Hi.
First I’d like to state that we’re new to APM (Arduplane) so I apologize in advance if the problem is something minor and simple or we’ve given incomplete information.
We’ve done a couple of flights with basic missions (20ish and 8ish waypoints) and came across some problems. We couldn’t manage to do a single proper auto mission which led us to frustration and then here J
Our setup is :
-APM 2.6 board (latest firmware)
-3DR GPS + compass (external)
-Speed sensor
-Volantex Ranger 757-3 plane
-Motor: T-Motor T60A 400 Hz ESC 2-6S 3A/5V Bec
-ESC: JP EnErg 600 O/R 1100 (C35-14) 3-4S LiPo
-Prop Size : 10X7
The things we’ve done pre-flight:
- Initial setup via Mission Planner wizard (we’ve done this in another area, not on flight site).
- We’ve waited for APM to initialize and GPS lock (8-9 satellites).
- We’ve configured our transmitter switch to switch between auto and manual modes.
- We took off manually and switched to auto mode mid-flight.
- All parameters are left default.
So we’ve came across 3 problems.
First was toilet bowling. When we switch to auto mode mid flight the plane goes straight or make a good turn for a couple of seconds, then it starts toilet bowling, constant turn to right and going down. After our research, we found out that this could be because of 2 things, not enough air speed makes APM go into stall or magnetic interference on compass. Since our compass was near of our components we’ve replaced it on the top of the plane away from components (front facing forward and leveled).
In one flight it dove when we switched to auto then on another flight same toilet bowling effect happened. So we thought it was not GPS related and we removed air speed indicator to let it calculate air speed by its own. After we’ve done that APM was constantly throttling up and down on air. Making some turns or going straight but completely ignoring the mission and waypoints but atleast was staying on air, not diving or toilet bowling.
Obviously we’re missing something and hoping that someone could help us about these issues.
Our tlogs are attached, sorry for so many manual auto switches J Also there’s a dataflash log of our last mission.
Thanks in advance.
Best regards.
Replies
Hi again, first I'd like to say thanks for your time and responses.
We've considered the things mentioned here and gave it a second try. However, in all modes(FBWA, stabilize, circle, autotune) the plane flew with the same behaviour, it could not be controlled on air in any mode other than manual.
But!
Then we decided to do everything again from scratch. We've loaded the firmware again, did initial setup all over again. While we were checking the autopilot's reactions to plane's position changes on the ground, we've discovered that rudder was moving along with wings, in example when we rolled the plane to the right, wings were positioning themselves to stabilize the plane, but rudder was also moving. Turns out there was a rudder mix.
Rudder Mix (ArduPlane:KFF_RDDRMIX)
The amount of rudder mix to apply during aileron movement 0 = 0 %, 1 = 100%
Range: 0 1
Increment: 0.01, it was set to 0.5.
The probable cause of our problem is that we had wings on reverse in mission planner but not the rudder and this was probably causing a contradictory movement between these two. We did not test if that was the case or not,
instead we removed the rudder mix and when we flew the problem was no longer persistent. As you stated, we did the auto tune first, then went into FBWA, stabilize, circle modes which worked perfectly.
We also did a 5 point auto mission which was also successful.
We had no idea there was a rudder mix parameter and it was 0.5 by default. We probably controlled autopilot's reactions without rudder connected when we were doing the tests or else we would've noticed it.
Thanks again.
Best Regards.
Couple of thoughts and observations: A compass error should give a "bad compass health" warning msg and auto analysis of your DF log shows no issues in mag variation so good there.
Your Z-axis has very high vibrations with the biggest jump from +9 to -21, so you'll have to spend some time balancing your prop and mounting your APM on vibration absorbing foam. Unfortunately an APM can't use EKF which can help a bit here.
Your battery voltage in that DF log drops to 12.76V at one point which is way below 14V lowest if your running a 4 cell pack, it also starts at 15V not ~16.8V (again assuming your running a 4 cell pack), something to keep an eye on.
How does the plane fly in FBW-A? Does it keep it's height and bank angle when you hold the stick full over to one side (roll only)?
The plane should fly REALLY well in manual so that the autopilot doesn't have to additionally correct a poorly flying plane.
FBW-A is exactly what the plane will use to fly a mission in Auto but just with you giving the commands rather than the nav system. So the plane must fly correctly, straight and positively in FBW-A before even trying Auto. Once the plane flies straight, flat and level in FBW-A (you may have to enable autotrim) then the next step is Autotune, then a Loiter and then only Auto.
Sorry if it sounds a bit harsh but there isn't a shortcut to get good results, although sometimes one can get lucky :)
Have you followed the guidance given in the wiki for your first flights, you need to tune your autopilot to make your plane fly properly, you can do this manually or using autotune as one of your flying modes, as I said it's all explained in the wiki for you.