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Re: AQ6 stable flight without gps

PostPosted: Thu Jun 18, 2015 11:06 pm
by LPR

I like your idea to simplify your quad. When you get APH to work well then slowly add equipment.

I always set my RC to -700 for manual and 0 for APH and 700 for mission just to be sure you don't end up in the wrong flight mode. I've had that happen once and that was more than enough so that now I'm careful with flight mode settings.


Re: AQ6 stable flight without gps

PostPosted: Fri Jun 19, 2015 12:15 am
by JussiH
Im afraid to say, gentlemen.

The nature of the UKF (the main position attitude and velocity estimation filter) means that when a GPS fix is aquired in flight, it will immediately begin to correct the heading and velocity estimates based on the GPS info that just became available.

If the UKF decides that the heading or velocitity estimates is off, it will correct it. This can manifest in manual flight as a slight twitching in the attitude control. Under normal conditions, this goes away as the filter converges, but it can be a bit unnerving. However, I have never had anything like what you describe happen in manual mode.

In very rare cases, if a GPS fix is aquired during while in PH mode, the position can get screwed and the craft goes for a new position with the full limit of what the nav controller allows. Its usually associated with limited or poor GPS reception close to the 3m threshold of the 3D lock state...which is something that can happen if your antenna or groundplane is not up to par.

However, if GPS lock is lost, you should not get any adverse behavior when its regained...but if you cant keep a lock in flight with a reasonable view of the sky, it points to a problem with the antenna that should be solved.

But looking at your logs, I definately see something odd going on in the 3rd flight. The PosN and VelN estimates makes a huge jump in the latter of that flight, and I bet that has something to do with the subsequent "flip". which may just have been the nav controller trying to go to a new position 20 meters away:


The fact that you went from inside to outside without a reboot and that you carried it around before taking off could also have set up the filter with a hard dataset to converge. Combined with a poor GPS reception this could have tipped the scale as the GPS accuracy decreased towards the end of the last flight...but its a guess.

A few recommandations:

Check the antenna and increase the size of the ground plane. The one you have on there is very small...probably that factors into the poor reception that your logs seem to indicate.

If you intend to use Position hold, you should always make sure you have a decent lock on the ground before taking off - give it some time after the blue LED comes on to improve the accuracy and check it in telemetry.

You should be able to get down to around 1m HACC on the ground - even with some trees around. But many trees obscuring the view of the sky will impede GPS signal reception, specially this time of year when there is leaves on the trees.

After GPS lock is aquired and settled, then takeoff and fly some straight lines back and forth and right/left about 10 meters i manual mode to allow the UKF to converge the heading and velocity estimates before trying a position hold.

You should make sure that your heading reported by QGC is as close to true as possible when the craft is on the ground. The compass is only used to estimate the initial heading of the craft before takeoff, so if its massively off, the UKF will correct the heading when GPS signals become available.

If the heading is off, redo the compass calibration routine and make sure the generated parameters are stored in the Flash or Eerprom and that they give a good heading estimate on bootup. Check that inclination and declination settings are correct for your location before doing the compass calibration.

Id like to see a copy of your params, pls.

On the upside, I think that your vibration levels and the overall balance of the craft is looking good. I think it should be something that could be made to fly good in any mode once we get to the bottom of this...

Re: AQ6 stable flight without gps

PostPosted: Sat Jun 20, 2015 5:56 pm
by johannes3154
Hello JussiH,
ok now i have a clue of whats going on.:D
I stripped it down to the absolute neccesary components and built one of those fancy gps shieldings.
Removing telemetry and 3dr radio didnt change anything, so i reattached everything as it was before.
The GPS-Shield resulted in a major improvement of signal quality.
But the problem still exists.
However i did some testing. First test was, placing the quad on the garden table which is about 80cm high.
There i had good gps reception. Second test was on the ground, about 4 m away. I held the copter above my head and throttled up. No bad behaviour absolute precision. I was able let it sit on my flat hand and it didnt move a bit.
I was able to switch to position hold. It behaved very well. when there was no movement of caused by my hand it switched of the motors, what means that there was no need to correct position. then i moved it a bit and it throttled up correctly to counter the movement.
Third test: I placed it on the ground and throttled up. After the lift off i tried to hover in a height of 30 cm. But after about 5 seconds it started to shake. So i cancled the lift off.
I fear my problem now is that i dont trust in the copters behavior and i m starting to slow?!
My problem here is that in my opinion the manual mode shouldnt be influence in any case by gps data and should be reduced to the absolute minimum.
What if there is really a problem with the antenna during the flight, then i probably cant save the copter by switching to manual?
Here is a link to logs and photos of the shielding and the params file.
Perhaps you can check if i have entered the params for the magnetic declination correctly. ... _pIJa?dl=0

