Hello,
I hope that's the right place to ask for help.
I've got an apm 2.6 with 3.2rc13 on a mini 250 quadcopter.
In short, when I switch to alt hold the copter does not hold altitude properly.
The longer version.
Since the inclusion of the mpu6k filter parameter set to 42Hz my 250 has been super stable, I am highly impressed with how well it behaves.
I believe all of the trouble must have started after a crash that I had due to installing a gimbal without recalibrating the PIDs. The quad would struggle with the gimbal anyway due to the additional weight on such a small model. The gimbal is removed now. The problem is that, although I can keep it at a fixed height in stabilise mode at around 50% throttle without much correction on the sticks when I switch to ALT hold it cannot keep up. The motors seem to throttle up and down constantly and the quad goes up and down without being able to hold altitude. There seem to be two oscillations at the same time one slow where the copter goes up and down many meters and one faster where it plays around it's position. The faster one matches with the oscillation I hear from the motors.
As this first occurred with 3.2rc9 I reset everything and started over again with rc13. After the reset, I thought I had it fixed as it behaved well during one flight but that did not last. The vibrations seem to be at acceptable levels and I tried different propellers without much difference. I went through various tests and logs but I just cannot figure out what is wrong. I am afraid that my barometer might be giving up.
I am attaching a log where you can see the slow oscillations at Alt R but not the faster ones.
Any help is highly appreciated!
Regards,
Yiannis
Replies
I set the onchip filter to 42Hz from when it was introduced in the code. Before that I couldn't even tune it properly. That is only relevant to mini quads with high KV motors though.
Although I haven't fully fixed the problem yet I now know it is not the barometer as I am using a different controller. The problem seems to be with the motors. Due to very good damping on my controller I couldn't see the motors' problem. So the guidline that vibrations within 4g are acceptable is irrelevant at that point. The reason is, and correct me if I am wrong, very good isolation conceals the broblem that some motors may have but that does not fix them. Bottomline, make sure each individual motor works well, check if they feel the same when you turn them by hand, take the bells off and inspect the magnets, balance the motors. I am currently rebalancing my motors and changing some bearings and I'll get back to this thread with my results.
If your althold works well but your loiter does not then you should look at your gps hdop and potentially try to tune the pid for the loiter mode.
Good luck,
Yiannis
Hi Yiannis,
Did you change the MPU6K FILTER to 42 hz cause your vibrations were high and you had not too good loiter/alt hold performance?
I'm currently struggling with that since my vibration levels have improved but not accordingly loiter performance
Regards
Pablo