Florin Mingireanu

Return to home- Ardupilot questions

Hi there,

 

I flew ardupilot for return to home in order to compare its performances with a "homemade" solution.

 

I had GPS lock before take off (I use Ublox GPS).

 

I tunned it so it does STABILIZATION very well.

However when I engage return to home, the plane just flies away, at most oscillating around pitch axis. It doesn't have ANY tendency to bank on right or left in order to return to home.

 

Questions:

 

1.) In order to tune it for return to home I see in manual that they recommend: 5) Now try RTL mode. The aircraft should come back to you. If it's flying away, increase 7-1 ("#define NAV_ROLL_P .6") by 25%. If it's still not responding enough, increase 7-2 ("#define NAV_ROLL_I .0"). If, on the other hand, the aircraft comes back to you but weaves and snakes, decrease 7-1. If that's not enough, increase 4-4 ("#define XTRACK_GAIN 00").

 

Is it neccessary to do the flight tunning for FLY BY WIRE A/B BEFORE I try to do the tunning for return to home?

I am not interested in FLY BY WIRE MODE so I would rather skip the flight tunning step for FLY BY WIRE if it is not neccessary for return to home.

 

2.) What is the effect of PITCH COMPENSATION parameter? What is its usual value for easystar airframe?

 

Thank you!

 

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Replies to This Discussion

Florin MingireanuPermalink Reply by Florin Mingireanu on August 26, 2010 at 12:12am
Just few more details: I am using Ardupilot firmware 2.7 ... shield V2...
Ryan BeallPermalink Reply by Ryan Beall on August 26, 2010 at 12:26am
2: Pitch compensation is a feed forward term used to help the altitude controller in turns. It feeds pitch propotional to bank angle so that as the lift vector is tilted due to bank angle, the extra angle of attack required to maintain altitude is closely approximated by this adhoc factor. With out it the altitude controller would have a much harder time compensating.

knowing now how it works you should be able to tweak the value to eyeball what would make sense for most cases. Big thing is just make sure the sign is correct or else it will do the opposite of help!

-Beall
Florin MingireanuPermalink Reply by Florin Mingireanu on August 26, 2010 at 3:57am
Thank you for your quick answer.
What about the first question?
"Is it neccessary to do the flight tunning for FLY BY WIRE A/B BEFORE I try to do the tunning for return to home?

I am not interested in FLY BY WIRE MODE so I would rather skip the flight tunning step for FLY BY WIRE if it is not neccessary for return to home."

Thank you!
Andrew BryginPermalink Reply by Andrew Brygin on August 26, 2010 at 5:46am
What kind of sensors do you use? Thermophiles or IMU?

IMHO, FBW mode is quite important in tuning process. It provides a way to estimate how correctly your setup reads pitch/roll angles. In my particular case, I found that roll angle was overestimated due to wrong position of Z sensor. I.e. AP was sure that current roll angle is 40 degrees whereas real roll angle was about 3 or 5 degrees. Such overestimation may obviously lead to inability to navigate in RTL mode.

So, my suggestion is to check whether pitch/roll angles are read correctly. And FBW mode is very convenient for this purpose.

Thanks,
Andrew
Florin MingireanuPermalink Reply by Florin Mingireanu on August 26, 2010 at 5:56am
Hi there,

I use XY thermopiles. I do not use Z sensor. Neither do I use airspeed sensor. I have it installed (since I have shield V2) but I chose not to use it for first tests. I also choose not to use throttle control through Ardupilot. My throttle is controlled manually from the radio receiver...

Since I already did STABILIZATION and it works, doesn't this mean that the pitch/roll angles are read correctly? Otherwise the AP wouldn't have been able to STABILIZE itself, would it?

Thanks!
Andrew BryginPermalink Reply by Andrew Brygin on August 26, 2010 at 6:27am
Stabilization mode is quite tolerant to overestimation of roll/pitch angles. It (the overestimation) just makes the stabilization more aggressive (i.e. plane stabilizes faster).
In FBW mode you can set desired roll angle via TX stick position, and can see whether AP is able to maintain this angle. It would be very helpful if you provide a flight log. There we can see what angles your sensors read.

Thanks,
Andrew
Florin MingireanuPermalink Reply by Florin Mingireanu on August 26, 2010 at 7:19am
Hi there,

Unfortunately I do not use a ground station for the Ardupilot. I can only provide screenshots with the plane on the ground and Ardupilot connected to my laptop through the FTDI cable.
We just try to compare ardupilot with our own homemade solution for AP following a map so we didn't buy the extensive ground station, telemetry equipment.

I can conclude, based on the above discussion, that one has to succesfully tune the aircraft not only for STABILIZATION but for FLY BY WIRE as well before one can move forward to RETURN TO HOME tunning. Is this a correct assumption?

Thanks!
Chris AndersonPermalink Reply by Chris Anderson on August 26, 2010 at 7:46am
Yes
Andrew BryginPermalink Reply by Andrew Brygin on August 26, 2010 at 7:49am
yes, this is correct. And Flight Tuning tips recommends such sequence of steps as well.

BTW, you can workaround a lack of telemetry equipment by a logging flight data into free part of EEPROM. To resolve this particular problem you need to know values of nav_roll and roll_sensor variables only.

Thanks,
Andrew
Florin MingireanuPermalink Reply by Florin Mingireanu on August 26, 2010 at 8:30am
Hi there,

One more thing:
for STABILIZATION I kept D and I terms with value 0 for both pitch and roll axis.
I only worked on P term in order to get the STABILIZATION. Right now with only the P terms the plane stabilizes very well and tracks excellent.

Would this amount of tuning be enough or I should be working on I term as well before moving to FLY BY WIRE tuning?

Since I have my plane with manual throttle I guess I should use FLY BY WIRE A, is this correct?

Thanks!
Andrew BryginPermalink Reply by Andrew Brygin on August 26, 2010 at 9:20am
If current set of PID gains works fine in stabilization mode, then you can move to FBW mode. You have no airspeed sensor, so you should use FBW_A.

Thanks,
Andrew
Florin MingireanuPermalink Reply by Florin Mingireanu on August 26, 2010 at 12:33pm
Which parameter controls how much control you have while the Ardupilot is in STABILIZATION mode?
This kind of parameter would basically be the mixing parameter between the STABILIZATION commands given by Ardupilot and the manual commands given from the ground by the operator...

Thanks!

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