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Re: [Paparazzi-devel] PID curve behave strange ?

From: Prof. Dr.-Ing. Heinrich Warmers
Subject: Re: [Paparazzi-devel] PID curve behave strange ?
Date: Thu, 11 Sep 2014 08:56:10 +0200
User-agent: Mozilla/5.0 (Windows; U; Windows NT 5.0; de-DE; rv:1.4) Gecko/20030619 Netscape/7.1 (ax)

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.



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:
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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