Scary bounce while executing mission

Info and discussion about the original AQ v6 flight controller

Scary bounce while executing mission

Postby nikivan » Wed Jul 10, 2013 5:20 pm

I had a scary experience yesterday when AQ started bouncing up and down while executing a mission. I could hear throttle going to max and see the frame tilting, I've switched to manual control and landed safely. This mission was executed previously several times without a problem. This time however the quad was 500g heavier to simulate camera payload. Here is the log file https://www.dropbox.com/s/u930a82mjm49zb3/006-AQL.zip Any suggestions how to troubleshoot this?
nikivan
 
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Re: Scary bounce while executing mission

Postby LPR » Thu Jul 11, 2013 1:23 am

Niki

I've had my octo do the bouncing while in Alt/Pos Hold if I raise Navigation Altitude Position P from default of .2 to .25.
I like the way the octo will quickly go to the home point even if the home point is a lot higher altitude when I use the P at .25. If I do a quick altitude change while flying in Alt/pos Hold in can get the octo to bounce up and down around two meters but a flip to manual and then back to A/P hold and it stops. I'll play with the PIDs and see if I can have both aggressive altitude hold and no bounce.

Larry
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Re: Scary bounce while executing mission

Postby Max » Thu Jul 11, 2013 1:55 am

Hi Nick, I checked your log. The ACC plots are very noisy (especially X) and towards the end they get really out of hand. Your motor pitch/roll values are too high, and in the end they saturate. MOT_PITCH is noisier and saturates first, which I'm guessing sets off the oscillations, which then exponentially increases the problem. It's also the noisiest MOT_YAW I've seen, and your yaw balance is a bit off. MOT_THROTTLE is very spiky as well.

All this could be caused by a number of factors. I'm guessing before you added the weight, your power system could still keep up with the noisy rates/accels, at least adequately enough (though I can't imagine it flew very smoothly). With the stress of the extra weight, it went past the point of being controllable. Looks to me like excessive vibrations, but that could be oversimplifying the issue.

Cheers,
-Max
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Re: Scary bounce while executing mission

Postby nikivan » Thu Jul 11, 2013 3:34 am

Thank you very much, guys. Regarding the noise, the motors are dynamically balanced and the props are statically balanced. I am thinkning I should try inserting some foam inside the arms.

I did several more flights today and I was able to reproduce the bounce, this time in position hold. Here is the log file: https://www.dropbox.com/s/6qq58l3qvznuv47/014-AQL.zip

I've made the following observations.
- Reducing Navigation Altitude Speed IM and OM to 500 reduces the overshoot and in some cases the AQ is able to recover on its own (no manual control intervention). I've also reduced Navigation Altitude Position PM and OM to 1.8, but I can't tell that has any effect. My idea was to "tone down" the loops a bit. If Navigation Speed Altitude I is less than 1.5, then AQ does not hold altitude very well. Vales above 1.7 make the quad go up and down with high frequency, so I ended up with value of 1.5.
- The chance for AQ to bounce increases with the wind speed. I've observed the quad sinking slowly during a gust, and at some point it throttles up, but overshoots, and the cycle repeats with increasing amplitude.
- When running on 3S, I could not reproduce the behaviour. But I use 4S batteries and with them the quad is more "nervous" in general.

Your thoughts?
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