Losing Altitude


I was doing a flight today and I found that my plane is losing altitude from 200m to 180m while doing a loiter. I changed location of the loiter but it was the same issue.

I did calibration for the airspeed sensor but nothing happened. The airspeed is the 3DR digital airspeed.

I found that the Compass was giving error but I don’t know if the compass would affect the altitude, will it affect?
The compas/GPSs is 10cm away from the Pixhawk and the 400Mhz dragon link.

I am using the genuine 3DR Pixhawk with the arduplane 3.7.0

So, what should I do to know the error?

You could start by looking at the BIN logs to confirm the altitude loss, and also replay the .tlogs to try to figure out what happened.

Maybe your loiter radius is too small for your aircraft. In turns you plane makes less lift, so you need more power to fly faster to not lose altitude.
Your maximum bank angle may need to be reduced. My default value was 4500 (centidegrees). Have you changed yours?

I have the logs and we didn’t see any the reason why yet.

We are doing a 250 meters radius then we changed to 300m radius but the issue was always there.

We are using the minimum bank angle, of course less than 4500.

@Captain without sharing the bin logs for others to look at, its extremely difficult to provide any answer as to why this happened.

here it is: https://www.dropbox.com/s/9u6no7oxhdzme7x/October%201%20-%20losing%20Altitude.7z?dl=0

hi,captain,have you fix the altitude problem? I think I have the same problem like you.

And I tried to change some para, like “TECS_SPDWEIGHT /TECS_PTCH_DAMP”,but take no effect .

@farstein I recommend that you upgrade to the latest version of firmware to see if that solves your problem. It might not, but this problem was posted a year ago, and many improvements have been made since then.

For anyone interested, I took a look at the log: The flight duration was 2 hours, and steadily over the course of those 2 hours, the plane’s POS.Alt shows a decrease of about 10m. However, the POS.RelAlt does NOT show this decrease, it shows a constant trend for the whole 2 hours.

I don’t know how the computation of POS.RelAlt differs from POS.Alt to assist in determining the cause. Can someone else shed light on this?

my firmware version is 3.7.1. Thanks for your reply, I’ll try a newer version.