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Re: [Paparazzi-devel] Rotorcraft stabilization

From: Felix Ruess
Subject: Re: [Paparazzi-devel] Rotorcraft stabilization
Date: Fri, 30 Mar 2012 14:43:13 +0200

Hi Eduardo,

first a general note: when posting something like this, please write what branch/revision and configuration you are using!
This is important information and as there are different stabilization algorithms, options, ... (also good feedback for us to know what is being used)
It's always hard to give proper answers without knowing the tested configuration that makes problems....

Felix, what hardware are you and other friends using on rotor craft.
Anyone using lisa/m with aspirin ?

Yes, I have a quad with Lisa/M + aspirin1.5
Yesterday i do 8 flight with my new quadrocopter.
result: 9 props broken.

I fly with all propeller very well balanced and the quad never stay horizontal.
Some times bank to left ... some times pitch up ... some times turn yaw.
BTW, the yaw have much jitter.
MAgnetometer need extra configuration to lock YAW ?

Sorry to hear that...
While my quad is not flying perfectly, it is working surprisingly well considering my motors/props are not balanced (even have slight damage) and that I haven't dampened the Lisa/IMU so far... but I clearly have a lot of vibration that is heavily affecting the accelerometer when the motors are running. But as this highly depends on your frame and whether or not you get some aliasing issues, I might just be lucky that it still works pretty well even with vibration induced "noise" on the accel in the order of one g and more.
So when I have some time, I'll definitely mount the Lisa differently and balance the props.

Regarding the mag, have you calibrated it? Did you check that your yaw estimate doesn't change if you are roll/pitch the quad?
What stabilization are you using? If you are using int_cmpl_quat on master, did you set AHRS_MAG_UPDATE_YAW_ONLY as per wiki ahrs int_cmpl_quat
Otherwise a bad mag calibration will affect roll and pitch as well...

for a test i put LOW-PASS filter in ACCelerometer.
The attitude work much better but continue with same issue (bank, pith randomly).

Before putting a low-pass filter (which should be added to the imu interface in a general way anyway...) on the accel values I would suggest to set a different output rate  of the ADXL345 in the aspirin driver and hence reduce the bandwidth. With the adxl345 the bandwidth is always half of the data rate. It is currently set to 800Hz data rate with 400Hz bandwidth.
See subsystems/imu/imu_aspirin.c line 96
In dev I just added a small change so that you can set a different rate/bandwidth from the airframe file, e.g to set it to 200Hz with 100Hz bandwidth:
<define name="ASPIRIN_ACCEL_RATE" value="ADXL345_RATE_200"/>
For possible values see adxl345.h
For complere de test, i put me mikrokopter controller in the same frame and the quad fly perfect. Completly horizontal and without any disturb.

Another test i do tomorrow is put my other IMU on lisa/m.
I am trying to connect IMU on i2c1 but i am havving some strange issue.

What issue?

Its possible ?

Sure. I don't see why not...

for now its my problem.
i never do a good flight with PPZ rotorcraft.
i fly rotorcrafts and helis for 4 year.

But then we need your help in making it better :-)

Cheers, Felix

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