Hi, I am new to ardupilot, asking for some help in investigating the possible cause of repeatable crashes of hand launched 90cm foam plane shortly after launch. It actually flew pretty well before installing airspeed sensor, still cannot say for sure if bad installation/calibration is a root cause. So I double-checked all servos making sure they are moving correctly both in response to TX and in response to plane tilt. Last two crashes were identical: battery is fully charged, autotune mode selected, arm, hand launch, first plane goes stable forward, reacts to nose up and gains some altitude, but then nose starting to dive and plane seems to be completely ignoring RC elevator request to lift the nose. From the log I see FC knows that nose is down and RC_IN for elevator is asking for nose up, but RCOU for elevator seems to be ignoring RC_IN and constantly commands for nose down until hitting the ground. Does anyone experienced something like this? Airspeed readings seem to be fine and pretty much correspond GPS speed estimate. I also used to launch in AUTOTUNE mode before without any issues. Here is a log: 00000044.BIN - Google Drive
I would start by not launching in autotune mode, use manual or if you have reasonably good tune, normal stabilized mode like Stabilize FBWA/B.
When selecting autotune be sure to be starting off with good height and flying level, if it turns bad just switch back to fbwa or manual and save it before it hits the ground if possible
During the first few seconds of the flight, autotune dropped the P gain by a factor to ~10, but even before that it looks to be that the gains were probably too low and there is almost no control response.
I agree with the others that you shouldn’t launch in autotune, but you may also want to reset the gains to default before trying again.
Thanks, that seems to be the reason. Appreciate all of advice, in stab mode it went ok. So the lesson is: before invoking autotune it is better to have a good altitude.