear parameters. I’m using Tarot gear and controller, I see no difference in behavior from previous version. As I’ve seen others note that the gear will not retract until pilot input cycle through deploy and then retract. Tried parameter set to all three possible choices. Thi of course is not a serious concern and the gear deploy in an auto land mode without fail. I also have been testing the new EPM grabber parameters, works well, I like the ability to release the cargo manually as well as auto mission.

Thanks for all the continued support,
Cheers, RB

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Hi Randy,

thanks for testing!
Re the landing gear, if you set LGR_STARTUP parameter to 1 or 2 you should see the landing gear either retract or deploy on startup instead of waiting for the pilot to move the switch on the transmitter.

Hi JohnM,

sounds like simple mode is on for one of the flight modes. By the way, it’s best to include a dataflash log file and probably open up a new topic in this Copter-3.5 category.

Hi Lucas,
Thanks, I wasn’t really sure what those commits were for when I wrote up the release notes, thanks for the clarification.

OK, I have the same results with parameter set at 0, 1, or 2. After take off I have to switch to deploy and then to retract to get the gear to come up. After the initial cycle the gear respond to retract and deploy normally. When you say the gear will retract or deploy on start up, do you mean APM start up or after arming and take off?


Hi rmackay9,
Thanks for that and you are correct. I will also start a new topic and include data logs for this problem and also the Auto tune problem when I get some play time in a couple or 3 days time. Still dont understand why a mode that I am not using, altho its available via mode switch, has this effect on Alt Hold but not on Stabilise. So much to learn!!
Thanks and Regards


Set PWM to 1900 deploy and 1100 retract - LGR_STARTUP “2”

Gear now retracts with single throw of switch and auto deploys on RTL or LAND

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Pixhawk 2.1 has no Optical Flow information.

When connected with battery, no Optical Flow information is being recorded. Works when powered with USB.

Hi Guys,

I am grateful that this project going in the direction of my imagination. Thanks.
I would like to tell you about my bad mistake and a possible solution for preventing.
In short, I was testing the stability of my Hexa (Pixhawk 1) and I didn’t connect the buzzer so I couldn’t hear the alarm for that because the battery was on 20% when the FS was triggered in RTL mode. Drone started climbing to RTL altitude (15m) and as I was not expecting such a thing, I turned the throttle stick to 0 and I started changing the flight modes… this was happening in a few seconds in terrible panic of losing the control over the drone …
When the drone was on altitude of 15m, FC accepted the stabilise mode, the motors stopped and the drone fell like a brick in my pool. In the first few minutes It was a relief because the drone didn’t fly away without control but after that it was a terrible feeling because I lost all drone electronics, the battery, the gimbal and the gopro.
Now, I’ve rebuild my Hexa and flying again but I would like if it is possible to have FS in situation if the drone starts falling in the case of the other pilots make the same mistake.
I know there is established the “throw mode” but “throw mode” works if the drone is thrown up or dropped down, so I was thinking, maybe the “throw mode” can be used in cases like mine, if it will be triggered when falling is detected during the flight.
If that FS option will be added in this or the next upgrade, I think that will be a great benefit for the safety of all of us.


It should detect that it is in the air, but you must have sort of tricked it into disarming by switching flight modes quickly or something. Maybe you should post a log of the flight.

I had a similar thing happen to me a couple years ago… I was testing a copter that was having compass/GPS issues so was often trying to fly off in a random direction. So, I was hovering it, seeing if I had good loiter performance, and it started shooting up into the air. In that split second I didn’t realize what was happening and flipped the motor stop switch to stop what I thought was a random fly-away, and forcefully bring it down. (I realize now, motor stop wasn’t the best choice in that situation, but I was a beginner)
Then I looked at the logs and realized it was just a battery failsafe…
Mine was the opposite of yours… Electronics OK, but my frame was a complete loss, so I had to rebuild it.

Great that you have the landing gear sorted.
The change with AC3.5.2-rc1 is that the user can set the state of the gear when the flight controller is powered on. So the user can make the gear immediately deploy or retract when the vehicle’s battery is plugged in.