I encountered a strange problem. I am in the process of tuning an x8 octocoper (the tune is not finished, therefore it is not perfect [or even acceptable t this moment]). The process is known to me, I’ve done it hundreds of times. This UAV went through the exactly same Diracs delta (manouver in the log) at least 78 times without any issue and 3 times after that, also without any issue. But during particular flight UAV did a strange rotation in the yaw axis.
I would consider this a desync if any motor went to max PWM (1950). However, the motor that seems to malfuntion got to only 1795 PWM and got “stuck there”.
The UAV is using PWM, the calibration of ESCs was done 3 days ago and went without any issues.
I am going out of my mind trying to understand what am I actually looking at.
Dear forum, I’d be very gratefull for your help. I attach the log below.
Can you, please, show me the moment when the mototr 3 is at the maximum PWM? According to what I see the max PWM motor 3 reached is the 1795 with the max beeing 1900.
The only motor reaching the max PWM 1900 is momentarly motor 4 with motor 6 comming VERY CLOSE to it (PWM 1896). Do you think that the issue might have been demanding higher speed in an axis that the UAV could deliver?
It was not only yaw, but also lost roll control. At the same moment when pilot change the pitch input from full forward to full backward.
The strange thing is that even if we assume the desync of motor3, the copter started to gain altitude, causing the FC to set Throttle control to zero. But even with the decreased total lift, the copter kept ascending for two seconds, it only stabilized after that.
Personally, I don’t think that it was a desync, it rather looks like a strong gust of wind, pushed the breaking copter upwards.
Sorry I didn’t read your original post very carefully, I assumed “max PWM” was where the motor PWM flatlined. Perhaps that PWM level (1795) was a dynamic limit imposed by the contoller to maintain stability? As @Eosbandi says, perhaps it was related to turbulence in conjunction with the demanded pitch rate.
Hello! As of now after about 100 take offs today it looks like the problem was caused by the UAV needing more power than the powertrain could provide. After setting up the max rate values the problem seems to have disapeared.
So it look like @kd0aij was absolutelly right in his diagnostic of the problem, for which I am extremall gratefull.
I think so. I have done about 100 or even more take offs since the problem was observed and continued with the tuning process. The tune is complete (or almost complete, if someone will be kind enough to point me in the direction to find a solution to a problem described below), but I have a question, maybe someone here will know the answer @kd0aij@Eosbandi@Leonardthall . The UAV seems to have quite a large I term buildups, which are affecting the rates. Is there any way to get rid of those? I mean the UAV flies very fine in alt hold, loiter,guided and auto, but I’d be much happier if the rates were tracking better during sharp deflations of the sticks. It’s only a cosmetical issue, but if anyone would have the time to analyse what is happening and devise any solution - I’d be grateful. The log showing this issue can be found below(and before anyone asks - if I go any higher with stab P I get oscilations visible in the log):
Thank you very much for looking at the log. I am very grateful and relieved to hear that it’s normal. In that case - I thank all of the users for the time spent on analysis and the humongous amounts of help everyone here has provided me. I am very grateful. The topic can be closed and I consider all of the issues as resolved.