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Re: [Paparazzi-devel] A couple more questions

From: Christophe De Wagter
Subject: Re: [Paparazzi-devel] A couple more questions
Date: Thu, 21 Jul 2011 10:28:15 +0200

Dear Chris,

This behaviour often happens when your plane is not trimmed properly. If your ailerons need a few % deflection to fly staight this can be achieved by setting the ins_roll_neutral to - X degrees. The roll error * roll gain will then create the required roll trim to fly straight. For small angles it's probably not catastrophic althought the nicer way would be to change the servo-center position.

Check the following: 

-Make sure your transmitter is trimmed to zero: check the RC-message to see that the commands are [-9600,0,0] (otherwise in auto1 you also give a turn command when not touching the sticks)
-Trim your plane as well as possible in manual, remember the actuator deflections and then trim the servo deflection millisecond settings in the airframe.xml with your transmitter trims back to zero.
-Your IMU should read zero degrees in the lab with the plane level. Do also check when suddenly turning the plane's heading 180 degrees if the attitude is not initially a few degrees off and then converging to zero... it can happen that the accelerometer origin does not match the gyro alignment. (e.g. the X-accelerometer bias should be the value that the x accelerometer measures when turning perfectly and only arround the z-gyro with the z-gyro aligned with gravity. This is not necessaly exactly the same as the value when the imu is flat on a table.


On Thu, Jul 14, 2011 at 11:56 PM, Chris <address@hidden> wrote:
I use the PpzUavimu and so far i am very happy with it, it is really working great,
but  it seems that the PFD indicator is behaving in a peculiar way.
After a couple of trimming flights i was forced to use -4 degrees for the INS roll neutral default
in order to make the plane fly level in AUTO1,
<section name="INS" prefix="INS_">
<define name="ROLL_NEUTRAL_DEFAULT" value="RadOfDeg(-4.0)" unit="radians"/>
<define name="PITCH_NEUTRAL_DEFAULT" value="RadOfDeg(0)" unit="radians"/>
and now the PFD shows that the plane is rolled to the right by the same amount (4 degrees)
although it flies straight in AUTO1 and AUTO2.
It also shows this when it stands on the ground level.
Shouldn't the PFD show that i am level since the plane actually is flying straight in the air?
I also want to ask why i need to input those 4 degrees since the Ppzuavimu is level on the plane
and the plane is trimmed mechanically for completely level flight in MANUAL mode.
Is there any settings that i can change in order to remove this -4 degrees?
(like tilting the actual imu or something else)
Another problem i have is when there is  strong wind blowing and the plane is making circles
it looses much altitude when the it changes from headwind to tailwind.
Is there any parameters i can tweak for the better?

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