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3DR Pixhawk IMU2 Accelerometer provides noisy data, worse than IMU1

Posted by Charlie on March 27, 2016 at 12:30am

I posted this in the copter 3.3.x forum, perhaps it was the wrong place? Reposting in the hope of getting some insight, google has let me down and I can't seem to find anyone else with this issue (suggests a possible fault with my pixhawk?)

Anyone?

Cheers :)

I have recently been carrying out mapping flights in somewhat more turbulent and windy conditions and it has brought to light a possible issue with noise in the accelerometer data from IMU 2. Specifically poor position holding, with a lot of drift and occasional loss of 1 or 2m altitude.

The issue only came up once I reduced vibrations to the FC to a reasonable level using hobbyking orange foam to suspend the pixhawk between the top and bottom plates of the frame.

As you can see from the attached figures the signal to noise ratio on all axes of the IMU2 accelerometers is much worse than the information from IMU1. Y axis is the least bad, Z axis the worst.

As you can see the range of the data and the averages are almost the same, but the (random?) noise in the IMU2 ACC data seems to reduce the signal to noise ratio in that data to almost nothing, surely making it much less useful than the IMU1 data.

Vibe charts also attached - they seem well within limits.

I decided to disable IMU2 and have noticed a significant improvement in the performance in pos. hold. and auto mode

Can anyone offer any insight into the issue?

Thanks very much.

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Replies

  • Andre K. March 27, 2016 at 11:15am

    test on ground whithout motors first.

    the data is coming from two different IMU's , made by two different manufacturers , with different hardware filtering, it's possible that your setup simply affects one more than the other due to aliasing etc..

    • Charlie > Andre K. March 27, 2016 at 12:12pm

      Thanks very much, it had occurred to me that the IMUs might be differently affected by the setup, I had just thought I might find someone else who had experienced this issue - the difference between flight with both IMU enabled and the just one was the difference between steady flight in winds of 15-25 kt and somewhat alarming performance leading to aborted auto flights.

      Any info on the differences in performance between the IMUs would be received with interest!

      I'm afraid I'm not sure how best to investigate the problem on the ground - would prefer to avoid major disassembly if possible, especially as the machine is actually flying very well at the moment...

      thanks very much,

      BR

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