Lost control, then 2 seconds later lost connection, on my Mavic Pro what happened ??

[mikeyway]

I have no doubt that other version might also be under risk.
I would love to test out the theory by placing a drone above a leaf blower or similar and try to reproduce the problem.

 

[BudWalker]

That right there is what I find most bizarre. I would have thought, at the very least, the down facing infrared sensor would be involved in determining whether the aircraft has landed or not. Making this determination solely based on the presence or absence of altitude loss is quite simply unbelievable.

I presume this was a Mavic Pro; can this possibly happen to other models in the Mavic line as well?

Edit: fixed quotation

The problem is that the down facing infrared sensor isn't accurate enough. It often shows a height of 0.1 meters while sitting on the ground.

 

[Mossiback]

...Out of curiosity, and for caution, how are the rotor motors cutoff when manually landing - is it the amount of seconds you have pushed down on the left stick combined with the absence of descent for a set time that triggers the motor cut off?...

Yes. With down stick the motors will stop after a couple seconds without a change in height. It also works in reverse. When you start the motors using the sticks and without stick input to rise, it will just idle because there is no change in height (it needs no more thrust to maintain position).

...Does the downward infrared sensor come into the equation at all?...

No. I hand catch with the downward sensors on (by grasping in front of the sensors) and after a couple seconds of down stick and no more movement the motors will stop.

 

[Deleted member 94047]

This all makes me ask what then is the function of the downward infrared sensor? Obstacle avoidance/detection? But there are cameras for that. So what purpose does it serve?

 

[sar104]

This is by far the weirdest crash incident I have read here. Flight computer decides aircraft has landed and cuts off motors while it is 120 meters in the air? WTH! OP, you have my deepest sympathies, I hope you take it up with DJI and that they will address it in future product development at the very least (it would be noble of them to give you a replacement too).

Out of curiosity, and for caution, how are the rotor motors cutoff when manually landing - is it the amount of seconds you have pushed down on the left stick combined with the absence of descent for a set time that triggers the motor cut off? Does the downward infrared sensor come into the equation at all? Or is it too complex and too contingent on several factors to describe here? I would greatly appreciate any explanation of how this works - and particularly the parameters that determine rotor cutoff.

Edit: Forgot to say thanks

This all makes me ask what then is the function of the downward infrared sensor? Obstacle avoidance/detection? But there are cameras for that. So what purpose does it serve?

To detect the ground, especially during landing in order to make a controlled landing rather than flying into the ground at 3 m/s.

 

[Deleted member 94047]

To detect the ground, especially during landing in order to make a controlled landing rather than flying into the ground at 3 m/s.

Yes, I would have thought that was its primary purpose. And yet the FC doesn't seem to query its reading in determining whether the aircraft has landed and whether to cut off power to the motors. I am honestly confused.

 

[Mossiback]

This all makes me ask what then is the function of the downward infrared sensor? Obstacle avoidance/detection? But there are cameras for that. So what purpose does it serve?

Like @sar104 states, it is to detect the ground. Your thread title shows you are using a Mavic Pro so the downward sensors are ultrasonic, not infrared, and the cameras are for the precision landing function which will not work well without adequate light.

 

[sar104]

Yes, I would have thought that was its primary purpose. And yet the FC doesn't seem to query its reading in determining whether the aircraft has landed and whether to cut off power to the motors. I am honestly confused.

I agree that it seems to make sense for it to be consulted before shutting down the motors, but clearly that didn't happen in this case.

 

[Mossiback]

Yes, I would have thought that was its primary purpose. And yet the FC doesn't seem to query its reading in determining whether the aircraft has landed and whether to cut off power to the motors. I am honestly confused.

When I hand catch my MP, the motors will shut off after a couple seconds of down stick and no detected elevation change. This is with the downward sensors on. I guess if the MP were in a prolonged updraft the motors would idle down (because the thrust is not needed to maintain position) and after a few seconds it might think it has landed and shut down. It may be a case of assumed sensor error, meaning that if upward thrust is not needed to maintain position it may assume that it has landed and other sensors (barometer) must be in error.

 

[sar104]

When I hand catch my MP, the motors will shut off after a couple seconds of down stick and no detected elevation change. This is with the downward sensors on. I guess if the MP were in a prolonged updraft the motors would idle down (because the thrust is not needed to maintain position) and after a few seconds it might think it has landed and shut down. It may be a case of assumed sensor error, meaning that if upward thrust is not needed to maintain position it may assume that it has landed and other sensors (barometer) must be in error.

The barometer was obviously the sensor that it was relying on - that was showing no descent.

 

[Deleted member 94047]

Thank you both for the explanations. I agree with sar, it makes little sense for the FC not to consult the reading from the downward sensor (I thought it was infrared, thanks for the correction) before deciding to cut power to the motors. And no this is not my thread. So I better stop spamming someone else's thread.

