Potential for Trad Heli In-flight motor shutdown in Auto and Guided modes in AC 4.0.7

Trad Heli Users,
I am writing to warn you of the higher probability for an in-flight motor shutdown in Auto or Guided flight modes. This is occurring because the autopilot declares land complete in flight which initiates the auto shutdown and disarm sequence. The root cause of this was determined to be due to the new integrator management implementation. That PR changed the landing detector logic which overrided the suppression of the land complete declaration when the aircraft was not in a landing state in auto or guided modes.

The best way to guard against this other than reverting back to AC 4.0.5 is to set the H_COL_MID parameter as low as possible to prevent the current collective from going below the H_COL_MID value (which is used to determine land complete). Suggest making the H_COL_MID value equivalent to - 2 deg of collective pitch which should be acceptable for extended ground runs with rotors turning in Loiter or althold modes. If you experience any issues with rotors turning on the ground, raise this value as needed but -2 deg should be safe. If you are using the collective to yaw mixing (H_COL_YAW non zero) then you may choose to revert back to AC 4.0.5 or turn off the collective to yaw mixing by setting H_COL_YAW to zero. The reason I say this is that the collective to yaw mixing feature uses the H_COL_MID parameter to set the zero thrust point(minimum torque) for the collective to yaw feedforward.

I am working to implement a fix to this bug as soon as possible. Planning to get it into 4.1.0 before it gets released as stable and potentially providing a point release to 4.0.7.


Trad Heli Users,
I was too late to be able to get this fix into AC 4.1.0. So this issue applies to this version of firmware as well. As I stated above, I will implement a fix as soon as possible and target it for 4.1.1 instead.

Thank you very much for the warning, Bill! I actually was aware of the problem, that setting H_COL_MID too high might lead to an inflight shutdown of the motor. That’s why I had it precisely set to zero thrust. Nevertheless I always was a little bit concerned, because my T-Rex 800 has a pretty low disc loading (like a lot of other helicopters do), so it can hover with very low collective pitch settings. I’m not sure, but I guess under unfavorable wind conditions (e.g. ridge lift) it might reach the H_COL_MID setting.

That’s why I really liked the H_LAND_COL_MIN parameter. Are there important reasons why it was removed from the code? I know it’s an additional parameter which might confuse new users. So I’d suggest the following: What if H_LAND_COL_MIN was added again and if left empty (or -1 or something like that) the code ignores it and uses H_COL_MID, just like it does right now. If the user changes the value (e.g. because he or she knows that the helicopter has a low disc loading and might experience problems) then the code would use H_LAND_COL_MIN instead and safely prevent unwanted motor shutdowns.

@Felix Yes this has been a concern and why there is a warning in the wiki about setting this parameter.

The primary reason for removing H_LAND_COL_MIN was that it was rarely properly set (typically left at default) and the fact it was an additional parameter. I am seeing the need to bring this parameter back

The problem with bringing it back with how the collective pitch is set up currently is that the code has no idea where -1 deg of collective pitch is. Remember that both H_ LAND_COL_MIN and H_COL_MID are set using PWM and there is no reference to actual collective pitch angle. So I just coded up over the weekend a PR that adds two parameters to have the user tell the code what H_COL_MIN and H_COL_MAX equate to in degrees of collective blade pitch. So the code has the PWM value with the corresponding actual collective blade pitch angle. Users know what they set for the min and max collective blade pitch so just have them enter it as two additional Params. Now I can easily set defaults for the zero thrust parameter and the land collective min parameter. They would still be able to adjust them as needed but the guesswork is no longer in question.


Yes, that’s true of course. With setting it to “-1” I meant switching the parameter off. (Telling it to use H_COL_MID instead.) But as we just saw, that can lead to confusion with blade pitch angle.

Wow, that’s a brilliant idea! Everyone knows the min/max collective blade pitch angle so it’s not increasing setup complexity and the code can do the rest… While advanced users still have the possibility to enter whatever value they like. Awesome! I really like your solution! Thanks again for your great work!

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Trad Heli Users,
This bug has been fixed in AC 4.0. The stable release with the fix is AC 4.0.8. Users can load the firmware but it needs to be done in the Setup Tab and select the Install Firmware. You will see the “All Options” below the install icons for each vehicle type. Select “all options”. You will then use the pull down menus to select the
Version Type: STABLE-4.0.8
Version: 4.0.8
Then click on Upload Firmware. You can see the selections in the image below. In this case, cubeblack was selected as the flight controller.


The bug fix also went into AC 4.1. A beta release will come out soon for AC 4.1.1 with this bug fix and some other fixes for 4.1.0.

If you have any questions, don’t hesitate to post here.

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two addtional params for min and max pitch degree had added into 4.0.8 ?

No. I didn’t add that change. it was only something I was considering for a future change to 4.1. This change just fixes the bug introduced by the new integrator scheme implementation. Sorry for the confusion