Mikrokopter I hate it when this happens...

[RTRyder]

Fourth FPV flight of the day, about 66 seconds into the flight the quad starts to lose altitude despite no change in throttle setting. As soon as I realized it was going downward I increased the throttle to climb as there were some trees coming up that were starting to look awfully close in the goggles. From the flight logs I can see the increase in throttle had no effect on the altitude loss, shortly afterward I realized there was no actual response to any TX commands so as the Nascar guys say, at that point I was just along for the ride. Wasn't a long ride either as soon afterward the quad clipped the top of a dirt pile and wound up smacking into the packed gravel on the other side, the results of which you see in the picture.

In the flight log I can see the flight controller recognized the TX inputs, it just didn't respond to them, continuing a rapid loss of altitude until gravity won. GoPro got tossed off the gimbal and memory card ejected, after I recovered the corrupted video file I only have about half the flight so no chance to see what happened at the end from the quad's point of view. As soon as can desolder the motor wires I'll hookup MKtools and see if the stack and BLs survived. Given that it hit hard enough to split the dome it wouldn't surprise me to find problems but on the other hand there are no visible signs of damage on the boards so maybe the dome did it's job and sacrificed itself to protect the electronics.

Ken

 

[Mactadpole]

Sorry Ken!!! That really sucks. Would be interesting to know your thoughts/theories on the control loss.

Shawn

 

[RTRyder]

Sorry Ken!!! That really sucks. Would be interesting to know your thoughts/theories on the control loss.

Shawn

Thanks, Shawn. Yeah it does suck but still not nearly as costly as if I did a pile driver with one of the gasser helis I used to fly! Provided none of the MK stack is damaged the repair cost should be around $200 or less which isn't that bad considering how it looks.

I will certainly try to get to the root cause but it may not be possible, nothing in the logs to incidate any real problem that I have been able to find so far and there's no video record that survived other than what I saw in the goggles. That all happened so quickly once the altitude started dropping that I can't clearly remember much between that point and the screen going to static as the video link with the quad was lost.

I had every possible failsafe in place and it didn't make any difference. Doesn't seem to have been a loss of signal as the MK log file sees all the TX commands right up to the last couple seconds, it seems the flight controller just went walkabout and ignored any further commands as it went in for an unintended landing all on its own. Sort of screams firmware bug to me but proving that would be d**n near impossible. It does seem really odd that the altitude can be clearly seen as rapidly decreasing in the log file while throttle is either unchanged or increased, that right there says something was seriously messed up, question is what though...

Ken

 

[Mactadpole]

Were you flying vario-AH on? What firmware version?

I was thinking about using my backup X8 as my FPV practice copter after the flyaway of my quad due to dead transmitter battery. When I see things like this it makes me realize I need a dedicated 'cheaper' fpv copter.

Hopefully the boards are safe.

Shawn

 

[RTRyder]

Were you flying vario-AH on? What firmware version?

I was thinking about using my backup X8 as my FPV practice copter after the flyaway of my quad due to dead transmitter battery. When I see things like this it makes me realize I need a dedicated 'cheaper' fpv copter.

Hopefully the boards are safe.

Shawn

I pretty much always fly my Mk in vario and this was no exception. Firmware is the recent .88 version and it's set to give a slow descent on loss of signal as well as having a diversity board with multiple satellite RX attached. Here's a screen shot of the log file that shows in the blue band that the quad has reached max altitude for this flight while the vertical speed is already starting to go negative showing that it's about to start a rather rapid descent. I have no idea what the number actually means other than it's not feet or meters, actual altitude was around 150 feet at the time it started to drop. If you look to the far right you can see under RC-sticks the throttle setting G81 stays steady for a few seconds until I realize the altitude is going away and I increase the throttle up to 102 and then start moving the sticks around to confirm that the quad isn't responding to any commands. Plain to see from the log that the F/C saw the commands, just didn't do anything other than keep dropping until it hit the ground...

