VTOL mysterious Bug can cause VTOL landing to water

ArduPlane VTOL Plane
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1

Hello.

you can refer to attached log for the error.

If q_assist_alt is not 0 and auto mission tries to lower the aircraft’s altitude below q_assist_alt,

it goes to QLAND(transition-fail-action) even though it is in fixed wing mode.

I could regenerate error with pull elevator stick in auto mode until climbing up 100m.

if q_assist_alt is set to 0, the error goes away.

I want to know the reason of this bug.

2

That behavior is not a bug
The Q_ASSIST_ALT function is working correctly.

3

but the Transition Fail Action was engaged without explicible transition order.

when you fly in auto mode, if you pull elevator stick to increase altitude, transition fail action will engage.

isn’t it bug? it is not intended behavior.

4

Could you explain why it is not bug and it is working correctly?

5

I can’t see here that Q_Assist is recognized as transition.

https://ardupilot.org/plane/docs/assisted_fixed_wing_flight.html

6

If the quad motor starts moving at an altitude lower than Q_ASSIST_ALT, it is not because the FC is trying to transit to QLAND.

Other parameters related to Q_ASSIST, There are Q_ASSIST_SPEED and Q_ASSIST_ANGLE.
Q_ASSIST_SPEED is the threshold value that FC determines the flight is unstable (there is a risk of crash) when the speed falls below Q_ASSIST_SPEED in plane mode, and the FC activates the quad motor to stabilize the aircraft.

Similarly, Q_ASSIST_ANGLE is the threshold that starts the quad motor to stabilize the posture when the roll or pitch exceeds a certain angle.

Q_ASSIST_ALT is the threshold below which the FC activates the quad motor to assist in maintaining the altitude so that the altitude will not drop any further. The reason quad motor works is not because FC is transitting to QLAND.

Therefore, setting the mission waypoint altitude lower than Q_ASSIST_ALT is incorrect planning.

7

You are misreading and explaining things not related to topic.

I didn’t said Q_ASSIST activation is bug. but you are saying activation of Q_ASSIST is bug, right?

I said <QLand after “transition_failed” error message> is bug, because I didn’t order transition and QLand.

and I already understand and knowing about Q_ASSIST mechanism. you don’t have to explain it. I didn’t question about Q_ASSIST mechanism.

8

and I said “Pulling elevator stick causes transition fail message and QLand” is bug.

but you are saying about Q_Asssit mechanism. it is totally nonsense.

9

I’m sorry that I can’t convey what I want to say to you because my English is poor.

I’m not saying that Q_ASSIST is a bug. Your flight plan is shown below. The problem is that the waypoint altitude is set to 30m and Q_ASSIST_ALT is set to 30m. I will explain below what happened.

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  1. According to Mission No. 17, the aircraft descended to 30m.
  2. However, Q_ASSIST_ALT was set to 30m, so the aircraft went into quad mode.
  3. The altitude exceeded 30m, so the mode shifted from quad mode to plane mode.
  4. Repeated steps 1-3 about 8 times!
  5. Altitude no longer exceeds 30m while in quad mode.
  6. Transitioning to Plane mode timed out and a “Transition failed” message was output.
  7. Landed by Mission No.19 VTOL_LAND.

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The “Transition failed” message did not mean that Q_LAND failed. This message indicated that transition to Plane mode failed.

Did it get through this time?

There is absolutely no software defect in the above behavior. It’s perfectly normal. If you understand the meaning of Q_ASSIST_ALT, you would never set Q_ASSIST_ALT and the waypoint altitude to the same value. That’s why I explained about Q_ASSIST.