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Brown Out after adding Airspeed sensor

Posted by Jamie Glover on May 19, 2013 at 1:07pm

Well, she hit hard today on the first flight of the day from 120 ft. The plane is a skywalker 1900 and it completely went unresponsive while in FBW-A. Im using 2.72 firmware. Can anyone help asses the logs to maybe pin point the problem? I noticed a drop in voltage twice on the log, but I cant seem to tie it in with a command. I have attached the tlog. Any help would be extremely appreciated.

Thanks,

Jamie

2013-05-19 11-36-57.tlog

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  • Developer
    Andrew Tridgell May 20, 2013 at 5:14am

    Hi Jamie,

    I don't think a brown out was your major cause of problems. As far as I can see the major issues were:

    • it looks like you have a MTK GPS, and it was having trouble retaining lock
    • your settings had raised AHRS_RP_P to 0.5, which increased the gain of the GPS in attitude correction
    • the GPS kept claiming it had lock when I think it had lost it, as evidenced by the very high AHRS.error_rp values and the small satellites_visible count

    This sort of problem with MTK GPS modules is one of the reasons I released 2.73, with a check on the satellite count to stop using GPS velocity for attitude correction.

    So what I think happened is this. The MTK GPS lost lock, but kept claiming lock. The AHRS DCM code kept using the (incorrect) GPS velocity numbers to correct the accelerometers. That led the DCM attitude solution to be way off. The APM thought it was level, when it fact it was rolled at 25 degrees. You had a quite low roll limit in FBWA, giving not much authority to correct the incorrect attitude.

    Additional factors that made things work:

    • you had an airspeed sensor enabled, but not working (it always read close to zero airspeed)
    • you had a ALT_MIX of 0.6, so altitude came 40% from GPS, and GPS was misbehaving
    • compass learning was off, and you had lots of magnetic interference, and poor offsets (about 2/3 of the magnetic field was from your motor/esc/battery, not the earth)

    Cheers, Tridge

    PS: As I mentioned in a private msg to you, we can go over the log in more detail together if you would like

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