Alt Hold glitch - APM 2.0 - Firmware Heli 2.7.3
In my case Alt Hold worked always really nice, within 1 m in calm conditions, and still does.
But one incident scared me a bit. A few sec after switching to Alt Hold in about 5m, the heli dropped to the ground. My first thought was a glitch caused by emf from the ESC. After I calmed down, I went for two other trials and like clockwork the same glitch again. But after the dropdowns I resumed flight with Alt Hold and it worked fine as always.
After a bit of analyzing the logs I came to the conclusion the glitch is caused by a kind of ‘Alt error reset’ after the GPS status goes high.
If you are in Alt Hold without GPS log ( Alt Hold needs no GPS log ) then as soon you get GPS log, the GPS status goes high, and the Alt error drops the same amount as your altitude to hold. If you in 5m the Alt error drops to -5 if you in 2m it drops to -2.
1. scare
1.test
2.test
So everything works fine as long as you have GPS log before switching to Alt Hold.
I think there needs to be looked in to this issue, to reduce the further scares :-))
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Comment by Ravi on September 21, 2012 at 7:50am -
hi manfred, i have you put the power filters on the sonar. do u have the shielded cable or the unshielded cable for sonar.
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Comment by Manfred Dickgiesser on September 21, 2012 at 12:13pm -
Hi Ravi thanks
I have no sonar, just barometer this are no emf problems.
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Comment by Bertrand Duchiron on September 21, 2012 at 1:10pm -
Did the barometer is enclosed or cover with some fabric as Chris Anderson adviced?)
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Comment by Manfred Dickgiesser on September 21, 2012 at 1:19pm
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In my case Alt Hold worked always really nice, within 1 m in calm conditions, and still does.
The barometer is covered.
Everything works fine as long as you have GPS log before switching to Alt Hold.
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Developer Comment by Randy on September 21, 2012 at 5:34pm -
Manfred,
Thanks for this detailed analysis. So I've just looked at the code and what's happening here is that on the first gps lock the init_home is run. This generally sets the horizonal position but it also appears to set the home altitude to 0. I'll talk to a couple others on the dev team but I think we will change this so that the altitude is only set when you disarm the motors.
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Developer Comment by Randy on September 21, 2012 at 5:34pm -
For now, I think you should ensure you have a gps lock before take-off.
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Developer Comment by Randy on September 21, 2012 at 6:05pm -
Sorry, I've looked at the code again and it's not the home altitude that's the issue, it's actually that we reset the next_WP to home in the init_home function that is causing the problem.
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Comment by Manfred Dickgiesser on September 21, 2012 at 8:06pm
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Hi Randy
Thanks for that
That’s great you found the cause of it. Of course we can live with that for now, but maybe to solve it with the next update or so, to prevent further scares or even damage.
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Developer Comment by Randy on September 21, 2012 at 8:25pm -
@Manfred,
Yup, should be fixed before 2.7.4 goes out.
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Developer Comment by Randy on September 22, 2012 at 9:01am -
After a quick discussion with Jason, I've checked in a small patch which should resolve this.
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