VTOL Crash; possible bad vibrations

Had a crash last week and would appreciate some input.
The firmware is almost stock, and previous flights were more successful, so I doubt it’s because of it.
What I noticed in this flight is higher vibrations than the last flight, all the way until it started misbehaving.
Previously they would show on the log only when slowing down, and then it would go back to normal.
There’s also something weird going on with the yaw.

I know such high vibrations aren’t good, but couldn’t see the until after the crash.



Sorry about the crash. Can you describe what actually happened or what you were trying to do and what it did instead? I don’t really know what went wrong here, so it’s very difficult to draw conclusions just from that.

We were tuning it before we try the transition.
Before it would either start pitching up because of aerodynamics, or go wild when stopping, so we tried to get it perform alright in MC mode at least.
I will attach previous flights as well, so maybe you get some better info.

This log is only from hover. All looked good, but there’s a software crash message.
Link: https://logs.px4.io/plot_app?log=2aa10a88-ec58-4c3e-94fd-ba7dd304fbed

Second one we were accelerating to around 20m/s in MC Position mode, and trying to tune parameters so it doesn’t get wild as it stops.
We have certain aerodynamics which are lifting our nose up all the time, so we decided to have our elevons act like flaps while we’re picking up speed, and then before transition put the flap command to zero, so it continues with normal elevon commands only.
For now, we had them fixed at certain angles, so it was flying from start to finish with elevons down.
It was at 50% output. It went well, but we wanted to avoid it getting nose down as speed increases, so decided to try with less deflection.
Link: https://logs.px4.io/plot_app?log=a85700f0-7f09-4eed-8737-b004b443d9d6

On third one, where it crashed, it was at 30% down deflection.
It all looked good, until stopping. It looked as in previous flight, then because of low motor commands started going pitch up, and stopped correcting. It gave almost immediate full throttle command to almost all the motors in one time, but they didn’t react, possibly because our ESCs got out of phase, that still has to be tested. But we didn’t want it in that situation anyway.

Link, same as in the first post: https://logs.px4.io/plot_app?log=f758b2cc-964f-43de-8edd-c123d9a967f7

Thanks for your help.

Just to paste the response I got on Discord from @sfuhrer

"Looks to me as if your hover controller is not tight enough to control the vehicle with high disturbances (like in this flight where you accelerated to 20m/s in hover). The main issue here though was that you don’t have airmode enabled (MC_AIRMODE to 1). That means that the plane was generating 100% of required lift with the wings, the MC motors were in idle and thus had no control effectiveness (there can’t be any differential throttle when all are close to 0). "

I think that pretty much solves the problem for now.


For future reference, this was the discord message: Discord

Great that @sfuhrer could resolve it. And gosh I hate the fact we have Discord and Discourse, what a mess.

Thanks for the link @junwoo0914 but unfortunately it’s not visible for Google.

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