Re: [Paparazzi-devel] Simulation inconsistency

[Pascal Brisset]

Hi,

Haiyang Chao wrote:
> Hello, everyone.
>
> I got a pretty strange inconsistent problem for the simulation part. I 
> changed "PITCH_NEUTRAL_DEFAULT" to the same value through two methods: 
> 1 simulation gcs and 2 the MyAirframe.xml. The strange thing is that I 
> got different results at least for altitude tracking.
The simulator takes into account the PITCH_NEUTRAL_DEFAULT value from 
the airframe file (flightModel.ml:142 and sim.ml:176 in sw/simulator) to 
simulate the IR sensor. So it won't make a difference in a simulation if 
you change this value in the airframe file: it will be added by the 
sensor simulation and then subtracted by the autopilot code 
(infrared.c:214). However, you will get something different if you 
change it during the simulation (with the GCS) ...
To tune this value, you have to fly level in AUTO1, at the desired 
throttle and speed and adjust the value until you don't need to touch 
the pitch stick. The simulator won't help you for this ...
In the same time, you can set the NOMINAL_CRUISE_THROTTLE value
To tune the vertical loop, you will have to set THROTTLE_PGAIN, 
AUTO_THROTTLE_IGAIN and PITCH_OF_VZ_PGAIN to be able to climb or descent 
at a constant rate. To keep an altitude, you then have to tune the 
ALTITUDE_PGAIN value.
We usually are able to get around a -5m+5m precision to fly level.

Good luck

--Pascal

> We have a tiny 13 board working for real-flight waypoint tracking 
> recently but the altitude is not well tracked (10 or 20 meters below 
> the desired one in 1 minute auto2 flight time). So I used the same 
> configuration file for simulation  and tried to locate the problem. 
> But I got increasing altitude in simulation all the time. I guess the 
> problem is from the "PITCH_NEUTRAL_DEFAULT" in IR section, which was 
> set as '5.72 degree' in real flight. Then I decreased this value to 
> 0.005 (in radiance) through simulation gcs. The simulation runs ok, 
> the UAV stopped climbing at +30 m and maintained there. However, I got 
> different results while changing PITCH_NEUTRAL_DEFAULT directly in 
> MyAirframe.xml and recompile the code. The altitude climbing showed up 
> again.
>
> Do u guys have any clue why this happened, or any good document for 
> parameter tuning?
> I already started to dig in the simulation code, but just takes some 
> time to understand.
>
> Thanks
> Haiyang
>
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