2 devastating crashes in a month using Wookong

[Cornforth Images]

Thanks again for all the feedback. From all the comments, it still sounds like a mixed bag about the reliability of DJI flight controls. Perhaps I just had the misfortune of buying a Wookong system with a flaw? Also, it sounds like I should plan on buying a new transmitter & receiver when I rebuild just to eliminate that possibility of potential trouble.

 

[ProPilotWannaBe]

Thanks again for all the feedback. From all the comments, it still sounds like a mixed bag about the reliability of DJI flight controls. Perhaps I just had the misfortune of buying a Wookong system with a flaw? Also, it sounds like I should plan on buying a new transmitter & receiver when I rebuild just to eliminate that possibility of potential trouble.

Best of luck on your next rebuild! I wish you many successful and fun flights on your next MR!

 

[dazzab]

For about a year now I've been reading about fly-aways and sudden uncontrollable flight. I've had it happen a few times myself flying with the APM running Arducopter. Recently a friend and I have been doing a lot of comparisons between his Droidworx copter flying with a DJI Wookong and my Droidworx flying with an APM. Until recently I couldn't figure out why the DJI flew so stable. Then it dawned on me that most people flying with DJI gear are using the GPS or 'GPS lock' even while taking off and landing. With the APM the Stabilize mode is probably equivalent to the Manual mode in the DJI. So basically we were comparing GPS assisted flight with Manual flight.

Taking this further I started talking with the developers of Ardupilot about the differences and sure enough they are adding the ability to take off and land in GPS mode but..... the general consensus among experienced pilots is that this is a very bad idea because GPS multipaths low to the ground and just isn't that reliable. As the conversation turned more and more about GPS I became very worried about ever flying in a mode that uses GPS. It seems there are quite a lot of reports about GPS skipping or errors that make your copter believe it's somewhere else so it does the right thing and rockets off to get back to where it think it should be.

For now, I'm going to just avoid GPS as I've had a couple of copters decide to take off on their own for what appeared to be no reason. My advice to the author of this thread is to try flying manually to see if things improve. For now I'm choosing to believe that GPS is a lurking evil out to get us all. Happy to be proved wrong.

 

[DennyR]

Interesting comparison as I have more or less stopped using GPS during any filming. I have some craft that have both stabilsed and FPV cameras fitted and I have noticed that even though the model may seem to be really tightly locked-in, the footage reveals that atti. mode is actually more stable. In the interests of saving weight I have stripped out the GPS units. My most stable small quad has nothing more than a tiny Afroflight32 controller from Time Cop. It's been taking abuse now for a couple of years. Before rushing out to get one, this is not as straightforward as a DJI, so expect to do some work.

 

[Benjamin Kenobi]

Why would you think GPS would be more stable for filming anyway. I think a lot of people make that mistake. All those constant little corrections work your gimbal hard. Even ATTI does that. Manual it's all your inputs so it can be as smooth as you like.

 

[DennyR]

Why would you think GPS would be more stable for filming anyway. I think a lot of people make that mistake. All those constant little corrections work your gimbal hard. Even ATTI does that. Manual it's all your inputs so it can be as smooth as you like.

There are some inspection tasks that are a lot easier when you have a precise position hold, Such as working close to the target from a distance and when a gust of wind may catch you out. If ones depth perception is challenged due to difficult locations then GPS is the best option. I sometimes have to work closer than 4 feet when I am 150 feet away. One mistake and you go down. When you are working from a boat that is constantly pitching and rolling it effects your inner ear balance mechanism and can impare your ability to position the craft. It is a different world from flying with your feet on the ground.

 

[Benjamin Kenobi]

You have now changed the subject. Make up your mind.

 

[ProPilotWannaBe]

We are also quite off-topic...

 

[Benjamin Kenobi]

There are so many of these topics and they are rarely resolved. New build. Lost heli. Blame manufacturer. That's the nature of forums.

 

[aForcefulThrust]

After the success of my initial test flights and breaking my batteries in, I was ready to perform my first duration test of my copter using a pair of batteries. I hovered my copter approximately 60’ in front of my house and 60’ above the ground while monitoring its performance and data, along with running a stop watch to test the duration. I successfully landed the copter at approximately 18:30 without any performance glitches. I then hooked up my second set of batteries to perform another duration test. My copter was hovering without any problems and the data was showing me that my batteries were at about 14.6V at about 16:30 into the flight. From the time, I knew that it was almost time to land my copter as its electronics were also getting close to the first low voltage warning set at 14.4V. Suddenly without any warning, my copter began to rotate counter-clockwise and accelerate to the right and would not respond to any of my control inputs. I tried flipping my fail-safe control switch to regain control of my copter and make it automatically return to home. The copter did not respond and continued on a trajectory that took it 200 yards over the top of some nearby apartment buildings at which point I lost sight of it, but it appeared to crash into the lake. I was devastated.

