[Paparazzi-devel] Vibration issues (?) on a quadrotor

[Loic Drumettaz]

Hello,

I have tried without success to fly my quadrotor in RC_CLIMB mode. Firstly, I had some problems with the altitude measured from the baro: i found out that the BMP085 mounted on the LISA M is sensitive to sunlight! I protected the sensor with foam and the altitude measurement is now OK. 

After this, i still didn't manage to use correctly RC_CLIMB mode: I found that the vertical speed (ins_zd) and accelerations (ins_zdd) are wrong.Vertical speed "zd" is varying from 3 to 5 m/s with the quad hovering.... And the acceleration "zdd" oscillates from -10 to 30 m/s² !!

Now, i guess that these vertical speed and acceleration errors comes from the accelerometers used in the ins kalman filter. In that case, i have several questions:

- What level of vibration/ noise of accelerometers is acceptable on a quad hovering? I have around +/- 7m/s²

- I have mounted the Lisa M on gel pads (http://www.rtom.com/moongel.htm), balanced the propellers, what else can be done to minimize vibrations on a quadrotor? Are there other things to pay attention?

- In case the vibrations can't be reduced, is it possible to tune the Kalman filter in the INS ? I have seen that the filtering is done in vff_float.c. In this file, the parameter ACCEL_NOISE is equal to 0.5: are there any chance to improve the filtering results by tuning this parameter?

- The vertical filter VFF can be turned off by removing the flag USE_VFF? What would be the consequences of such tuning? in other words, how ins_zd and ins_zdd are then calculated?

- I also updated aspirin.c file, in order to use +/-16 G range on the accelerometers. 

- Any suggestions to fix this problem?

Thanks for helping. I have started to describe the block diagrams of the rotorcraft vertical control loops, in order to add them to the paparazzi wiki. So I hope to contribute myself to the paparazzi project soon!

Regards

Loïc