Hi everyone,
A few friends and I have assembled a hexacopter based on Pixhawk. We bought the autopilot, a GPS/compass, and a radio pair from 3DR, a Tarot 680Pro frame, and the jDrone 30A ESCs and 850KV motors. We powered this assembly using two 3S 6000mAh batteries connected in parallel.
We set up the PX4 firmware using QGC, and we did the calibration of the sensors and the ESCs, which I think went well.
Yesterday we performed two really good flights in which we switched from manual mode to position control, and we were very impressed with the stability of the position control mode. We did notice a slight "twitch" during the transition in terms of pitch and roll, but it handled the oscillation
well.
On the third flight, however, we had a crash that we haven't been able to explain as a mechanical failure. When our pilot switched from manual mode to position control, Pixhawk basically set the setpoint pitch and roll to (what seems to us as) very large values. As a result, the hex rolled almost 180 degrees and fell off the sky.
We were hoping to get some advice to figure out why this happened. Is it a matter of PID tuning? If so, how come the transition in the first two flights was relatively stable and in the third one it is not?
Here are two data logs from the Pixhawk's sd card, one from our second (stable) flight and
one for the third one, which crashed:
(crashed) https://drive.google.com/file/d/0B7LJyS3YWjYhNHpDeDdnSU5MRXpaMW16S1V2cjNtXy1nb0cw/view?usp=sharing
(stable) https://drive.google.com/file/d/0B7LJyS3YWjYheXhBZ1JlakZFcHFZblZ5VEkzN1RwSVN4dVlv/view?usp=sharing
Also, here are a few plots showing the effect of switching from manual to position control for the two flights being compared, on the angles and rates setpoints.
(crashed, roll pitch setpoints vs actual)
(crashed, roll pitch rate setpoints vs actual)
(stable, roll pitch setpoints vs actual)
(stable, roll pitch rate setpoints vs actual)
Any suggestions would be appreciated.
Thanks,
Florian
PS: The all-up weight of our setup is 3.5kg and we were very careful about monitoring the voltage of the batteries during each flight through telemetry via QGC.
Replies
Do you try the beta vers? there is a bug with stable release that Randy solved in beta, perhaps is that your problem? http://diydrones.com/forum/topics/copter-3-3-beta-testing?xg_source...
Thanks for replying. That bug fix is for the APM firmware, though, right?