 

[RTRyder]

Last evening I disconnected the motor wires and powered up the stack while connected to MKtool, everything came up clean and green with no errors so all of the electronics survived it appears! On the downside, the frame is a total loss other than the flexlander legs. Both of the centerplates are broken and all of the arms are either broken off or badly twisted, if it weren't for the rubber standoffs mounting the F/C it probably would have been damaged as the centerplate was ripped away from the bottom of one of the mounting points.

I priced the pieces I need to fix the current frame and decided it just isn't worth it so I ordered one of Rusty's UAP1 frame kits and I'll be rebuilding the quad into that reusing the Flexlander gear and Hisight II mount for the GoPro. This frame should provide a bit better protection for the electronics and the 12mm carbon fiber arm tubes are much cheaper to replace than the aluminum MK arms, plus Rusty guarantees the G10 parts to not break and will replace them if they do. I have crash tested his frame parts before and found they stand up quite well, much better than the MK frame does although I hope to not test this one for crashworthiness!

Ken

P.S. it appears I'll never find out exactly what happened to cause the crash, there's absolutely nothing in the log files to indicate a problem and lacking any other evidence of a failure I'll just have to rebuild and go on from there.

 

[Pjtyros]

Hi Ken, sorry to hear about the crash. Did you look at the bl temps? I have removed the dome from both of my craft because of high temps, I use a crash cage instead. Just a thought.
Paul

 

[Benjamin Rowland]

Hate to see that. Makes my stomach turn. If you figure it out, let us know.

 

[RotorKoph]

Forgive me if this is a dumb question, but what about the lipo? Fully charged and no problems with it?

My sympathies to you for the unfortunate incident.

 

[RTRyder]

Quick update, I never did find an actual problem that the crash could be attributed to, been through the data in the flight log and taken the entire thing apart and inspecting each piece and reassembling it all in another frame with several successful test flights since.

BL temps well within range, they all have heatsinks on the FETs and even when flying in close to 90 degree ambient temps they are cool to the touch after a full pack with the dome on. First thing I checked after the crash was battery voltage, even though its clearly displayed in the OSD data I see while flying, 16 volts at the connection to the power board and 5 volts on the flight controller, doesn't appear to be anything power related.

Only conclusion I can come up with is a firmware glitch caused it to hang the processor and it just descended until it ran out of altitude with the resulting carnage being the end of the flight.

Today I found I had enough good pieces in my parts stash to rebuild the MK frame which is now completed. As soon as the new motors arrive I'll finish wiring it up and give it a maiden flight. That was the other major issue with the crash, it bent the shafts in all 4 motors so a set of replacments should be here tomorrow, a bit more powerful with a slightly lower KV rating as I think I was starting to get close to the max loading on the old motors as I added more things on, won't be a problem now.

Hope to be back in the air with the same configuration and new motors this weekend...

Ken

 

[Meez]

Ken,

glad to hear your recovery.

i'll blame the batteries first because i had enough with cheapo batery. Now, i use either Mk's or TP only and no issue until now.

 

[Bartman]

Forgive me if this is a dumb question, but what about the lipo? Fully charged and no problems with it?

My sympathies to you for the unfortunate incident.

Sorry to hear it Ken! It does sound like the batteries went weak, what's the voltage look like in the log file?

THose aluminum MK arms do twang pretty easily.

 

[RTRyder]

Sorry to hear it Ken! It does sound like the batteries went weak, what's the voltage look like in the log file?

THose aluminum MK arms do twang pretty easily.

Absolutely certain it was not a voltage problem, no indication of it in the flight data log and I didn't see it in the OSD. I've since done a couple flights with the same packs, no problem.

I suspect it was a motor problem that brought it down as a couple of them have rough notchy feel to the bearings now, problem is they all got stuffed in the crash so there's no way of telling if the bearings were OK before the crash or not. They all turned smoothly when I did the preflight at the beginning of the day, now all four have bent shafts and two have bad bearings but also got slammed hard enough to bend the prop adaptor as well as the shaft. On one motor the bell was completely off the motor on the ground at the crash site, circlip gone, maybe the reason it crashed? No way to really know.

It will be back in the air soon with new motors, I'll keep it low, close, and in the middle of a large empty field for a few flights to see what happens...

Ken