Hey folks!


Yesterday I had my biggest, worst and most scary crash with my 3DR Quad.

Our local firefighters had an open day for public and presented their equipment, did some presentations, they had a jumping castle for the kids, BBQ and beer for the bigger ones.

A friend of mine who is always acting as a spotter for me when doing video flights planned to do some aerial footage of the place and in a second flight film the firefighter team during a car rescue.

So I picked up my quad with full loaded batteries, pre checked everything in my office and went to the starting locations. Here I powered the quad up und waited to get a GPS lock. I didn't need the GPS, but I just wanted to make it absolutely right, because I would be flying over a crowded place.

So after 2 minutes of patience I had a stable GPS lock, made sure I had the right flying mode dialed in, in this case I used stabilize with simple mode, so I could concentrate on the flying location while my spotter would give me advises how to align the camera.

A quick spin up test, everything was fine, so I took of, stabilised the copter in mid air 2 meters from the ground for a couple of seconds and pulled the throttle up to get some height.

First position was reached (no mission, no fpv, just plain odd manual control) so I headed to the second position and yawed the copter 90 degrees to the left. After the yaw I felt the copter beginning to drift a little so I pushed him backwards towards me and reverted yaw so the copter looked away from me.

I wanted to fly back to me whitch meant backwards for the copter but the quad started to lean more and more forward. I had fully deflected the stick backwards, but the copter would not come back, ist slowly increased pitch for some reason.

Because of the kids and the people under the copter the only way to recover safely from this situation was to apply throttle and let the copter drift away over the firehouse, keeping it in the line of sight until I could be sure it was over the building towards free space and then shut the motors down.

The result: most important: nobody injured, for gods sake!!!

2 Motors broken

2 arms damaged

GPS unit destroyed

IMU shield defective

maybe more to come, I didn't disassemble and tested everything right now

I have absolutely no clue what happened! So any help in order to understand what went totaly wrong would help!

Greets

Marc

P.S.: Board Version 1.4, Quad with 850 motors, all settings to stock, Firmware version 2.7.1

Views: 6701

Attachments:

Reply to This

Replies to This Discussion

I've broken plenty of props on bad landings. I've also crashed before. It was my 20th flight.   I moved every switch I had set to see if I could gain control.  My copter fell from 30 meters, luckily, it veered into a ponderosa pine tree which broke its fall and the only damage was a couple of broken props and a landing foot.  It turned out to be a faulty cell in the LiPo and The quad lost power intermittently.  I was certainly not afraid to try the capabilities of the APM to save my quad.  I have no doubt that had you had more flights with your quad, you would not have been afraid to touch the only things that have a chance of changing the situation at hand.


I agree about bug and error notification.

Tony,
sorry but I have to disagree. All of what you are saying is correct, I would have tried every switch to gain control again, but not with the crowd the copter was moving at.
I had enough flights to know the capabilities of the copter and of me as a pilot. If it gets to the point where someone could get injured, there are no more possibilities.
This could have happened on the airfield, too. What would you have done if the copter began to move against the visitors and no switch would have worked? You loose time the longer you try to save the copter. A copter is nothing, just money. Don't think of it, think of the health of the spectators watching.

Marc,

I agree with what you did.  I've said two or three times that you did an excellent job of avoiding the crowd.  On the crash on my twentieth flight, I wasn't around people.  I wasn't familiar enough with the hardware yet to fly around people.


I'm comfortable enough with my current setup to fly around people.  If something goes wrong, I'm comfortable enough with all of the modes that I fly to at least try to save my craft.  Time does play a part. I wouldn't risk the health of people over saving my craft.  However, I will spend enough time flying alone so that if something does happen around people, I won't panic and be afraid to touch the controls.  What would have happened to the people around you if your craft suddenly dove towards them?   I was using your quote to show the fear you felt.  Someone even detected it in your writing and told you to breathe.


I

Hi Marc

I looked at your video, and your log file using APMLogVisualizer 1.34, and I've determined that your roll but mainly pitch sensors failed mid flight.

I wish you had logged your motors, you need to turn them on using the CLI, but even without that data, Ervine was right in saying that the roll/pitch was one way, and it was flying the other.

I suppose it could be a fierce wind that would do the same thing, but I see no evidence of that anywhere else in your video.  

So to summarize, after you pulled it back toward you, it starts moving away from you.  At that point the log file says you're pitched backwards, and in fact, looking at the video, you're pitched forward.

Dan Gray

Tony,

please let me quote and comment what you have said in your last post:

I agree with what you did.  I've said two or three times that you did an excellent job of avoiding the crowd.

Thank you again.

On the crash on my twentieth flight, I wasn't around people. I wasn't familiar enough with the hardware yet to fly around people.

Good decision, this is what I have learned. I was comfortable with my current hardware setup, but I should have tested the software a couple of times more.


I'm comfortable enough with my current setup to fly around people.  If something goes wrong, I'm comfortable enough with all of the modes that I fly to at least try to save my craft.

Sorry (or glad) to say that, but this is theoretical thinking, because you did not have been in this situation. You would REALLY try to safe your aircraft FIRST?

Time does play a part.

I absolutely agree. If the copter is high/far/uncritical enough, thats for sure the first thing to try. Get the beast stable and then move away and land.

I wouldn't risk the health of people over saving my craft.

Two sentences above you said the opposite thing?

However, I will spend enough time flying alone so that if something does happen around people, I won't panic and be afraid to touch the controls.

As every crash/misbehaviour of the copter is different, you simply cannot say how you will react and how the copter will react to your tries of saving the situation. What if changing the flight mode makes things worse? You lost important time! Would you really do this?

