Hey all,
noticing very strange behaviour when I have the following setup connected:
Pixhawk with a v-tail plane connected to channels 1 and 2, with the Mediatek GPS from 3DR connected. When the GPS has a good fix nothign weird happens, but the moment the GPS has no fix I notice the following behaviour:
-When flight mode is MANUAL nothing weird happens, servos respond as expected (no input, no output).
-When flight mode is FBWA something weird happens, the servors start jittering, and when I look in the logs (see attached files for images) I see that there is still no RC input for both channels, but a RC output is generated.
The images show the RC_INPUT and RC_OUTPUT for channels 1 and 2 respectively. From t=0 to approximately t=51 the plane is in MANUAL mode, then from t=51 to t=151 the plane is in FBWA mode, then after that again in MANUAL mode. (Please note, the time scale is not actual time but log entries, I didn't think putting actual time there was worth it but for what its worth the total time scale is approximately 23 seconds).
This was a simple ground test to reproduce the issue, it has also happened in flight once when we were in an area where the GPS signal was not as good, and as you can expect it definitely hinders flight stability.
Anyone else seen this and able to point me to what's leading to this behaviour?
Thanks!
Replies
Try 3.5.0 beta and see if that helps.
http://diydrones.com/profiles/blogs/apm-plane-3-5-1beta1-released
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Wow I have this issue too.
Hope this is the solution Hans, gonna temporarily turn that setting off to test.
At the moment I haven't flown with current setup. Bix3, Pixhawk, Arduplane 3.4, just trying to make sure I am happy with moments on the ground.
All seemed absolutely fine when changing the angles etc, watching the FC respond to my movements.
Then I raised the throttle, (I was trying to test if the models glide pitch was set correctly when on no throttle vs when it was powered, but when I raised throttle the servos started twitching / jittering like mad. Did not happen at all before I raised throttle significantly, and it gets worse the more throttle I give.
It was not caused by interference the graphs show Pixhawk doing it deliberately.
It so bad that I am sure it would damage the servos if I let it go on for any length of time.
I don't know how this can ever be acceptable, surely if Pixhawk has no GPS lock it should turn off that parameter automatically. I am now worried about losing lock in flight, my GPS df13 plug is a bit loose, I figured with flying FPV it wouldn't be a gamebreaker if I lost GPS, but now, looks like a crash wouild be result.
Did it work for you? For me changing AHRS_GPS_USE to 0 did not change anything, so I'm going to change it back. I did however figure out a parameter that does influence it, although I cannot explain why. More detailed discussion on it was held here http://ardupilot.com/forum/viewtopic.php?f=107&t=11229, although I don't think anyone ever got to a conclusion on how to fix this.
Hi , sorry for slow reply.
I put my Bix3 away for Christmas, and haven't had it back out yet, we had a very wet and windy January, I wouldn't mind flying in less than perfect conditions once I have it setup well, but at the moment I don't want it coming down in a bad place.
Anyway, no I haven't tested that parameter.
I was also intending to test other fly modes than just FBWA, I thought I did try others but I am going to try ones that presumably don't use GPS. Such as Stabilise as I think that just keeps it level?
I am also not 100% sure its the GPS issue thats causing my jitter has I haven't even had the plane in the clear with good GPS yet. although from what I've read it sounds exactly like it.
I read that forum post you mention above. he thinks its caused by THR_MIN parameter, I will have to check the setting of mine again, as I don't know what it is atm. However my jitter does change when altering Throttle sometimes getting extreme, so I think its the same issue. for me.
I forget exactly how THR_MIN is used, but some similar parameters do rely on GPS to estimate speed, for altering Throttle. So there would seem to be a possible connection.
I think there is clearly a bug somewhere tbh. I can't see how the jitter I'm getting should ever be acceptable, its not just small movements, the control surfaces are moving through 30-40 degs, even more once but I turned it off quick..
Yes GPS is important to me, but if I loose GPS lock, I could still fly home manually on FPV, I don't want this jitter causing me to lose control before that happens, so I'd like to figure this out.
Perhaps a more clear image. This shows the difference between GPS fix and no GPS fix. Hopefully someone can help me with this!
In the part in the graph from 0 to 20.000 the plane is indoors, lying on a table. It does the jitter, as I described before. It becomes worse when I give some input on my RC transmitter (from 12.000 to 18.000 in the graph).
The GPS (blue line) has NO FIX. The plane is in FLY BY WIRE A the entire time.
In the part in the graph around 22.000 I move the plane outdoors (so there’s some small movement there, which is expected since I’m not able to move it without pitching and rolling accidentally).
Now, from approximately 24.000 and on the GPS has a fix. The jitter is gone.
Even when I again try to give an input with my RC transmitter (this time between 29.000 and 34.000) there is NO jitter.
Easy. The GPS plays a part in attitude estimation. You can turn this off in the parameters (AHRS_GPS_USE) but it's not recommended.
What about Stabilize mode? does that use GPS also? if not shouldn't FBWA auto switch to that if it loses GPS lock.