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

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Hey Monroe,
I will post a full set of pictures of the copter, assembled and disassembled as well, the logs are attached in the original post.
I am not sure if we will find the real reason because the imu seems to be damaged due to the crash. Or it was the reason of the crash. Whatever, I will check every single piece of the copter.
Marc

I've reviewed the logs here for about an hour trying to piece together what happened and I think I know now.

When you armed, the actual Yaw was incorrect. It was about 20° off of the true Yaw value. The DCM inited at zero and should have inited at the Compass heading. This has been fixed in 2.7.2 and caught a few testers off-gaurd as well. It was fixed right away after we pinned down the init issue.

The Yaw seemed to drift again in flight leaving you with an incorrect Yaw. I believe this happened when you Yaw'd back and forth quickly. This can happen if the Magnatometers aren't fully calibrated or the calibration isn't right.

Then your roll and pitch became partially transposed due to Simple mode having the wrong yaw and the magnetometer induced yaw drift. The hard left roll you were inputting was becoming pitch forward. 

You may not have noticed since you attributed it to Gyro drift. In fact the quad was under full control the entire time.

I lost a few under similar circumstances in the past. I've gotten pretty good at checking mid flight for Simple mode yaw issues by doing quick check of pitch and roll to verify all is OK in the air. It's a shame it happened to you and I'm sorry to hear about your crash.

Jason

Hi Marc, i'm sorry about your crash, I advise you to not fly over people with four engines, is already risky to do it with 6 or 8, but with 4 chances that something nasty happening increase greatly, if you lose an engine in flight you half mad that falls swinging wildly.

A killswitch would have lead to a fatal ending. It should always be in the decision of the pilot how to recover from a dangerous situation. In this case, the only decision was to keep the people and kids away from serious injury. I still get a cold shiver when I think of what could have happened.
Marc

@R Lefebvre That is scary "the Amp "senses a problem and automatically shuts things down on it's own  with no pilot input . And people are demanding it ? I am with you on this one and this is an example of the reason why it should not be implemented . There  are not to many successful landings with"God" flying the plane. I remember just one time  Back in the 1980.s cessna was flying along The edge of the rocky mountains  at night they were 75 miles from the nearest community There was a pilot a minister and 2 passengers they were at 8000 feet and had an engine failure they set up a glide of  200 feet a minute  let go of the controls and began to pray. the plane came down in a slew(avalanche takes the trees down) nocked the wings off but other wise they were all right  a helicopter picked them up the next  day they figured it was the only clear spot without trees in 15 miles  on the accident report they wrote 'God"was flying the plane.

Monroe,

you are absolutely right that the firmware is still experimental. The only person I can blame is myself, that I forgot about that. Be sure, I have my lesson learned. Absolutely.

Jason, thank you for your time you spent on this issue!

What you found out pretty much describes what happened and how the copter reacted.

Simple Mode made things more complicated in this case... Sad...

Next thing for me is to inform some guys I was helping with their copters who are still using fw 2.7.1 and do not follow the developement like we nerds do...

Lesson learned!

Marc

Marco,

thank you for your advise. You are absolutely right. I have about 24 years of experience in flying rc models. I have crashed a lot of airplanes, learned a lot. I have my standard procedures before every flight and I know, every flight could be the last one. I know of the danger of having only 4 motors on a copter.

What drives me mad is the thing that I simply had put to much faith in the software and a simple, small bug told me that I was wrong.

I was planning to rise a project with the local firefighters and the local government I am working for to develop a drone for aerial assistance in certain situations like fire, flood, etc. This flight should have been an introduction into the thematics and inform the interested people what is possible with todays electronic equipment.

Well, the presentation did not had the success it should have had...

The sad thing is, I don't have a dollar-printer in my house, so the rebuild will have to wait for a longer time. An crashed airplane wouldnt be the problem, wood is cheap, but electronics...

Just a side note on experimental code:

I just took a quick look on the diy store and udrones website. At no point there is being said the software is experimental. All the descriptions say this thing is rock solid and shiny.

Well, in general, it is. I know its experimental, use it at your own risk, you know it, I hope we all know it. But out there are enough people who do not know this, maybe a little safety advise would be good on the website, don't you think?

Absolutely!

People should see the capabilities of this project but be aware that it is still "work in progress" and strange/dangerous things can happen.

I don't want to know how many people here are flying without a proper insurance...

I searched the forum and there are a couple of topics already touching this thematics from various approaches. This is work for the leading guys, not for the following crowd. Make your safety rules, publish them, follow them, advise people to follow them, keep them informed. Simple, but it has to be done from top to bottom.

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