Bad AHRS prohibits Arming on Plane

ArduPlane Plane 3.8
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1

I run Arduplane 3.8.5 on Pixracer with all compasses disabled which is not critical for planes anyway. I get the “Bad AHRS” error message, even after good GPS lock, which disallows the plane to arm. Even moving the plane in heading direction to help Arduplane find the heading via gps does not help. It would be good to have a way to ignore Bad AHRS message during arming without disabling the whole Arming checks flag in mission planner.

2

Getting the exact same thing…it’s also causing a flashing yellow light which shows the failure of the pre-arm checks. Tried re-calibrating the acceleration but it doesn’t help…

3

I found a solution for this issue. The reason for it happening is because of compass absence, the autopilot is not able to calculate the heading direction. I throw thee plane in nose direction close to the ground on long grasses so the Arduplane can calculate the heading direction from GPG coordinations. I hope it helps you to solve the issue as well. Please let us know whether it works for you out as well.

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4

I have the same problem. It seems something related to EKF and disabled compass, I need to fly with compass disabled. The plane behaves normally but the “bad AHRS” alarm is anoying.

5

2 solutions:

  1. Wait a while. Bad AHRS will go away eventually.
  2. Set Arm check to 0 (zero)
6

I do not recommend disabling Arm check completely. Instead, I would suggest to update firmware to the latest version. Then, in flight filed while plugging in the battery, keep the plane still and wait a while. Hopefully, the Bad AHRS won’t show up. However, if it does, try the solution I have mentioned above.

7

@pekote there was an issue causing AHRS flags in plane setups without compass that has been fixed in july 2018: https://github.com/ArduPilot/ardupilot/commit/63d385ffb

conventional planes’ performance without compass has been well tested and proved since then, so if you’re still getting AHRS flags, it’s likely

  • you’re using a pre july firmware version or
  • you’re not effectively having the compasses disabled or
  • there’s something else causing these flags that needs to be adressed, like suboptimal acc calibration or sub par GPS fix (hdop > 1.5)

like @epm157 wrote, disabling arming checks bears the risk of masking issues that could lead to critical flight situations, so imho you’d prefereably want to figure what exactly is causing these flags and get it fixed. current plane FW is definitely providing full support for no-mag setups without that type of warnings.

cheers, basti.

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