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Permalink Reply by agmatthews on October 30, 2011 at 2:15pm

Heino,
I had the same thoughts (that it was ok to have uncalibrated sonar) until I checked the alt hold code. It uses the absolute value of sonar range and blends it with barometer data. If the sonar data is off then the blend point can be quite low - loosing the benefit of the sonar, or to high - above the limits of the aonar and possibly triggering a fly away scenario.
This is all independant of the problems with noise in the sonar data which is a separate issue.

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Permalink Reply by Heino R. Pull on October 30, 2011 at 3:37pm

Andrew,

 

I read your other thread more closely and I have a better idea of what your seeing. I think though that the MB1200 is the recommended sensor for most users and I can see needing scaling of some sort particularly for other sensors that are scaled differently. I flew an MB1260 scaled and unscaled on my quad with Jason's earlier code and it seemed to work pretty well.  I had  "fly aways" early on and it was due to noise spikes jumping from 500cms (actual) to 90 (bad) cms for many samples when the reality was nothing close to that. Motor noise was definitely causing my fly aways. I think your I2C approach is the ultimate solution  to the noise issues and that calibration will be needed for some cases (such as I.S. optical flow comment or using different sensors), but not by most general users if they're in standard configuration. It's just confusing trying to get the sonars to work and scaling by an arbitrary scaling factor is expensive computationally (fixed point multiply) unless your scaling in powers of 2.

Seeing a log of sonar alt, baro alt on  "fly aways" that don't have noisy sonar data would be very interesting.

 

 

 

 

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Permalink Reply by Ruben Wijnhoven on October 30, 2011 at 11:48pm

An other problem is wat I suspect to be the built in error correction in the mb1200. Pls fly for about 15mins with alt-hold on on your quad lets say 20m away and back. and so on and so on. Then after about 15min the sonar will be completely off and will only output the default 32cm and nothing else. My suspision is that after to many error the sonar just shuts down. After waiting for about one hour. The sonar will work again. I think this has to do with the complete discharge of the entre quad.

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