I had a similar crash to this one about a month ago. During this flight it was flying very well, just like it always did. No hiccups or signs of anything out of the ordinary. I tried POI mode out for the first time and it worked beautifully. Towards the end of my flight, just flying around in GPS-ATTI my hex began to spin uncontrollably, very fast. It seemed to spin in one spot, still holding position. The spinning got faster, and faster, it was so fast it was impossible to tell the orientation of the hex (faster then if you were holding 100% yaw on the stick). At this point, I was thinking "Oh **** what can I do". I flipped on IOC in home-lock mode to try and bring it back to me. Around the same time I did this is when the craft started to wobble a little, right before it flipped upside down and flew into the ground. All that happened in a matter of about 10-20 seconds. Looking back at it, I should have maybe gone manual mode and tried to stop the spinning, or just throttled down and landed where it was.

I got my WKM about 12 months ago, and had a faulty GPS unit. Got the GPS replaced before I ever flew with my WKM. I flew probably over 100 flights on my hex and it flew fine, never any problems. Before my crash I had updated to 5.24 firmware, and set up a channel to use POI and IOC modes. I did a quick hover around the house with the new FW, and everything seemed to be fine, even flew more stable I thought.

I'm still also at a loss, and can't figure out why my hex crashed. except maybe it was a firmware issue.. I will be going back to an older firmware before I fly again.

 

[Cornforth Images]

aForcefulThrust



Thanks for all of your information. I upgraded my firmware before I started test flights. I got 1.5 hours of stable flying in GPS & AT mode while also testing IOC Course Lock, but mostly flying with IOC Off. Perhaps my GPS was faulty, but how will I ever know now that my copter is at the bottom of the lake? At least I am getting a bit more info to back up my credit card dispute of charges. I'm not yet sure what kit I will rebuild, but I will use NAZA or SuperX on my next copter.

 

[ProPilotWannaBe]

I had a similar crash to this one about a month ago. During this flight it was flying very well, just like it always did. No hiccups or signs of anything out of the ordinary. I tried POI mode out for the first time and it worked beautifully. Towards the end of my flight, just flying around in GPS-ATTI my hex began to spin uncontrollably, very fast. It seemed to spin in one spot, still holding position. The spinning got faster, and faster, it was so fast it was impossible to tell the orientation of the hex (faster then if you were holding 100% yaw on the stick). At this point, I was thinking "Oh **** what can I do". I flipped on IOC in home-lock mode to try and bring it back to me. Around the same time I did this is when the craft started to wobble a little, right before it flipped upside down and flew into the ground. All that happened in a matter of about 10-20 seconds. Looking back at it, I should have maybe gone manual mode and tried to stop the spinning, or just throttled down and landed where it was.

I got my WKM about 12 months ago, and had a faulty GPS unit. Got the GPS replaced before I ever flew with my WKM. I flew probably over 100 flights on my hex and it flew fine, never any problems. Before my crash I had updated to 5.24 firmware, and set up a channel to use POI and IOC modes. I did a quick hover around the house with the new FW, and everything seemed to be fine, even flew more stable I thought.

I'm still also at a loss, and can't figure out why my hex crashed. except maybe it was a firmware issue.. I will be going back to an older firmware before I fly again.

Can I ask why your first inclination is to think its the firmware? Sure, it's the one thing that changed, but there are other factors.
Have you checked all the ESCs, motors, solder points, props? Did you happen to have a data logger? (Like the iOSD.)

 

[aForcefulThrust]

I think it's the firmware because it's the only thing that changed, and I haven't found anything else that I think could have caused this. All motors spun up after the crash, and All ESC's worked after the crash except one, that was obviously broke in the crash. I'm not an expert on brushless motors but I do think it's possible to have a bad motor with a short in the winding's and it won't show itself until the motor is under a load. So I haven't ruled that out as a possibility either.. Im changing out all motors. I use CF props and I always give them a good inspection for cracks and nicks before any flight, so i'm confident the props were fine. Before I fly again, I will be strapping my hex down and giving it max throttle for a few packs to check the temperature of all my wires and for good solder joints. I don't have a data logger but that may be my next investment.

I have a smaller Y6 I fly with naza, and have also never had any issues with it. I would recommend naza as a cheaper alternative. Overall I would say i'm satisfied with DJI's performance, I love the way both of the crafts fly. Just this crash I can't explain has really has shattered my confidence in flying. You never know when it will bug out on you and could hit someone or something. I even had a sheriff watching me fly when this thing crashed lol.

 

[tombrown1]

The crash described by the op sounds very much like an esc being programmed for lipo failsafe. This means that your esc will automatically shutoff when you reach a certain voltage. You don't want that. Whenever you set up a new mr you need to be sure to program all of your escs. I'm not sure whether the stock s800 escs are pre programed or not.