@mikeyway Hope you hear form DJI soon, and please do share when you do. Thanks! And all the best of luck

 

[zxcflyer]

I have not looked at any of the files, but I have a few wierd experiences with my mavic 2 pro and I discovered something the other day while flying in Vietnam.

the day before my flight, I flow within the town of Dalat with no problems, everything went perfect. The next day I went to my family's coffee farm to film there new strawberries. I had alot of problems connecting to the fly cam. It would connect, then disconnect. I finally thought I connected, but on takeoff it started to fly in its own, I was able to land safely. I then decided to put my phone in airplane mode, no problems, strong connection, and finished a great flight.

I think if you have weak cell signal, or in a rural area, you need to go to airplane mode. I may always download maps and fly in airplane mode on my phone in the future from this experience.

I had several GO4 disconnects over a period of a few months. The controller stayed connected and I was able to controll the craft. Only recently I came to the conclusion that they were all caused by the phone loosing the cell signal. I select airplane mode when flying to avoid this.

 

[PeRo]

When I hand catch my MP, the motors will shut off after a couple seconds of down stick and no detected elevation change. This is with the downward sensors on. I guess if the MP were in a prolonged updraft the motors would idle down (because the thrust is not needed to maintain position) and after a few seconds it might think it has landed and shut down. It may be a case of assumed sensor error, meaning that if upward thrust is not needed to maintain position it may assume that it has landed and other sensors (barometer) must be in error.

This case shows a new and concerning aspect of the - at least - MP1 behaviour, from which I have taken benefits for Hand landing so far.
Prior to grabbing the MP (full sensors on) I am using the Stop button to suppress any movement for a couple of seconds.

My observation: When grabbing the MP and with full throttle down, motors are often throttled up for approx. 2-3 sec to escape from the downward "obstacle". By even slightly lifting the AC during this phase, the behaviour is suppressed and the props are stopping after 1 sec max. - without any fight.

Could it be that a slight wind related upturn has caused the effect of shortening the shutdown time to 1 sec, which is now surprising for all of us? As mentioned, this upward movement can be in the range of 30 cm / 10 inches to become effective (full throttle down assumed).

 

[Meta4]

I had several GO4 disconnects over a period of a few months. The controller stayed connected and I was able to controll the craft. Only recently I came to the conclusion that they were all caused by the phone loosing the cell signal. I select airplane mode when flying to avoid this.

Cell signal or no cell signal makes no difference at all.

 

[zxcflyer]

Cell signal or no cell signal makes no difference at all.

That was in response to user Bohica, a bit off topic.

 

[Mossiback]

...My observation: When grabbing the MP and with full throttle down, motors are often throttled up for approx. 2-3 sec to escape from the downward "obstacle"...

If it throttles up then it is detecting your hand. If you grasp it in front of the downward sensors this does not happen. Here is a video showing how to do it:

 

[PeRo]

If it throttles up then it is detecting your hand. If you grasp it in front of the downward sensors this does not happen. Here is a video showing how to do it:

Thanks Mossiback. However, the reference to the hand landing experience should only serve as example for a behaviour which was specifically discussed in posts #7 - #11.
There was some astonishment about the rapid shutdown of motors within 1 sec of no movement where the expectation was that Throttle down with no movement need to be applied for a significantly longer period.
Getting into upwind conditions while throttling down with result of even slight ascent might lead to a shorter shutdown period as observed. Should be considered for future flights in similar conditions...

 

[Mossiback]

Thanks Mossiback. However, the reference to the hand landing experience...

I was addressing your comment about it detecting your hand when grabbing it.

 

[Gryphon962]

What happened is that the FC killed the motors because it thought that it was on the ground.

​

95.291 : 8465 [L-FMU/FSM]state changed. cur: on ground​

95.320 : 8467 [L-FMU/MOTOR] Stop. reason:landing.RC_Thr​

95.320 : 8467 [L-FMU/MOTOR]Total start times: 1, time: 95.32​

95.320 : 8467 [L-PWM]set actuator mode:IDLE​

95.320 : 8467 [L-FLYMODE]CTRL reset all by motor stopped​

95.321 : 8467 [L-FMU/FSM]state changed. cur: motor off​

95.337 : 8468 [L-IMU]set imu switch level = 1​

95.398 : 8471 [L-TAKEOFF]alti: 1801.617188 tors: 91.809647​

As for why the FC thought it had landed, the only thing I see is that when you applied full down throttle at 94.4 seconds there was no descent recorded for over 1 second. I thought that it required 3 seconds of no descent to stop the motors, but perhaps not on this firmware.

Can someone please confirm that FULL down throttle is required for > 1 second before this can occur? If so, I guess the only thing we can do until they fix the firmware is to avoid use of full down throttle.

If it can turn itself off with just partial down throttle then....that's not good.

 

[sar104]

Can someone please confirm that FULL down throttle is required for > 1 second before this can occur? If so, I guess the only thing we can do until they fix the firmware is to avoid use of full down throttle.

If it can turn itself off with just partial down throttle then....that's not good.

It's a very unusual scenario for the aircraft to attempt to descend but lose no altitude but, in that situation, I don't think it needs full down throttle to conclude that it landed.