Wookong down!

[quaddemon]

It could be of interest so I would like to share my experience and ask some help to the experts out there
Today I was flying my Wookong-M quad for maybe the 20th flight; no issues whatsoever till today.
The only variant was that this time I have installed FrSky sensor hub and vario sensor.
Albeight little windy, the WK-M behaved as usual, rock steady in GPS and alt hold for minutes while I was taking shots and a little video of the quad against the moon.
When I decided (well within the battery autonomy) to came down, still in GPS/alt hold, and lowered the throttle.... the control was lost!

It wasn't respondind to my inputs, but started to drift away following the wind.
I changed to Atti mode...nothing
Then switched to manual and suddenly the motors stopped and the quad went down upside down

The gimbal with the Gopro was smashed, as the battery compartment that exploded and bounced away, the quad itself landed between some soft bushes breaking four APC props. Thanks to the tought dome, the electronics and the enclosed GPS antenna suffered no damage at all.
Ah, the crash ended 1 meter from a small river...lucky me!

I can't think of another reason for the crash other than some kind of electronic interference between the vario sensor and/or hub and the WK-M electronics.
Everything was perfect despite the wind until I, slowly as usual, lowered the throttle. Another thing I noticed was that the vario continued to display 19 meters, the previous alt hold reading, after the crash!
I'm not an electronic guru, so could someone please give his comment about what happened?
Thanks a lot
Pierluigi

 

[RTRyder]

In the video it sounds like the motors stopped, did you have the throttle below 10% while descending? The WKM will shut the motors down if you lower the throttle too much while in the air, not one of their better features. I've setup an audible alarm on my TX if the throttle gets down to 15% so I know not to go any lower!

Ken

 

[quaddemon]

Ken
the motors stopped only when I switched to manual, I piloted the WKM for months and know the dreaded 10% throttle cut off!
Interesting the 15% alarm: how do you manage to program it, which radio?

Anyway I no longer trust the WKM like before and it's a pity 'cause due to many flawlessy flights I considered it a great machine until yesterday...:upset:

 

[Multirotorcraft UK]

Quaddemon that was so close to going into the river!! your were lucky.. I have been building a CX-4. My Wookong has been tried and tested along with the ESC's and before this flight I had done around 40 mins testing the CX and just doing little adjustments, with nothing unexpected and then I had a very scary moment. I was just mooching around in GPS mode and then it dropped the port side. I quickly flipped to ATTI and recovered. Confidence is low at the moment

 

[FlyEYE]

View attachment 3023
Crashed mine yesterday.

Brought it up to 60m and it just kept going up, at 80m I was reducing the throttle more and more until I suspect I went below 10% (forgot to put it in intelligent cut off) I was flying over a muddy field and it crashed with a big splash.
I'm having a hard time with the altitude hold and have little confidence in it, I'm still hoping it's just a tuning issue I can't figure out. My MK held altitude a hell of a lot better.
The thing that ticked me off the most... is that my gopro video got corrupted in the crash

 

[vislaw]

...the thing that ticked me off the most... is that my gopro video got corrupted in the crash

Speaking of corrupted gopro video files, I didn't know about the S.O.S. recovery function that lets you recover corrupted footage: http://goprohacks.blogspot.com/p/how-to-restore-gopro-mp4-corrupted-or.html

 

[FlyEYE]

View attachment 3085View attachment 3084Vislaw, thanks it worked kind of for me, the perl script. Recovered 2 minutes of video, unfortunately not the crash was still going up as the video stopped. Here's a couple screen captures, the soft landing pad and the highest point the video captured.

 

[DennyR]

I do have what I believe is the answer to this problem. I am going to start a blog with some extracts from my online book "All you ever wanted to know about MR's" There are two main scenarios that can cause a departure. A departure is when the model stops a reaction to the computerized flight control inputs mainly due to an aerodynamic stall.

So with a WKM, it does not like you making a fast descent, especially in windy conditions, and also when your battery is low, in fact it tries to stop you doing it..

If you are in the descent you should avoid making any rudder turns because this will stall two of the blades as they have to slow down. If your model starts to enter a departure the only recovery is to open the throttle and fly back to home with plenty of forward speed. My own F1 now has stabilize vanes to assist the yaw command and keep motor rpm's more equal. The more weight you have the more acute the problem is.

If you have selected very low kv. motors then on low battery you may not have enough reserve of power to to increase the RPM to the point where it can still stabilize and hold the hover.

It is quite normal for people to start exploring the envelope. but you need to be very cautious in the fast descent.

hope this helps your understanding of how these things work.

 

[Stacky]

The rudder turns warning is very helpful, thanks Denny. Let us know when you get that blog online

 

[Totallycommitted]

Hi Denny,

what you have to say there is very interesting about the departure and in particular the descent issue, I flipped my octo in exactly that way coming down quite fast quite windy and whoop flipped almost 360......recovery made by instant throttle increase. Now what about lock out ????? I been flying in the same area in good not windy conditions time and again and then boom same place same weather ....lock out ??? I just don,t know how to logically work this out and i didn,t have enough time to turn the reciever off and on to reset it = crash. the only thing that i had changed was adding superlights and a 6v battery to my system. Very frustrating !!! Any lock out issues or preventitive measures out there ?

Matt

 

[Dewster]

Interesting thread! I have many flights on the WK-M. Each successful flight adds confidence to the system. These stories make me think about how to fly the craft.

 

[Multirotorcraft UK]

My initial issues turned out to be a suspect ESC. Since changing it all has been great for what is now about 4 hours of flight time. Its been perfect.