PID curve behave strange ?

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PID curve behave strange ?

Eltonwu
This is my PID parameter.
<define name="THETA_PGAIN"  value="500"/>
<define name="THETA_DGAIN"  value="380"/>
<define name="THETA_IGAIN"  value="0"/>
<define name="THETA_DDGAIN"   value="0"/>
This is my PID curves:


It is strange, the vibration is not around the set point, it vibrate above the set point, but never exceed the set point,I try to decrease the dgain, and the curve exceed the set point, but vibration become violent.

Anyone can explain it for me?
Thank you very much
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Re: PID curve behave strange ?

Hwarm
Hi Eltonwu,
i can you send a paper from 2006 that noticed the same behaviour of
PD-feedback controllers for muticopters.
We had a similar problem  by fitting a small multicopter 200g 100mm
motor distance with paparazzi in 2012.
We had the situation that the system hovers, when vibrations occurs even
the throttle stick  where set to zero.

What is the source of vibrations in you system?
1. Not  fitting values of the controllers?
2. Unbalanced propellers or motors bells?
3. Sagged motor axes?
4. Weak motor mounting or structure of the multicopter?
5. To weak mounting of the electronic?

For small multicopter i test the situation by holding the multicopter in
my hand.
Therefore i mount  a  handle for safety  an to protect the electronic in
crash situations.
If i feel vibrations i do not start.

You can find the basic setting by the hand test.
If you give hits in roll or pitch direction  with you hand (by holding
the system with you hand)  you can monitor  the basic stabilization.
If the reaction is to hard  you have to decrease the d  or and p gain.
I found that with this method good values for the first  flight   are  
found in  about  five to ten minutes.
The PD control system is able to do the basic stabilization of the
multicopter.
Sometimes it is difficult to find out the source  of  vibrations.

Regards

Heinrich










Eltonwu schrieb:

>This is my PID parameter.
><define name="THETA_PGAIN"  value="500"/>
><define name="THETA_DGAIN"  value="380"/>
><define name="THETA_IGAIN"  value="0"/>
><define name="THETA_DDGAIN"   value="0"/>
>This is my PID curves:
><http://lists.paparazziuav.org/file/n16104/%E5%B1%8F%E5%B9%95%E5%BF%AB%E7%85%A7_2014-09-10_%E4%B8%8B%E5%8D%883.png>
>
>It is strange, the vibration is not around the set point, it vibrate above
>the set point, but never exceed the set point,I try to decrease the dgain,
>and the curve exceed the set point, but vibration become violent.
>
>Anyone can explain it for me?
>Thank you very much
>
>
>
>--
>View this message in context: http://lists.paparazziuav.org/PID-curve-behave-strange-tp16104.html
>Sent from the paparazzi-devel mailing list archive at Nabble.com.
>
>_______________________________________________
>Paparazzi-devel mailing list
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>
>  
>


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Re: PID curve behave strange ?

Eltonwu
Thank you, please send me a paper about the behavior.