jon@thefullers. Posted at 2015-8-10 16:26
No scab here to pick, I, more than anyone would like to know the cause of my loss of control.  Howev ...

I can only say again that my intent (or feeling) is not one of superiority. I suppose the polite thing to do here is apologize for the way I write.

I'll try to be as succinct as I can given the subject matter:

- Jon is 100% correct in his other thread: horizon drift in the gimbal is an indicator of calibration issues (specifically pre-takeoff). If your horizon isn't level on the ground, don't take off. In Jon's video you can see this pretty clearly along with movement / judder in the gimbal that doesn't seem related to the motors CSC'ing. All alarm bells.

- The reason why is because DJI copters have multiple IMU's. The gimbal has it's own and the flight controller has it's own. The flight controller sends it's data to the gimbal controller over CANBUS and the gimbal controller combines it's own IMU data with the flight controller IMU data (as well as stick input data) to compute stability and drive the gimbal motors.

- As an aside you can see that the two systems have direct interaction for yourself: start your Inspire 1 on a level surface and without starting the motors bank the roll stick left/right. You can see the gimbal roll in anticipation of an orientation change, the slowly drift back to level as it it begins to understand (based on the IMU data) that no level change has actually happened.

- When you start up an Inspire 1, the LED code does a quick green/yellow alternation. This is the flight controller "warming up". Part of this is that the flight controller quickly calibrates the IMU to level and then combines it's "warmed up" understanding of level with the IMU calibration it has saved (as part of the "calibrate IMU" procedure you do in the app). If the flight controller IMU is in any way in motion when this warmup phase is occurring you can have issues.

- Incidentally, this is what the "MOD" is - the difference between the warmup understanding of level (or direction in the case of the compass) and calibrated understanding of level (or direction in the case of the compass). This should also explain why Jon started up his Inspire 1 after his incident and didn't see problems with the MOD values - as long as there was no damage and he started it up on the bench cleanly, there probably wouldn't be.

Based on Jon's video there are also some good best practices that were missed: low hover before you fly to verify a lack of drift, TBE, etc. This way you can put it down quickly if you have to. Jon indicated that he felt the takeoff area was a little tight so he tried to get altitude quickly but in general if it's safe enough to fly it's safe enough to hover at a couple of metres and ensure the aircraft is responding and behaving as expected before you add altitude.

Also, remember that it's always acceptable to intentionally bring your copter down hard if the alternative is uncontrolled flight. Better for you to lose your Inspire than someone else gets a 15" rotating carbon fibre blade turning at thousands of RPM's to the face.

To be fair, a lot of this is in fact DJI's fault in the sense that they're increasingly writing the manuals for their RTF products (Inspire 1, Phantom) in such a way as to obfuscate the way they actually work in favour of creating the illusion that these are not things the operator should / needs to understand.

SimonMW Posted at 2015-8-10 22:49
Jon, there are many things to consider.

Did you check your flight zone for potential interferences  ...

None of the things you say to check for will actually cause any interference with the possible exception of solar activity and maybe in a very rare case depending on what they were using, other rc traffic. Not an expert on how the signal works but I've seen 10+ people flying phantoms and inspires at the same time with no issues.  Now with only 8 video channels that would no longer be possible, you could still technically fly but you would have video problems.

SimplePanda Posted at 2015-8-11 01:00
I can only say again that my intent (or feeling) is not one of superiority. I suppose the polite t ...

That's a great, and very informative post, thank you.

I'm still unsure, should I be back on the same beach location tomorrow , if I would attempt a 2m hover to ascertain safe flight, as there were a few people about, and it's very, very sudden desire to travel at nearly 40mph (out of control) at head height on a populated beach really could have been nasty. I think in this particular case, with it high, fairly quickly, I was in much greater danger of losing it in the sea, or crashing into the cliff, than hitting someone. Anyways, for me, understanding the operating system some more is great, and I thank you. (I've witnessed the gimbal behaviour you speak of, anticipating aircraft movement with stick input and figured this is a vastly complicated setup).

I've flown a fair bit since the incident, including a fair bit of ATTI mode flying inside a warehouse, backing out through open roller shutter doors and pulling up, and it hasn't missed a beat, but as stated before, I now start the bird, and once it's finished it's startup procedure, I religiously  rotate the gimbal from stop to stop and check a level horizon throughout before starting the motors, I strongly believe this is a very good indicator of a healthy bird (or should I say glitch free session).

Jon

Quote:

"Getting that thing out of GPS mode when the sensors are all over the place should be one of your first reactions"

I take on board your comments, but I honestly don't think removing GPS from the equation here would have made any difference.

As I see it, it thought it was level, when actually, it was tilting at probably 20 degrees, this thing is gonna fly in the direction of that tilt, fast, regardless of GPS/ATTI.  It sounds to me like my big mistake, was not noticing the way off level horizon prior to flight.  Lots of stuff wasn't right about the inspire on that flight, and it appears my user error was mostly in the pre flight stage, not noticing stuff, doing every check etc. But as I said, this thing had flown so very well, for so many flights (every one I've done) that it obviously lulled me into a false sense of security, coz they do sometimes have a brain fart, for whatever reason.

