The crash that almost was

Afternoon all.
Could use your input on an almost crash today.
I have been flying this quad for sometime now with out incident. Today was an awesome day, cool sunny no wind. It was my second time out this season so taking it slow to get back into it.
I took off in Loiter, she went up perfectly. I stopped it about 5 meters or so up and then sent it out about 30 meters, made a turn back and she went another 30 meters. I was starting a left turn when suddenly I noticed that the forward speed was dropping. I knew something was amiss so I stopped the forward flight and dropped the throttle just as I heard “Potential Thrust Loss (1)”
I got it to the ground and disarmed it.
Brought it back to the bench and powered it up. Armed it…it spun fine and then shut it down. I didn’t want to risk it.
Any thoughts would be appreciated.

Log is attached here for a week.

Cheers all


Cant see anything definitive although when looking at Des/v/Actual there is a pitch anomaly just before the thrust loss message.

I could not see any great variance in RCout
But I did notice an RCin variance on pitch

From what I can see here, the speed increased with your input on CH2 until it reached maximum speed just over 8m/s where its speed oscillation started, usually indicating max angle reached or being cut back to maintain altitude.
The only other thing I noticed was the decrease in speed every time you input Yaw.

So maybe your pitch needs a little tune ??

Hey Mike
Thanks for your input. I think the speed versus Yaw is just me. I was trying to do a coordinated turn and was dropping the elevator input as I inputted the Yaw for the turn. Sloppy flying.
Tomorrow I am going to pull the motor and ESC to see if there is something going on.
But I am at a loss at this point as to teh thrust loss and forward speed suddenly being reduced.

The thrust loss seems to have been triggered when the Actual Pitch fell short of the Desired Pitch, have a look at your actual versus your desired in the logs.

I did not see any real drop in PWM output to any motor, usually indicated by an increase to that motor and a dropping of the opposite motor.

I am more inclined to think the thrust loss message was caused by an out of tune event.

Hey Mike thanks again for your input.
If I understand what your saying. The flight controller says I desire to be in this position of pitch and the machine ends up somewhere else. There is now a difference between the two resulting in the flight controller assuming a loss of thrust as the cause.

I have not had any issues with this bird for sometime so I am a bit puzzled.
That said I am going to give it a good physical exam tomorrow. I want to see if there is a physical reason to have not performed right. I can then run a new pitch tune. But something is telling me it’s a physical issue. I think the tune has been pretty good on it…that said I am no expert.

Hi Ricky
Try reducing these yaw params a bit to
and it might allow better pitch/roll control. This shouldnt affect yaw very much.

Your ATC_RAT_PIT_D and ATC_RAT_RLL_D could possibly go up by +50%, but it might be easier and safe to rerun Autotune with AUTOTUNE_AGGR,0.075

Maybe reduce MOT_SPIN_ARM to about 0.12 or 0.10 too, but that’s not related to any thrust loss issue.
There appeared to be a bit of oscillation going on at arming. This and the lower Yaw params might help.

Hey Shawn. Hope all is well with you and yours will run another tune on it. But I am going to inspect it for anything loose. Like I said this has been flying for ages with no issues.
Well except one. I get this oscillation just as I throttle up…it annoys the crap out of me so I am really interested in your thoughts about that… My MOT_SPIN_ARM is already set to 0.15 so I will dial it down a bit more.
But any other thoughts would be appreciated.

If I understand your thoughts in Yaw.
Take ATC_RAT_YAW_P,1.34549
and reduce it to which one These are two very different values.

As for ATC_RAT_PIT_D and ATC_RAT_RLL_D I will run a new tune on it after I complete a hardware check. Just in case. It can’t hurt even if this issue was tune related.
It also looks like with the new firmware I need to start up the FFT engine and redo the filtering before I tune it.

cheers man.

Sorry, I meant
ATC_RAT_YAW_I,0.08 ← I term

hahah no worries.
I will make the changes. First however inspection.

ok I did an inspection. Found nothing which really bothers me. This machine has been flying for a while.
Anyway I updated the params per your suggestion. Will get to the field as soon as I can.