XAircraft x650 Pro - SuperX - Crash - Post Mortem Help Request

[mjmurray68]

Greetings,

Humbling as it is to admit, I had my first, and rather spectacular crash just 1 hour ago, and was hoping that I could enlist some gurus to help me with the post mortem. As I watched it happen there was no obvious cause that I could readily see. Sifting through the wreckage, everything that was still whole looked pretty normal. I'm willing to concede being a complete neophyte, and I really just want to root out the cause of the crash so I don't repeat it again. My concern is that everything appeared completely normal before the carnage, and all I was doing was descending.

There was an awesome moon this evening, so in early twilight, I decided to try and capture some images. Basically I had two flights, one with the gopro set to capture stills every 2 seconds, and the second with video running. Both flights were exactly the same, well aside from the obvious. I was flying in GPS/Attitude mode for both.

1. I waited for GPS lock.
2. I turned on the Gopro
3. I rose straight into the air. Approximately 90m on the first flight and 125m the second.
4. I rotated in place at peak altitude
5. I descended.

Both flights were less than two minutes duration. My battery pack was fully charged. (after the crash, having secured my lipo in a burn proof location, I checked the battery and it showed approximately 15.6v charge).

I was standing just below and fortunately to the side of the copter when things went sideways. Funny I can still see it very clearly in my mind. At about 18m (per Blackbox), the following happened:

1. The two rear motors appeared to give out, and the copter pitched nose up to about 45/50 degrees.
2. In this attitude the copter free fell about 3 meters or so, and then all the motors revved hard.
3. I applied more throttle, not maximum, but I'd say at least 50%. I did not touch my right hand controls at all.
4. The copter pitched about 45 degrees forward, motors screaming, but could not recover, it fell straight out of the sky.

There was no rotation, spinning or cartwheeling, it just plummeted straight nose down into the ground, only about 2 meters from the initial take off/GPS lock.

Here is the Black Box <Note I'm removing the BB Link, if you'd like to see it please PM me>, and I'm attaching the Flight Report as well. Unfortunately the last entry in black box was just before happened, not much good that, and I'm very curious why that would be, or if that perhaps is indicative of something in and of itself.

Additional info: Radio: Tx: Futaba 8FG Super/Rx: 6208SB

I send out my thanks in advance to anyone who can help me figure this one out. Please let me know if there is any additional information I can provide.

I've also removed the flight report as well.

 

[iflynavy]

@MJ

MJ not that you probably didn't think about this, but I'd be careful with the Blackbox link on the forums. Whose ever house you were flying at you just kinda gave away their address. You might want them to stock up on the beer when we all drop by

It's hard to tell on the Flight Report for sure, but it almost appears as if M2,3 and 4 completely drop in speed, at the same time M1 is going up, then they all drop. That leads me instinctually to a controller issue that something in maybe the attitude hold or something told M1 to power up the rest to drop, then it caused the rest of it to happen and it couldn't recover.

I suppose an ESC or something could cause that. Did you loose a prop by chance? I could also see a prop coming off causing the controller to full power that motor and decrease the rest in order to compensate for the hold.

The only other time I have seen a quad pitch at 45 and loose control is when a battery came loose and slid to one direction of the quad.

Did you youtube the video by chance or do a test flight since?

 

[mjmurray68]

iflyNavy,

My better half had the exact same concern about the black box information. I'm going to remove the link, as well as the attached document which also has the GPS coordinates. If anyone would like to see them, I'll take it on faith if you willing to ask for the report nicely you'll at least ping me before showing up for a beer. Trust me several beers were consumed after this event.

I literally just received a detailed crash analysis from Jingchen at Xaircraft, and will be updating this post with his findings. The initial assessment is that it was operator error, which is as much as I suspected, as well as some potential build errors. Once I've had a chance to absorb his message I'll post the findings.

The level of detail in his assessment as well as the fact that he responded in less that 12 hours is a pretty damned impressive piece of customer service, even if he IS telling me I'm a bit of a moron.

 

[iflynavy]

I'd be interested in how they came to that conclusion. Looking forward to hearing.

 

[Naterpin]

The black box is interesting Jingchen was able to tell that. The multirotor was hovering with a wind from the North-West. It is nice to look at your setup's performance.

 

[mjmurray68]

Okay, humble pie time:

Again, I want to thank Jingchen at XAircraft for his prompt and detailed analysis and providing me an actual "Crash Report" in which he actually overlaid annotation onto the flight controller data.

There were basically two anomalies found in his assessment.

1. While likely not a contributing factor, my M2/M4 motors were constantly running about 15% higher output, indicating misalignment. I had not detected this as I had only ever flown in GPS/Attitude mode which was constantly compensating for this. Frankly, I just tightened down the motor mount screws and didn't pay much attention to alignment. Given that my two front rotor arms snapped off in the crash, it's not something I can look further into. I did go back through all of my BlackBox flights, and the anomaly was present in all prior flights.

2. The root cause of the crash, I confess is user inexperience. As I mentioned in my flight description, this was just a straight throttle on, lift, throttle down, lower flight. I was not maneuvering. From looking at the throttle input, it is very evident that I under throttled and caused the coper to lose lift. I can fully accept this, as I know during the descent, it 'felt' from time to time like the copter had stopped descending. Blame it on my old eyes and lack of depth perception, but the reality is I must have been having some level of 'target fixation' and kept fading the throttle.