Jon

This is a tough crowd for sure.  forgive me, but this is my first post here.  I am the type of person who readily admits mistakes.  In fact, over a year ago when I owned the Phantom 2+, I did something stupid and crashed it.  I came down too quickly and by the time I tried to reverse or stop, it was too late.  Thankfully no damage was caused.

I then accidentally hit the side of my hot tub when attemtping a landing (my backyard is not the straightest and it would tend to tip upon landing).  Well, after it hit the hot tub, it landed on the concrete below and broke the camera off the gimbal.  I sold it on a photography forum for a very cheap price and full disclosure.

Fast forward a year and I purchased the Phantom3 Professional.  I've not had any problems that were not caused by me.  I STUPIDLY acted like a little boy experimenting, glued my GoPro to the top, thus obliterating the GPS signal, flew it and it flew away.  MY FAULT.  I admit it.  No question.  Dumb, idiotic, moronic.  

That same night someone knocked on my door and said, "I have your drone."  I was shocked.  it landed in a maple tree in his tree nursery about half mile away.  He took out the card from the gopro, reviewed the footage, recognized my house and the route I live on, and returned it along with the gopro.  I gave him a handsome reward.  Lesson learned.

So all of the above seems to be off topic and for that I apologize in advance.  But it's not.  Why?  Because when I F up, I admit it.  But when I follow all preflight checks and the drone, in this case the I1, stops reacting to the sticks, something is wrong.

In the few hours between losing the P3 and recouping it, I ordered an I1.  Even though I got the P3 back and could've canceled the order, I wanted it.

So I get the I1, update the firmware before flying on the craft, the controller, and all 3 batteries I have.

I flew over the next 2 weeks every day with no problem whatsoever, probably over 20 times.

One day I'm in my backyard, where I had always flown it, did all the preflight checks, and began to fly.  It was about 30 feet from me and all of a sudden I could not control it.  it started to fly on it's own and thankfully crashed into the grass.  No harm done other than a grass covered lens filter.

I have/had no idea why that happened.  Next evening I flew it again without incident.  That continued for the next two weeks or so.

I then took it to a park about 20 miles away.  I went through all preflight checks.  Compass calibration, 17 satellites, and took off, flew up and over 3 baseball fields (the park was empty, no people at all), flew over an outdoor running track.  Nice open area to get some nice practice and handling in, nice sweeping turns, sharp turns, no problem whatsoever.

Back home flew it again a few times without trouble.

Back to the same park and I'm hovering about 100 feet up, about 50 feet back, fliming a backhoe tearing down a small one story bldg.  I was getting great video.  And I was far enough away that dust from the site was not an issue.  After filming that for a few minutes, I went up to about 150 feet and once again flew out over the ball fields (also tennis courts), the track and the parking lot I was standing in  I was probably in the air for about 10 minutes, at least 50 percent battery left (I was using the higher capacity battery I purchased separately), and I decided it was time to land.  This was actually behind the gym I go to and I was going to workout.  I began flying back to where I was standing to land.  When the I1 was no more than 50 feet away, perhaps 30 feet up, it once again ceased to accept commands from the sticks.  It immediately started to fly backwards and hit a tree amongst a thousand other trees.  I ran over 50 feet or so and looked up but couldn't see it.  I looked and looked.  (I could still see the camera's view, but it was just showing leaves.)  

I did not know if it was in the tree or had fallen to the underbrush below.  It all happened so quickly.  My only option was to try revving the props to see if I could hear it.  Well, hear it I did.  It was indeed stuck in a branch about 30 or 40 feet up.  I contemplated asking the driver of the backhoe across the parking lot to come shake the branch but didn't as I was just filming him and I figured he may not have been too happy about that. (turns out I saw him a week later, is a good friend of a close friend of mine who is a builder and said had I mentioned my buddy's name, which I never would have thought of doing, he would have driven over in a second to get it down for me.)

So my only option was to rev the props.  Two were stuck, two were spinning.  After about 20 or 30 seconds it cut its way loose and fell to the cushioned underbrush.  But the two props that were stuck smoked out.  A long puff of smoke rose up from them just before it came down.  Two engines literally melted off.

I contacted DJI and told them the exact situation I recount above.  It is 100 percent gospel, exactly what happened.  I took and take full responsibility for burning out two engines, but it was the only way I could retrieve it after it flew away inexplicably.

DJI sent me a return label so I did not have to pay shipping which was very nice of them.  I am waiting to hear what they find.

I've learned long ago that just becasue something has never happened to me, or you, doesn't mean it hasn't happened to someone else.

jon@thefullers. Posted at 2015-8-11 06:58
Quote:

"Getting that thing out of GPS mode when the sensors are all over the place should be one of ...