Also don't use the wkm battery failsafe. Use a timer and a lipo alarm.

Learn how to fly in manual mode, preferably with a cheap toy quad.

Be sure to only use firmware that is known to be stable. The latest that I know of and use exclusively is 5.16.

Sorry for your loss. Good luck.

 

[Cornforth Images]

tombrown1

Thank you for your information. I am new enough to flying copters that I am unaware that I need to program and test my escs. How do I do that? Why would my dealer not tell me that I needed to do this? Perhaps this explains my recent flyaway, but I'm not sure that is what happened with my S800 in the Arctic.

I've read a few threads about not using the WKM battery failsafe. Good thing to know now, but too late? I was also running a timer during my recent flyaway as well as using a LiPo alarm that told me that I had more voltage than the Wookong iOSD was reporting.

I am definitely going to learn to fly in Manual going forward. I did not realize that firmware updates could also cause a crash, but I will be more vigilant going forward with my next build.

I am very grateful that neither of my flyaways caused any property damage or injured anyone. All I want to do is take a copter out in nature to take some beautiful pictures. Anyone flying one of these things around crowds seems to be asking for trouble.

 

[tombrown1]

You can start here:
http://www.rcgroups.com/forums/showthread.php?t=1874616

Not sure about s800 escs. But most every other esc should be programmed according to the instructions in the esc packaging.

Iosd is great. Don't run your lipos any lower than 3.5v per cell IN FLIGHT. That will be about 3.7v resting. Set the lipo alarm at 3.5.

You should know that this industry is in the Wild West stages. Things do not always work the way the packaging tells you it should. It is imperative, though very tiring, to read on these forums about the things the manufacturers don't tell you.

You may have a really old GPS - what fw did the wkm ship with? You could have had excess vibrations reaching the imu from the infamous s800 frame. It's possible you have the very old escs that were defective for s800.

It is a bit overwhelming what you need to know to do this reliably and safely- that is why ver few people do this at a high level. It is, however extremely rewarding if you have the patience.

Best,

Tom

 

[Cornforth Images]

tombrown1

Thank you for the link about the ESC programming card. Definitely the first time that I have ever heard of it. I'll be ordering one when I order my next kit.

I had my iOSD set to alert me via the WKM app to the default settings using a 4S LiPo. I did notice that my battery alarm was not showing as low voltage and it was set to start beeping at 3.5V.

I bought my Wookong & S800 in late June as a promotion. I only upgraded to the 5.24 firmware when I rebuilt with the new kit 2 weeks ago. I did purchase the vibration kit for my IMU, but on my new hexacopter I attached the IMU directly to the main body.

I do understand that this industry is much more disorganized than I had estimated when I bought and purchased my Phantom in the spring. I travel all over the world, especially to photograph marine life like whales, sharks, and dolphins. I can envision some unique new images from an aerial perspective that I won't have to worry about too many other photographers repeating any time soon. However, I definitely under-estimated how much effort this would require. I've got probably 400 hours into researching, building, flying, etc since I started this and I am still learning every day. It is definitely overwhelming, but I am determined enough to keep trying. The photography business is not what it used to be, so I am constantly trying to push my work to a new level, but it's going to take me a while before I feel confident enough to start flying from a boat. Wish me luck.

 

[aForcefulThrust]

tombrown1

I am very grateful that neither of my flyaways caused any property damage or injured anyone. All I want to do is take a copter out in nature to take some beautiful pictures. Anyone flying one of these things around crowds seems to be asking for trouble.

Yes It's a very scary thought to think about your heli flying into someone. I thought my heli was rock solid and got pretty confident flying it around people. I'm very lucky my crash did not hit anyone or anything, and I will not be making that mistake again. Even if you're flying far from people, it's possible in a flyaway your heli could travel a long distance and still hit someone :/ This has shattered my confidence in these machines.

ALSO i'm sure s800 esc's come pre-configured and do not require any programming. That does not explain that crash...

 

[Quantumlight]

Sorry to hear that you had so much bad luck!

In the DJI manual they say that the GPS don't work as it should above the polar circle.

What I noticed where I live I have dodgy gps reception for some reason and I can see that I go from green to three red blinks (naza) and all between sometimes really quickly and the way the multirotor reacts is that the same position moves sometimes really far so it shoots of in that direction. Scary every time but I learned to compensate. Also sometimes switching to ATT and M. I don't know if you have but practice allot to fly in M mode it might save your day sometime.

But as you also say sometimes you like loose all reception to the multi-rotor it happened to me once.
During this short time I did three things. First compensate in GPS mode. Then Atti and Manual.
http://youtu.be/bV2bbzDe1mw

 

[mbsteed]

Not sure if anyone else has mentioned this... didn't read the entire thread but don't test your ships in your driveway or anywhere near built-up areas (you mention the ship flying out of control over an apartment building). Go to to a rural location with open fields for obvious reasons.