I am DESPERATELY trying to figure out why my hexacopter won't fly level in stabilize mode (not altitude hold, just regular stabilize). Please please please help! I'm using a Pixhawk. The hex flew fine on an old frame, then, I moved to a new frame and all of a sudden stabilize mode won't work. I didn't change anything! Double checked that motors are laid out correctly and spin the right way!
When the copter takes off it's very "swirly" and unresponsive. I tried upping the values in the PID loops but this didn't seem to help at all. Strangely, when it takes off, it does so level, but then over the course of a few seconds I feel like I have to deflect the sticks more and more to keep level. And then eventually I cannot deflect the sticks anymore and just tips one way and crashes.
After tuning didn't work I then used mission planner to reset the parameters to their default values, thinking that I may screwed something up that I didn't know about. No luck, same behavior.
I've attached three logs from these flight attempts. I'm at a total loss for what's wrong. If anyone could identify a possible culprit I would be very grateful!
So it looks to me like the vibrations are insanely high, but I'm not very good at reading logs. Can someone confirm this for me? That would be strange since the Pixhawk is mounted on vibration-dampening gel, so I'm not sure why it would be that bad.
But for starters, does my hunch about vibrations look right, judging from the logs?
Props balanced? Motor mounting loose?
Ok it's update time. The first thing I did was balance the props. This didn't make any difference. Same swirly behavior followed by a crash.
Then, I made a setup to strap down the hex and rev up the motors without taking off. This was key in testing vibrations without doing any more damage. After careful experimenting, the problem turned out to be the vibration dampening setup. I'd been mounting the Pixhawk on four small pieces of this Kyosho Vibration Foam. Admittedly, I just used it because people on other multicopter forums/blogs said it was the best, and it seemed to work on previous things I've built.
But clearly not in this case, where vibrations were out of control. I tried lots of different things, but ultimately the only thing that truly seemed to work was another internet recommendation: earplug mounting. See my picture below. It's mounted on four earplugs. It does pretty well, though not spectacularly. Accel values on the x & y axes are in the 8-10 m/s/s range - well above the 3 m/s/s recommendation but well below the 24-30 m/s/s I was getting before. It takes off and flies well in level mode. However, the accel values in the z range are still in the +- 60 m/s/s range, which means I can't imagine that altitude hold mode will work.