What would have happened to the people around you if your craft suddenly dove towards them?

Well, it probably could have seriously injured someone. What would your copter do to people if he would dive into them? Any difference? For sure not.

I was using your quote to show the fear you felt.  Someone even detected it in your writing and told you to breathe.

Believe it or not, but during the misbehaviour of my copter before the crash I was not in panic. I was clearly thinking and deciding what to do to save the situation. It was my decision to pull over the crowd and than ACTIVELY crash/destroy the copter.

The fear came about 1 hour later when I was realising what could have happened if I would not have crashed the copter. This is what you quoted.

So at the bottom line what do you want me to tell? That you would have saved the copter? Glad to hear that. I did not, I preferred to safe the health of some people in the first place.

As long as you cannot analyse the cause of the crash/misbehaviour of my copter, I beg you to continue our conversation over pm's if you wish.

Right now I am dissasembling the copter and checking the discrete parts and will post my results soon.

Regards

Marc

.

Dan,

thank you very much for spending your time on this.

In the first place, I was convinced by the analysis of Jason Short that a init bug inside of the apm caused the crash, as the copter did not read out the magnetos settings correctly. I did have the time to take a look at the logs using your neat little tool and came to the same conclusion like you did.

The copter did not change its "virtual" orientation as the heading error did sum up, it began to drift and lean on the pitch axis.

As the copter crashed the board got disconnected from the lipo's so the log files stopped. But at the end of the log files you see some sinus waves of the sensors, which means - if you compare it to the video - the sensors went mad because the copter rotated along the z-axis, not along the x or y axis.

I just connected the board to the mission planner and I when I knock softly on the sensors, the wild spinning begins immediately on the artificial horizon.

Anyway, I am just about to dissasemble and every single part and will post the results shortly.

With kind Regards

Marc

Ok, it's time to get things to the end and come to a conclusion.

I have checked every singe component of the copter and found nothing except that the sensors on the IMU are not working correctly. Could be due to improper solder connections or a defect of the sensors themselves. Take a look at the video, than you will se what I mean.

And here comes the rest of the stuff.

First, the copter himself.

The motors.

The GPS. It has been torn off the copter and laid about 2 meters away.

A closer look on the arms and the screws, pretty much force must have been used "redesign" them.

And last but not least the charging state of the lipo cells.

Conclusion:

As the board shows odd behavior, it probably could have been the source of the problem. The variant from Jason, the dcm init error is plausible, but a closer look from Dan with the log visualiser shows that the yaw calculation seems ok. And, as the copter started to "lean" i pulled back, which was the exact opposite direction it was leaning to and orientated. So the yaw error must have been nearly 180 degree, summed up from two turns in the opposite direction.

If it's the sensors on the board and they werde not soldered properly, they could be resoldered. If not, the IMU would be the most expensive part, relative to the arms and the motors.

Your video seems to show exactly what might have gone wrong, somehow in mid flight the sensors stopped working as they should and the inputs you did to try to stabalise the quad would have been to no avail as it would be impossible to fly in stabalise mode (acro maybe?).


Now the issue is why would the sensor stop functioning properly in such a dramatic fashion, a short perhaps? Maybe a stray wire or drop of water landed where it shouldn't have?

Well why the sensors failed will be difficult to find out. I can definitvely say it was no moisture/water, nor was it an unisolated wire. I build all my electric stuff very carefully, no open wires anywhere.
The failure could have been due to some earlyer crashes, the g-forces during a drop are pretty high, that could have ripped some of the solder joints loose.
I remember my dad used to test electrical components on a vibrating platform, to make sure nothingnwas loose. Maybe I should consider to build one and use it for future parts.
Does 3DR check the boards against vibrations?

The DCM uses the compass to nudge the Z gyro back into perfect alignment. It takes time and works very slowly. The Z gyro is very good, but drifts slightly over time for numerous reasons, but this is true in all systems.

The compass data is run through a small gain filter and added to the Z gyro solution. This keeps the noise from the Compass data from hurting your Yaw.

The key thing to keep in mind is the idea that it takes 20-30 seconds for a major change in the compass to finally nudge the DCM Yaw solution to a new solution.

The DCM was initing to 0 in the rev of code you used. When you took off it did not have enough time to nudge the Yaw to the correct heading. I saw at least 30° error on the yaw in your logs by measuring the buildings from your video. This bad heading was saved at arming as your simple mode reference heading. The Yaw error was compounded as you took off due to high current interfering with the Mag.

If you're calibration isn't great it can effect you a lot. I believe this made up for the rest of the difference. Once that happened your pitch was now your roll and vice versa. Pulling back made it roll and correcting the roll made it pitch forward. 

Ive had this happen to me 3-4 times over development and testing. There was a very old bug that went away after Tridge rebuilt the DCM that was a spontaneous rotation of Yaw. That would do the same thing. If you could catch it you could rotate your body to get a better reference to forward and bring it home. 

If you're not expecting it, you won't see it as a Yaw bug in the air and correct it. It's best to let go of the sticks, then push forward and see where it's going. Then rotate your radio to align with the new orientation and bring it home immediately.

Jason

Hello - I have some questions on  using Mission Planner with SITL:

1) Is it possible to maneuver the copter manually as you would with an Remote Controller ?

2) How would I use SITL with my own customized copter  build or a beta version of a

copter build ?

Robert

Reply to Discussion

RSS

Groups

Season Two of the Trust Time Trial (T3) Contest 
A list of all T3 contests is here. The current round, the Vertical Horizontal one, is here

© 2019   Created by Chris Anderson.   Powered by

Badges  |  Report an Issue  |  Terms of Service