Re: [Paparazzi-devel] Lisa/M2 field test

[Felix Ruess]

Hi Gerard,

I finally have a proper location where I can do some field testing. I'm using a recent (2 weeks) master branch with
venus skytraq GPS and eagletree airspeed sensor.

Could you please provide the exact paparazzi_version?

 

A maiden flight has already been executed with a couple of surprises on handling, but all went ok.
The entire flight was on manual and I had a chance to test and see how photo's were made.

Today I attempted to make a stabilized flight to see how the aircraft handles that and to test some new camera
settings to improve overall focus. I had to abort during final response verifications:

1. At one point in time, the control surfaces locked and there was no response whatsoever. Unfortunately I did not
   look at the PFD at this point. Switching to manual worked and control surfaces responded correctly and timely in that mode.
   I repowered up and then stabilized mode was reasonable again.

What mode were you in, etc..? Do you have the logs to check this?

2. Does the IMU initialize at the start?  I had the aircraft leaning on one wing and the PFD showed a 10 degree roll
   to that side. I repowered up with the aircraft level and this disappeared. Basically, must the aircraft be completely level
   at startup?

At startup the ahrs_aligner runs and takes the low-passed gyro values as initial bias. By default no accelerometer bias is done for exactly that reason.

So it only shouldn't move during initialization (although there is some basic check so that it will only run the aligner if the movement/noise is low enough).

3. I eventually aborted the takeoff when I noticed that yawing the plane around in a plane parallel to the ground, the
   discrepancy in roll moved to the pitch, then back to roll (other side) and back to pitch. This sort of behavior *can* be produced
   if the yawing plane is not parallel to the ground, but I paid very close attention to this process. I would expect the discrepancy
   in roll to move along during the yaw motion, but this did not happen.

What imu exactly are you using, which ahrs algorithm? Are you using the mag, is it calibrated?

Can you please post at least the firmware section of your config?

(Or do you have it on github? Or maybe put it on pastebin...)

4. I'm also getting the famous "Invalid argument "latlong_of_utm""  error when the GPS is 3D locked (actually, after 30 seconds or so). 
    The "utm_zone" should be 25, but it switches to 96 (which does not exist), even though I'm roughly at 8S, 35W.  
    I think there's a serious error with units in that subsystem. Velocities and ground speeds seem to work ok, as well as vertical speeds.
   Binary command set is here: http://www.sparkfun.com/datasheets/GPS/Modules/AN0003_v1.4.14_FlashOnly.pdf 
    (NAVIGATION DATA MESSAGE).
   I have "GPS_USE_LATLONG" defined and it does indeed come up in the make settings of the compiled binary.

Are you aware of the limitations of the skytraq binary protocol?

See https://github.com/paparazzi/paparazzi/issues/167

You can compute the missing information yourself, but this is not done so far.

Afaik the skytraq was only used for rotorcrafts quite a while ago, you might be the first one using it for fixedwings...

(I even wanted to buy one, but the documentation on those is so bad and the navilock GPS with skytraq chip doesn't have a binary mode at all...) 

Anyway, the utm_zone is initially set according to the coordinates in your flight plan. It is re-calculated when you call nav_reset_reference.

In the standard flight plans this is automatically called from the GeoInit after you have a gps fix.

Btw, you don't have to add the GPS_USE_LATLONG define yourself as it is already added in the makefile: conf/firmwares/subsystems/fixedwing/gps_skytraq.makefile

5. The venus skytraq lat/lon is scaled to 1e7. Is the UBX lat/lon scaled the same way?

Yes, lat/lon is stored in 1e-7rad in the gps struct. See http://paparazzi.github.com/docs/latest/structGpsState.html

 

6. The alt also seems a bit off. I did a manual flight of around 12-20 meters altitude, but the altitude never reported anything higher
    than a meter. I'm guessing it's off by a 100.  What is the scale for UBX altitude?

The scale is millimeters, see the generic GPS interface (see sw/airborne/subsystems/gps.h or the generated doc link above).

Cheers, Felix