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DeveloperPermalink Reply by jasonshort on November 1, 2011 at 3:03pm

The PIPI loop is like this:

Angle of copter * Stabilize P = desired rate

(actual gyro rate - desired rate)  * Rate P = output

output is converted to PWM and sent out to the motors.

We have a basic crash avoider that reduces the speed of the opposing motor. if the required PWM goes past 100%. I'm sure we could do more if your up for some investigation and testing.

Jason

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Permalink Reply by Augusto Sala on November 1, 2011 at 3:59pm

Interesting!! So, if the crash avoider is working good in dealing with channel saturation, the RATE_I parameter might be really effective in stopping the flip (more than RATE_P or STABILIZE_I) without affecting too much the behavior when no failure is present (as STABILIZE_I would do).

Complex story to analyze stability, though.

Thank you Jason

I hope to do some testing asap or a simple simulator or excel page to help understanding the behavior...

If anyone finds it helpful attached is the log of the crash.

 

Attachments:

• 20111029-crashLog.log, 3.2 MB

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Permalink Reply by Augusto Sala on November 5, 2011 at 7:37am

Ok, I did some tests and got some results.

I have 90 MB for 25 videos of tests on different PID settings so whoever wants them can have them (or is there anywere I can upload them)... The RATE_I parameter is the one that does the trick but pretty high values are needed and can lead to instability. Against my odds the STABILIZE_P doesn't play such an important rule and actually it does seems that the less STABILIZE_I the faster the copter recovers... which doesn't make sense. I also tried negative STABILIZE_I which gave me good results... what does this means? How are negative values treated?

Also the whole recovering thing looks more difficult when higher throttle is applied.

The ideal settings for my hexa are:

STABILIZE_P    3.2
STABILIZE_I    0.005
RATE_P        0.075
RATE_I        0.120

 

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Permalink Reply by Johannes Huss on November 5, 2011 at 10:36am

Thanks for sharing this, Augusto. My Hexa (with 4 cell Lipo) reacts very nervous at the moment, so I am thankful for every hint.

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Permalink Reply by Augusto Sala on November 5, 2011 at 11:59am

No problem. Just be careful 'cos I never tested such a high RATE_I in flight. I was flying with RATE_I = 0 and today I tied 2 of the 6 arms on a bench and did the tests on the RATE_I. As soon as rain stops I'll try flying.

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Permalink Reply by nicolas grunbaum on November 6, 2011 at 2:47am

I'm flying a hexa and I have very different PIPI values. StabP is more like 1.6 and a very high rateP. I also have some hig I values (like 0.3). This way a have a stable platform not too nervous and without oscilations. 

I will try to download from the APM( I restore my pc and lost all config stored). It's a mk hexa xl with Jdrones 30 esc and Jd 880 motors (12x4.5 props)

 

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