You would be correct in your assumption re: ATTI vs. GPS.  

ATTI mode means a lot of things on DJI controllers but the unifying theme is that ATTI always means the IMU (and compass if the copter has one) gets used to maintain level flight and the positional inputs (GPS and/or the visual systems on the P3/I1/M100) are ignored. In ATTI, the copter will stay level and hold altitude and heading but the wind (or even the prop wash if you're flying low) will drift it.

Great for nice smooth tracking shots. Not so great for dealing with IMU issues. Where it's useful is if you suspect you're not going to have reliable GPS signal.

As a total digression...

What DOES help on NAZA / A2 / WKM copters is "manual mode", where the copter is basically ignoring sensor data and you are correcting for all drift in realtime. This is a highly recommend (and incidentally, extremely fun) skill to learn if you have a copter that offers this mode - and as an added bonus it can save your bacon because you can fly it even if the IMU goes insane.

The Inspire 1, alas, does not have manual flight mode as far as I can tell - though given that it's camera is gimbal stabilized it doesn't make much sense anyways so I haven't really looked. Flying in manual mode through a gimbal is probably not impossible but I'm certainly not going to bother trying it with $3k worth of my own aircraft. ;p

mdjak@aol.com Posted at 2015-8-11 07:23
This is a tough crowd for sure.  forgive me, but this is my first post here.  I am the type of perso ...

Will be interesting to hear what DJI says. Do you know what FW version it was running?

Before 1.2.0.3/6 there had been a few reports of loss of stick control. These firmware versions introduced changes to the radio code (most notably they reduced the channel selection for North American copters as I think they were mistakenly using illegal channels before that).

mdjak@aol.com Posted at 2015-8-11 07:23
This is a tough crowd for sure.  forgive me, but this is my first post here.  I am the type of perso ...

Hey mdjak, I don't usually respond to these type of threads, but I appreciate your honesty.  

I hope everything works out for you, DJI will be able to tell what happened from your logs and inform you from there.  I would suggest you keep flying, you seem to be a positive person and learn from your experiences.  Keep using the sim when you can't fly outside and increasing your experience level.  I have been in RC for 30+ years and experienced a number of things so I am somewhat jaded when I read about "fly-aways".  In my experience, a "fly-away" today is generally the lack of experience and control when something bad starts to happen.  When I was young and inexperienced, I was asked by my father to take his pickup truck full of chickens to be butchered.  Lucky me, I thought.  Headed out, and the road was wet and full of water, I was driving faster than my abilities and lost control in a large puddle, then sadly over corrected the steering in a skid and went into a very deep ditch.  Knowing what I know today, I could have easily prevented that accident by driving more slowly or more importantly, not over correcting when something bad started to happen. I was at fault, but my inexperience didn't help.  Flying is very similar.  These are very complicated pieces of equipment that can lull the inexperienced pilot into attempting things they should not, or in the very least - simplify flight to the point that anyone thinks they can fly, until something starts to happen that exceeds their ability - at which point most yell it just flew away!  Some fly-aways in my experience are when the craft (and/or person) become disoriented, that is to say it is responding to commands differently than what you expect.  If you were able to break it down second by second, you might see the orientation of the craft in the persons mind (or with a compass error, in the mapping window) is different than the actual orientation of the craft in the air.   Left is now forward, back is now left.  Experience is what allows your mind to immediately adjust accordingly, quickly check your controls, adjust what you need to, and fly it home.  It has happened twice to me in the last 3 months with different test equipment.  Once was my fault for launching from an area with heavy magnetic properties.

My story is simply that there is no substitute for experience and I am glad that you have a positive outlook, hang in there and gain that experience and I think you will be a great pilot one day.   Hope your I1 gets returned quickly.  

I'm pretty sure it doesn't use the compass in atti mode. Why would it need to know what direction it's going when you control all movements? That's why switching you atti from for will save you from compass error erratic flight. If I'm woo

If I'm wrong I'd love to know what function compass serves in atti. Im pretty sure only imu is used to control level flight and altitude, neither of which can be determined by a compass afaik, lol

So I first appreciate the replies and kindness.  I wanted to return to this thread.  It's been about five weeks and I received an email update from DJI.   It did not indicate what if anything they found wrong but did say they are replacing it with a brand new craft as a one time courtesy.  It should arrive next week.  I don't know if it will come with an explanation of what they found.  I've been practicing with my Phantom 3 professional in the meantime without incident.  I'm updating the firmware on it now.

Thanks again.
mark

No flyaway here, just make sure you calibrate IMU , calibrate compass and never, ever take off unless the battery is fully charged .

Good here..  Just fly and enjoy your Inspire 1. Feel good about it and have fun.

Rich

dji products tend to fly away i heard.
i always thought pilot error
but then this happened

Never had an issue......
I guess there are tens of thousands of flights across the globe every day.....the only ones you hear about are the bad experiences, not the other 99.9% of good ones