After that i checked the heading of the mag. First with my phone, there it is about 15° off, then with the compass of my watch, there it is 5° off. I think i have to get a real mechanic compass to check.

Re: AQ6 stable flight without gps

PostPosted: Sat Jun 20, 2015 11:52 pm
by LPR

Six months ago I built a quad that is similar to yours. I use Ultra ESC and I had the set to freewheeling.

If I remember correctly I found the having Freewheeling turn off gave me a smoother flight.

I also found that I had to lower the CTRL_TLT_RTE_D 1.200000E+04 down to around 4000.


Re: AQ6 stable flight without gps

PostPosted: Sun Jun 21, 2015 3:57 pm
by johannes3154
good news everyone:-)
I did some testing with the new antenna and the new gps shield and now i can say its flyable even with a 3d fix. After taking of i have some nervous motor speed changes but they disappear after a few seconds. I just had to overcome this.
I did some testing in Position hold but only while the aircraft was sitting on my hand and it reacted normal to position changes.
My testing today was in bad wind conditions so i consider the performance as good:-)
@Larry Thanks i will test lowering the tilt rate D
Guys im very happy its flyable now, now i can go on testing and finally attaching the gopro when pos hold is a success:-))))

Re: AQ6 stable flight without gps

PostPosted: Sun Jun 21, 2015 8:23 pm
by chschmid
Hi Johannes

I am glad you have it right now.


Re: AQ6 stable flight without gps

PostPosted: Sun Jun 21, 2015 9:27 pm
by kinderkram
Good on ya. :D

Now for the real life testing: always keep your finger on the switch. Try PH first high enough so you can catch it in manual mode if something goes wrong.
Keep an eye on the GPS hACC and vACC values.

Once confident, set a new home position at least 5m up and several meters away from you, then fly it away from the home position in a straight line, let it hover and switch to RTH. If it comes back and hovers reliably you can start some more games like flying it further away or only change altitude on RTH, fly in DVH mode to get a feeling...

Re: AQ6 stable flight without gps

PostPosted: Mon Jun 22, 2015 4:21 am
by LPR

Great to hear you now able to use APH.

Angle (afernan) has been working with PID control more than me and he has some interesting PID settings that I would try if I was using PID firmware now.


Re: AQ6 stable flight without gps

PostPosted: Mon Jul 13, 2015 9:05 pm
by johannes3154
Hey guys,
today i had a major drawback.
During the last week i added a landing gear and did some great flights during sunny days:-).
So i decided to do a test flight today after the rain. It was still cloudy. I got a HACC Gps reception of approx 0.68 and decided to take off. After the takeoff it lost gps 3d fix for a second and regained it. As soon as it lost the 3d fix i completly lost control, it started to tumble and to drift towards the trees. With some effort i was able to land it, but the touchdown made it fall to the side, while the props were still spinning. This cost me a kiss esc. After the next arming it started to burn with a bright flame:-((.
I forgot about putting a sd card into the autoquad, so this is just a post with a psychological effect for me :D .
I add some pics of the fallen beauty, to sad, i cant attach sad music to the post. :lol:
I recently bought 4 used esc32, can i use the logical part of them directly on 4s, or am i forced to add a bec?^^
Now i grab a beer.

Re: AQ6 stable flight without gps

PostPosted: Mon Jul 13, 2015 9:10 pm
by johannes3154