Replies to This Discussion

3D RoboticsPermalink Reply by Chris Anderson on March 18, 2012 at 3:13pm

Are you using an airspeed sensor?

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Permalink Reply by Andke on March 18, 2012 at 3:23pm

yes.

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3D RoboticsPermalink Reply by Chris Anderson on March 18, 2012 at 3:31pm

Try disabling that and see if it makes a difference. That would give us useful info to debug. 

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3D RoboticsPermalink Reply by Chris Anderson on March 19, 2012 at 7:20am

Also, make sure you don't have Absolute Altitude selected. You should be using Relative. 

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Permalink Reply by Andke on March 19, 2012 at 7:38am

Thank you for the advice, I'll fly soon (with airspeed sensor disabled in setup) - and report the results.

BTW: regarding the situation of my first report: I did use relative altitude.  - and the altimeter was not displaying wildly wrong altitude before flight. (maybe + a few meters.)

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Permalink Reply by Andke on March 19, 2012 at 8:32am

YES.

You were right.  The plane flew the mission perfectly. 

Even at the sharpest turn, 320degree at 40degree bank angle - it stayed within the altitude of the whole trip between 110-118m   - VERY nice.

The are two major differences between yesterday's and todays flight:

today, very little wind, yesterday - strong wind.

yesterday I had APM connection using TCP (GSM) - today - I forgot my Android - and were not able to remote control my workstation, and connect.

Are you still confident that the bug is related to the airspeed ?

- should I get back ASAP and redo the flight with telemetry ?

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Permalink Reply by Andke on March 21, 2012 at 11:51am

Would you mind to take a look at http://code.google.com/p/ardupilot-mega/issues/detail?id=569

- lots of tlog data and other info that might help hunting this bug down. :)

Thank you.

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Permalink Reply by Andke on March 19, 2012 at 11:00am

Bug reported:  http://code.google.com/p/ardupilot-mega/issues/detail?id=569

Chris: thanks for help - I assume you had reasons to suspect airspeed related routines. Hope we see a fix soon.

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Permalink Reply by Veikko Vierola on March 19, 2012 at 1:52pm

What was the conclusion of this case? Did the negative pitch have something to do with the AS-sensor?

I had same kind of issues with RTL and I thought they were caused by the failed (not precise) initial GPS calibration of the altitude. The plane flew nicely when I made a warm reboot from the APM button after the power up initialization.

I also think the gyros should be calibrated so that the plane has about 1-3 degrees nose up attitude.

Please let me know if you have some other opinions.

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Permalink Reply by Andke on March 19, 2012 at 2:18pm

if you follow the bug link, you'll see that airspeed sensor was to blame. (or - rather the code apm that uses airspeed) however - I've never seen it interfere with RTH.

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Permalink Reply by Veikko Vierola on March 19, 2012 at 2:24pm

But why the APM wants to fly down when AS-sensor is operating. Is the airspeed minimum speed set too high so that the APM tries get more speed by setting nose down or what? 

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Permalink Reply by Andke on March 19, 2012 at 2:36pm

no, it reduces the throttle to 0%  , and then keeps nose down as speed increases up to cruise speed. This would not be a way to recover from/avoid stall.

-We don't even have a place to ever stall-speed.

-also - remember that it's fully capable to RTL with airspeed sensor enabled.

This bug affects only AUTO mode. if other paramters were wrong, RTL would fail too.

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