If anyone has questions, or wants to give me hard time feel free to do so. Also if anyone is interested in seeing Jingchen's Crash Report let me know and I'll forward it on.

 

[iflynavy]

I have to chuckle for a few reasons.

In looking at it, I assumed that wasn't you on the throttle

We have all been there, even in my middle age eyes I can't always tell if it's descending, but I've been flying FPV for so long now that I have a "Cheat". Which brings up a more interesting question and maybe JinChen answered it, what is a safe decent rate in meters per second?

I'd be interested in seeing the report of it PM'd it over.

 

[XAircraft America]

Hey Mj

I just sent you an email and actually came to the exact same conclusion, you were going WAY low on throttle on the way down. Right before you lost control, the quad was descending at 4.7m/s (more than 10 MPH) at 3% throttle and I would guess that when you got below the tree line the change in wind caused the quad to tilt and the pressure of the fall was too much to overcome. If you compare the crash flight with the successful flight, you will see that your throttle and decent rate were very different. During the successful flight, you were descending at 2.5m/s and around 30% throttle. The crash flight had speed as much as 4.7m/s. At that kind of speed, assuming that you had a weight of around 4lbs, that quad would require more than 50lbs of force to stop in 1sec, 20 in 3sec and any kind of tilting would be uncontrollable. Really sorry to hear you had your first uh-oh and if you will send me a list of what all broke I will send you replacements on me if you will cover shipping. Lets all learn from this accident (Make sure that you are really watching your throttle on descent) and thank you for reaching out to the community!

 

[XAircraft America]

One other thing for everyone to consider is that with GPS ATT mode enabled, 50% throttle will hold altitude, and anything above or below will increase or decrease altitude. Keep that in mind when flying and you will be able to better control your descents. I think that around 35% throttle will always be a safe descent throttle %, but obviously from the black box, you can do as little as 27%.

 

[mjmurray68]

Drew, what? 2% is too low? (self deprecating humor attempt).

I've redacted the links to blackbox/gps but otherwise here is the PDF I received from XAircraft.

One additional bit, apparently when the copter lost lift, it flipped. Neither my wife nor I recalled this happening. I'm certain from the black box it did, I'm basically mentioning this as a testament to the quality of 'eye-witness' testimony...

View attachment 13289

 

[iflynavy]

I'm digging the information contained in the blackbox. I don't believe the wookong does any of that does it?

 

[RCJardin]

As someone who is about to fit a Super X basic to a quad I must say I am impressed that Jingchen has taken the trouble to analyse the crash. No doubt it will be impossible for his team to provide this service all the time for everyone but as long as Xaircraft keep the customer in mind at all times then they could certainly give the opposition a run for their money. I look forward to using the product especially as some interesting enhancements seem to be reputably on the horizon.

 

[XAircraft America]

Just a heads up that the Black Box link is in that PDF! Don't want the old lady getting mad!

 

[XAircraft America]

XAircraft has certainly stepped up their customer service game and the Black Box is an amazing way to get objective information on what happened in any situation. The numbers don't lie!

 

[Naterpin]

RCJardin I agree that Jingchen will not be able to do this for everyone. But being able to look a crash cases on the black box will help everyone learn to diagnose issues.

 

[mjmurray68]

Thanks Drew, I didn't realize my edit didn't re-render the PDF.

 

[mjmurray68]

Hey Mj

I just sent you an email and actually came to the exact same conclusion, you were going WAY low on throttle on the way down. Right before you lost control, the quad was descending at 4.7m/s (more than 10 MPH) at 3% throttle and I would guess that when you got below the tree line the change in wind caused the quad to tilt and the pressure of the fall was too much to overcome. If you compare the crash flight with the successful flight, you will see that your throttle and decent rate were very different. During the successful flight, you were descending at 2.5m/s and around 30% throttle. The crash flight had speed as much as 4.7m/s. At that kind of speed, assuming that you had a weight of around 4lbs, that quad would require more than 50lbs of force to stop in 1sec, 20 in 3sec and any kind of tilting would be uncontrollable. Really sorry to hear you had your first uh-oh and if you will send me a list of what all broke I will send you replacements on me if you will cover shipping. Lets all learn from this accident (Make sure that you are really watching your throttle on descent) and thank you for reaching out to the community!

Drew, that is way above and beyond the call of duty. You shouldn't be put out because I made a rookie mistake. Sorry to just be replying to this, somehow I missed the post earlier today.

 

[XAircraft America]

Last thing I want is a bad taste in your mouth about your XAircraft experience so get me the list and I'll at least get you a great deal on everything you need to get flying again. Just get me a cool video to share with everyone when your done!

 

[mjmurray68]

Drew,

Between the time the folks at XAircraft took time to analyze my crash, the growing community support, and your more than generous offer, I have no bad taste what so ever.

I'll send you over an email with the list shortly.

 

[Teamflail]

Wow, just lurking on this post but Drew, hats off to you and your company's support. I don't think I have seen that level of support from any type of company for a long, long time. Looking at the Super X flight controller to replace my Wookong, possibly and you just might have convinced me.