Gyro vs. Temperature on a Pixhawk

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1

Hey there,

I now have had the pixhawk for a few weeks and really like it with all its capabilities. But since a few days I am noticing some strange behavior of the AHRS. I can’t say if it has been there all the time or if I am just noticing it now. When leaving the copter completely stationary the pitch and roll values drift around in a range between -5 and 5 deg. I would guess at 0.2 deg. per sec. After finding no real solution or explanation by googling I looked at the graphs of the raw imu data and noticed a drift in the bias of the gyro. The other sensors weren’t showing any unexpected behavior. I then looked at the temperature as measured by the barometer and it seems to me like i can make out a correlation here. I have plotted attitude of roll and pitch vs gyro x and y vs temperature of a completely cooled down pixhawk for about 25 min. At about 21 minutes I power cycled the device to force a gyro calibration. I have left the pixhawk sitting for some 30 additional minutes now and it is perfectly stable.

My question is now is this normal behavior? 25 minutes for it to get to an operational temperature?
And this does not even consider real world influences on temperature like the sun heating up the enclosure or cooling through wind.
Is it possible I just ended up with an imu sensor on the worst end of the spectrum in terms of sensibility to temperature?
Or maybe I am just doing something stupid causing all this.

I also plotted what is called scaled_imu2. It seems more stable. Is this the second imu of the pixhawk or a corrected version of the raw imu data?

Thanks in advance for helping me out and in general for this great autopilot.

Best
Gabriel

2

Could you please post the log you got those from?

It is normal for gyro bias to vary with temperature, but if it is so bad that you can’t fly without warming up first, you probably should ask 3DR for a different board.

You could also get the latest 3.2 release candidate and try the EKF. It is probably much better at handling this kind of thing.

3

I only have telemetry logs and haven’t found a way to open these yet. Maybe someone still might be able to do something with them, so I have uploaded them here anyway (file is over 8 MiB, so it’s to big for the forum).

I’ll have a go with the EKF and report back.

4

@blaugold,
Use Google Drive to store the logs and then provide a link in your post to the Drive location.
Regards,
TCIII GM

5

Ok, here is the link to the log file in google drive:
https://drive.google.com/file/d/0B8lozzsFZ7fMVjJHUWIwNmN2ZnM/edit?usp=sharing

6

I’ve taken a look and I recommend just contacting 3DR for a new PIXHAWK.

7

Thanks! I will do that.