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Non-voluntary 5-rotor test

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Hi folks!
Yesterday I had the fantastic experience to get evidence of the function of the 5-rotor mode. After the pre-flight routine I took off, made my standard moves to verify function and then started for a slow ascent to a height of 80 meters. After a big slope the H920+ suddenly started tumbling around, regaining stable flight after roundabout 8m descent. I returned it back to me, recognizing that the left front motor had stopped. I gave it (and me too) some seconds to recover, checked for any obvious reasons for the motor to stop (FOD, temperature, loose prop) and started the motors again and everything was fine. I continued flying in close proximity and low height for another 13 minutes, swapped for my secondary pair of batteries and had another 18 minutes of flight time without any issues.
Returned home I checked the flight data in the UAV Toolbox and except for the battery warning there were no entries?! Since my laptop was (and probably still is) busy with rendering a mapping surface file I couldn't gain any further information (GUI and other) on what had happened. But I'm on it 😉. Having absolutely no idea why it shut off the motor is not that kind of confidence I like to build on - even if I now know, that the 5-rotor mode kicks in and ensures a safe landing!
Conclusion up to now: 5-ROTOR MODE WORKS!!!
(Gonna keep you updated on any news gained from failure log etc.)
 

DoomMeister

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If you haven’t got it already, try Q500log2kml.exe from @h-elsner to analyze your flight log files. You can get it from downloads on his website Private Homepage h-elsner.
I use this program to analyze telemetry on all of Yuneec’s drones. It is my go to app for this purpose.
 
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Update: read out the complete telemetry, but still got no clue why it switched off one motor. I have a error flag #32 during the tumbling and the #1 short before landing - so no real or reasonable problem!?!
I will do a complete check of the hardware to make sure there is no loose connector or cold soldering but I doubt it to be a hardware problem. Nevertheless a good reason to continue on working on my test bench 😉⚒.
 

DoomMeister

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Update: read out the complete telemetry, but still got no clue why it switched off one motor. I have a error flag #32 during the tumbling and the #1 short before landing - so no real or reasonable problem!?!
I will do a complete check of the hardware to make sure there is no loose connector or cold soldering but I doubt it to be a hardware problem. Nevertheless a good reason to continue on working on my test bench 😉⚒.
Error 32 is a compass calibration warning and an error value of 1 is the 1st low battery voltage warning.
If you are using Q500log2kml there should be a column for Motor Status telling you which motor failed. Hovering the mouse over a value in the table will give you the written meaning.
 

Steve Carr

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A couple of years ago I got a 5 rotor warning on the H when it was about 1500' away. I flew it back and landed. Inspected everything. Changed batteries and everything worked normally. It's still flying and I've never seen the warning again. Just one of those little mysteries of flying.
 
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@DoomMeister thx for reminding me of the additional functionality of the "elsner Software". Too many copter-related software on my desktop 😜. The failure modes are also part of my field book / flight checklists - that's were I looked them up first.
But even with an detailed read-out of the status and failure events it stays a mystery why it happened?! I'll check the hardware tonight, probably even swapping the motorarm against one of my spares - just to be sure. But perhaps it's really like @Steve Carr said, just the ghosts in the machine 😜.
 
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PatR

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This is another area the 920+ demonstrates lower capability from the original 920. 5 rotor mode was incorporated through installation of the Typhoon H FC and software when Yuneec removed the original 920 flight controller and software during the so called “upgrade” recall.

The 920 did not possess “5 rotor mode” as it was neither necessary or as yet developed. The 920 could lose a rotor/motor and self stabilize by offsetting loss of thrust at one boom through the remaining motors due to having ample “headroom” in the power system.

That process of self stabilization is much faster than 5 rotor mode. Had it still been in the original 920 configuration it would have compensated for the motor loss almost instantly, preventing the tumble you experienced.
 
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@PatR would there be any signs of a 5-rotor mode being activated? Like I wrote, there are no changes in flight mode (always angle mode) logged in the files and there was also nothing displayed on the ST16? I simply assumed, that it stabilized itself due to that mode. Would the 5-rotor mode be displayed or signaled in any way?
 

PatR

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I don’t know. One thing I do know is the telemetry will not isolate the cause of a motor stoppage.
 
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As soon as I'm home I'll remove the faulty motor arm and replace it with one from my stock. The motorarm will be thoroughly tested before it goes into the replacement stock or even not - we'll see.
If time allows I'll give my Yuneec buddies a call tomorrow - up to now they were very supportive. Perhaps they have a clue on what happened or at least what I'm dealing with.
 

PatR

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I think you’ll find the arm and motor not to be the culprit. Unless a motor is wedged tight with debris it will turn when power is applied.

So if it wasn’t wedged immobile when it landed the problem originated at an ESC or very small break in the circuit. It is also possible one of the output plugs is barely seated at the flight controller.

A smart move would be to remove the top cover and seat all the servo leads in the FC.
 
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The three bullet connectors that connect the arm to the power distribution board are also a potential failure source.
 
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On my H920 plus, I lost a prop due to the screws that bolt onto the motor for the quick release props pulling out. Dropped like a brick.
 
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On my H920 plus, I lost a prop due to the screws that bolt onto the motor for the quick release props pulling out. Dropped like a brick.
Uurgh! That's bad! These screws are part of my pre-flight check since I noticed that they tend to loosen themselves by time. Loctite is a must and I put a little scratch mark on all parts to help visual detection of any movement on these screws.
 
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Uurgh! That's bad! These screws are part of my pre-flight check since I noticed that they tend to loosen themselves by time. Loctite is a must and I put a little scratch mark on all parts to help visual detection of any movement on these screws.
Unfortunately for me, it was the first flight. Needless to say, after Yuneec repaired it (under warranty, and several, several months later), I removed all the screws that hold the quick disconnect portion to the motors and put blue loctite on them. If I remember right (this was in 2017), I found one screw that had a different thread pitch, a couple of screws that were a different length that the rest, and several that were not very tight at all.
 
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Unfortunately for me, it was the first flight. Needless to say, after Yuneec repaired it (under warranty, and several, several months later), I removed all the screws that hold the quick disconnect portion to the motors and put blue loctite on them. If I remember right (this was in 2017), I found one screw that had a different thread pitch, a couple of screws that were a different length that the rest, and several that were not very tight at all.
Holy sh..! As a Quality Manager I feel a shiver running down my back... I wouldn't know where to start with writing non-conformity-reports and whose head to chop off...
 

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