F550 Erratic behaviour (spinning) in RTL

hi, hope someone can help.
Just setup a F550 hexacopter running arducopter 3.5.2 on a pixhawk 2.1 with Here GNSS GPS.

I tried a first flight with a Hobbyking multistar 3s 5200 mA battery using propdrive 2826 1000kv motors. I can see from the telemetry log playback that the initial RTL was caused by low battery. The Copter clearly draws too much current for C rating of the battery and it pulled the voltage down to below the RTL threshold. Obviously I need a higher C rated battery which I will purchase in due course.
When it entered RTL it went into an almost out of control spin. It did try to return to launch but was spinning a lot and therefore was almost out of control. It did eventually come down whilst still spinning and then I had to throw my coat over it as the props were still spinning. Arducopter then recognised this as a crash and eventually disarmed.
Maybe the spinning was caused by a compass problem. Ive included a screen shot of the compass calibration screen. Is this setup correctly? I just selected Pixhawk/PX4 for the quick configure parameters - does this setup the compasses correctly or do you need to do it manually?

I’ve also included the telemetry log if this helps?



2017-09-03 17-21-06.tlog (512.9 KB)

A bit hard to see anything definitive from the tlog.

Can you upload the data flash log from the flight controller?

Sorry I didn’t realise the dataflash log contained more/different data. I’m fairly new to mission planner.
I’ve upload a link to the log (it wouldn’t let me upload the log for some reason saying it was too big, but it isn’t) but also had a look before and did an “Auto analysis”. Seems there is a lot of vibration, I may need to re-calibrate the accelerometer and the motor averages might be wrong (but not sure what that means)? Perhaps ESC’s need to be re-calibrated.

First off, PropDrive motors are crap for a multirotor.
Compass calibration looks fine.

I looked at the log, and the vibrations look pretty nasty…

What I’m wondering is what props are you using, and how much does the aircraft weigh in grams with the battery and every thing else installed?

Spinning if not due to motors/esc problem(s) is probably due to compass problems.
I assume you did calibrate your ESC?
Equally, all your propellers are fully and precisely balanced? (This will minimise vibrations)
You did fill the CF tubes in between the frames and motors with foam to avoid CF tube resonance on various frequencies?

You did let the internal compass enable (I wouldn’t).
When doing the compass calibration, after calibrating (again) the accel, select precise instead of default. Insure your main battery is present when you do the calibration.

On a different level, do not use a switched power source for your FC and for your GPS external compass.

In short, with a new aircraft, place all the chances on your side.



Thanks, I’ve done most of those things except select “precise” and disable other compass. (is it not better to have a spare compass as a backup for diversity (even if it is internal and potentially subject to interference?) also I don’t have any CF tubes as the frames are held apart by the arms (I think that’s what you are referring to)
Bought it second hand and the motors weren’t good on test. Also the arms were the cheap flexible ones so I’ve also replaced them all. Also accurately balanced the props. Since doing this and recalibrating compass and accel it’s is sweet now. I did everything one by one and the stiffer arms made a huge difference to the copter’s stability in all modes.
I did however have problems calibrating compass - MP kept freezing and the green bar wouldn’t go any higher. Had to re-do it about 5 times until it got to the end and successfully calibrated. Not sure why but don’t need to recalibrate for now so not a huge problem.


Maybe off topic but Hobbyking Multistar are not just terrible, they are the worst thing you can buy :roll_eyes:

The constant rating of 10C is bullshit, it’s closer to 3C. Something 30% lighter and 2 times cheaper than good brand one’s should have ticked me off.

Lost 50 hours of work because of it

I also find that multistar are no where near 10c and this means a 3s 5200mah is basically unusable on my f550 because the voltage is instantly pulled down too low above about 15A. But I can get away with a 4s 8000mah. I have this lying around from a Skywalker 1900 plane. If the impact of the voltage drop is manageable (I. E. Voltage drop is not enough of a problem), then I think they do have their place because they do provide more capacity in a lighter package. Obviously they are not great in punching out high throttle/amps but this is a compromise ogiven extra capacity.
I’m not an expert on other types of batteries but as far as I’ve seen higher C means heavier. Unless someone knows different?